U.S. patent application number 14/486115 was filed with the patent office on 2015-03-19 for polarization insert for a cryogenic refrigerator.
The applicant listed for this patent is Bruker Biospin Corporation, Millikelvin Technologies LLC. Invention is credited to Matthew Hirsch, Neal Kalechofsky.
Application Number | 20150075183 14/486115 |
Document ID | / |
Family ID | 52666697 |
Filed Date | 2015-03-19 |
United States Patent
Application |
20150075183 |
Kind Code |
A1 |
Hirsch; Matthew ; et
al. |
March 19, 2015 |
POLARIZATION INSERT FOR A CRYOGENIC REFRIGERATOR
Abstract
A method includes pneumatically expelling a sample of
magnetically polarized material along a pneumatic flow path from a
cryogenic environment.
Inventors: |
Hirsch; Matthew; (Stoneham,
MA) ; Kalechofsky; Neal; (Stow, MA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Bruker Biospin Corporation
Millikelvin Technologies LLC |
Billerica
Braintree |
MA
MA |
US
US |
|
|
Family ID: |
52666697 |
Appl. No.: |
14/486115 |
Filed: |
September 15, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61878424 |
Sep 16, 2013 |
|
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|
Current U.S.
Class: |
62/3.1 |
Current CPC
Class: |
G01R 33/1276 20130101;
G01R 33/282 20130101 |
Class at
Publication: |
62/3.1 |
International
Class: |
F25B 21/00 20060101
F25B021/00 |
Claims
1. A polarization insert for use in a refrigerator, comprising a
pneumatic flow path that pneumatically expels a sample of
magnetically polarized material from a cryogenic environment.
2. The polarization insert of claim 1, wherein the pneumatic flow
path comprises: a pneumatic port that is connected to and provides
a gas flow path with a gas tube having a gas tube distal end, where
the gas tube comprises a plurality of gas tube heat exchangers
adjacent to the gas tube to cool gas within the gas tube; and a
sample port that is connected to and provides a flow path with an
ejection tube, where the ejection tube is substantially parallel
with the gas tube and has an ejection tube distal end connected to
the gas tube distal end via a coupling that forms a gas flow path
between the gas tube and the ejection tube, where the coupling
includes a base surface having a metallic heat exchanger.
3. The polarization insert of claim 3, where the polarization
insert is substantially U-shaped as formed by the gas tube, the
coupling and the ejection tube.
4. The polarization insert of claim 3, where a pulse of pressurized
gas applied to the pneumatic port provides a motive force that
flows through the gas tube and is coupled to the ejection tube via
the coupling to discharge the sample of magnetically polarized
material located within the ejection tube at the ejection tube
distal end from the sample port.
5. The polarization insert of claim 1, where the source of the
motive pneumatic force is helium gas.
6. The polarization insert of claim 1, where the cryogenic
environment is produced using the dilution refrigerator.
7. The polarization insert of claim 3, where a superconducting
magnet is used to maintain a large magnetic field on the
sample.
8. The polarization insert of claim 1, where a magnetic field is
maintained on the sample during expulsion.
9. The polarization insert of claim 4, where the sample contains at
least one methyl rotor group.
10. The polarization insert of claim 10, where the sample contains
MR active nuclei such as 1H, 13C, 15N, 129Xe, 31P.
11. The polarization insert of claim 4, where the speed of
expulsion is in excess of 1 msec.
12. The polarization insert of claim 1, where the temperature of
the sample is less than about 20 K during expulsion.
13. The polarization insert of claim 1, where the sample of
magnetically polarized material is a liquid at room temperature and
is expelled from the polarization insert in the frozen state.
14. The polarization insert of claim 1, wherein the pneumatic flow
path comprises: a pneumatic port that is connected to and provides
a gas flow path with a gas tube having a gas tube distal end, where
the gas tube comprises a plurality of gas tube heat exchangers
in-line with the gas tube to cool gas within the gas tube; and a
sample port that is connected to and provides a flow path with an
ejection tube, where the ejection tube has an ejection tube distal
end connected to the gas tube distal end via a coupling that forms
a gas flow path between the gas tube and the ejection tube.
