U.S. patent application number 12/152032 was filed with the patent office on 2008-10-23 for diamond structures as fuel capsules for nuclear fusion.
This patent application is currently assigned to General Nanotechnology LLC. Invention is credited to Victor B. Kley.
Application Number | 20080256850 12/152032 |
Document ID | / |
Family ID | 39870792 |
Filed Date | 2008-10-23 |
United States Patent
Application |
20080256850 |
Kind Code |
A1 |
Kley; Victor B. |
October 23, 2008 |
Diamond structures as fuel capsules for nuclear fusion
Abstract
Fuel capsules usable in inertial confinement fusion (ICF)
reactors have shells made from materials having a diamond
(sp.sup.3) lattice structure, including diamond materials in
synthetic crystalline, polycrystalline (ordered or disordered),
nanocrystalline and amorphous forms. The interior of the shell is
filled with a fusion fuel mixture, including any combination of
deuterium and/or tritium and/or helium-3 and/or other fusible
isotopes.
Inventors: |
Kley; Victor B.;
(US) |
Correspondence
Address: |
IMPERIUM PATENT WORKS
P.O. BOX 587
SUNOL
CA
94586
US
|
Assignee: |
General Nanotechnology LLC
|
Family ID: |
39870792 |
Appl. No.: |
12/152032 |
Filed: |
May 10, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11067588 |
Feb 25, 2005 |
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12152032 |
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60623283 |
Oct 28, 2004 |
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60622520 |
Oct 26, 2004 |
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60602413 |
Aug 17, 2004 |
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60557786 |
Mar 29, 2004 |
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60554690 |
Mar 19, 2004 |
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60553911 |
Mar 16, 2004 |
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60552280 |
Mar 10, 2004 |
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60550571 |
Mar 3, 2004 |
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60547934 |
Feb 25, 2004 |
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Current U.S.
Class: |
44/502 ;
427/551 |
Current CPC
Class: |
G01Q 70/14 20130101;
Y02E 30/10 20130101; G01Q 30/10 20130101; G21B 1/19 20130101; Y10S
977/879 20130101; B82Y 35/00 20130101; Y02E 30/16 20130101; G01Q
20/02 20130101; G01Q 80/00 20130101; Y10S 977/871 20130101; G01Q
30/02 20130101; Y10S 977/858 20130101; B82Y 30/00 20130101 |
Class at
Publication: |
44/502 ;
427/551 |
International
Class: |
G21C 3/07 20060101
G21C003/07; B05D 3/06 20060101 B05D003/06 |
Claims
1-113. (canceled)
114. An article of manufacture, comprising: a shell enclosing a
hollow volume; wherein a nanocrystalline diamond film having a
surface roughness less than about 400 nm comprises the wall of said
shell.
115. The article of claim 114, wherein said diamond film comprises
a surface roughness less than about 200 nm.
116. The article of claim 114, wherein said diamond film comprises
a surface roughness between about 10 nm and about 75 nm.
117. The article of claim 114, wherein said wall further comprises
a thickness from about 5 microns to about 1000 microns.
118. The article of claim 114, wherein said wall further comprises
a thickness from about 10 micrometers to about 200 micrometers.
119. The article of claim 114, wherein said wall further comprises
a thickness uniformity of better than about +/-b 1%.
120. The article of claim 114, wherein said enclosed hollow volume
comprises a length between about 0.3 mm and about 5 mm along a long
dimension.
121. The article of claim 120, wherein at least one filling
selected from a solid and a fluid is disposed therein said hollow
volume.
122. The article of claim 120, wherein at least one fusion fuel
selected from deuterium and tritium is disposed therein said hollow
volume.
123. The article of claim 122, wherein said fusion fuel further
comprises a frozen layer of deuterium-tritium (DT) fuel and a
central DT gas core.
124. The article of claim 122, wherein said fusion fuel comprises a
pressure greater than about 1 atm.
125. The article of claim 114, wherein said diamond film further
comprises a dopant.
126. The article of claim 124, wherein said dopant comprises up to
about 5% of the atomic fraction of the coating.
127. The article of claim 124, wherein said dopant comprises at
least one element selected from: hydrogen, carbon, argon, boron,
oxygen, nitrogen, sulfur, tungsten, tantalum, and phosphorus.
128. The article of claim 114, wherein the wall comprises at least
one perforation.
129. The article of claim 126, wherein said perforation comprises a
diameter between about 5 micrometers and about 200 micrometers.
130. A method of fabricating a diamond shell, comprising: providing
a substrate; symmetrically depositing a diamond film on said
substrate; removing said substrate so as to produce a hollow core;
refilling said hollow core with a nuclear fuel; and focusing an ion
beam on one or more fill perforations in a C.sub.14H.sub.10
atmosphere so as to produce a target use for inertial confinement
fusion.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of, and claims priority
under 35 U.S.C. .sctn.120 from, nonprovisional U.S. patent
application Ser. No. 11/067,588 entitled "Diamond Structures As
Fuel Capsules For Nuclear Fusion," filed on Feb. 25, 2005, now U.S.
Pat. No. ______, the subject matter of which is incorporated herein
by reference. Application Ser. No. 11/067,588, in turn, claims the
benefit under 35 U.S.C. .sctn.119 of the following nine U.S.
Provisional Applications: [0002] U.S. Provisional Patent
Application No. 60/547,934 filed Feb. 25, 2004, entitled "Diamond
Molding of Small and Microscale Capsules"; [0003] U.S. Provisional
Patent Application No. 60/550,571 filed Mar. 3, 2004, entitled
"Diamond Molding of Small and Microscale Capsules"; [0004] U.S.
Provisional Patent Application No. 60/552,280 filed Mar. 10, 2004,
entitled "Diamond Molding of Small and Microscale Capsules"; [0005]
U.S. Provisional Patent Application No. 60/553,911 filed Mar. 16,
2004, entitled "Diamond Molding of Small and Microscale Capsules";
[0006] U.S. Provisional Patent Application No. 60/554,690 filed
Mar. 19, 2004, entitled "Diamond and/or Silicon Carbide Molding of
Small and Microscale or Nanoscale Capsules and Hohlraums"; [0007]
U.S. Provisional Patent Application No. 60/557,786 filed Mar. 29,
2004, entitled "Diamond and/or Silicon Carbide Molding of Small and
Microscale or Nanoscale Capsules and Hohlraums"; [0008] U.S.
Provisional Patent Application No. 60/602,413 filed Aug. 17, 2004,
entitled for "Diamond and/or Silicon Carbide Molding of Small and
Microscale or Nanoscale Capsules and Hohlraums"; [0009] U.S.
Provisional Patent Application No. 60/622,520 filed Oct. 26, 2004,
entitled "Diamond and/or Silicon Carbide Molding of Small and
Microscale or Nanoscale Capsules and Hohlraums"; and [0010] U.S.
Provisional Patent Application No. 60/623,283 filed Oct. 28, 2004,
entitled "Diamond and/or Silicon Carbide Molding of Small and
Microscale or Nanoscale Capsules and Hohlraums."
[0011] The respective disclosures of these applications, including
any attachments and appendices thereto, are incorporated herein by
reference for all purposes.
[0012] The following U.S. patents and patent applications,
including any attachments and appendices thereto, are also
incorporated herein by reference for all purposes: [0013] U.S. Pat.
No. 6,144,028, issued Nov. 7, 2000, entitled "Scanning Probe
Microscope Assembly and Corresponding Method for Making Confocal,
Spectrophotometric, Near-Field, and Scanning Probe Measurements and
Forming Associated Images from the Measurements"; [0014] U.S. Pat.
No. 6,252,226, issued Jun. 26, 2001, entitled "Nanometer Scale Data
Storage Device and Associated Positioning System"; [0015] U.S. Pat.
No. 6,337,479, issued Jan. 8, 2002, entitled "Object Inspection
and/or Modification System and Method"; [0016] U.S. Pat. No.
6,339,217, issued Jan. 15, 2002, entitled "Scanning Probe
Microscope Assembly and Method for Making Spectrophotometric,
Near-Field, and Scanning Probe Measurements"; [0017] U.S.
Provisional Application No. 60/554,194, filed Mar. 16, 2004,
entitled "Silicon Carbide Stabilizing of Solid Diamond and
Stabilized Molded and Formed Diamond Structures"; [0018] U.S.
patent application Ser. No. 11/067,517, filed on Feb. 25, 2005,
entitled "Diamond Capsules and Methods of Manufacture"; [0019] U.S.
patent application Ser. No. 11/067,521, filed on Feb. 25, 2005,
entitled "Methods of Manufacturing Diamond Capsules"; [0020] U.S.
patent application Ser. No. 11/067,600, filed on Feb. 25, 2005,
entitled "Methods of Manufacturing Diamond Capsules"; and [0021]
U.S. patent application Ser. No. 11/067,609, filed on Feb. 25,
2005, entitled "Apparatus for Modifying And Measuring Diamond and
Other Workpiece Surfaces with Nanoscale Precision."
RELATED DOCUMENTS INCORPORATED BY REFERENCE
[0022] The following documents provide background information
related to the present application and are. incorporated herein by
reference: [0023] [KOMA] R. Komanduri et al., "Finishing of Silicon
Nitride Balls," Oklahoma State University, Web Page at asset (dot)
okstate (dot) edu (slash) asset (slash) finish.htm (updated Aug.
21, 2003); [0024] [LIND] J. Lindl, "Development of the
Indirect-Drive Approach to Inertial Confinement Fusion and the
Target Physics Basis for Ignition and Gain," published in Physics
of Plasmas, November 1995; [0025] [PHYS] Physik Instrumente (PI)
GmbH, "Datasheets: Options and Accessories," Web page at www (dot)
physikinstrumente (dot) de (slash) products (slash)
prdetail.php?secid=1-39; [0026] [NOOL] Nonlinear Optics and
Optoelectronics Lab, University Roma Tre (Italy), "Germanium on
Silicon Near Infrared Photodetectors," Web page at optow (dot) ele
(dot) uniroma3 (dot) it (slash) optow.sub.--2002 (slash) labs
(slash) SiGeNIR files (slash) SiGeNIR.htm; [0027] [SAIN]
Saint-Gobain Ceramics, "ASTM F2094 Si.sub.3N.sub.4 Cerbec Ball
Specifications," Web page at www (dot) cerbec (dot) com (slash)
TechInfo (slash) TechSpec.asp; [0028] [STOL] C. R. Stoldt et al.,
"Novel Low-Temperature CVD Process for Silicon Carbide MEMS"
(preprint), C. R. Stoldt, C. Carraro, W. R. Ashurst, M. C. Fritz,
D. Gao, and R. Maboudian, Department of Chemical Engineering,
University of California, Berkeley; [0029] [SULL] J. P. Sullivan et
al., "Amorphous Diamond MEMS and Sensors," Sandia National Labs
Report SAND2002-1755 (2002); and [0030] [UWST] University of
Wisconsin-Stout-Statics and Strength of Material, (Physics
372-321), Topic 6.5: Pressure Vessels--Thin Wall Pressure Vessels,
Web page at physics (dot) uwstout (dot) edu (slash) StatStr (slash)
Statics (slash) index.htm.
[0031] Copies of these documents are being made of record in the
present application.
TECHNICAL FIELD
[0032] The present invention relates in general to diamond
structures, and in particular to diamond structures that are usable
as fuel capsules for nuclear fusion reactors.
BACKGROUND
[0033] Nuclear fusion occurs when two relatively light atomic
nuclei (e.g., isotopes of hydrogen, helium or lithium) are brought
into such close proximity that they fuse into a single heavier
nucleus, releasing tremendous amounts of energy in the process. For
over half a century, the theoretical potential of nuclear fusion as
a clean, reliable, and virtually inexhaustible energy source has
been known and has motivated an array of research and development
projects.
[0034] Practical fusion technology, however, remains elusive.
Fusing two nuclei requires confinement; i.e., the nuclei must be
held in very close proximity to each other for a period of time
sufficient to allow the fusion reaction to occur. Confinement
requires overcoming the Coulomb barrier that causes the positively
charged nuclei to repel each other. The most common approach to
overcoming this barrier involves directing the nuclei toward each
other with sufficient momentum to penetrate the Coulomb barrier and
achieve confinement.
[0035] Over the years, various techniques have been tried for
imparting the necessary momentum to the nuclei. For instance,
inertial confinement fusion (ICF) is being investigated at various
research centers, including the National Ignition Facility (NIF).
In ICF, the fusion fuel (typically a deuterium-tritium mixture) is
placed within a spherical capsule that has a thin outer shell
(called an ablator). An inner shell made of the fusion fuel in a
solid or liquid state usually lines the inner wall of the ablator,
and the interior of the inner shell is filled with a low-pressure
gas of the fusion fuel. When heated, the ablator rapidly expands
outward, driving the inner shell inward and compressing the fuel.
Under the right conditions, the compressed fuel forms a central
"hot spot" containing 2-5% of the fuel, in which confinement is
attained. Heat released from the resulting fusion reactions in the
hot spot then radiates outward to create an expanding thermonuclear
burn front.
[0036] Heating of the ablator can be done directly or indirectly.
In "direct drive" ICF, a conventional energy source, such as a
laser or ion beam, is directed onto the capsule surface to heat and
expand the ablator material, driving an implosion of the fuel. This
approach demands very uniform illumination of the capsule surface
to avoid hydrodynamic instability that would preclude confinement
or the development of a sustained burn front. In "indirect drive"
ICF, the fuel-containing capsule is placed in a "hohlraum," a
symmetric cavity with walls made of a high-Z material such as gold,
lead, or uranium that acts as a blackbody radiator. Laser or ion
beams are directed onto the walls of the hohlraum, which radiates
x-rays into the cavity. The x-rays heat and expand the ablator
material, driving an implosion of the fuel. The use of a hohlraum
reduces sensitivity to hydrodynamic instability, resulting in
relaxed requirements for uniform illumination. Nevertheless, a
symmetric implosion of the fuel is crucial.
[0037] Thus, capsule design is an important factor in ICF. For
example, inner shells with a large radius and small thickness
achieve high implosion velocities. In addition, nonuniformities in
the ablator, and to a lesser extent in the inner shell, can result
in asymmetry in the implosion so that confinement does not
occur.
[0038] Various capsule dimensions and compositions have been
proposed and studied. For example, one existing capsule design
provides a plastic (CH) ablator with an outer radius of about 1.1
millimeters (mm) and a thickness of about 0.15 mm. The inner shell
was made of solid deuterium-tritium (DT) ice about 80 micrometers
(.mu.m) thick; the interior was filled with DT gas at a pressure of
0.3 mg/cm.sup.3 at a temperature of about 4 K. Another capsule had
similar dimensions, but the ablator was made of beryllium doped
with sodium and bromine. Other capsule designs use glass or silicon
dioxide microballoons with diameters on the order of 150 .mu.m and
wall thicknesses on the order of 5-10 .mu.m as ablators.
[0039] In practice, existing capsules have generally not produced
satisfactory results. Typical problems include nonuniformity in the
ablator thickness or composition, as well as deviations from
sphericity and defects in the surface finish of the ablator. Any of
these problems can lead to asymmetry in the implosion of the fuel.
In addition, while a relatively thin ablator is generally
desirable, the ablator needs to be thick enough to resist the
pressure of the fuel inside, and the strength of the ablator
material can be a limiting factor on the density of the fuel.
[0040] It would therefore be desirable to provide an improved fuel
capsule for an ICF reactor.
