U.S. patent application number 11/137508 was filed with the patent office on 2006-10-12 for ultracryostat and frigidity supplying apparatus.
This patent application is currently assigned to YOKOGAWA ELECTRIC CORPORATION. Invention is credited to Kunio Kazami.
Application Number | 20060225437 11/137508 |
Document ID | / |
Family ID | 35497544 |
Filed Date | 2006-10-12 |
United States Patent
Application |
20060225437 |
Kind Code |
A1 |
Kazami; Kunio |
October 12, 2006 |
Ultracryostat and frigidity supplying apparatus
Abstract
A ultracryostat is provided with a frigidity supplying member to
supply frigidity to the ultracryostat which uses cryogen such as
liquid helium, wherein the frigidity supplying member comprises a
heat pipe and one end of the heat pipe is connected to a frigidity
generating member of a cryocooler and the other end of the heat
pipe is connected to a thermal anchor of a cryostat.
Inventors: |
Kazami; Kunio; (Tokyo,
JP) |
Correspondence
Address: |
WESTERMAN, HATTORI, DANIELS & ADRIAN, LLP
1250 CONNECTICUT AVENUE, NW
SUITE 700
WASHINGTON
DC
20036
US
|
Assignee: |
YOKOGAWA ELECTRIC
CORPORATION
Tokyo
JP
|
Family ID: |
35497544 |
Appl. No.: |
11/137508 |
Filed: |
May 26, 2005 |
Current U.S.
Class: |
62/51.1 ;
62/6 |
Current CPC
Class: |
F25B 2500/12 20130101;
F25D 19/006 20130101; F25B 25/005 20130101; F25B 9/14 20130101;
F25D 29/001 20130101; F25B 23/006 20130101 |
Class at
Publication: |
062/051.1 ;
062/006 |
International
Class: |
F25B 9/00 20060101
F25B009/00; F25B 19/00 20060101 F25B019/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 2, 2004 |
JP |
2004-164266 |
Claims
1. An ultracryostat with a frigidity supplying member to supply
frigidity to the ultracryostat which uses cryogen, wherein one end
of a heat pipe is connected to a frigidity generating member of a
cryocooler and the other end of the heat pipe is connected to a
thermal anchor of a cryostat.
2. The ultracryostat as claimed in claim 1, wherein the heat pipe
is made of stainless steel.
3. The ultracryostat as claimed in claim 1, further comprising a
member to take in and out gas in the heat pipe from and to outside
of the cryostat, wherein the member comprises a tube to take in and
out gas from a part of the heat pipe.
4. The ultracryostat as claimed in claim 3, wherein the narrow tube
is made of stainless steel.
5. The ultracryostat as claimed in claim 3, wherein the member to
take in and out gas in the heat pipe comprises a gas supplying
member to supply gas, connected to the narrow tube through a first
bulb, and a vacuum pump to discharge gas, connected to the narrow
tube through a second bulb.
6. The ultracryostat as claimed in claim 5, wherein the first and
second bulbs open or close in conjunction with switching of the
cryocooler, when the cryocooler is ON, the first bulb opens to
supply gas from the gas supplying member to the heat pipe, the
second bulb closes and the vacuum pump is OFF, and when the
cryocooler is OFF, the first bulb closes to stop gas supply from
the gas supplying member to the heat pipe, the second bulb opens
and the vacuum pump is ON to discharge gas in the heat pipe.
7. A frigidity supplying apparatus comprising: a cryocooler and a
heat pipe having controllable thermal conductivity, wherein the
cryocooler comprises a frigidity generating member, one end of the
heat pipe is connected to the frigidity generating member, and the
cryocooler supplies frigidity from the other end of the heat
pipe.
8. The frigidity supplying apparatus as claimed in claim 7, wherein
thermal conductivity of the heat pipe is controlled in conjunction
with switching of the cryocooler, and the thermal conductivity when
the cryocooler is OFF is lower than the thermal conductivity when
the cryocooler is ON.
9. The frigidity supplying apparatus as claimed in claim 7, wherein
the both ends of the heat pipe are made of copper and a wall of the
heat pipe is made of stainless steel.