15. The polarization insert of claim 14, wherein the coupler
comprises: a metallic heat exchanger; a heating element that
applies heat to a metallic coupler surface; and a thermometer that
provides a signal indicative of temperature at the metallic coupler
surface.
16. A cryogenic refrigerator polarization insert, comprising a
pneumatic port that is connected to and provides a gas flow path
with a gas tube having a gas tube distal end, where the gas tube
comprises a plurality of gas tube heat exchangers in-line with the
gas tube to cool gas within the gas tube; and a sample port that is
connected to and provides a flow path with an ejection tube, where
the ejection tube is substantially parallel with the gas tube and
has an ejection tube distal end connected to the gas tube distal
end, via a coupling that forms a gas flow path between the gas tube
and the ejection tube, where the gas tube and the ejection tube
form a pneumatic flow path that pneumatically expels a sample of
magnetically polarized material from an ejection tube proximal end
in response to pressurized gas being applied to a proximal end of
the gas tube.
17. A dilution refrigerator polarization insert, comprising a
pneumatic port configured and arranged to provide a gas flow path
with a gas tube having a gas tube distal end, where the gas tube
comprises a plurality of gas tube heat exchangers in-line with the
gas tube to cool gas within the gas tube; and a sample port that is
connected to and provides the gas flow path with an ejection tube,
where the ejection tube has an ejection tube distal end connected
to the gas tube distal end via a coupling in the gas flow path
between the gas tube and the ejection tube, where a sample of
magnetically polarized material is expelled from an ejection tube
proximal end in response to pressurized gas being applied to the
pneumatic port.
18. A method comprising: pneumatically expelling a sample of
magnetically polarized material along a pneumatic flow path from a
cryogenic environment.
19. The method of claim 18, further comprising: actively cooling
the pneumatic flow path.
Description
1. CLAIM OF PRIORITY
[0001] This application claims priority from U.S. Provisional
Patent Application Ser. No. 61/878,424, filed Sep. 16, 2013, which
is hereby incorporated by reference.
2. FIELD OF TECHNOLOGY
[0002] The prevent invention relates to sample handling in a
cryogenic environment, and in particular to a polarization insert
for use in a cryogenic environment comprising a pneumatic flow path
that pneumatically expels a sample of magnetically polarized
material from the cryogenic environment.
3. RELATED ART
[0003] A hyperpolarized nuclear spin system is one in which the
nuclear magnetic moments of the sample are more strongly aligned
with an external magnetic field (B.sub.0) than in the Boltzmann
thermal-equilibrium state for given temperature (T) and B.sub.0.
Such samples can provide correspondingly large signals in NMR, MRI,
magnetic resonance spectroscopy (MRS), or MRS imaging (MRSI).
Molecular carriers of nuclear hyperpolarization are thus highly
valued as high-sensitivity probes for imaging or spectroscopy.
[0004] U.S. Patent Application Publications US2009/0016964 and
US2011/0062392, both incorporated herein by reference, describe a
process to generate hyperpolarization for use at moderate
temperatures, by first polarizing the sample at ultra-low
temperature (ULT), for example from tens to hundreds of millikelvin
(mK), and high field (e.g., B.sub.0>5 T). This relies on the
fact that the usual Boltzmann polarization from ULT and high-field
conditions becomes hyperpolarization if transferred to higher T
and/or lower B.sub.0. Co-pending U.S. patent application Ser. No.
14/161,172 discloses an improved sample preparation method for
ultralow temperature hyperpolarization and is also hereby
incorporated by reference.
[0005] U.S. Pat. No. 6,758,059 discloses a dilution refrigerator
assembly. As discussed therein in order for a dilution refrigerator
to be used to investigate samples in high magnetic environments, it
is known to use an elongate, tubular extension to the mixing
chamber which extends into the bore of the magnet. A problem with
conventional elongate, tubular extensions, also known as an insert,
is that the magnetically polarized sample material is not easily
removed from the insert.