SUMMARY
[0041] Embodiments of the present invention provide fuel capsules
usable in inertial confinement fusion (ICF) reactors. The capsules
have shells made from diamond materials, including crystalline,
polycrystalline (ordered or disordered), nanocrystalline, and
amorphous diamond. As used herein, "diamond" refers generally to
any material having a diamond lattice structure on at least a local
scale (e.g., a few nanometers), and the material may be based on
carbon atoms, silicon atoms, silicon carbide, or any other atoms
capable of forming a diamond lattice. The interior of the shell can
be filled with a fusion fuel mixture, including any combination of
deuterium and/or tritium and/or helium-3 and/or other fusible
isotopes. Other embodiments of the invention provide methods for
manufacturing diamond shells and for filling diamond shells with a
fusion fuel mixture.
[0042] According to one aspect of the invention, a capsule has a
shell made of a diamond material, the shell defining an interior
region. A fusion fuel mixture is contained within the interior
region of the shell, and the capsule is usable within an inertial
confinement fusion reactor. The shell may be made of various types
of diamond material including polycrystalline diamond material
(which may have oriented or disoriented crystal grains),
nanocrystalline diamond material, or amorphous diamond material.
The diamond material may be a carbon-based diamond material, a
silicon based diamond material, or any other material with atoms
arranged in a diamond lattice.
[0043] Various fusion fuel mixtures may be used. In one embodiment,
the fusion mixture includes deuterium (.sup.2H) and/or tritium
(.sup.3H) and/or helium-3 (.sup.3He). In another embodiment, the
fusion fuel mixture includes helium-3 deuteride. A solid form of
the fusion fuel mixture may line an inner wall of the shell, and/or
a gas form of the fusion fuel mixture may fill the interior. The
gas form of the fusion fuel mixture can be held at a pressure
higher than an ambient pressure.
[0044] In preferred embodiments, the shell is substantially
spherical. For instance, local deviations from smoothness on the
inner and/or outer surfaces of the shell can be controlled to be
less than about 4 nm.
[0045] In some embodiments, the shell has an access port
therethrough. A valve may be disposed in the shell and adapted to
prevent a fluid within the capsule from escaping through the access
port when the valve is closed. The valve can be, for instance, a
deformable flap of material or a displaceable tapered filament.
[0046] In some embodiments, the diamond material includes a dopant.
The dopant may have various effects, such as increasing an
electrical conductivity of the diamond material, modifying an
electromagnetic absorption property of the diamond material, and/or
modifying a thermal property of the diamond material. The dopant
can be disposed nonuniformly in the diamond material such that a
first region of the shell has a higher concentration of the dopant
than a second region of the shell, thereby imparting nonuniform
properties to the shell.
[0047] In some embodiments, a layer of a coating material is
disposed on an outer wall of the shell. The coating layer can have
small thickness variations forming a capsule identification
pattern. Examples of coating materials include but are not limited
to silicon, germanium, silicon carbide, silicon dioxide, silicon
fluoride, magnesium fluoride, silicon nitride, titanium, titanium
carbide, titanium dioxide, titanium nitride, tantalum, tantalum
carbide, tantalum nitride, molybdenum, molybdenum carbide,
molybdenum nitride, tungsten, tungsten carbide, tungsten nitride,
boron carbide, boron nitride, chromium, chromium carbide, chromium
nitride, chromium oxide, and aluminum oxide.
[0048] In some embodiments, the shell comprises two substantially
hemispherical shell sections. The shell sections may be connected
by complementary latch members located near respective peripheral
edges of the shell sections. Alternatively, the shell sections may
be connected by an interference member located near a peripheral
edge of one of the shell sections. In another embodiment, adjacent
shell sections are connected by a bonding material disposed between
respective peripheral edge surfaces of the adjacent shell sections.
The bonding material may include an adhesion layer, a coupling
layer, and a bondable layer; or silicon and spin on glass; or a
noble gas at a low temperature; or other materials.
[0049] According to another aspect of the present invention, a
method for making and filling a capsule includes aligning a
plurality of shell sections made of a diamond material and joining
the plurality of shell sections together at respective peripheral
edges thereof to form a capsule shell. The shell sections are
joined in an atmosphere containing a fusion fuel mixture such that
the capsule shell contains at least some of the fusion fuel
mixture. The sections may be hemispherical or may have other
shapes.
[0050] In one embodiment, joining is performed in a low-temperature
environment. Respective peripheral edges of the shell sections are
held in proximity to each other such that a joint area is defined,
and a noble gas is supplied to the joint area via a heated passage.
The low temperature is sufficiently low that the noble gas
condenses in the joint area.
[0051] In another embodiment, the shell sections are subjected to
machining, chemically modifying, polishing, lapping, or grinding to
form complementary latch or interference members therein, and the
shell sections are joined by aligning the shell sections such the
complementary latch or interference members engage.
[0052] In still another embodiment, the shell sections are joined
by a process that includes creating a temperature difference
between two of the shell sections such that one of the shell
sections is warmer than the other. An interference member at a
peripheral edge of the warmer one of the shell sections is
overlapped with a peripheral edge of the other one of the shell
sections, and the temperature difference is reduced while holding
the shell sections in overlapping relation to each other.
[0053] In a further embodiment, a bonding agent is applied to a
peripheral edge of at least one of the shell sections, and the
peripheral edge with the bonding agent is held in contact with a
peripheral edge of another of the shell sections so that a bond
forms, thereby joining the shell sections. Applying the bonding
agent may include: applying an adhesion layer, a coupling layer,
and a bondable layer; or applying a silicon sputter and a spin on
glass. In some embodiments, the bonding agent includes at least one
of germanium, antimony, tellurium, astatine, polonium, bismuth,
and/or arsenic, including alloys thereof.
[0054] In some embodiments, the shell sections are formed by
growing the diamond material on a mold substrate. The mold
substrate advantageously includes surface features, each surface
feature conforming to a shell section shape, and the diamond
material is grown over the surface features such that the diamond
material conforms to the surface features. For example, a surface
feature can be convex and substantially hemispherical or concave
and substantially hemispherical. At least one of the surface
features may also define a latch or interference member at a
peripheral edge of one of the shell sections. After growing the
shell sections, they can be removed from the mold substrate, e.g.,
by wet or dry etching of the mold substrate material.
[0055] According to still another aspect of the invention, a method
for making a capsule includes growing a shell of a diamond material
over a form substrate such that the shell covers all of the form
substrate. An opening is formed through the shell, and the form
substrate is removed through the opening. The capsule is then
filled with a fusion fuel mixture.
[0056] According to yet another aspect of the invention, a method
for making a capsule includes growing a shell of a diamond material
over a form substrate such that the shell covers most or all of the
form substrate. The substrate is removed through an opening in the
shell. An access port is formed through the shell, and the shell is
filled with a fusion fuel mixture via the access port.
[0057] The access port can be formed in various ways. In one
embodiment, one or more pins are held in contact with the form
substrate during the act of growing the shell, and after growing
the shell, the one or more pins are separated from the form
substrate, thereby opening the access port. The pins can include a
tube of a material different from the diamond material of the
shell, and separating the one or more pins may include etching away
the tube.
[0058] In other embodiments, the method also includes forming, in
the shell, a valve member operable to open or close the access
port. For instance, the access port and the valve member can both
be formed by holding a pin in contact with the form substrate
during the act of growing the shell, with the pin being held such
that an access port with a deformable flap is formed in the shell.
After growing the shell, the pin is removed, and the valve member
includes the deformable flap.
[0059] Alternatively, the access port and the valve member can be
formed by holding a first structure in contact with the form
substrate during a first phase of growing the shell, thus creating
an opening in the shell. After the first phase, the first structure
is replaced with a second structure and a second phase of the act
of growing is performed. The second structure substantially covers
and extends beyond the opening in the shell created by the first
structure.
[0060] In still another embodiment, the access port and the valve
member can be formed by a process that includes coating a tapered
filament made of the diamond material with a material other than
the diamond material. An end of the coated filament is held in
contact with the form substrate during the act of growing the
shell. After the act of growing the shell, the coating is removed
from the filament, so that the filament is displaceably held in the
shell and operable as the valve member.
[0061] A capsule with a valve can be filled in various ways. In one
embodiment, the capsule is placed into an environment containing
the fusion fuel mixture at a high pressure and held there until a
pressure equilibrium is reached between the capsule and the
environment. After the pressure equilibrium is reached, the capsule
environment can be modified (e.g., by lowering the external
pressure) such that the pressure of the fluid on the valve member
closes the access port.
[0062] In any of the above methods, various fusion fuel mixtures
can be used. In one embodiment, the fusion fuel mixture includes
deuterium (.sup.2H) and/or tritium (.sup.3H) and/or helium-3
(.sup.3He). In another embodiment, the fusion fuel mixture includes
helium-3 deuteride.
[0063] In any of the above methods, the shell may be made of
various diamond materials, including polycrystalline diamond,
nanocrystalline diamond, and/or amorphous diamond. The shell can be
substantially spherical, and local deviations from smoothness on
the inner and/or outer surfaces of the shell section may be
controlled to be less than about 4 nm.
[0064] Diamond materials can be grown using various processes,
including a chemical vapor deposition process, a plasma enhanced
chemical vapor deposition process, a hot wire diamond growth
process, or a laser induced amorphous diamond growth process. In
some embodiments, a dopant is introduced into the diamond material
during the growing step. Examples of suitable dopants include but
are not limited to astatine, polonium, americium, antimony,
bismuth, arsenic, germanium, iodine, tellurium, selenium or
bromine. In some embodiments, at least a portion of the diamond
material is coated or implanted with one or more other
materials.
[0065] According to a further aspect of the present invention, a
method of filling a capsule with a fusion fuel mixture includes
forming an access port in a shell of the capsule, the shell being
made of a diamond material, and filling the capsule with the fusion
fuel mixture in a fluid form via the access port. After the capsule
is filled, the access port can be closed.
[0066] Various fusion fuel mixtures can be used. In one embodiment,
the fusion fuel mixture includes deuterium (.sup.2H) and/or tritium
(.sup.3H) and/or helium-3 (.sup.3He). In another embodiment, the
fusion fuel mixture includes helium-3 deuteride.
[0067] Many techniques can be used to close the access port. In one
embodiment, closing the access port includes inserting a plug into
the access port. In another embodiment, closing the access port
includes growing the diamond material to cover the access port.
[0068] Access ports can be formed in various ways. In one
embodiment, forming the access port includes using an energetic
beam of charged particles, a laser, or machining. In another
embodiment, forming the access port includes coating the shell with
an etch resist; patterning the etch resist to define a location of
the access port; and etching the shell at the location of the
access port to create an opening through the shell.
[0069] According to a still further aspect of the invention, a
method of filling a capsule with a fusion fuel mixture includes
placing a capsule into an environment containing the fusion fuel
mixture in a fluid state and maintaining the environment at a
suitable temperature and pressure to induce diffusion of the fusion
fuel mixture into an interior region of the capsule. After a period
of time, the environment can be modified to a different temperature
and/or pressure such that diffusion of the fusion fuel mixture out
of the capsule is inhibited.
[0070] Various fusion fuel mixtures can be used. In one embodiment,
the fusion fuel mixture includes deuterium (.sup.2H) and/or tritium
(.sup.3H) and/or helium-3 (.sup.3He). In another embodiment, the
fusion fuel mixture includes helium-3 deuteride.
[0071] In some embodiments, the temperature of the capsule or the
environment can be altered so as to control a pressure of the
fusion fuel mixture within the capsule. In other embodiments, a
pressure of the fusion fuel mixture within the capsule is
controlled by controlling a time period during which diffusion of
the fusion fuel mixture takes place.
[0072] According to another aspect of the present invention, a
system for inducing nuclear fusion includes a capsule. The capsule
has a diamond shell defining an interior region and a fusion fuel
mixture contained in the interior region. The capsule is disposed
within a target region having an energy density sufficient to
induce an expansion of the shell and an implosion of the plurality
of fusion fuel atoms. Various fusion fuel mixtures can be used. In
one embodiment, the fusion fuel mixture includes deuterium
(.sup.2H) and/or tritium (.sup.3H) and/or helium-3 (.sup.3He). In
another embodiment, the fusion fuel mixture includes helium-3
deuteride. The fusion fuel mixture may be maintained in various
states including solid and/or liquid and/or gas states.
[0073] In preferred embodiments, a hohlraum substantially encloses
the target region and is configured to radiate x-rays into the
target region. An energy source is configured to direct energy
toward the hohlraum. The energy source may include, e.g., a laser
generator or an ion beam generator.
[0074] According to yet another aspect of the invention, a method
for inducing nuclear fusion includes creating a region of high
energy density and placing in the region a capsule having a diamond
shell defining an interior region and a fusion fuel mixture
contained in the interior region. The energy density in the region
is made sufficiently high to induce an expansion of the diamond
shell and an implosion of the plurality of fusion fuel atoms. The
region of high energy density can be created inside a hohlraum,
e.g., by directing one or more laser beams onto a wall of the
hohlraum or directing one or more ion beams into the hohlraum.
[0075] Various fusion fuel mixtures can be used. In one embodiment,
the fusion fuel mixture includes deuterium (.sup.2H) and/or tritium
(.sup.3H) and/or helium-3 (.sup.3He). In another embodiment, the
fusion fuel mixture includes helium-3 deuteride. The fusion fuel
mixture may be maintained in various states including solid and/or
liquid and/or gas states.
[0076] The following detailed description together with the
accompanying drawings will provide a better understanding of the
nature and advantages of the present invention. This summary does
not purport to define the invention. The invention is defined by
the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0077] FIG. 1 is a cross-sectional view of a spherical capsule
according to an embodiment of the present invention;
[0078] FIGS. 2A and 2B are schematic illustrations of diamond and
graphite atomic lattices, respectively;
[0079] FIG. 3 is a cross-sectional view of a capsule having a shell
that is lined with a layer of fusion fuel in a solid state
according to an embodiment of the present invention;
[0080] FIGS. 4A and 4B are cross-sectional views of a capsule with
an access port in the shell according to an embodiment of the
present invention;
[0081] FIG. 5 is a flow diagram of a process for making a capsule
from shell sections according to an embodiment of the present
invention;
[0082] FIGS. 6A-6M are cross-sectional views of capsule structures
at various stages of the process of FIG. 5;
[0083] FIGS. 7A-7F are cross-sectional views illustrating a
technique for forming a hole in a capsule according to an
embodiment of the present invention;
[0084] FIG. 8 is a flow diagram of a process for making a capsule
according to another embodiment of the present invention;
[0085] FIGS. 9A-9H are cross-sectional views of a capsule structure
at various stages of the process of FIG. 8;
[0086] FIGS. 10A-10F illustrate a diamond capsule and support
apparatus at various stages in the fabrication of a capsule
according to an embodiment of the present invention;
[0087] FIG. 11 is a flow diagram of a process for forming multiple
diamond capsules in parallel according to an embodiment of the
present invention;
[0088] FIGS. 12A-12I are views of a diamond capsule and growth
apparatus at various stages of the process of FIG. 11;
[0089] FIGS. 13A-13C are views of an access port structure with an
integral valve member according to an embodiment of the present
invention;
[0090] FIGS. 14A and 14B are cross-sectional views of access port
structures with integral valve members according to further
embodiments of the present invention;
[0091] FIGS. 15A-15F are cross-sectional views of capsule
structures at various stages of a process for forming a capsule
with an integral valve according to an embodiment of the present
invention;
[0092] FIGS. 16A-16F are cross-sectional views of a valve member
for a diamond capsule according to an embodiment of the present
invention;
[0093] FIGS. 17A-17F are perspective and cross-sectional views of a
capsule and support structures at various stages of a process for
forming a capsule according to another embodiment of the present
invention;
[0094] FIG. 18 is a cross-sectional view of a filling assembly for
filling a capsule that has an access port according to an
embodiment of the present invention;
[0095] FIG. 19 is a perspective view of a storage container for
fuel-containing capsules according to an embodiment of the present
invention; and
[0096] FIGS. 20A and 20B are cross-sectional views of fusion
reactors according to embodiments of the present invention.