10. The frigidity supplying apparatus as claimed in claim 7,
further comprising a gas regulating member to take in and out gas
in the heat pipe.
11. The frigidity supplying apparatus as claimed in claim 10,
wherein the gas regulating member comprises a tube to take in and
out gas in the heat pipe.
12. The frigidity supplying apparatus as claimed in claim 11,
wherein the tube is made of stainless steel.
13. The frigidity supplying apparatus as claimed in claim 11,
wherein the gas regulating member further comprises a gas supplying
member to supply gas and a vacuum pump to discharge gas, the gas
supplying member being connected to the tube through a first bulb,
the vacuum pump being connected to the tube through a second
bulb.
14. The frigidity supplying apparatus as claimed in claim 13,
wherein the first and second bulbs open or close in conjunction
with switching of the cryocooler, when the cryocooler is ON, the
first bulb opens to supply gas from the gas supplying member to the
heat pipe, the second bulb closes and the vacuum pump is OFF, and
when the cryocooler is OFF, the first bulb closes to stop gas
supply from the gas supplying member to the heat pipe, the second
bulb opens and the vacuum pump is ON to discharge gas in the heat
pipe.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an apparatus for extending
low temperature retention time of a cryostat using a
superconducting quantum interference device (SQUID) for
biomagnetism measurement. In more detail, the present invention
relates to an ultracryostat and a frigidity supplying apparatus to
reduce evaporation of helium. Further, the present invention
relates to an ultracryostat and a frigidity supplying apparatus
applicable not only to an ultracryostat for biomagnetism
measurement but also to the other cryostat, for example a helium
cryostat for MRI (magnetic resonance imaging system) using
superconductive magnet and one used in physicality study.
[0003] 2. Description of Related Art
[0004] As shown in FIG. 2, an ultracryostat in earlier development
is such that a freezer 106 is connected to an upper part of an
cryostat 105 installed in a magnetic shield room 104 (for example,
JP Tokukai 2004-116914A (page 4, FIG. 14). A rotary bulb 107 for
intaking and exhausting compression gas is connected to this
freezer 106, and high and low pressure gas tubes are connected to a
compressor 108. A frigidity generating member 109 of the freezer
106 is exposed to a helium gas tank 110 which forms a separate room
inside the cryostat 105. The generated ultra low temperature
refrigerates helium gas so as to refrigerate the whole helium gas
tank 110. A SQUID sensor 112 is connected to a sensor mounting
stage 111 attached to a lower part of the helium gas tank 110, and
the SQUID sensor 112 is refrigerated by the action of heat
conduction. A vacuum layer 113 for heat insulation is formed in
space which surrounds the helium gas tank 110. A heat radiation
shield foil, which is omitted in the figure, is installed in the
vacuum layer 113, so that heat transmission by radiation is
reduced.
[0005] However, a common problem in the ultracryostat described in
description of related art, i.e. a cryostat for biomagnetism
measurement is that sufficient heat shield cannot be obtained
because vacuum heat insulation layer is structurally thin. This
problem is caused by a purpose of measurement. That is, sufficient
SN (a ratio of signal to noise) cannot be obtained unless a
measurement is performed in a condition that a sensor under ultra
low temperature is placed as close as possible to a feeble magnetic
signal source. Thus, liquid helium used as cryogen evaporates
rapidly and a refill cycle thereof is one week at longest. When
volume of the cryostat is made larger, structural distortion
becomes large and the thin vacuum heat insulation layer may brake
to cause a thermal short. Therefore, it cannot be made larger
blindly.
[0006] In order to solve such problems, a method of direct
refrigerating by a freezer is suggested. However, it has not been
into practical use due to the following problems regarding magnetic
noise.
[0007] (1) Generation of magnetic noise by a magnetic coolant: A
freezer includes an antiferromagnetic material or superconductive
material inside an expansion device for generating frigidity.
Vibration thereof caused by pressure pulsation of internal flowing
gas generates feeble variations of magnetism and magnetic gradient
around the device. These vibrations are as high as several tens to
several hundreds of pT (pico Tesla), and could be an extremely high
disturbing signal in a measurement of feeble biomagnetism of
several tens of fT (femto Tesla) to several tens of pT.