[0006] There is a need for an improved technique for removing
magnetically polarized material from an insert within a cryogenic
environment.
SUMMARY OF THE DISCLOSURE
[0007] A method includes pneumatically expelling a sample of
magnetically polarized material along a pneumatic flow path from a
cryogenic environment. The method may include actively cooling the
pneumatic flow path.
[0008] A polarization insert for use in a refrigerator comprises a
pneumatic flow path that pneumatically expels a sample of
magnetically polarized material from a cryogenic environment.
[0009] The pneumatic flow path may comprise a pneumatic port that
is connected to and provides a gas flow path with a gas tube having
a gas tube distal end, where the gas tube comprises a plurality of
gas tube heat exchangers in-line with the gas tube to cool gas
within the gas tube. The pneumatic flow path may also include a
sample port that is connected to and provides a flow path with an
ejection tube, where the ejection tube is substantially parallel
with the gas tube and has an ejection tube distal end connected to
the gas tube distal end via a coupling that forms a gas flow path
between the gas tube and the ejection tube, where the coupling
includes a base surface having a metallic heat exchanger.
[0010] The polarization insert may be substantially U-shaped as
formed by the gas tube, the coupling and the ejection tube.
[0011] A pulse of pressurized gas may be applied to the pneumatic
port to provide a motive force that flows through the gas tube and
is coupled to the ejection tube via the coupling to discharge the
sample of magnetically polarized material located within the
ejection tube at the ejection tube distal end from the sample port.
The source of the motive pneumatic force may be helium gas.
[0012] The cryogenic environment may be produced using the dilution
refrigerator. A superconducting magnet may be used to maintain a
magnetic field on the sample.
[0013] The sample may contain at least one methyl rotor group. For
example, the sample may contain MR active nuclei such as 1H, 13C,
15N, 129Xe, 31P.
[0014] The speed of expulsion of the sample may for example be in
excess of 1 msec. The temperature of the sample may be for example
less than about 20 K during expulsion.
[0015] The pneumatic flow path may comprise a pneumatic port that
is connected to and provides a gas flow path with a gas tube having
a gas tube distal end, where the gas tube comprises a plurality of
gas tube heat exchangers adjacent to the gas tube to cool gas
within the gas tube. The pneumatic flow path may also comprise a
sample port that is connected to and provides a flow path with an
ejection tube, where the ejection tube has an ejection tube distal
end connected to the gas tube distal end via a coupling that forms
a gas flow path between the gas tube and the ejection tube.
[0016] The coupler may comprise a metallic heat exchanger and a
heating element that applies heat to a metallic coupler surface. A
thermometer may provide a signal indicative of temperature at the
metallic coupler surface.
[0017] In one embodiment a cryogenic refrigerator polarization
insert includes a pneumatic port that is connected to and provides
a gas flow path with a gas tube having a gas tube distal end, where
the gas tube comprises a plurality of gas tube heat exchangers
adjacent to the gas tube to cool gas within the gas tube. The
insert also includes a sample port that is connected to and
provides a flow path with an ejection tube, where the ejection tube
is substantially parallel with the gas tube and has an ejection
tube distal end connected to the gas tube distal end via a coupling
that Bonus a gas flow path between the gas tube and the ejection
tube. The gas tube and the ejection tube form a pneumatic flow path
that pneumatically expels a sample of magnetically polarized
material from an ejection tube proximal end in response to
pressurized gas being applied to a proximal end of the gas
tube.
[0018] In another embodiment a dilution refrigerator polarization
insert includes a pneumatic port configured and arranged to provide
a gas flow path with a gas tube having a gas tube distal end, where
the gas tube comprises a plurality of gas tube heat exchangers
adjacent to the gas tube to cool gas within the gas tube. The
insert also includes a sample port that is connected to and
provides the gas flow path with an ejection tube, where the
ejection tube has an ejection tube distal end connected to the gas
tube distal end via a coupling in the gas flow path between the gas
tube and the ejection tube. A sample of magnetically polarized
material is expelled from an ejection tube proximal end in response
to pressurized gas being applied to the pneumatic port.