DETAILED DESCRIPTION
[0097] Embodiments of the present invention provide fuel capsules
usable in inertial confinement fusion (ICF) reactors. The capsules
have shells made from diamond materials, including crystalline,
polycrystalline (ordered or disordered), nanocrystalline, and
amorphous diamond. As used herein, "diamond" refers generally to
any material having a diamond lattice structure on at least a local
scale (e.g., a few nanometers), and the material may be based on
carbon atoms, silicon atoms, silicon carbide, or any other atoms
capable of forming a diamond lattice. The interior of the shell can
be filled with a fusion fuel mixture, including any combination of
deuterium and/or tritium and/or helium-3 and/or other fusible
isotopes. Other embodiments of the invention provide methods for
manufacturing diamond shells and for filling diamond shells with a
fusion fuel mixture.
I. Capsule Structures
[0098] A. Capsule Shell
[0099] As used herein, the term "capsule" refers to any
three-dimensional object having a shell with an identifiable inner
wall that substantially encloses an interior region. For use in
fusion applications, the interior of the shell is advantageously
filled with "fusion fuel," which may be in solid, liquid, gas or
other states. Examples of suitable fusion fuels are described
below.
[0100] FIG. 1 is a cross-sectional view of one embodiment of a
spherical capsule 100 having a diamond shell 102 that is thin
compared to the overall dimension of the capsule. Shell 102 is
advantageously of uniform thickness, and its inner wall 105 defines
an interior region 104. Like all drawings herein, FIG. 1 is not to
scale, and different embodiments may be of different sizes; e.g.
the shell may have a diameter (measured at the outer surface of the
shell) with a length anywhere between about 20 microns and about 1
meter. In one embodiment, the outer diameter of capsule 100 is 2
millimeters (mm), the inner diameter is 1.850 mm, and the shell
thickness is 75 micrometers (.mu.m). In preferred embodiments, the
shell thickness is uniform to within 50 to 100 nanometers (nm) to
insure the concentricity of the inner and outer capsule walls.
[0101] In some embodiments, diamond shell 102 is made of
crystalline diamond. As is well known in the art, a crystal is a
solid material consisting of atoms arranged in a lattice, i.e., a
repeating three-dimensional pattern. In crystalline diamond, the
lattice is a diamond lattice 200 as shown in FIG. 2A. Diamond
lattice 200 is made up of atoms 202 connected by sp.sup.3 bonds 206
in a tetrahedral configuration. (Lines 208 are visual guides
indicating edges of a cube and do not represent atomic bonds.) As
used herein, the term "diamond" refers to any material having atoms
arranged in a diamond lattice as shown in FIG. 2A and is not
limited to carbon atoms or to any other particular atoms. Thus, a
"diamond shell" may include predominantly carbon atoms, silicon
atoms, and/or atoms of any other type(s) capable of forming a
diamond lattice, and the term "diamond" as used herein is not
limited to carbon-based diamond.
[0102] In other embodiments, diamond shell 102 is an imperfect
crystal. For example, the diamond lattice may include defects, such
as extra atoms, missing atoms, or dopant or impurity atoms of a
non-majority type at lattice sites; these dopant or impurity atoms
may introduce non-sp.sup.3 bond sites in the lattice, as is known
in the art. Dopants, impurities, or other defects may be naturally
occurring or deliberately introduced during fabrication of shell
102.
[0103] In still other embodiments, diamond shell 102 is made of
polycrystalline diamond. As is known in the art, polycrystalline
diamond includes multiple crystal grains, where each grain has a
relatively uniform diamond lattice, but the grains do not align
with each other such that a continuous lattice is preserved across
the boundary. The grains of a polycrystalline diamond shell 102
might or might not have a generally preferred orientation relative
to each other, depending on the conditions under which shell 102 is
fabricated. In some embodiments, the size of the crystal grains can
be controlled so as to form nanoscale crystal grains; this form of
diamond is referred to as "nanocrystalline diamond." For example,
the average value of a major axis of the crystal grains in
nanocrystalline diamond can be made to be about 100 nm or less.
[0104] In still other embodiments, diamond shell 102 is made of
amorphous diamond. Amorphous diamond, as described in
above-referenced document [SULL], does not have a large-scale
diamond lattice structure but does have local (e.g., on the order
of 10 nm or less) diamond structure around individual atoms. In
amorphous diamond, a majority of the atoms have sp.sup.3-like bonds
to four neighboring atoms, and minority of the atoms are bonded to
three other atoms in a sp.sup.2-like bonding geometry, similar to
that of graphite; FIG. 2B depicts graphite-like sp.sup.2 bonds 214
between an atom 210 and three other atoms 212. The percentage of
minority (sp.sup.2-bonded) atoms may vary; as that percentage
approaches zero over some area, a crystal grain becomes
identifiable.
[0105] Thus, it is to be understood that the term "diamond
material" as used herein includes single-crystal diamond,
polycrystalline diamond (with ordered or disordered grains),
nanocrystalline diamond, and amorphous diamond, and that any of
these materials may include defects and/or dopants and/or
impurities. Further, the distinctions between different forms of
diamond material are somewhat arbitrary not always sharp; for
example, polycrystalline diamond with average grain size less than
about 100 nm can be labeled nanocrystalline, and nanocrystalline
diamond with average grain size less than about 10 nm can be
labeled amorphous.
[0106] Shell 102 may include multiple layers of diamond material,
and different layers may have different composition. For example,
some but not all layers might include a dopant; different
polycrystalline oriented layers might have a different preferred
orientation for their crystal grains or a different average grain
size; some layers might be polycrystalline oriented diamond while
others are polycrystalline disoriented, and so on. In addition,
coatings or implantations of atoms that do not form diamond
lattices may be included in shell 102.
[0107] Shell 102 may be fabricated as a unitary diamond structure,
which may include crystalline, polycrystalline or amorphous
diamond. Alternatively, shell 102 may be fabricated in sections,
each of which is a unitary diamond structure, with the sections
being joined together after fabrication. Examples of both types of
fabrication processes are described below.
[0108] Shell 102 is advantageously made with very smooth interior
and/or exterior surfaces. For example, surface smoothness may be
defined based on the maximum or root-mean-square (RMS) deviation
from a given locus defining a "perfect" surface shape or from a
measured locus defining an average surface shape. Smoothness may be
measured by sampling the entire surface or just within a certain
region on the surface. In one embodiment, the maximum deviation is
controlled to within about 4 nm.
[0109] Shell 102 can also be made with very uniform thickness.
Using techniques described below, the shell thickness may be
controlled such that a maximum or RMS deviation of the distance
between the inner and outer surfaces does not exceed a specific
value; for example, the maximum deviation may be less than about
200 nm. Where shell 102 is spherical, uniform thickness implies
concentricity of the internal and external shells; as a result, the
spherical capsule will exhibit a highly symmetric mass
distribution, which is helpful in providing a symmetric implosion
of the fusion fuel.
[0110] In other embodiments, the shapes of the inner and outer
surfaces of shell 102 can be controlled to provide a non-zero
concentricity offset. Concentricity can be measured by sampling
points on each of the inner and outer surfaces and using those
points to determine an "inner center" and an "outer center"; to the
extent that these two centers are different, the spheres are not
concentric. Concentricity can be controlled by controlling the
thickness of the shell during fabrication thereof; specific
techniques are described in section II below and in
above-referenced application Ser. No. 11/067,609. In some
embodiments, shells may be made with a precisely controlled
concentricity offset, which may be near zero or non-zero as
desired.
[0111] Methods of measuring smoothness and concentricity are
described in above-referenced application Ser. No. 11/067,609.
Suitable techniques described therein include scanning probe
microscopy (SPM), atomic force microscopy (AFM), interferometric
microscopy (IM) using electromagnetic or acoustic waves, and the
like.
[0112] B. Fusion Fuel
[0113] For use in fusion applications, the interior of shell 102 is
filled with a mixture (referred to herein as "fusion fuel")
consisting essentially of some number of fusible atoms or ions.
Atoms or ions of any element susceptible to nuclear fusion may be
included in the fuel mixture, including but not limited to hydrogen
isotopes such as ordinary light hydrogen (.sup.1H), deuterium
(.sup.2H), tritium (.sup.3H), and/or helium isotopes such as
.sup.3He or .sup.4He. Any combination of fusible atoms, including
atoms of different elements and/or different isotopes of the same
element, may be used. For example, in one embodiment, the fuel
mixture consists primarily of deuterium and tritium in
approximately equal concentration; such a fuel mixture is referred
to herein as "D-T". In another embodiment, the fuel mixture
includes deuterium, tritium and .sup.3He and is referred to herein
as "D-T-.sup.3He". In still another embodiment, the fuel mixture
includes deuterium and .sup.3He with little or no tritium and is
referred to herein as "D-.sup.3He".
[0114] In yet another embodiment the fusion fuel mixture is (or
includes) a chemical formulation of helium-3 deuteride. In
particular, .sup.3He.sup.2H is expected to be a stable gas with a
higher liquefaction and solidification temperatures than either of
its constituents; the compound also provides the desired ratio of
constituents for the fusion reaction of .sup.3He and deuterium.
[0115] Helium-3 deuterides, including .sup.3He.sup.2H, can be
prepared by a reaction of pure or nearly pure .sup.3He with pure or
nearly pure .sup.2H using a disassociative Ryberg process (e.g.,
using laser absorption by or electron beam interaction with helium
orbital electrons) and cooled by laser or electron cooling to a
stable temperature; such processes are known in the art for
reacting non-isotopically purified Helium and Hydrogen to form
helium hydrides.
[0116] The fuel can be held in solid, liquid, and/or gas states.
For example, FIG. 3 is a cross-sectional view of a capsule 300 in
which shell 302 is lined with a layer 304 of fusion fuel in a solid
state. The interior 306 is filled with the same fuel in a fluid
(e.g., liquid or gas) state. In one embodiment, a charge of D-T
fuel in capsule 300 exerts a pressure of around 300 atmospheres at
room temperature.
[0117] C. Access Port
[0118] In some embodiments, the capsule shell may form a complete
barrier preventing access to the interior. In other embodiments,
the shell includes one or more openings (referred to herein as
"access ports") that permit access to the interior, e.g., for
purposes of filling the capsule with the fusion fuel. FIG. 4A, for
example, is a cross-sectional view of a capsule 432 with an access
port 434 in the shell 436 that provides access to interior 440. The
access port may be a simply be a hole whose size is measured as a
percentage of missing surface area. Access ports can range in size
from nearly 0% to about 50% of the surface area. The port can be
normal to the surface or at an oblique angle, and may provide a
straight path, bent path, or curved path connecting the exterior
and interior of the shell.
[0119] In some embodiments, a sealable member (e.g., a valve, plug
or other structure) may be provided, allowing the port to be opened
or closed. FIG. 4B schematically illustrates a plug or valve 438
that closes port 434 of capsule 432. Plug or valve 438 can be
opened to allow material to be inserted into or removed from the
interior, or it can be closed to keep material in or out of the
interior. Plug or valve 438 can be formed as an integral part of
the shell, e.g., as a deformable flap 406 of diamond material, or
as a separate structure. Further examples of access ports and valve
or plug structures for closing access ports, as well as techniques
for fabricating such features, are described in Section II
below.
[0120] C. External Coating
[0121] As is known, carbon-based diamond crystals, whether
synthetic or naturally occurring, can be damaged by exposure to
high temperatures in an oxidizing environment. To protect a
carbon-based diamond capsule 100 (FIG. 1), a stabilizing coating,
such as a silicon carbide film, may be applied to the outer surface
of shell 102. The stabilizing material may be applied as a coating
over the diamond shell or implanted between the crystal grains.
Such stabilizing coatings are advantageously kept to a minimal
thickness so as not to affect implosion of the capsule; in some
embodiments, capsule 100 might not have any stabilizing coating.
(Uncoated capsules can be protected by avoiding exposure to
damaging environments.)
[0122] In some embodiments, a unique pattern can be made by small
variations in the thickness of the stabilizing coating. These
variations, which are detectable under ultraviolet (UV) and/or
x-ray examination of the shell, can be used to provide a unique
signature to each capsule. In addition, silicon carbide layers may
be incorporated into shell 102 to facilitate and control
fabrication of a relatively thick shell 102. A further discussion
of silicon carbide coatings for stabilization and identification
can be found in above-referenced U.S. Provisional Application Ser.
No. 60/554,194. Unique identification can be used, e.g., to track
individual capsules during research aimed at optimizing capsule
design and/or fuel mixtures, and can also be used during
large-scale production for inventory tracking and quality control
purposes.
[0123] A variety of materials may be used to coat and stabilize
diamond shells. Examples include silicon, germanium, silicon
carbide, silicon dioxide (including quartz), silicon fluoride,
magnesium fluoride, silicon nitride, titanium, titanium dioxide,
titanium carbide, titanium nitride, tantalum, tantalum carbide,
tantalum nitride, molybdenum, molybdenum carbide, molybdenum
nitride, tungsten, tungsten carbide, tungsten nitride, boron
carbide, boron nitride, chromium, chromium carbide, chromium
nitride, chromium oxide, or aluminum oxide (including alumina).
Suitable materials also include various other oxides, carbides,
nitrides, fluorides or the like.
II. Methods of Making and Filling
[0124] As noted above, the shell of a capsule can be made in
sections and then assembled, or the shell can be grown
substantially complete as a single section. Examples of both types
of processes will now be discussed. Additional description of
methods of making and filling capsules may be found in
above-referenced application Ser. No. 11/067,517, entitled "Diamond
Capsules and Methods of Manufacture".
[0125] A. Forming and Attaching Sections of a Shell
[0126] FIG. 5 is a flow diagram of a process 500 for forming a
diamond capsule according to an embodiment of the present
invention, and FIGS. 6A-6K are illustrations of the capsule at
various stages of process 500. In process 500, sections of a shell
for a capsule are grown on suitably shaped substrates or molds,
then attached or bonded together.
[0127] At step 501, a suitably shaped substrate (also referred to
herein as a "form substrate" or "mold") is obtained. The mold has a
surface shaped to the desired inner or outer surface configuration
of a portion of the capsule such that diamond material grown on the
mold takes the desired shape.
[0128] For instance, FIG. 6A is a cross-sectional view of a form
substrate (mold) 600 that may be obtained at step 501. Mold 600
includes a 1-0-0 silicon wafer 602 having a top surface 603 on
which hemispherical surface structures 604 are provided for forming
substantially spherical capsules. Structures 604 may be formed
integrally to wafer 602, e.g., using conventional silicon growth or
etching processes. Alternatively, structures 604 may be formed
separately from wafer 602, then bonded thereto. Structures 604 are
advantageously shaped and finished to the desired shape and surface
quality of the inner surface of the capsule shell. The shape and
finish of structures 604 may take into account differences in
thermal expansion characteristics and other properties between the
substrate material and the diamond material to be grown
thereon.
[0129] It is to be understood that while hemispherical structures
are shown in FIG. 6A, structures with other shapes may be
substituted to produce capsule sections in shapes other than
hemispheres. In some embodiments, the surface structures of a mold
may include recessed (concave) structures instead of or in addition
to the convex structures depicted in FIG. 6A.
[0130] Where silicon molds are used, conventional techniques for
preparing the substrates; shaping, smoothing, polishing or
otherwise working the diamond material grown thereon; and removing
the substrate material from the diamond material may be used.
However, the present invention is not limited to silicon molds; any
material on which diamond can be grown may be substituted. Examples
of suitable materials include silicon, silicon carbide, silicon
nitride, silicon dioxide (including quartz), titanium, titanium
carbide, titanium nitride, tantalum, tantalum carbide, tantalum
nitride, molybdenum, molybdenum carbide, molybdenum nitride,
tungsten, tungsten carbide, tungsten nitride, boron carbide, boron
nitride, chromium, chromium carbide, chromium nitride, aluminum
oxide (including alumina), or a suitable glass. In addition, the
bulk of a mold structure such as structure 604 may be made of a
first material that is easily shaped to high precision but not
necessarily suited to growing diamond and coated with a layer of a
different material more suited to growing diamond.