[0008] (2) The expansion device of a cold-head of the cryocooler is
composed of stainless steel (SUS) having low heat conductivity,
which is magnetized though it is feeble. Since a variation of
expansion gas pressure generates a vibration thereof, magnetic
noise occurs as described above.
[0009] In view of the foregoing, it is difficult to attach a
cryocooler directly onto a cryostat in a field of biomagnetic
measurement.
[0010] While gas layer is refrigerated in the above case in earlier
development, there has been another attempt in which a frigidity
generating member of a freezer is connected to a thermal anchor
continued to a thermal shield member.
[0011] However, because of large magnetic noise derived from a
freezer, it is difficult to use any of the above devices for
measurement when the freezer is in operation.
[0012] Further, when the freezer is not in operation during a
measurement, heat flows back immediately. Thus, noise increases in
SQUID due to instability of the internal temperature as well as
evaporation rate of helium extremely increases.
SUMMARY OF THE INVENTION
[0013] In view of the foregoing, the object of the present
invention is to provide a means to avoid heat flowback when a
freezer is not in operation for a cryostat connected with a freezer
for biomagnetic measurement, so as to solve the problem when a
freezer is not in operation.
[0014] According to the first aspect of the invention, a
ultracryostat is provided with a frigidity supplying member to
supply frigidity to the ultracryostat which uses cryogen such as
liquid helium, wherein the frigidity supplying member compises a
heat pipe, one end of the heat pipe is connected to a frigidity
generating member of a cryocooler and the other end of the heat
pipe is connected to a thermal anchor of a cryostat.
[0015] The heat pipe is preferably made of stainless steel.
[0016] The ultracryostat may further comprising a member to take in
and out gas in the heat pipe from and to outside of the cryostat,
wherein the member may comprise a narrow tube to take in and out
gas from a part of the heat pipe.
[0017] The narrow tube is preferably made of stainless steel.
[0018] The member to take in and out gas in the heat pipe may
comprise a gas supplying member to supply gas, connected to the
narrow tube through a first bulb, and a vacuum pump to discharge
gas, connected to the narrow tube through a second bulb.
[0019] The first and second bulbs may open or close in conjunction
with switching of the cryocooler. That is, when the cryocooler is
ON, the first bulb opens to supply gas from the gas supplying
member to the heat pipe, the second bulb closes and the vacuum pump
is OFF, and when the cryocooler is OFF, the first bulb closes to
stop gas supply from the gas supplying member to the heat pipe, the
second bulb opens and the vacuum pump is ON to discharge gas in the
heat pipe.
[0020] According to the second aspect of the invention, a frigidity
supplying apparatus comprises: a cryocooler and a heat pipe having
controllable thermal conductivity, wherein the cryocooler comprises
a frigidity generating member, one end of the heat pipe is
connected to the frigidity generating member, and the cryocooler
supplies frigidity from the other end of the heat pipe.
[0021] Preferably, thermal conductivity of the heat pipe is
controlled in conjunction with switching of the cryocooler, and the
thermal conductivity when the cryocooler is OFF is lower than the
thermal conductivity when the cryocooler is ON.
[0022] Preferably, the both ends of the heat pipe is made of copper
and a wall of the heat pipe is made of stainless steel.
[0023] The frigidity supplying apparatus may further comprise a gas
regulating member to take in and out gas in the heat pipe.
[0024] Preferably, the gas regulating member comprises a tube to
take in and out gas in the heat pipe.
[0025] Preferably, the tube is made of stainless steel.
[0026] The gas regulating member may further comprises a gas
supplying member to supply gas and a vacuum pump to discharge gas,
the gas supplying member being connected to the tube through a
first bulb, the vacuum pump being connected to the tube through a
second bulb.
[0027] Preferably, the first and second bulbs open or close in
conjunction with switching of the cryocooler, when the cryocooler
is ON, the first bulb opens to supply gas from the gas supplying
member to the heat pipe, the second bulb closes and the vacuum pump
is OFF, and when the cryocooler is OFF, the first bulb closes to
stop gas supply from the gas supplying member to the heat pipe, the
second bulb opens and the vacuum pump is ON to discharge gas in the
heat pipe.