[0019] It is to be understood that the features mentioned above and
those to be explained below can be used not only in the respective
combinations indicated, but also in other combinations or in
isolation.
[0020] These and other objects, features and advantages of the
invention will become apparent in light of the detailed description
of the embodiment thereof, as illustrated in the accompanying
drawings.
DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1A illustrates an embodiment of a polarization insert
for a dilution refrigerator.
[0022] FIG. 1B illustrates a more detailed illustration of a distal
end of the polarization insert of FIG. 1A showing the coupling of
the ejection tube and the gas tube.
[0023] FIG. 1C is a side view illustration of the structure set
forth in FIG. 1B.
[0024] FIGS. 2A and 2B illustrate first and second heat exchangers
respectively adjacent to (e.g., in line) with the gas introduction
tube (shown here in -90.degree. rotation relative to their
positions for normal operation). FIGS. 2A and 2B depict the
exchangers with nominal temperatures of 160 K and 5 K,
respectively. In each, the spiral path of the tube is represented
by adjacent cross sections through the tube, which are wrapped
around a solid copper cylinder.
[0025] FIG. 3 illustrates the base region of a U-tube, where gas
introduction and eject arms are adjoined (shown here in -90.degree.
rotation relative to position for normal operation). A portion of a
thermal strap connects the base of the U-tube to a mixing-chamber
(MC) plate is shown at the top of the figure. The mixing chamber
plate, while not depicted here, may be situated to the far right of
the portion in shown in this schematic. The strap makes close
thermal contact to a high-purity copper piece at the base (left
side in the figure). This piece contains a set of fingers into
which the silver sinter is packed. Helium gas introduced at the gas
introduction tube condenses at the adjoining space and contact this
sinter, thus completing the transmission of cooling power from the
mix chamber plate and on to the sample. The latter rests on a pair
of wires depicted here as a vertical line cutting across the eject
tube.
[0026] FIG. 4 illustrates a portion of the insert that may include
a plurality of knife edges.
[0027] FIGS. 5A-5G illustrate a plurality of views of an insert,
including a perspective view and rotated views of the insert along
with views of components thereof.
[0028] FIG. 6 illustrates an alternative embodiment closed cycle
refrigerator polarizer.
[0029] The invention can be better understood with reference to the
following drawings and descriptions. The components in the figures
are not necessarily to scale, instead emphasis being placed on
illustrating the principles of the invention. Moreover, in the
figures like reference numerals designate corresponding parts. In
the drawings:
DESCRIPTION
[0030] A dilution refrigerator (DR) is a cryogenic device that
provides continuous cooling to temperatures as low as about 2 mK,
via the heat of mixing of Helium-3 and Helium-4 isotopes. A
dilution refrigerator is a common piece of cryogenic equipment used
throughout the scientific world. In a preferred embodiment, a
polarization insert may be used as an insert for a so called
"top-loading" dilution refrigerator. For example, the polarization
insert may be mated with an Oxford Instruments Model Kelvinox 400
Dilution Refrigerator, with a base temperature of less than about
10 mK, and maximum magnetic field (B.sub.0) of about 14 T. Other
embodiments for dilution refrigerator systems, providing a distinct
base temperature and/or magnetic field, and from other
manufacturers are of course contemplated in the context of the
present invention. In addition, it is contemplated that the present
invention may be used in cryogenic environments that use a
cryogenic refrigerator other than a dilution refrigerator.
[0031] The inventive polarization insert transforms a dilution
refrigerator into a nuclear-spin polarizer capable of accepting a
material sample, polarizing its nuclear spins in an ultra-low
temperature (ULT), high B.sub.0 environment. Subsequently the
polarization insert then ejects the sample from the polarizing
environment, either for transport/storage in more-moderate
conditions (i.e., a lower ratio of B.sub.0 to T) or for immediate
melting and usage. In completing that transport, the polarization
insert converts the nuclear spin polarization established in ULT
and high- B.sub.0 conditions into `hyperpolarization`, i.e., a spin
polarization that exceeds the well-known Boltzmann equilibrium
value for the new conditions of lower (B.sub.0/T).