[0131] Referring again to FIG. 5, at step 502, one or more layers
of crystalline, polycrystalline, or amorphous diamond material
(i.e., any material having a diamond lattice structure at least on
the scale of a few nanometers) is grown on at least a portion of
the mold surface to form a shell section. The surface of the
layer(s) generally follows the shape of the substrate surface. For
example, FIG. 6B shows hemispherical diamond shell sections 606
formed on hemispherical structures 604 of mold 600.
[0132] Conventional techniques for growing a diamond layer on a
flat surface may be employed in combination with the non-flat
surface of mold 600 to grow a diamond layer on the mold surface. If
appropriate, the surface of structures 604 may be seeded to
facilitate growth of the diamond material thereon. Various growth
processes may be used. For example, crystalline or polycrystalline
diamond can be grown using chemical vapor deposition (CVD), plasma
enhanced chemical vapor deposition (PECVD), hot wire diamond
growth, or the like. Amorphous diamond can be grown using pulsed
laser deposition (PLD) or other processes known in the art.
Suitable process parameters for each of these techniques are known
in the art and may be employed to form shell sections 606.
[0133] Where polycrystalline or nanocrystalline diamond is grown,
the growth process may foster the formation of crystal grains with
either a preferred or random orientation relative to a surface of
the layer. Techniques known in the art for growing ordered or
disordered polycrystalline or nanocrystalline diamond may be
employed.
[0134] In some embodiments, multiple diamond layers are grown
successively during step 502 (FIG. 5), and different layers may
have different grain sizes (e.g., some layers might be
polycrystalline while others are nanocrystalline or amorphous). The
grains in different layers may have the same preferred crystal
orientation, different preferred orientations, or random
orientations as desired. In some embodiments, the surface
structures of the mold define fittings at or near peripheral edges
of some or all of the shell sections, and the fittings are grown as
part of the shell sections. For instance, recesses may be formed on
one section that match protrusions on another section; such
fittings can be used in capsule assembly, as described below.
[0135] In some embodiments, dopants or other materials are
introduced during the growth process to provide desired electrical,
thermal or mechanical properties in the completed shell. The term
"dopant" as used herein refers to atoms of a type other than the
type of which the diamond lattice is predominantly composed that
occupy lattice sites. Dopant atoms may provide more, fewer, or the
same number of bonding sites as the majority atoms and may be
introduced for a variety of purposes. For example, dopants may be
added to make certain layers, certain regions, or all of the shell
electrically conductive. Dopants or other materials may also be
used to stabilize the shell from oxidation at high
temperatures.
[0136] Some dopants may also affect the behavior of the shell in an
ICF reactor environment. For example, adding dopants can change the
absorption cross section for various forms of radiation (e.g.,
x-rays) that may be incident on the shell. Dopants may also be used
to modify the thermal expansion coefficient, specific heat, or
other thermal properties of the shell. Such dopants may be
introduced uniformly throughout the shell. Alternatively, one or
more dopants may be selectively introduced (e.g., introduced only
in certain regions of the shell or introduced at different
concentrations in different regions of the shell) to impart desired
gradients in various thermal and/or electromagnetic properties. In
an ICF reactor, such gradients can impart a specific shape to the
explosion or ablation of the shell and thereby also shape the
spatial distribution of the imploding fuel mixture.
[0137] For these and other purposes, a variety of dopants may be
used, including but not limited to boron, nitrogen, astatine,
polonium, americium, antimony, bismuth, arsenic, germanium, iodine,
tellurium, selenium, silicon, and bromine.
[0138] Other materials can also be introduced, e.g., as discrete
layers between two layers of diamond material or covering the
outermost layer of diamond material. Examples include stabilizing
materials, such as silicon, germanium, silicon carbide, silicon
dioxide (including quartz), silicon fluoride, magnesium fluoride,
silicon nitride, titanium, titanium dioxide, titanium carbide,
titanium nitride, tantalum, tantalum carbide, tantalum nitride,
molybdenum, molybdenum carbide, molybdenum nitride, tungsten,
tungsten carbide, tungsten nitride, boron carbide, boron nitride,
chromium, chromium carbide, chromium nitride, chromium oxide, or
aluminum oxide (including alumina). Suitable materials also include
various other oxides, carbides, nitrides, fluorides or the like.
Still other suitable materials provide adhesive properties;
examples include the above materials as well as gold, silver,
copper, nickel, platinum, indium, palladium, lead and uranium.
[0139] Dopants or other materials can be introduced during growth
of a diamond or other material layer, or during separate ion
implantation, diffusion, or coating steps that may be performed at
various stages during growth of the shell sections. Processes known
in the art may be used to introduce dopants during diamond growth
or to grow or deposit layers of other material between stages in
diamond growth. Where a multilayered shell section is grown,
dopants or other materials may be included in some, all or none of
the layers.
[0140] In some embodiments, dopants or other materials help to
facilitate and control growth of the shell. For example, where
relatively thick shells are being formed, introduction of dopants
or other materials at various stages during diamond growth can help
reduce strain on the diamond lattice, e.g., by creating layers with
varying interatomic distances resulting from the dopant atoms or
material layers. Introduction of such layers can help to maintain
the proper atomic spacing (thus reducing strain) within the
different layers of polycrystalline or nanocrystalline diamond
material as the diameter of the shell increases. Layers of
amorphous diamond can also be introduced to relieve strain.
[0141] In one such embodiment, for a spherical shell with an inner
diameter of 1.95 mm, and an outer diameter of 2 mm (or more),
diamond might be grown to a thickness of at least 50 micrometers
(about 5% of the radius of the sphere). Thereafter, a silicon
coating can be deposited over the diamond layer, followed by
implantation of germanium into the silicon and further diamond
growth. The surface of the shell may be reseeded prior to further
diamond growth. It is to be understood that other dopants or
combinations of dopants may also be used and that such dopants may
be added continuously throughout the diamond growth process or only
during selected stages of diamond growth as desired.
[0142] Referring again to FIG. 5, at step 503, following growth of
the shell material, the shell surfaces may be further shaped to
impart desired properties (e.g., smoothness or desired surface
features) thereto. Prior to such shaping, the substrate may be cut
apart (e.g., by dicing the wafer) and some or all of the excess
material stripped away, allowing each section to be processed
separately; FIG. 6C illustrates a shell section on a wafer portion
602' that may result from dicing wafer 602 of FIG. 6B.
Alternatively, a group of shell sections may be processed together
while still attached to a common substrate, and dicing is not
required. In some embodiments, the shell sections 606 may be
removed from the molds 600 prior to post-growth shaping, allowing
both inner and outer surfaces of the shell sections to be
shaped.
[0143] A variety of shaping operations may be performed. In some
embodiments, the inner and/or outer surfaces may be chemically
modified, polished, lapped, or ground to a desired smoothness,
e.g., such that a maximum or RMS local deviation from smoothness on
the surface is less than about 4 nm. Conventional micromachining or
nanomachining processes may be used. Additional tools and processes
for shaping diamond surfaces at nanoscale precision are described
in above-referenced application Ser. No. 11/067,609.
[0144] In other embodiments, portions of the surface of a shell
section 606 may be machined or chemically modified to provide
fittings for a mechanical connection between sections. For example,
FIG. 6D shows a hemispherical shell section 608 with complementary
fittings 610, 612, which may be grown during step 502 using
suitably shaped molds, then machined during step 503 to precise
tolerances. Two shell sections 608 can be interlocked using
fittings 610, 612 as described below.
[0145] In still other embodiments, some or all of the diamond shell
sections may be differentially heated to provide or enhance a
desired chemical, structural, mechanical, acoustic, optical,
electrical or magnetic property that depends on absolute
temperature of the object and/or on a temperature differential
between different portions of the object. In some embodiments, the
difference in properties between shell sections may persist after
the completed shell reaches thermal equilibrium; in other
instances, a transient difference in properties (e.g., a size
difference between shell sections due to thermal expansion of one
of the sections) is induced and exploited to assemble shell
sections as described below.
[0146] Referring again to FIG. 5, at step 504, the shell sections
are removed from the mold. FIG. 6E is a cross-sectional view of
hemispherical diamond shell sections 606 of FIG. 6B after removing
mold 600, including hemispherical sections 604.
[0147] In some embodiments, removal of the mold involves
destruction of at least part of the mold material. For instance,
all or part of the mold material may be removed using conventional
wet or dry etching processes that chemically dissolve the mold
material but not the shell material. Where the substrate is made of
silicon, a well-known dry etchant such as CF.sub.6 might be used.
Examples of wet etchants include liquid sodium hydroxide, which can
be used at 300.degree. C. in the Bayer process to dissolve alumina;
lye; aqua regia; hydrofluoric acid; and the like.
[0148] In other embodiments, the removal process does not destroy
the integrity of the mold, allowing the mold to be reused. For
example, in FIG. 6C, if shell section 606 covers about 50% (or
less) of a spherical surface, then the mold 602 can be popped out
by slightly flexing shell section 606 and/or mold 602.
[0149] Referring again to FIG. 5, at step 505, the shell sections
606 (FIG. 6E) are aligned and joined at their peripheral edges 609
to form a capsule, as shown in FIG. 6F. Joining step 505 may be
accomplished using various mechanical or chemical bonding
techniques. In some embodiments, joining step 505 is performed in a
fluid environment, and the resulting capsule is thereby filled with
fluid. Examples of joining techniques will now be described; it is
to be understood that other techniques could be substituted.
[0150] In some embodiments, the peripheral edges 609 of shell
sections 606 are shaped such that they interlock when pushed
together. For example, FIG. 6G shows a magnified view of a
complementary latch 614 and socket 616 at the junction of two shell
sections 613, 615. Latch 614 on a peripheral portion of the inner
surface 617 of shell section 613 has a protrusion 618 with a
sloping interior surface 619 followed by a recess 620 in the
opposite direction from the slope. Socket 616 of shell section 615
has a recess 621 on the outer surface 622. The two sections 613,
615 interlock when pushed together in relative alignment, as shown
in FIG. 6G.
[0151] In other embodiments, the two-shell sections are joined
using a form fit or interference member that extends in a band
around the widest point of the capsule to hold the sections
together under pressure. For example, FIG. 6H shows a magnified
view of shell sections 625, 626 that are held together by an
interference ring 627. The interference ring 627 is made as a
protrusion approximately parallel to the surface 628 of shell
section 625 and may be an integral part of shell section 625.
Interference ring 627 is shaped such that its inner surface aligns
with the outer surface 630 of the other shell section 626. In some
embodiments, in order to join the sections, a temperature
differential is created such that section 626 is at a lower
temperature than the section 625 while sections 625 and 626 are
pushed together as shown. The resulting shell is then allowed to
come to thermal equilibrium while sections 625 and 626 are held in
place. As equilibrium is reached, section 625 contracts and/or
section 626 expands so that the outer surface 630 pushes into the
inner surface of interference ring 627, thus creating an
interference contact.
[0152] For instance, shell section 626 may be cooled to 4 K while
shell section 625 is kept at a higher temperature (around 20 K)
such that the interference ring 627 is a close but sliding fit on
the target shell section 626. The two sections 625, 626 are pushed
together and allowed to reach equilibrium temperature at 4 K,
thereby contracting ring 627 into interference contact with section
626 and completing the assembly. This assembly procedure can be
executed in a fluid environment (e.g., a hydrogen atmosphere), and
the resulting capsule will contain some amount of the fluid.
[0153] In other embodiments, the shell sections are joined using a
bonding agent. For example, as shown in FIG. 6I, shell sections 606
can be placed in recesses 635 of a coating and alignment substrate
637 and aligned under a mask 639 so that edges 609 are exposed.
Coatings 641 are then applied to edges 609, e.g., using sputtering
or evaporation techniques well known in the art. The coatings 641
are advantageously chosen to have a melting point that is higher
than the maximum operating temperature of the finished capsule but
lower than the melting point of the diamond shell material.
[0154] As shown in FIG. 6J, after coatings 641 are applied, edges
609 of section 606 are placed in contact with corresponding edges
609' of a complementary section 606', to which corresponding
coatings 641' have been applied. Proper alignment of section 606
with section 605' may be achieved by forming complementary
alignment structures in the respective substrates 637, 637', as is
known in the art. The entire structure is baked (e.g., in a vacuum
or inert gas oven) at a temperature and pressure sufficient to
soften or reflow the coatings 641, 641', resulting in a bond
between sections 609, 609'.
[0155] Coatings 641 may be applied to the entire surface of edges
609 or to selected contact regions on edges 609 as long as each
contact region is sufficiently large (e.g., at least about 4
.mu.m.sup.2) to create a bond. These contact regions may have
different orientations with respect to each other so that parts may
be joined at complex bond angles; for instance, the edges to be
joined can be rotated or tilted at any angle with respect to each
other and are not required to be parallel to each other.
[0156] As shown in FIG. 6K, coatings 641 advantageously include
multiple materials, such as an "adhesion" material 643 that adheres
well to the edge of the diamond shell and a "bond" material 645
that can be softened or reflowed to connect the two sections. In
some embodiments, an additional "coupling" material 644 that
adheres well to both the adhesion material 643 and the bond
material 645 can be deposited between adhesion material 643 and
bond material 645; adhesion material 643 and bond material 645 need
not adhere particularly well to each other, as long as each adheres
well to coupling material 644. In other embodiments, the same
material may provide both adhesion and bonding.
[0157] Coating 641 are advantageously made of materials that will
provide a strong bond at the intended operating temperature of the
resulting part. For example, for high-temperature applications
(e.g., from about 200.degree. C. up to about 800.degree. C.), metal
bonds may be used. In one embodiment, hemispherical shell sections
606 form a spherical capsule with a 2-mm diameter when assembled. A
carbide-forming adhesion material 643 (e.g. titanium, silicon,
chromium, or iron) is sputtered or evaporated onto edges 609 to a
thickness of about 50 to 100 nm. A similar thickness of a coupling
material 644 (e.g. nickel) is then applied, followed by a 200 nm to
2 micron thickness of a bond material (e.g. copper). The shell
sections 606 are then placed in contact with each other and baked
at a sufficient temperature (e.g., 900.degree. C.) and pressure of
about 50 g/mm.sup.2 to bond the two copper coatings together. Those
having ordinary skill in the art will recognize that other coating
materials may also be used to provide higher or lower temperature
performance.
[0158] For lower temperature applications (e.g., below about
200.degree. C.), a similar process may be used, except that an
additional material that adheres well to copper and has a lower
melting point than copper may be applied after the copper bond
material 645. Examples of suitable materials include silver, silver
tin, tin, and/or lead, and other solder-like materials. The shell
sections can be bonded at a lower temperature, e.g., 250.degree.
C.
[0159] For even lower temperature applications (e.g., below about
100.degree. C.), edges 609 can be sputtered with silicon, over
which a spin-on glass is applied. The shell sections can then be
bonded at a temperature of, e.g., 150.degree. C.
[0160] In another embodiment, coatings 641 include the adhesion,
coupling and bonding materials 643-645 described above, along with
a further coating of germanium or any alloy thereof including
antimony and tellurium. In still other embodiments, coatings 641
may include alloys or layers of astatine, polonium, bismuth, and/or
arsenic. These materials provide good bonding performance at low
temperatures and also impart electromagnetic absorption
characteristics that can be helpful in inducing symmetric expansion
of the shell in an ICF reactor.
[0161] In some embodiments suitable for ultra-low temperature
applications (e.g., about 4 K or below), various gases can be used
as "cryoglues" to hold the shell sections together. For example, as
shown in FIG. 6L, a band 650 is placed around shell sections 606,
enclosing the joint line 652. Shell sections 606 are held at an
ultra-low temperature (e.g., around 4 K), while a gas is directed
inside band 650 using a heated pipe 654. The gas cools and hardens
against the diamond joint area 652, providing an adhesive bond.
[0162] Gases suitable for use as cryoglues are mechanically inert
and provide sufficient strength to hold the sections of the capsule
in relative alignment. Examples include neon, argon, krypton, xenon
and radon. In particular, neon's extremely low thermal
conductivity, nearly five orders of magnitude less then
carbon-based diamond, and relatively low melting point (24.48 K)
make it a preferred choice as a cryoglue for many applications.
[0163] It will be appreciated that the bonding agents and
techniques described herein are illustrative and that variations
and modifications are possible. Any material or combination of
materials that provides adequate adhesion between peripheral
surfaces of adjacent shell sections at the desired operating
temperature may be used.
[0164] Referring again to FIG. 5, at step 506, after the shell
sections have been joined to form a capsule, an additional layer of
diamond may be grown on the outer surface of the capsule. Any of
the methods described above may be used, and techniques described
below in Section II.B. for uniformly coating a three-dimensional
object may also be employed. In some embodiments, the additional
growth tends to fill any gaps between the shell sections, providing
a smoother surface finish.
[0165] In some embodiments, the shell sections are joined in an
atmosphere containing the fusion fuel in a fluid (e.g., liquid or
gas) state, and the completed shell encloses some quantity of the
mixture, with the precise quantity depending on the volume enclosed
by the shell and the pressure of the atmosphere. The shell sections
may also be joined in a low temperature environment in which the
fusion fuel is frozen into a solid, in which case a solid ball or
other shape of "fusion fuel ice" can be enclosed in the shell.
[0166] In other embodiments, an access port may be formed through
the capsule (step 507), allowing access to the interior after the
capsule is assembled. Access ports can be used for filling the
capsule and also for providing access to the capsule for purposes
of working the inner surface of the capsule and/or for working with
other material (e.g., fusion fuel ice) that may be enclosed in the
capsule.
[0167] Access ports may be made in various ways. For example, an
energetic beam of electrons, ions or photons may be used to remove
the diamond material from some portion of the shell, thereby
creating an opening to the interior. Femtolasers, which provide
very short pulses of energetic photons, can be used to create
small, well controlled openings. In other embodiments,
nanomachining techniques guided by atomic force microscopy (AFM) or
scanning force microscopy (SFM) may be used. Suitable techniques
are described in above-referenced application Ser. No.
11/067,609.
[0168] In other embodiments, an access port may be etched through
the diamond material. For example, FIGS. 7A-7F are cross-sectional
views showing a capsule at various stages of etching a port through
the shell. In FIG. 7A, a diamond shell 702 is coated with an etch
resist 704 such as aluminum. (It is to be understood that coating
thicknesses are not shown to any particular scale in the drawings.)
In FIG. 7B, a layer of photoresist 706 covers etch resist 704. In
FIG. 7C, photoresist 706 is patterned (e.g., by focused pattern or
focused spot, or laser spot or electron beam) so that photoresist
706 covers etch resist 704 except over a region 708 where the
access port is to be located. In FIG. 7D, the exposed etch resist
704 has been etched to expose the diamond surface. In FIG. 7E,
shell 702 has been etched through opening 710 to create an access
port 712. Diamond shell 702 may be etched using, e.g., an oxygen
plasma or phosphoric acid. In some embodiments, photoresist 706 is
also removed by the etchant used to remove the diamond, leaving
exposed etch resist 704, which protects diamond shell 702
everywhere except in region 712. In FIG. 7F, the rest of etch
resist 704 has been etched away, producing a diamond shell 702 with
an access port 712.
[0169] In still other embodiments, an access port can be formed by
not enclosing some portion of the joint area where two sections are
joined during step 505.
[0170] In some embodiments, the access port may be sealed after
access to the interior is no longer necessary. For example, where
the port is used to fill the capsule with a fluid, additional
diamond material can be grown to cover or fill in the port after
the capsule has been filled. Masking techniques or other techniques
may be used to preferentially grow diamond inside or over the port.
In other embodiments, a valve or plug may be provided for sealing
the port. Examples of valves and plugs are described below,
particularly in Section II.C.
[0171] Referring again to FIG. 5, at step 508, the exterior of the
capsule is advantageously coated with a protective material, such
as silicon carbide. Such a coating may be of the type described in
Section I.D above and may be applied using techniques described in
above-referenced Application No. 60/554,194 or other suitable
techniques.
[0172] In some embodiments, the coating provides resistance to
oxygen penetration along with specific optical and identification
functions. By suitably varying the materials and thickness of
successive layers, one can construct a coating with specific
optical properties, allowing different capsules to be uniquely
identified, e.g., by a combination of scattered light and/or by
coherent light signatures. In addition, the mass of the capsule can
be used for at least partial identification.
[0173] In a specific embodiment, the coating material, e.g. silicon
carbide may be doped to be conductive or left in its intrinsic form
as an insulator. The silicon carbide layer may be directly coated
onto the diamond, or in the case of carbon diamond, a layer of
silicon may be deposited to act as an adhesion layer between the
carbon diamond and the silicon carbide. In another embodiment, a
carbon diamond structure may be implanted with a seed layer of
silicon, forming silicon carbide sites. A silicon carbide coating
can then be applied by CVD growth of the silicon carbide. The
technique is well known in the art and is described, e.g., in the
above-referenced article [STOL]). Alternatively, a silicon carbide
plasma arc can be allowed to condense on the seeded surface. In yet
another embodiment, a vacuum arc of a the desired coating material
is applied to a diamond surface that has been made conductive by
dopants or by exposure to ultraviolet or x-ray radiation; a vacuum
arc can be used to coat diamond surfaces at a wide range of
temperatures from near 0 K up to about 1000.degree. C.
[0174] A variety of materials may be used to coat and stabilize
diamond shells. Examples include silicon, germanium, silicon
carbide, silicon dioxide, silicon fluoride, magnesium fluoride,
silicon nitride, titanium, titanium dioxide, titanium carbide,
titanium nitride, tantalum, tantalum carbide, tantalum nitride,
molybdenum, molybdenum carbide, molybdenum nitride, tungsten,
tungsten carbide, tungsten nitride, boron carbide, boron nitride,
chromium, chromium carbide, chromium nitride, chromium oxide, or
aluminum oxide. Suitable materials also include various other
oxides, carbides, nitrides, fluorides or the like.
[0175] It will be appreciated that process 500 is illustrative and
that variations and modifications are possible. Steps described as
sequential may be executed in parallel, order of steps may be
varied, steps may be modified or combined, or some steps may be
omitted. For example, in some embodiments, the shell sections may
be removed from the form substrate before any post-growth
processing or between post-growth processing steps. An access port
might or might not be made, depending on whether access to the
interior is desired in a particular embodiment.
[0176] Surface modifications may be applied to the shells at
various stages in manufacture, e.g., using nanomachining techniques
as described in above-referenced application Ser. No. 11/067,609.
For example, the outer or inner surface of shell sections 606 can
be machined while sections 606 are still attached to mold 600 or
after removal therefrom. In other embodiments, the outer surface of
a finished capsule may be modified. In still other embodiments the
inner surface of a finished capsule may be modified via a set of
suitably positioned access ports. Fusion fuel ice enclosed in the
capsule may also be modified via access ports, and fusion fuel ice
may also be modified prior to insertion in the capsule using
nanomachining techniques at sufficiently low temperatures, e.g., to
shape a surface of a ball of fusion fuel ice to high smoothness or
sphericity.
[0177] In addition, while hemispherical sections are described
herein, it is to be understood that any number of substrate
sections may be used. For instance, FIG. 6M is a cross-sectional
exploded view of a capsule 660 formed from three sections 662, 664,
666. Further, the process is not limited to spherical capsules;
capsules of any shape may be created by using suitably shaped form
substrates or molds, as described in above-referenced application
Ser. No. 11/067,517.
[0178] B. Growing a Unitary Shell
[0179] FIG. 8 is a flow diagram of a process 800 for forming a
diamond capsule according to an alternative embodiment of the
present invention, and FIGS. 9A-9H are illustrations of the capsule
at various stages of process 800. In process 800, a capsule shell
is grown around a form substrate such that the shell covers more
than half of the surface area of the form substrate.
[0180] At step 801, a suitably shaped form substrate is obtained.
The form substrate advantageously has the intended shape of the
inner surface of the shell, e.g., spherical, elliptical,
cylindrical, or polyhedral. The form substrate may be made of any
material on which diamond can be grown, and the substrate may have
a smooth or featured surface as desired. Any of the materials
described in Section II.A above as being suitable for molds may be
used to make a form substrate, and a form substrate made of one
material may be coated with a different material.
[0181] In one embodiment, a spherical form substrate 900 as shown
in FIG. 9A is made from an alumina or silicon dioxide (quartz) or
glass core 902 that is finished to some degree of smoothness, and a
coating 904 applied to the outer surface to provide enhanced
smoothness. Coating 904, which may be at least twice as thick as
the maximum surface variation of the core 902, is advantageously
made of a very hard material (such as SiC or Si.sub.3N.sub.4) that
can be finished to a finer, smoother surface, sphericity, shape
conformity, or shape variability than alumina or silicon dioxide.
For example, in one embodiment, the RMS or maximum local deviation
from smoothness on an outer surface of form substrate 900 is less
than about 4 nm. If the form substrate core 902 is made from a
material which can provide the desired degree of smoothness, then
an additional coating 904 is not required.
[0182] Referring again to FIG. 8, at step 802, the form substrate
900 is suspended by or positioned on a support structure in
preparation for diamond growth. For example, FIG. 9B illustrates a
support pin 905 holding form substrate 900. It is to be understood
that multiple support pins 905 may be provided. Support pin 905 is
advantageously made of a material with poor adhesion to diamond or
a material that can be etched away after diamond has been grown on
form substrate 900.
[0183] Other support structures may also be used, including
structures with multiple contact points. The support structures may
include relatively narrow pins (or rods) that provide a small
contact area with form substrate 900, pedestal structures that
provide a larger contact area, or the like. In some embodiments,
the support structure may include a suspension structure that
contacts form substrate 900 from above. Further examples of support
structures are described in Section II. C below.
[0184] At step 803, a diamond shell is grown over the form
substrate; FIG. 9C shows a diamond shell 906 grown over coating 904
of form substrate 900. Selected areas on the surface of form
substrate 900 may be patterned and seeded prior to diamond growth,
and any of the techniques described in Section II.A above for
growing diamond on a shaped substrate may be used for growing the
diamond shell at step 803. In some embodiments, step 803 may
include growing multiple layers, introducing dopant atoms or other
materials, and/or forming coating layers, as described above.
Depending on the composition of support structure 905, diamond
might or might not coat the surface of structure 905 where it
extends beyond the outer wall of shell 906.
[0185] In preferred embodiments, diamond shell 906 is made to be
relatively uniform. For example, seeded form substrate 900 may be
placed on a continuously moving element in the diamond growth
chamber, such as a spinning disk with a track along which form
substrate 900 can roll, so that all portions of the surface of
substrate 900 are approximately uniformly exposed to the plasma or
vapor. In another embodiment, form substrate 900 may be moved
(e.g., rotated) intermittently during diamond growth to allow
diamond shell 906 to grow uniformly over the surface of substrate
900. Pin 905 (or other support structures) may remain in contact
with the same point on form substrate 900, or it may move to
different points as form substrate 900 is rotated. Where a track is
used, the track may provide the support structure, and pin 905 or
similar structures may be omitted.
[0186] At step 804, after diamond shell 906 is formed, the assembly
is removed-from pin 905 or other support structures for further
processing, including removal of form substrate 900. Removal of the
diamond shell may result in one or more holes through diamond shell
906 where pin 905 was in contact with the surface of form substrate
900. For example, FIG. 9D illustrates a hole 908 left by pin 905.
In some embodiments, hole 908 is usable as an access port. At this
stage, any excess diamond material that may have formed around pin
905 may also be removed (e.g., by cutting, grinding, or the
like).
[0187] At step 805, one or more additional access ports may be
created through diamond shell 906, e.g., if pin 905 or another
support structure did not create a suitable hole 908, or if more
access ports or larger ports are desired. Techniques described
above with reference to step 507 of process 500 (FIG. 5) may be
used to create these additional access ports or to enlarge hole 908
into a suitable access port.
[0188] Referring again to FIG. 8, at step 806, the form substrate
material is removed through the access ports. The form substrate
may be removed by wet or dry etching using suitable etchants to
dissolve the form substrate material, leaving the diamond shell
intact. One suitable etching process is illustrated in FIGS. 9E-9G.
A first etchant selectively removes coating material 904 until
surface 910 of form core 902 is reached, as shown in FIG. 9E. For
instance, if coating material 904 is SiC or Si.sub.3N.sub.4,
CF.sub.4 and/or other etchants known in the art may be used.
[0189] Thereafter, a second etchant selectively removes core
material 902 through opening 912, as shown in FIG. 9F. For example,
if core 902 is made of alumina, liquid sodium hydroxide may be used
in the well-known Bayer process to selectively remove core 902. If
core 902 is made of silicon dioxide, hydrofluoric acid may be used
to etch away the material. The remainder of coating 904 may then be
removed using the first etchant (or a different etchant), to obtain
the hollow shell 906 shown in FIG. 9G.
[0190] It is to be understood that the invention is not limited to
specific form substrate materials or etchants, and different
techniques for removing core material through an access port may be
substituted. In general, the speed with which material can be
removed depends at least in part on the number, size, and relative
placement of the access ports used for removal, with more and/or
larger ports generally correlating with faster removal.
[0191] Referring again to FIG. 8, after removal of the form
substrate material, at step 808 the interior of the capsule can be
filled with a fluid via access port 908 of FIG. 9G, and at step 809
access port 908 is filled or sealed. A wide variety of fluids may
be inserted at step 808, and specific examples are described below;
in other embodiments, the interior of the capsule is left hollow.
In some embodiments, access port 908 is sealed through further
diamond growth, e.g., through a mask as described above with
reference to step 514 of process 500 (FIG. 5). Diamond may be grown
so as to cover or fill in port 908. In other embodiments, various
plug or valve structures may be provided for closing access port
908. Specific examples of valve or plug structures and techniques
for fabricating them are described below.
[0192] For example, in one embodiment, shell 906 with access port
908 (shown in FIG. 9G) is placed into a chamber that is filled with
a fusion fuel such as D-T, D-T-He or D-He as described above. In
some embodiments, methane may be mixed with the fusion fuel. The
pressure in the chamber is held above 500 atmospheres for a time
(t.sub.e) long enough to allow the internal and external pressures
to reach equilibrium. Thereafter, the pressure in the chamber is
rapidly reduced to around 1 atmosphere), and further diamond growth
over a time (t.sub.g) that is much shorter than te closes the
access port, trapping the high-pressure fusion fuel inside.
[0193] Diamond growth at step 809 may be continued until the ports
are sized appropriately to the needs of the application. In some
instances, the ports may be completely filled or only partially
filled.
[0194] In some embodiments, electrical charge may be used to
promote or deter diamond growth in or near the access port. For
example, all or part of the diamond shell can be made conductive by
doping with boron, nitrogen or other suitable dopant. During a
diamond growth process, the conductive portions of the shell can
then be charged so as to repel the plasma; if the area inside or
around the access port is not charged (or is not doped), diamond
growth will preferentially occur in or around the access port so
that the port can be closed or constricted as desired. It should be
noted that for other applications, the conductive portions of the
shell could also be charged so as to attract the plasma, so that
diamond growth would preferentially occur on the conductive
portions of the shell.