[0032] In primary applications for such hyperpolarized samples, the
molecules are used as ultrasensitive probes for nuclear magnetic
resonance (NMR), magnetic resonance imaging (MRI), magnetic
resonance spectroscopy (MRS) and MRS imaging (MRSI). A polarization
insert described herein utilizes the cooling power and ULT, high-
B.sub.0 environment of the dilution refrigerator to convert a
molecule with near-zero spin polarization into one whose
polarization approaches the ideal value of P=1. Traditional
NMR/MRI/MRS/MRSI observe signals from only very weakly polarized
nuclear spins (e.g., P.about.10.sup.-5-10.sup.-6). Thus, when the
dilution refrigerator polarization insert instead provides P
approaching 1 for in vivo use near room or body temperature, then
dramatic imaging enhancements are available, namely ultrasensitive
and essentially background-free detection of signals from the
hyperpolarized nuclei. An example target molecule is pyruvic acid,
typically enriched with .sup.13C at the C.sub.1 carbon site. This
and other molecules are well-known targets of MRI/MRS/MRSI
measurements, for example, enabling the imaging of metabolic
processes to illuminate cancer diagnoses, inform treatment
protocols and to test drug efficacy. That is possible using
.sup.13C hyperpolarization levels that yield nearly up to 5
orders-of-magnitude sensitivity enhancements.
[0033] FIG. 1A illustrates an embodiment of a polarization insert
100 for a dilution refrigerator. In one embodiment, starting at the
top of the inner vacuum chamber (IVC) of a dilution refrigerator
and working down, the insert includes a room-temperature flange 102
at the top of the cryostat, several radiation baffles (e.g.,
104a-104f) between the room-temperature flange 102 and straps 106
that connect to a 4K plate for example, straps 108 that connect to
a 1K plate, straps 110 that connect to a distillation (or `still`)
plate, straps 112 that connect to a cold plate, and straps 114 that
connect to a mixing chamber plate. The straps 114 of the mixing
chamber plate is where the lowest temperatures in a dilution
refrigerator are produced. The other plates and components allow
for a controlled thermal gradient between these ULT values and the
room-temperature environment outside the dilution refrigerator. The
baffles 104a-104f may be for example, highly polished pieces of
copper or aluminum that block room-temperature radiation from
reaching the lower, colder areas of the dilution refrigerator. Any
insert lowered into the top of the dilution refrigerator for
purpose of introducing a sample to be cooled to millikelvin
temperatures must be properly thermally connected, or `sunk`, to
the various stages listed above. For this reason, the polarization
insert 100 may include various plates and thermal braids made of
for example high purity copper. These elements are purposefully
located throughout the polarization insert 100 to transmit the
cooling power to the insert from the various temperature stages,
i.e., the plates listed above. These thermal connections prevent
the heat that is transmitted down the insert from reaching the
ultimate ULT stage. This allows the bottommost section of the
insert 100 to reach millikelvin temperatures in spite of the
modification of introducing an insert to the dilution
refrigerator.
[0034] Referring still to the embodiment illustrated in FIG. 1A, a
basic form of the insert 100 is a U-shaped tube. One `arm` of the
U-shaped tube is narrower (e.g., about 0.25'' O.D., 0.21'' I.D.)
and is used for both sample insertion and ejection from the
polarization insert 100, and may be referred to as an ejection tube
120. A larger tube (e.g., up to about 0.375'' O.D. in parts)
constitutes the other aim of the U-shaped tube, and is used to
transmit gas from the top of the insert (the room-T environment
outside the dilution refrigerator) to the bottom, and may be
referred to as a gas tube 122. The joining of these two tubes in a
"U-shape" via a coupling 124 at the bottom of the insert enables
rapid pneumatic ejection of the sample from the ejection tube 120.