[0195] In other embodiments, all or a portion of the surface 910
that defines access port 908 (see FIG. 9G) is made conductive by
doping one or more layers of diamond shell 906, at least around the
desired portions of surface 910. The layers may be doped as shell
906 is grown (e.g., while support structure 905 is present). Any
conductive portion along the length of surface 910 may be made to
encourage or inhibit diamond growth by inducing an appropriate
charge to attract or repel the plasma. In yet another embodiment,
diamond growth can be promoted in the portion of surface 910
nearest inner wall 912 by lowering the growth temperature and
adjusting the platen temperature of the layer, shell, or coating
being grown. In this manner, the size of the access port for each
layer, coating, or shell may be controlled, and the size of the
port may be varied as a function of depth within the shell.
[0196] In other embodiments, access port 908 can be narrowed to a
specified diameter (e.g., about 5 microns or less) for some
distance along surface 910, as shown in FIG. 9H. The port may then
be closed using a diamond plug 914. Diamond plug 914 may be as long
as or shorter than the full depth of port 908. Plug 914 can be
formed by growing diamond in a suitably shaped mold or by machining
diamond parts to the desired shape. Port 908 can be prepared to
accept plug 915, e.g., by reaming port 908 to remove excess
material and/or by polishing the surface 910 to a desired
finish.
[0197] Referring again to FIG. 8, at step 810, post-growth
processing is performed. Such processing may include machining or
shaping the capsule, coating the capsule, or other steps to provide
a finished capsule with the desired properties; these steps may be
similar to the post-growth processing steps described in Section
II.A above. It should be noted that in some embodiments, coating
with silicon carbide, alumina or other oxygen transport inhibitors
is advantageously performed before the capsule is filled with
fusion fuel.
[0198] It will be appreciated that the process described herein is
illustrative and that variations and modifications are possible.
Steps described as sequential may be executed in parallel, order of
steps may be varied, steps may be modified or combined, or some
steps may be omitted. For example, any of the modified and
alternative processes described below may be used in place of any
or all of the steps shown in process 800.
[0199] C. Additional Processes [0200] 1. Multiple Support Pins
[0201] In one modification to process 800, a form substrate may be
set upon multiple support pins mounted in a base. FIGS. 10A-10E
illustrate a capsule at various stages of such a manufacturing
process. FIG. 10A shows a form substrate 1002 set upon multiple
pins 1004 that are mounted in a base 1006. The ends of pins 1004
that contact substrate 1002 may be pointed (as shown in the
enlargement at the right of FIG. 10A), flat, or concave (or convex)
so as to conform to the shape of the form substrate, and the cross
section of the pins along line A-A may be generally circular,
rectangular, or any other desired shape.
[0202] Pins 1004 may support substrate 1002 from the bottom (as
shown) or from the side, or substrate 1002 may be suspended from
pins 1004 that contact substrate 1002 from above. In addition, pins
1004 may be oriented normally, obliquely, or tangentially to the
surface of substrate 1002 at the point of contact.
[0203] FIG. 10B shows a diamond shell 1008 grown over the form
substrate 1002 while substrate 1002 remains in contact with pins
1004. FIG. 10C shows shell 1008 after its removal from pins 1004; a
number of access ports 1012 through shell 1008 have been created.
FIG. 10D shows shell 1008 after the removal of form substrate 1002
through access ports 1012. After removing form substrate 1002,
ports 1012 may be closed, as shown in FIG. 10E, to create a hollow
capsule. In an alternative embodiment, ports 1012 may be closed
without removing form substrate 1002, so that the interior of the
resulting capsule is filled with a solid material as shown in FIG.
10F.
[0204] 2. Processing Multiple Form Substrates in Parallel
[0205] In another modification, a large number of form substrates
may be processed in parallel. FIG. 11 is a flow diagram of a
suitable process 1100, which is a variation of process 800
described above, and FIGS. 12A-12I illustrate various stages and
features of this process.
[0206] At step 1101, a number of recesses (or holes) are formed in
a substrate wafer of a suitable material. For instance, FIG. 12A
shows a wafer 1204 with a number of recesses 1208 formed therein.
Wafer 1204 may be made of silicon, silicon carbide, sapphire or
other suitable material in which recesses 1208 can be formed.
Recesses or holes 1208 may be created by any process including but
not limited to lithography and etching, conventional machine tools,
electric discharge machining (EDM), or water jets, and each recess
1208 is advantageously made to be larger than the dimensions of a
capsule to be formed therein.
[0207] At step 1102, fingers 1202 for supporting a form substrate
1206 are formed in the recesses 1208, as shown in inset 1210 of
FIG. 12A, which also shows a form substrate 1206 in place in recess
1202. Fingers 1202 are advantageously made of a substrate material
such as silicon nitride, silicon carbide, silicon oxide, sapphire
or the like. In one embodiment, the length of fingers 1202 is at
least 1.5 times the intended thickness of the capsule shell; the
transverse cross section of fingers 1202 may be rectangular with
dimensions on the order of 200 .mu.m by 0.1 .mu.m, or approximately
circular with an area of under 20 .mu.m.sup.2.
[0208] As shown in side view in FIG. 12B and end view in FIG. 12C,
each finger 1202 may be made of one or more tubes 1210 on or
embedded in a support structure 1212. Tubes 1210 may be hollow or
solid tubes formed of silicon nitride. In some embodiments, tube
1210 is a multilayer structure, e.g., with a hollow or solid
silicon nitride core surrounded by polysilicon and further
surrounded by a coating of silicon nitride. In one embodiment, each
tube 1210 has a rectangular cross section of about 3.5 .mu.m by
about 5 .mu.m and is at least as long as the intended thickness of
the capsule shell. Support structure 1212, which is fixed to the
side of recess 1208, may be made of silicon, silicon carbide,
silicon oxide, sapphire or other suitable substrate material. Tube
1210 is placed on support 1212 such that end 1211 will be in
contact with form substrate 1206.
[0209] At step 1103, diamond 1214 is grown over fingers 1202, as
shown in side view in FIG. 12D. At step 1104, a release material is
applied to wafer 1204, including fingers 1202. Any material with
low adhesion to diamond may be used as a release material; examples
include tantalum nitride, silicon carbide, or the like.
[0210] At step 1105, a spherical form substrate (or mold) 1206 is
inserted into each recess 1208. Form substrates 1206 may be
generally similar to the spherical form substrates described above,
and may be inserted in various ways. For example, a number of forms
1206 may be rolled or shaken over wafer 1204, allowing a form 1206
to drop into each recess 1208. As shown in FIG. 12E, forms 1206
drop into recesses 1208 and contact the diamond coating 1214 of
fingers 1202 at a surface 1216.
[0211] At step 1106, a diamond layer is grown on forms 1206 to a
thickness less than the total desired thickness of the capsule
shell but large enough to provide a shell with sufficient
structural integrity and rigidity to be self-supporting. FIG. 12F
shows a form 1206 with diamond 1218 grown thereon so as to form a
shell. (For convenience, only a portion of shell 1218 is
shown.)
[0212] At step 1108, forms 1206 with diamond shells 1218 are
removed from recesses 1208; the presence of a release material
between diamond finger 1214 and shell 1218 allows for easy
separation of the two. During removal, the position and orientation
of each shell 1218 is advantageously maintained or otherwise
registered so that each shell 1218 can be returned to the same
recess 1208 in the same orientation. Upon removal from recess 1208,
shell 1218 has openings therein corresponding to the contact area
of fingers 1202. At step 1110, form substrate 1206 is removed
through these openings, e.g., using etching processes as described
above, leaving hollow diamond shells 1218.
[0213] At step 1112, the support material 1212 in region 1216 of
finger 1202 is removed, as shown in FIG. 12G, leaving the under
side of tube 1210 exposed. Conventional etching processes may be
used to remove this material. After removal of the support material
1212, tube 1210 and diamond coating 1212 remain in region 1216,
which is at least as long as the intended final thickness of the
diamond shell.
[0214] Thereafter, at step 1114, diamond shells 1218 are replaced
in recesses 1208. Preferably, each shell 1218 is replaced in the
same recess from which it was removed, with the same orientation
relative to fingers 1202 as it previously had. At step 1116,
diamond growth over shells 1218 is continued, until shells 1218
reach the desired thickness as shown in FIG. 12H.
[0215] At step 1118, shells 1218 are removed from recesses 1208;
this step may involve cutting through diamond 1214, e.g., using a
laser or mechanical cutting device. At step 1120, final processing
(e.g., polishing and coating as described above) is performed. It
should be noted that a portion of diamond coating 1214 from the
finger 1202 advantageously becomes part of diamond shell 1218.
[0216] FIG. 12I shows the resulting diamond capsule 1220, in which
tube member 1210 provides an access port. In some embodiments, tube
member 1210 may have a hollow core; if the core is not hollow, tube
member 1210 or its core may be removed, e.g., using a suitable
etching process. Capsule 1220 can be filled via the access port
provided by tube member 1210, which can then be closed, e.g., by
filling it with additional diamond or a plug as described
above.
[0217] 3. Forming an Integrated Valve Structure
[0218] In other embodiments a valve can be formed integrally with
the shell. The valve provides a sealable opening into the interior
of the capsule through movement or deformation. In one embodiment,
the valve is formed from a flap of diamond that can deform slightly
under a pressure differential to seal the capsule.
[0219] A shell with an integral valve flap can be made using a
process similar to process 1100 described above with a slight
modification in placement of the support fingers relative to the
form substrate. FIG. 13A shows a representative finger 1302 that
includes a tube member 1310 resting on a support member 1312.
Finger 1302 is coated with diamond 1314. Fingers 1302 may be
similar in structure and composition to fingers 1202 of FIGS.
12B-12D and may be arranged in recesses 1208 in a wafer 1204 as
shown in FIG. 12A. Fingers 1302, however, are arranged to contact
the surface of form substrate 1306 at a shallower angle (i.e., more
nearly tangential to the surface) than that shown in FIG. 12C.
Process 1100 can be used with fingers 1302 to form a shell for a
capsule.
[0220] The resulting capsule 1320 is shown in FIG. 13B. Shell 1322
has an access port 1324 formed from tube member 1310 of FIG. 13A.
Access port 1324 penetrates through shell 1322 at an angle a with
respect to a surface normal 1326, as shown by the dotted lines. A
relatively thin flap 1326 of diamond material is thereby formed.
When the pressures inside and outside shell 1322 are nearly equal,
flap 1326 is in its neutral position, and access port 1324 is open,
allowing material to enter the shell. If the pressure inside shell
1322 exceeds the pressure outside, flap 1326 deforms outward toward
member 1328, closing access port 1324. Thus, capsule 1320 can be
filled with a fluid by placing capsule 1320 in a high-pressure
fluid environment and allowing capsule 1320 to reach equilibrium,
then quickly reducing the external pressure so that flap 1326
deforms outward, sealing the high-pressure fluid inside.
[0221] The sealing behavior of flap 1326 can be further enhanced by
suitably shaping the end 1330 of tube member 1310 (FIG. 13A) that
contacts form substrate 1306. For instance, FIG. 13C illustrates a
tube member 1310 with flanges 1332 formed near end 1330.
[0222] In another variation, the end of a pin used to support the
form substrate is shaped such that a flap will be formed as the
diamond shell is grown. FIGS. 14A and 14B illustrates examples of
shaped pins 1402, 1404; sections of respective diamond shells 1406,
1408 with flaps 1410, 1412 formed around pins 1402, 1404 are shown.
After the shell (1406 or 1408) is grown, pin 1402 or 1404 can be
extracted or etched away to open an access port. It should be noted
that shaped pins such as pins 1402, 1404 may be used to define
access ports regardless of whether the shell is formed as a unit
(e.g., as in process 800 of FIG. 8 described above) or in sections
(e.g., as in process 500 of FIG. 5 described above).
[0223] In still another embodiment, an integrated valve structure
can be formed by introducing different support members at different
stages in diamond growth, e.g., in a further variation of process
800 described above. FIGS. 15A-15F illustrate one suitable
procedure. FIG. 15A shows a form substrate 1502, which might be,
e.g., 2 mm in diameter, supported by a first support member 1504
(e.g., a pin as described above), allowing formation of a uniformly
thick diamond layer 1506, which may be, e.g., 10 nm to 100 .mu.m
thick. In FIG. 15B, first support member 1504 has been removed and
replaced by a second support member 1508. Second support member
1508 is advantageously large enough to cover the opening 1510 in
layer 1506 that was created by removing first support member 1504
and to extend beyond opening 1510 in at least one direction. With
second support member 1508 in place, a diamond layer 1512 is grown
over layer 1506. The combined thickness of layers 1506 and 1512
might be, e.g., 50 .mu.m to 100 .mu.m.
[0224] Thereafter, as shown in FIG. 15C, support member 1508 is
removed, creating an opening 1514 contiguous with opening 1510.
Form substrate 1502 is advantageously removed through openings 1510
and 1514, e.g., as described above in process 800. Next, as shown
in FIG. 15D, a third support member 1516 is introduced, and a final
diamond layer 1518 is grown. FIG. 15E shows the finished capsule
1520 after removal of support member 1516; opening 1522 created by
support member 1516 is contiguous with opening 1514, creating an
access port to the interior of capsule 1520. The access port
includes a deformable flap 1524. As shown in FIG. 15F, when capsule
1520 is filled with a fluid at higher pressure than the external
environment (pressure is indicated by the arrows), flap 1524
deforms outward, sealing capsule 1520.
[0225] In some embodiments, the access port may be used to fill
capsule 1520 with a fluid at temperatures as low as a few degrees
K, after which capsule 1520 and its contents are brought up to a
higher temperature (e.g., room temperature, around 20 C) while
opening 1522 is covered. At temperatures at which the fluid inside
capsule 1520 is a gas, the high pressure (e.g., up to 500
atmospheres) pushes on diamond flap 1524 to seal capsule 1520, as
depicted in FIG. 15F, and opening 1522 can be uncovered.
[0226] To provide a high-quality seal, the walls of the access port
may be polished as they are formed or before the capsule is filled.
Where the diamond surface of the port walls can be brought to a
surface smoothness (RMS deviation) of less than 10 nm, a
diamond-to-diamond seal is adequate for many applications.
[0227] In other embodiments, e.g., where the walls of the access
port are not smooth surfaces, the sides of the access port may be
coated with a compliant sealing material to improve the quality of
the seal. Examples of compliant sealing materials include
germanium, silicon, silicon nitride, silicon carbide, aluminum,
antimony, bismuth, polonium, astatine, americium, platinum or gold;
the coating may be 10 nm to 50 .mu.m thick, depending on the grain
size of the diamond material.
[0228] In still other embodiments, an access port with an integral
valve flap may be made using focused ion beam (FIB) and/or
AFM-guided nanomachining after the capsule is formed.
[0229] 4. Discrete Valve Structures
[0230] In another embodiment, the valve or plug that closes the
access port is a discrete structure, which may be made of diamond
or other suitable material, rather than an integral part of the
capsule shell.
[0231] For example, FIGS. 16A and 16B are, respectively, a side
view and an end view of a filament valve 1602 made of a diamond
material. Filament 1602 is advantageously at least as long as the
intended thickness of the capsule shell and has a tapered section
1605, 1606 at each end. Its cross section may be rectangular as
shown in FIGS. 16A and 16B, round, or other shapes as desired.
Slots 1604 are cut or formed in one tapered section 1606 of
filament 1602.
[0232] In one embodiment, shown in FIG. 16C, filament 1602 is
coated with silicon nitride or other removable material 1606. As
shown in cross section in FIG. 16D, the non-slotted end face 1607
of coated filament 1602 is held in contact with the surface of a
form substrate 1608 while a diamond shell 1610 is formed. Shell
1610 is advantageously formed with one or more openings (other than
at filament 1602) through which form substrate 1608 can be removed.
After shell 1610 is formed, coating 1606 is removed (e.g., by
etching), exposing filament 1602.
[0233] Once coating 1606 is removed, filament 1602 is operable as a
valve. FIG. 16E is a cross-sectional view of shell 1610 and
filament 1602 in a filling arrangement. Filament 1602 is displaced
inward by pressure (arrows) of a filling fluid outside the capsule.
Slots 1604 in tapered section 1606 allow for deformation sufficient
that the filling fluid can pass into the capsule through spaces
1612 surrounding filament 1602. In one embodiment, the capsule is
filled at a low temperature as described above.
[0234] After the capsule is filled, a pressure differential between
the interior and exterior of the capsule is created, e.g., by
raising the temperature of the capsule, such that the fluid inside
is at higher pressure than the pressure outside the capsule. As
shown in FIG. 16F, the resulting outward pressure (arrows)
displaces filament 1602 outward, sealing the capsule.
[0235] It is to be understood that FIGS. 16A-16F are illustrative.
Valve structures may be made of diamond or any other suitable
materials and may have any desired shape. Valves may open or close
by displacement (e.g., as shown in FIGS. 16E and 16F), by expansion
and contraction, by deformation, or by other movements.
[0236] 5. Alternative Support Structures
[0237] In embodiments described above, pins, fingers or similar
support structures were shown as having a relatively small area in
contact with the form substrate. In other embodiments, the support
structure may have a larger contact area, which can create a larger
opening and provide for faster removal of the form substrate
material.
[0238] For example, FIGS. 17A and 17B are, respectively, a
perspective view and a side elevation view of a pedestal 1700 on
which a form substrate may be placed. Pedestal 1700, which has a
trapezoidal cross section, is formed or mounted on a substrate base
1702 and, as best seen in FIG. 17B, top surface 1704 of pedestal
1700 has a concave shape with a curvature approximately matching
the curvature of the form substrate (not shown in FIG. 17B) that
pedestal 1700 is intended to support.
[0239] In one embodiment, pedestal 1700 can be formed in a silicon
substrate 1702 using conventional MEMS techniques, followed by
machining of surface 1704 to match the radius of curvature of the
form substrate, then coated, e.g., with a silicon carbide or
silicon nitride coating.
[0240] A form substrate (not shown in FIGS. 17A or 17B) is seeded
and placed on pedestal 1700, e.g., using a mounting material such
as carbon dag (a suspension of fine carbon particles in ethyl
alcohol, methyl alcohol, or other alcohol). A diamond growth
process, e.g., any of the processes described above, is used to
create a diamond shell with an opening corresponding to the shape
of surface 1704 of pedestal 1700. For instance, FIGS. 17C and 17D
are, respectively, a side cross-sectional view and a bottom view of
a shell 1706 that has been formed on a form substrate 1708 held on
pedestal 1700 (not explicitly shown in FIGS. 17C and 17D). An
opening 1710 corresponding to the shape of top surface 1704 of
pedestal 1700 has been created. Opening 1710 is relatively large,
allowing for rapid removal of form substrate 1710. At this stage,
shell 1706 advantageously has a thickness less than the desired
final thickness but sufficient to provide structural integrity and
rigidity.
[0241] After substrate 1710 has been removed through opening 1710,
it will generally be desirable to close or constrict opening 1710
to provide a more complete shell for the capsule. In one
embodiment, a cap member for the capsule is created with form
substrate 1708 in place. After removing the cap member and
extracting form substrate 1708 the cap member is replaced and fused
to the rest of shell 1706 by further diamond growth.
[0242] Formation of a cap member is illustrated in cross-sectional
view in FIG. 17E. Form substrate 1708 with shell 1706 formed
thereon is placed in a holder 1712, with opening 1710 now oriented
upward. A mask plate (or cap plate) 1714 covers most of shell 1706,
leaving opening 1710 and a relatively small surrounding area
exposed. To create an access port for later use in filling the
capsule, a diamond stub 1716 with an internal tube member 1720,
which may be similar to diamond-coated tube 1210 described above,
is placed atop form substrate 1708 and held in place by a suitable
support structure (not shown). The support structure may include,
e.g., a suspension structure or a support member connected to mask
plate 1714. The exposed area, including mask plate 1714 and opening
1710, is coated with a release material, then seeded with diamond,
and further diamond growth forms a cap member 1718. Cap member 1718
may be thicker than shell 1706 but is advantageously still not as
thick as the final capsule thickness.
[0243] After cap member 1718 is formed, it is removed to expose
opening 1710. In one embodiment, cap member 1718 can simply be
pulled free due to the coating of release material between cap 1718
and the surfaces of shell 1706, form substrate 1708, and mask plate
1714. Shell 1706 is removed from holder 1712, form substrate 1708
is removed through opening 1710 and any remaining release material
on shell 1706 or cap member 1718 is stripped away. Cap member 1718
is then replaced in opening 1710, and further diamond growth over
shell 1706 and cap member 1718 can be performed until a desired
final thickness is obtained, as shown in FIG. 17F. The capsule can
be filled via an access port defined by tube member 1720 as
described above.
[0244] It will be appreciated that the size and shape of the
pedestal is illustrative and that other shapes may be substituted.
The pedestal is advantageously shaped such that the cap member that
is formed in and removed from the pedestal location can be replaced
in the opening in only one orientation (as is the case for a
trapezoidal shape, although other asymmetric shapes also provide
this property). For example, in one embodiment, the pedestal might
cover up to 50% of the surface area of the form substrate and may
have an arbitrary shape. In one embodiment, the shell can be formed
in two sections shaped like the flaps of a baseball, which are then
attached to each other. In other embodiments, all or part of the
pedestal might be replaced by a coating of a material such as
tantalum nitride that inhibits diamond growth on coated portions of
the form substrate.
[0245] In addition, rather than using pedestals or other masking
materials to prevent shell growth over some section of the form
substrate, an opening such as opening 1710 could be formed in shell
1706 after it is grown to an intermediate thickness. For example,
laser cutting of the diamond material of shell 1706 could be used
to create opening 1710, or opening 1710 could be created by using
an O.sub.2 plasma or other suitable etchant to etch away the
diamond material through a suitably patterned mask applied to shell
1706.
[0246] Due in part to the larger openings, such configurations
permit fast removal of the substrate, e.g., by etching, since more
substrate material is exposed to the etchant at a given time.
Further, in some instances, depending on the size and shape of the
covered portion of the substrate, the substrate can be removed by
slightly deforming (flexing) the shell and/or the substrate,
allowing the substrate to "pop" free. Flexural removal can be
practiced where the form substrate material is silicon carbide or
another material with poor adhesion to diamond and where the
fraction of the substrate surface area covered by the shell
material is small (e.g., about 50% or less) or where the shell
material is arranged so as not to require the substrate to pass
through a constricted opening, as in the case of the hemispherical
shell sections described in Section II.A above or in the case of a
"baseball flap" shell.
[0247] 6. Filling Capsules with Solid Materials
[0248] In some embodiments, it is desirable to fill a capsule with
solid fusion fuel. Where the capsule is formed in sections, solid
fusion fuel can be enclosed in the capsule when the sections are
joined, assuming that the joining is performed under temperature
and pressure conditions in which the fusion fuel remains
solidified. Where the capsule is formed as a unitary structure,
solid fusion fuel can be introduced by filling a hollow capsule in
an environment in which the fuel mixture is in a fluid state
(liquid or gas), then cooling the capsule to solidify the fuel.
[0249] For example, FIG. 18 is a cross-sectional view showing a
filling assembly 1805 for filling a capsule 1800 that has an access
port 1802 according to an embodiment of the present invention.
Capsule 1800 is first brought to a desired filling temperature in a
vacuum environment so that the interior 1804 is empty. The filling
temperature may be any temperature at which the filling material is
in a fluid state. A filling assembly 1805 that includes a fill tube
1806, a fill valve 1808, and a fluid reservoir 1810 is connected to
access port 1802, either before or after capsule 1800 is brought to
the filling temperature. Fill tube 1806 is advantageously designed
to make a good seal against capsule 1800 in the area of access port
1802 so that minimal fluid escapes during filling. Fluid reservoir
1810 contains the fusion fuel mixture 1812 in a fluid state. Fill
valve 1806 controls the flow of fluid through fill tube 1806.
[0250] Once fill tube 1806 is in place, the environment can be
pressurized to enhance the seal between fill tube 1806 and capsule
1800. Fill valve 1808 is then opened, and a desired quantity of the
fluid fusion fuel mixture 1812 is released into capsule 1800. To
control the quantity of fluid delivered to capsule 1800, fill valve
assembly 1808 may contain a meter, or the amount of fluid present
in reservoir 1810 may be controlled, or other techniques may be
used. Once the desired quantity of fluid has been delivered, fill
valve assembly 1808 is closed, and capsule 1800 is cooled to a
temperature at which the fusion fuel mixture 1812 solidifies.
Access port 1802 may then be closed using techniques described
above (e.g., filling with material, inserting a plug, or the like).
Alternatively, access port 1802 can be left open in embodiments
where capsule 1800 is maintained at a sufficiently low temperature
and high pressure that the filling material 1810 is not lost
through melting or sublimation.
[0251] 7. Diffusion Techniques for Filling Capsules
[0252] In other embodiments, the interior of a capsule may be
filled by diffusion of a fluid through the shell, without an access
port being provided. Diffusion techniques are useful where the
fluid is made of small atoms, small ions or small molecules (such
as hydrogen atoms or hydrogen ions) that are capable of diffusing
through the interstices of the diamond lattice. The capsule is
placed into an environment containing the fluid at an appropriate
temperature and pressure and allowed to reach an equilibrium state
in which as many atoms are diffusing out as are diffusing in, then
removed from that environment to a different environment.
[0253] In preferred embodiments, the filling temperature is higher
than an ambient temperature at which the capsule is to be used;
with the atomic lattice expanded at high temperature, the
high-pressure fluid will diffuse through the shell with relative
ease until equilibrium is reached. Once the capsule is returned to
ambient conditions, the lattice will contract in the cooler
temperature, so that diffusive leakage will be relatively
minor.
[0254] The process can be controlled by choosing the fluid
pressure, the temperature and the time period during which the
diffusive transfer of the fluid takes place. The spacing of atoms
in the diamond lattice will generally be different for different
atoms; accordingly, the range of atoms or molecules that can be
diffused into the interior of the shell, as the spacing between
atoms depends upon the type of atoms in the diamond lattice.
[0255] For example, in one embodiment, the fusion fuel mixture is
any of D-T, D-T-.sup.3He and D-.sup.3He as described above.
Diffusion occurs in a pressure chamber at a pressure of around 400
atmospheres and a temperature at the capsule shell of about
600.degree. C. These conditions are maintained for a sufficient
time to allow the pressure to reach equilibrium between the
interior and exterior of the shell, after which the shell is
returned to room temperature (around 20.degree. C.) and the
pressure reduced.
[0256] Those of ordinary skill in the art will recognize that the
technique of filling a capsule by diffusion is also applicable to
capsules that do not have a diamond lattice structure. Atoms or
molecules of a fluid can diffuse through a shell having any atomic
lattice as long as the lattice spacing is large enough to
accommodate the fluid atoms or molecules, and the diffusion rate
will depend on the size of the fluid atoms or molecules, the
lattice spacing, and the thickness of the shell. For example, atoms
or molecules of a fluid can be diffused into fullerenes, nanotubes,
and other nanoscale shells.
III. Quality Control
[0257] Capsules produced by any of the above or other methods are
advantageously subjected to quality control measurements and
modifications. Such techniques advantageously make use of scanning
probe microscopy (SPM), atomic force microscopy (AFM), interference
microscopy (IM), and/or acoustic wave apparatus, e.g., as described
in above-referenced application Ser. No. 11/067,609 that are
capable of operating at extreme temperatures. For example, where
the shell contains D-T, D-T-.sup.3He or D-.sup.3He that includes an
ice component, temperatures at or below 4 K may be required to keep
the fusion fuel ice solid.
[0258] In one embodiment, an (IM) apparatus with detectors in the
infrared or microwave band can be used to monitor thermal
distribution or material gradients in the object, including its
core. For example, in a multicomponent fusion fuel such as D-T,
D-T-.sup.3He or D-.sup.3He, gradients in the relative concentration
of different components can be detected.
[0259] In another embodiment, ultrasonic standing acoustic waves
are monitored using an SPM or IM apparatus to measure minute
thermal or material gradients in a sample by observing material
displacement and local wavelength variations of the standing
acoustic waves.
[0260] In still another embodiment, AFM-guided nanomachining at
ultralow temperatures can be used to nanolap or thermally ablate
fusion fuel ice in order to shape the frozen surface to a desired
symmetry (or asymmetry). For example, a heated SPM tip made of
diamond, titanium, platinum or other material having an affinity
for hydrogen can be used for this purpose. The fusion fuel ice can
be worked while it is encased in the capsule shell, provided that
the capsule has access ports (or larger holes) distributed across
the surface. Long SPM tips designed to extend through the access
ports and reach the fuel ice inside the shell are advantageously
used. After the surface has been shaped as desired, the access
ports can be cleaned out (e.g., using a suitable reamer) and
closed.
IV. Shipping and Storing Fuel Capsules
[0261] In some embodiments, the capsules are designed to store the
fusion fuel as a gas at high pressure (e.g., on the order of 500
atmospheres) at room temperature. When shipping or storing the
capsules, it is possible that they may be exposed to temperatures
considerably higher than room temperature, which could increase the
internal pressure on the capsule enough to rupture or damage the
diamond shell. For instance, it is well known that a spherical
shell of carbon-based diamond with a radius of 1 mm and thickness
of 0.5 mm is resistant to internal pressures up to 34,542
atmospheres; thinner walled capsules would have a lower limit. By
Gay Lussac's law, the ratio of pressure to temperature is constant
for a gas confined to a constant volume. If the internal pressure
is 500 atmospheres at room temperature (around 20.degree. C.), then
at around 100.degree. C., the internal pressure would near the
limit for carbon-based diamond. If the pressure at room temperature
is around 50 atmospheres, then the capsule would remain intact at
temperatures up to about 750.degree. C.
[0262] It is desirable to ship and store fusion fuel capsules at
room temperature rather than using special cryogenic equipment. In
addition, to prevent damage due to fire or other heat exposure, the
capsule should be impervious to high temperatures (e.g., up to
1000.degree. C.) during shipping and storage.
[0263] To simplify shipping and storage of fusion fuel capsules,
the present invention provides a shipping and storage container
adapted to the purpose. FIG. 19 is a perspective view of a storage
container 1900. A base member 1902 and a lid member 1904 can be
attached to each other via complementary latch members 1906, 1907.
The respective contact surfaces 1908, 1910 of base member 1902 and
lid member 1904 are advantageously rubberized or otherwise adapted
to form a substantially airtight seal so that the inside of
container 1900 can be pressurized when container 1900 is closed.
When closed, the interior of container 1900 provides enough volume
to store one or more fuel-filled diamond capsules. If multiple
capsules are to be stored, the interior may be divided into
sections (not shown), e.g., by perforated or permeable walls, with
one capsule being stored in each section, or multiple capsules may
be stored together in contact with each other.
[0264] The outer walls and seals of base member 1902 and lid member
1904 are advantageously made of a high-temperature ceramic such as
aluminum oxide or silicon carbide and are advantageously thick
enough to sustain an internal pressure in excess of 50,000
atmospheres at a temperature of 1000.degree. C. and to resist
impact forces exceeding 50 times gravity (50 g).
[0265] Lid member 1904 includes a tube 1912 and valve 1914. When
container 1900 is closed, its interior can be pressurized by
connecting a source of high-pressure gas (or other fluid) to tube
1912 and opening valve 1914 to allow the gas to flow into container
1900. When the desired pressure has been reached, valve 1914 is
closed and tube 1912 is disconnected from the source of
high-pressure gas. In some embodiments, a pressure gauge may be
mounted on tube 1912 or elsewhere on container 1900, allowing the
internal pressure to be continuously monitored, regardless of
whether tube 1912 is connected to an external source of
high-pressure gas.