A bayonet coupling at the top of the insert 100 to mate to the
ejection tube 120 and the gas tube 122. The ejection tube 120 may
include a slight spiral 128 in it to prevent room temperature
radiation from traveling down the inside of the tube to the
ultra-low temperature region. Referring to FIGS. 1A-1C, at the
bottom of the ejection tube 120 are for example two stainless steel
wires 129 (e.g., about 0.015'' diameter). These run across the tube
diameter, perpendicular to the direction of sample travel and
airflow. The wires act as a back-stop, holding samples aloft in the
ULT environment, while also allowing a high throughput of gas
necessary for later ejection of the sample.
[0035] The insert 100 may also include for example two heat
exchangers 130, 132 adjacent to (e.g., in line with) the gas flow
tube 122. These are used to control the T of gas, e.g., when
transmitted to the sample for ejection. Referring now to FIGS. 1A,
2A and 2B, each of the exchangers 130, 132 may be a spiraled copper
tube, located at strategic places within the insert and cooled by
appropriate thermal contacts. The uppermost heat exchanger 130 is
located between the room temperature flange 102 at the top of the
cryostat and the straps 106 connecting to the 4K plate. The first
exchanger 130 is cooled to approximately 160 K by radiation and
exchange gas to its nearby environment. The second heat exchanger
132 is located near the straps 106 connecting to the 4K plate and
uses thermal braids to transmit cooling power from the 4K plate to
its copper spiral. These thermal braids can be altered (e.g., in
thickness) to vary the cooling power of the 4K heat exchanger. The
two heat exchangers 130, 132 may be designed for example to cool
incoming helium gas from about 290 K to about 20 K in cases where
that gas is flowing at about 0.5 1/min for 10 minutes, followed by
about 25 1/min for 1 second. This is needed, for example, as
low-flow gas may be used to precool the ejection tube 120 after
establishing high polarization and just before ejection, whereas a
shorter pulse of high-flow gas to the gas tube 120 via the flange
134 allows sample ejection with a tolerably small increase in
sample temperature.
[0036] The insert 100 may also include a third heat exchanger 136,
for example located at the bottom of the insert, where the flow and
eject tubes are joined in a U, as shown in FIGS. 1B, 1C and 3. It
has a distinct form and function relative to the other noted heat
exchanges. The third heat exchanger 136 is designed to deliver
cooling power in the millikelvin T regime from a mixing chamber
plate of the refrigerator to the sample. This facilitates achieving
the high nuclear spin polarizations in the sample that occur with
ULT and high field. Referring to FIGS. 1A-1C and 3, a large thermal
strap 138, made for example of either high purity copper or silver
transmits the cooling power of the mixing chamber plate to this
lower heat exchanger 136. The third exchanger 136 may be composed
of for example silver sinter 140 pressed into an array of
high-purity copper fingers, which protrude up from the bottom of
the U-tube. The silver sinter 140 may be for example a porous,
high-surface-area material with excellent thermal conductivity. Its
porosity, surface area and they properties facilitate the further
transmission of cooling power into liquid helium within the U-tube.
The liquid helium then carries this to the sample. Thus overall,
the insert 100 transmits the cooling power of the mixing chamber
plate through the large thermal strap 138, into the silver sinter
140 at the base of the U-tube, then into liquid helium which
penetrates that sinter and carries the cooling power to the sample.
The last of these steps may entail sufficient helium to submerge
the sample where it sits on the wires at the base of the ejection
tube 120, or merely enough that a helium film flows from the
sinter, up some portion of the tube 120 and then covers the sample.
The liquid helium may be pure Helium-4, Helium-3 or a
Helium-4/Helium-3 mixture.
[0037] Because there will be liquid helium in the bottom of the
U-shaped tube at millikelvin temperatures, the insert 100 accounts
for the superfluid behavior, which is a well-known property of
helium-4 at these extreme temperatures. One aspect of superfluid
behavior is fluid `creep` over all surfaces, defined as the flow of
a thin film of high-thermal conductivity liquid helium over every
surface of its container. Typically, this creep continues until the
thin layer finds a region whose T is above the critical value at
which helium-4 ceases to be a superfluid. Unfortunately, such films
then act as superb conductors of heat from the region of elevated T
to environment intended for ULT conditions. Thus, referring now to
FIG. 4, to prevent this film flow, the insert 100 may include
knife-edges 142 to stop superfluid creep. As shown in FIG. 4, the
insert may include for example four knife edges. These occur on
either side of a break in both the gas tube 122 and the ejection
tube 120 that together form the U-shaped tube along with the
coupler 124. The breaks may be located along the U-tube in the
region between the thermal straps to the cold plate and to the
mixing chamber plate. A re-sealable indium-sealed junction
reconnects the break in both the gas and ejection tubes. At the
discontinuity, both sections of each tube 120, 122 are machined to
a knife-edge to prevent liquid helium from creeping beyond the
break and up to sections of the insert 100 that are at higher
temperatures. If necessary, use of indium-sealed junctions also
allow a film burning heater to be incorporated. Two of these (or
one common to each arm) may be readily wound about the high-T side
of the tubes.
[0038] Temperature monitoring and control are important throughout
the insert. Thermometers and heaters may be attached to each heat
exchanger. For example, referring to FIG. 1C, thermometer 144 and
heater 146 may be attached to the third heat exchanger. These
enable observations of the helium gas as it flows to or over the
sample in preparation of polarization and then later in preparation
for and during ejection.
[0039] The sample may include a cylindrical film affixed or frozen
to the interior of a form of some other rigid material that
provides a carrier. See example, U.S. patent application Ser. No.
14/161,172, incorporated herein by reference. The form protects the
sample, while allowing either helium submersion or film flow to
transmit cooling power to a large surface area of the sample. In
addition, to facilitate rapid sample ejection, in spite of this
open geometry, the sample design may include a light-weight large
cross-sectional area "wad" situated behind the sample with respect
to the direction of flow. The wad reduces the amount of helium gas
needed for ejection.
[0040] A gas handling system (GHS) located near the dilution
refrigerator controls the flow of ultra-high purity (UHP) helium
gas into the U-shaped tube. The GHS may include a gas source (e.g.,
a tank) to provide enough helium gas to liquefy and fill the lower
section of the U-shaped tube to conduct the cooling power to the
sample. The GHS can also control the flow rate and time for pulses
of helium gas applied to the flange 134 for ejection of the sample
from the ejection tube 120.
[0041] Devices for extracting samples from a cryogenic environment
are known in the art. Generally, these require removing the entire
cryogenic device from a refrigerator, with the sample mounted
internally to the device. A second method known in the art is to
have a sample mounted on a long stick, and removing that stick from
the refrigerator. In these approaches temperature control of the
sample during warming is generally not considered important; that
is, the sample is allowed to warm--usually back to room
temperature--at whatever rate is imposed by ambient conditions.
[0042] In contrast, the insert 100 uses pneumatic pressure to eject
samples from a cryogenic environment; this approach allows the
sample to be maintained during expulsion. Moreover the insert
allows the ambient temperature and magnetic field environment of
the sample to be controlled during expulsion. The use of gas also
allows the ejection tube 120 to be pre-cooled, which reduces sample
warming during expulsion.
[0043] The components of the insert 100 are preferably designed
such that they can be readily incorporated into any commercially
available cryogenic environment including for example dilution
refrigerator platforms such as so-called "wet", "dry", "bottom
loading" or "top loading" units. With the addition of a substantial
magnetic field, such as that produced by a superconducting magnet,
the device can be used to introduce samples into, and expel samples
from, a very high B/T environment suitable for producing large
nuclear polarizations in a variety of molecules.
[0044] The insert 100 allows materials to be expelled from an
ultra-low temperature environment, both rapidly and without
excessive sample warming, using pneumatic flow. This is beneficial
for polarization applications because nuclear polarization can
decay rapidly once the sample is removed from the high B/T
environment. This is especially the case when the target molecule
contains one or more methyl rotor groups. As described in U.S.