[0266] In one embodiment, one or more capsules filled with fusion
fuel are placed in container 1900 at a low temperature (e.g.,
between zero and 10 K). Container 1900 is then pressurized to a
pressure corresponding to about 300 atmospheres at room temperature
by introducing hydrogen, then removed from the low-temperature
environment. Pressurizing container 1900 with hydrogen
advantageously reduces diffusion of the fuel mixture out of the
capsules during storage, but it will be appreciated that other
gases or gas mixtures may also be used. Container 1900 can then be
transported and stored anywhere on earth without requiring
additional equipment to maintain a cryogenic or pressurized
environment.
VI. Generation of Nuclear Fusion
[0267] According to another aspect of the present invention, a
fuel-containing diamond capsule is used in an indirect-drive
inertial confinement fusion (ICF) reactor. In such systems, the
diamond shell is exposed to x-ray radiation that heats the shell.
The diamond shell expands outward, driving an implosion of its
contents. If the implosion reaches sufficient temperature and
density, a fusion reaction will be initiated.
[0268] FIG. 20A is a cross-sectional view of an indirect-drive ICF
reactor 2000 according to an embodiment of the present invention.
Fusion reactor 2000 includes a hohlraum 2002, which is a cavity
with walls made of a high-Z material (e.g., gold, lead, or
uranium). Optical apertures 2008 are provided at either end of
hohlraum 2002 to permit entry of laser beams 2004 generated by
laser sources 2006, and hohlraum 2002 is configured to radiate
x-rays when heated by laser beams 2004. In some embodiments,
multiple laser sources 2006 are used; in other embodiments, one
laser source generates multiple beams 2004 (e.g., by using beam
splitters) that are directed into hohlraum 2002 from different
directions using suitable optical elements as is known in the art.
Laser beams 2004 are advantageously arranged symmetrically, so that
the walls of hohlraum 2002 are approximately uniformly heated.
Hohlraum 2002, laser sources 2006, and optical components for
directing laser light 2004 from laser sources 2006 onto the walls
of hohlraum 2002 may be of generally conventional design.
[0269] In the center of hohlraum 2002 is a fuel capsule 2010 held
in place by a support web 2012. Capsule 2010 is advantageously a
diamond-shell capsule containing a fusion fuel mixture such as D-T,
D-T-.sup.3He or D-.sup.3He. Any of the capsule structures described
above or other similar structures may be used as capsule 2010, and
any of the fabrication techniques described herein or other
techniques may be used to fabricate capsule 2010 and fill it with
the fusion fuel mixture.
[0270] In one embodiment, fusion reactor 2000 is implemented on a
size scale comparable to that of the National Ignition Facility.
For example, fuel capsule 2010 may be a sphere with a radius of
about 1 mm and a thickness of 50 to 500 .mu.m; the fusion fuel may
include a layer of fuel ice lining the inner surface of capsule
shell 2010 and fuel gas filling the interior. Laser sources 2006
may provide a total energy of around 1.8 megajoules (MJ) and power
output of around 500 terawatts (TW).
[0271] In other embodiments, the reactor can be scaled down in
size. For instance, fuel capsule 2010 can be made with a diameter
of 20 .mu.m or less and a thickness of about 0.5-5 .mu.m or less. A
smaller hohlraum, requiring less laser energy, can then be used. In
one such embodiment, reducing the capsule diameter by a factor of
100 reduces the input energy requirement by a factor of about
10.sup.6.
[0272] FIG. 20B is a cross-sectional view of an indirect-drive ICF
reactor 2050 according to another embodiment of the present
invention. Fusion reactor 2050 is somewhat similar to fusion
reactor 2000 of FIG. 20A, except that the energy in reactor 2050 is
supplied by ion beams 2052 incident on either end of a hohlraum
2054. Hohlraum 2054 includes absorber sections 2056 at either end
that absorb the ions and radiate electromagnetic energy into
hohlraum 2054 to produce x-ray radiation in the cavity.
[0273] In the center of hohlraum 2054 is a fuel capsule 2058 held
in place by a support web 2060. Like capsule 2010 (FIG. 20A),
capsule 2058 is advantageously a diamond-shell capsule containing a
fusion fuel mixture such as D-T, D-T-.sup.3He or D-.sup.3He. Any of
the capsule structures described herein or other similar structures
may be used as capsule 2058, and any of the fabrication techniques
described herein or other techniques may be used to fabricate
capsule 2058 and fill it with the fusion fuel mixture.
[0274] A symmetry shield 2062 is advantageously provided to
redirect the electromagnetic energy from absorber sections 2056
away from capsule 2058 toward the walls of hohlraum 2054 to provide
more uniform x-ray heating of capsule 2058.
[0275] Like fusion reactor 2000, fusion reactor 2050 can be
implemented on various size scales, with capsule diameters ranging
from 20 .mu.m or less up to 2 mm or more.
[0276] It will be appreciated that the fusion reactors described
herein are illustrative and that variations and modifications are
possible. Different fusion fuel mixtures may be substituted for
those described herein, and the capsule dimensions (thickness,
outer diameter, and so on) may vary.
VII. Conclusion
[0277] While the invention has been described with respect to
specific embodiments, one skilled in the art will recognize that
numerous modifications are possible. One skilled in the art will
also recognize that the present invention provides a number of
advantageous techniques, tools, and products, usable individually
or in various combinations. These techniques, tools, and products
include but are not limited to: [0278] formation of a sphere,
capsule or pellet for containing nuclear fusion fuel using any or
all of the following: (a) molding or form coating of CVD or PECVD
diamond to form parts of a capsule or pellet; (b) construction of a
sphere by the accumulation of polycrystalline, stress relieved
amorphous or homeoepitaxial diamond; (c) construction of a hollow
sphere by the accumulation of polycrystalline, stress relieved
amorphous or homeoepitaxial diamond; (d) construction of a sphere
by the accumulation of polycrystalline, or homeoepitaxial silicon
carbide; and (e) construction of a hollow sphere by the
accumulation of polycrystalline, or homeoepitaxial silicon carbide;
and/or [0279] a sphere, capsule or pellet for containing nuclear
fusion fuel where the inner surface is smoothed by the form or
mold; and/or [0280] a sphere, capsule or pellet for containing
nuclear fusion fuel where the form or mold is used as a support
and/or holder to complete modifications of and additions to the
outer surface; and/or [0281] a sphere, capsule or pellet for
containing nuclear fusion fuel in which the outer surface is
smoothed by the mold or form; and/or [0282] a sphere, capsule or
pellet for containing nuclear fusion fuel in which the form or mold
is used as a support and/or holder to complete modifications of and
additions to the inner surface; and/or [0283] assembly of a capsule
for containing nuclear fusion fuel using interference fits, locking
clips or any structure molded, formed or machined into sections of
the diamond shell; and/or [0284] assembly of capsules for
containing nuclear fusion fuel using an adhesion layer on the
diamond plus other materials to bond the sections of the capsule;
and/or [0285] assembly of capsules for containing nuclear fusion
fuel using an inert gas solid at temperatures below the inert gas
melting point; and/or [0286] a hollow precision sphere or other
shape for containing nuclear fusion fuel formed by growing diamond
on a ball form made or coated by any of silicon, silicon dioxide
(including quartz), silicon carbide, silicon nitride, titanium,
titanium carbide, titanium nitride, tantalum, tantalum carbide,
tantalum nitride, molybdenum, molybdenum carbide, molybdenum
nitride, tungsten, tungsten carbide, tungsten nitride, boron
carbide, boron nitride, chromium, chromium carbide, chromium
nitride, a suitable glass, aluminum oxide (including alumina), or
any material on which diamond can be grown, where after growth the
interior material is etched out through one or more openings or
holes in the diamond material; and/or [0287] a diamond sphere for
containing nuclear fusion fuel grown on a ball form or mold in
which the diamond coated ball is processed to external dimensions
and finishes of any given precision; and/or [0288] a diamond sphere
for containing nuclear fusion fuel formed by a growth process in
which the ball form is rotated during diamond growth to promote
even coating of the form with the diamond film; and/or [0289] a
diamond sphere for containing nuclear fusion fuel formed by a
process in which a hollowed diamond sphere with one or more
openings is returned to the growth environment and diamond is grown
until the sphere is complete (without any openings) to obtain a
continuous hollow diamond sphere; and/or [0290] processing a
surface of a hollow diamond sphere to any degree of precision to
obtain a precise hollow. diamond spherical shape for containing
nuclear fusion fuel; and/or [0291] a closed shape for containing
nuclear fusion fuel, the shape being made of diamond grown on
seeded substrate material that is supported by support structures
to promote growth of diamond material over the entire structure
except in the vicinity of the support(s), where the substrate
material can be removed mechanically or by an etchant; and/or
[0292] a closed shape for containing nuclear fusion fuel, the shape
being made of diamond grown on substrate material supported by
support structures in which the support holes are reduced in size
by additional diamond growth to 5 micron or less openings; and/or
[0293] a closed shape for containing nuclear fusion fuel, the shape
being made of diamond grown on substrate material supported by
support structures in which the diamond has been partially or fully
boron doped and in which the shape is electrically charged such
that in the region around the holes diamond growth is promoted
while elsewhere it is inhibited; and/or [0294] a closed shape for
containing nuclear fusion fuel, the shape being made of diamond
grown on substrate material supported by support structures in
which the diamond has been partially or fully boron doped and in
which the shape is charged so as to promote growth everywhere
except in the holes; and/or [0295] a closed shape as described
above in which a mechanical means, magnetic field means or chemical
means prevents the growth of boron doped diamond around the holes;
and/or [0296] a closed shape as described above in which the boron
is removed by chemical or mechanical means after the shape is
coated with the boron coating; and/or [0297] a closed shape for
containing nuclear fusion fuel, the closed shape made of diamond
with an electrically conductive additive, in which the electrically
conductive additive to the diamond is nitrogen; and/or [0298] a
closed shape for containing nuclear fusion fuel, the closed shape
made of diamond with an electrically conductive additive, in which
the electrically conductive additive is any suitable conductivity
inducing material, including various forms of carbon; and/or [0299]
a shell such as described above in which the coating built up to
compose the shell is boron carbide and/or boron nitride and/or
silicon carbide and/or silicon nitride and/or tantalum carbide
and/or tantalum nitride and/or tungsten carbide and/or tungsten
nitride and/or any other obdurate material capable of being formed
to extremely high finishes and tolerances; and/or [0300] a shell
such as described above in which the holes are narrowed by the
control of growth temperature and heat applied to the shell; and/or
[0301] a shell such as described above in which the holes are
narrowed to a diameter of 5 microns or less along some portion of
their length; and/or [0302] any machined, molded or formed plug
used to plug up the holes created in the grown diamond shell;
and/or [0303] a process of building a rough mold or form out of
alumina or quartz, then putting an appropriate hard film on the
formed alumina or quartz, followed by further lapping and polishing
to bring this surface to a desired accuracy and resolution for
purposes of growing a diamond shell, where holes to the hard inner
film or to the alumina or quartz are preserved during diamond
growth, and after diamond growth etching is used to remove the
alumina or quartz while other etch means (e.g., a dry etch) are
used to remove other coatings such as silicon nitride or silicon
carbide; and/or [0304] a process of correcting condensed fusion
fuel (which may contain, e.g., deuterium and/or tritium and/or
.sup.3He) in gas or ice states by methods described herein (AGN,
heating of just the tip area around the point of the tip etc,) in
conjunction with long cantilevers which can reach by rotation of
the ball into all the interior surface; and/or [0305] a hollow
diamond shell as described herein in which the holes through which
the shell's interior was etched are grown closed in an atmosphere
of deuterium and/or tritium and/or .sup.3He and optionally also
including compounds of carbon, capturing the high-pressure fluid in
the interior of the shell; and/or [0306] a hollow diamond shell as
described herein, in which very small holes are made in the sphere
by any means including laser, or femtolaser machining, conventional
machining or AFM guided nanomachining; and/or [0307] a hollow
diamond shell filled with high-pressure fusion fuel, where the high
pressure is at least 500 atmospheres or more; and/or [0308] a
hollow diamond shell filled with fusion fuel, in which fusion
ignition is obtained by use of a small compact optical and/or x-ray
and/or other energy source; and/or [0309] a hollow diamond capsule
filled with high-pressure fusion fuel, in which the hollow diamond
capsule is less then 20 microns in diameter; and/or [0310] a hollow
diamond capsule filled with high-pressure fusion fuel in which the
capsule is greater then 20 microns in diameter; and/or [0311] a
fusion fuel capsule having a diamond shell that is coated with
silicon carbide, either directly or over an intervening layer;
and/or [0312] a fusion fuel capsule having a diamond shell that is
coated with any or all of silicon carbide, silicon, silicon dioxide
(quartz), silicon fluoride, magnesium fluoride, silicon nitride,
titanium, titanium dioxide, carbide, titanium nitride, tantalum,
tantalum carbide, tantalum nitride, molybdenum, molybdenum carbide,
molybdenum nitride, tungsten, tungsten carbide, tungsten nitride,
boron carbide, boron nitride, chromium, chromium carbide, chromium
nitride, chromium oxide, or aluminum oxide; and/or [0313] any
diamond structures for containing nuclear fusion fuel where the
structures are stabilized and strengthened by being layered or
incorporated into layers of silicon carbide; and/or [0314] any
device, structure or mechanism usable for containing nuclear fusion
fuel, the structure being composed in whole or part of diamond
stabilized by silicon carbide and/or coated with layers in any
order consisting of any or all of silicon carbide, silicon, silicon
fluoride, magnesium fluoride, silicon nitride, titanium, titanium
dioxide, carbide, titanium nitride, tantalum, tantalum carbide,
tantalum nitride, molybdenum, molybdenum carbide, molybdenum
nitride, tungsten, tungsten carbide, tungsten nitride, boron
carbide, boron nitride, chromium, chromium carbide, chromium
nitride, chromium oxide, aluminum oxide, or any stable oxide, any
stable fluoride, or any stable nitride; and/or [0315] a
fusion-fuel-containing diamond capsule with a mechanism to allow
only one way flow into the capsule; and/or [0316] a valve for a
fusion-fuel-containing diamond capsule using a double tapered
single crystal diamond structure; and/or [0317] a solid or hollow
diamond structure for containing nuclear fusion fuel in which the
shape is obtained in whole or in part by direct machining or
lapping; and/or [0318] a diamond part, including hollow diamond
spheres for containing nuclear fusion fuel, in which the diamond
mass and shape are the principal mechanical, electrical, optical
and/or thermal load bearing members of the part; and/or [0319] a
diamond part, including diamond spheres for containing nuclear
fusion fuel, in which the structural diamond is engineered to
engage a core material by deformation when a load limit is reached;
and/or [0320] diffusion control of hydrogen and/or its isotopes
and/or .sup.3He and/or other fluid atoms or molecules to increase
or decrease the amount of such material inside a diamond form,
where the diamond form might be carbon-diamond or any other
material or combination of materials; and/or [0321] diffusion
control of hydrogen and/or its isotopes and/or .sup.3He and/or
other fluid atoms or molecules into a diamond form that includes
carbon and any other material or combination of materials; and/or
[0322] diffusion control of hydrogen and/or its isotopes and/or
.sup.3He and/or other fluid atoms or molecules into a diamond form
in which the diamond material is polycrystalline diamond with
single or multiple crystal sizes from 100 nm to 4 or 5
angstroms.
[0323] Thus, although the invention has been described with respect
to specific embodiments, it will be appreciated that the invention
is intended to cover all modifications and equivalents within the
scope of the following claims.
* * * * *