Patent Application Publication US2011/006239, the details of which
are incorporated here by reference, the presence of a methyl rotor
group can cause the rate of nuclear magnetization loss (known in
the art as T.sub.I.sup.-1) in one or more nuclei in the material to
be very rapid. The rate of polarization loss is particularly severe
if the temperature of the material is at or near where the
rotational correlation frequency of the methyl group is close to
that of the nuclear Larmor frequency. This temperature regime is
known in the art as the "valley of death" and can cause the
material to lose all or most of the polarization that was induced
at lower temperatures. Relaxation times in the "valley of death"
are also generally a function of the ambient magnetic field,
becoming even faster as the field is lowered.
[0045] A proximal length (e.g., the upper half of the ejection
tube) must be cooled prior to ejection to prevent the sample from
warming into or near the "valley of death" during its travel
through the tube. If not actively cooled, the upper half of the
ejection tube 120 would have a temperature gradient across it from
for example 6 K, near the 4 K plate, to room temperature (293 K),
at the top of the insert. The sample, when ejecting from the insert
100, would quickly equilibrate with the temperature of the ejection
tube 120 which would greatly increase the rate of polarization
loss. There are several methods for cooling the ejection tube 120,
such as for example, blowing cold helium gas (<20 K) through the
ejection tube, or thermally strapping the ejection tube to the 4 K
plate of the dilution refrigerator. The insert 100 may include a
copper section of the ejection tube 120, or an outer sleeve of
copper wrapped around the stainless steel ejection tube, in either
case extending from the 4 K plate up to just below the bayonet
coupling. This copper section would then be thermally strapped to
the 4 K plate of the dilution refrigerator to provide cooling to
the ejection tube.
[0046] Commercially available polarizers avoid this problem by
rapidly melting the sample, typically by mixing it with superheated
water or buffered solution, without first extracting it from the
polarizing cryostat. However this has the consequence that the
polarized material, now in solution form, must be utilized
immediately; once in the liquid state nuclear polarizations
generally only last a minute or two at most.
[0047] As described in U.S. Patent Application Publication
US2011006239, expelling the sample in the solid state permits it to
then be transported, if desired, from one site to another without
excessive polarization loss. The insert facilitates maintaining the
sample at a desired temperature and ambient magnetic field during
expulsion.
[0048] FIGS. 5A-5G illustrate a plurality of views of an insert
including a perspective view, rotated views and views of components
thereof.
[0049] FIG. 6 illustrates a closed cycle refrigerator polarizer
200. The polarizer includes a gas inlet port 202 which provides a
flow line through a first stage heat exchanger 204 (e.g., a 30 k
heat exchanger) and then through a second stage heat exchanger 206
(e.g., a 5 k heat exchanger). The ultralow temperature gas (e.g.,
helium) is then provided along a flow path 208 to an insert
assembly 210. The insert assembly 210 receives the ultralow
temperature gas via a gas inlet of the insert assembly. A distal
end of the insert is located between superconducting electromagnet
214 to polarize a sample deposited into the insert. The insert 210
includes a sample port 218 into which the sample to be polarized is
deposited, and from which the polarized sample is pneumatically
ejected. As proximal length of the insert is preferably stainless
steel, which a distal length of the insert is preferably formed
from a more thermally conductive material such as for example
cooper. A copper strap 220 may be used to connect the distal length
of the insert to a flange (e.g., a 30k flange).
[0050] The sample deposited into the sample port 218 comes to rest
at a base surface 223. A pulse of gas of sufficient pressure and
duration is supplied to the gas inlet port to provide a motive
force to pneumatically expel a sample on the base surface to the
port sample.
[0051] Although the present invention has been illustrated and
described with respect to several preferred embodiments thereof,
various changes, omissions and additions to the form and detail
thereof, may be made therein, without departing from the spirit and
scope of the invention.
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