[0028] According to the ultracryostat and frigidity supplying
apparatus of the present invention, when the cryocooler is ON, gas
is supplied into the heat pipe. Thus, frigidity is supplied by
repeating condensation of gas in the heat pipe by the action of
frigidity of the cryocooler and internal evaporation of the
condensed gas by the action of heat supplied from the thermal
anchor. On the contrary, when the cryocooler is OFF, the gas supply
bulb closes and the bulb of the vacuum pump opens, so that the gas
in the heat pipe is discharged. Thus, even if the temperature of
the cryocooler rises, heat does not flow into the thermal anchor by
heat conduction and convection. Further, penetration of heat caused
by heat conduction at the heat pipe wall is low, since a material
having low heat conductivity such as stainless steel (SUS) is
used
[0029] When the cryocooler in ON, although noise is large,
evaporation rate of helium decreases since heat is discharged. On
the contrary, when the cryocooler is OFF, although heat is not
discharged, the device can be operated with small noise as same as
an ordinal cryostat. Further, evaporation does not increase
needlessly since the cryocooler is not connected thereto.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] The present invention will become more fully understood from
the detailed description given hereinbelow and the appended
drawings which given by way of illustration only, and thus are not
intended as a definition of the limits of the present invention,
and wherein;
[0031] FIG. 1 is a block diagram of the ultracryostat of the
present invention, and
[0032] FIG. 2 is a block diagram of the ultracryostat of earlier
development.
PREFERRED EMBODIMENT OF THE INVENTION
[0033] Hereinafter, the ultracryostat of the present embodiment is
explained in more detail with reference to the drawings.
Embodiment 1
[0034] The feature of the invention is that the heat pipe having
thermally variable conductance, i.e. having variable thermal
conductivity, connects the cryocooler as the frigidity generating
member with the thermal anchor continued to the radiation shield of
the cryostat which requires the frigidity.
[0035] That is, by using the heat pipe which can switch frigidity
transporting effect, frigidity conducts from the cryocooler to the
thermal anchor when the cryocooler is ON, and heat does not conduct
from the cryocooler to the thermal anchor when the cryocooler is
OFF.
[0036] Here, for the following explanation, the frigidity
designates an absorption of heat and has opposite meaning of heat
diffusion or heat flow. Further, a high pressure supplying pipe and
gas compressor and the like included in the cryocooler are
omitted.
[0037] FIG. 1 is a whole constitution of the ultracryostat of the
invention, and shows an embodiment in which the cryocooler is
connected to the cryostat through the heat pipe, where reference
numeral 11 denotes an outer container of the cryostat, reference
numeral 12 denotes an inner container and space between inner and
outer container, 11 and 12 is kept vacuum. Reference numeral 13
denotes a helium reservoir in which a SQUID sensor 14 is immersed
and refrigerated. Reference numeral 15 denotes a measuring section
to insert a human head, and a constitution of magnetoencephalogram
meter is shown here. Reference numeral 16 denotes a neck portion of
the cryostat, in which heat is exchanged with sensible heat of
helium gas evaporation. Reference numeral 17 denotes a heat
insulation material which prevents penetration of heat from upward.
Reference numerals 18 and 19 denote metal-made thermal anchors
connected to the neck portion 16, which block heat radiation toward
the outer container 11 by frigidity being supplied from evaporating
helium gas and the frigidity being transmitted to heat shields 20
and 21. Reference numeral 22 denotes the cryocooler and reference
numeral 23 denotes the frigidity generating member. Reference
numeral 24 denotes a connecting member to retain heat insulation
and vacuum, and reference numeral 25 denotes a heat pipe to
transmit frigidity. The cryocooler 22, frigidity generating member
23, thermal anchors 18 and 19, and heat pipe 25 constitute a
frigidity supplying device. In the frigidity supplying device, one
end of the heat pipe 25 is connected to the frigidity generating
member 23 of the cryocooler 22, and the other end thereof is
connected to the thermal anchor 18 of the cryostat.
[0038] A narrow tube 26 made of a material having low heat
conduction such as stainless steel is connected to the heat pipe
25. A vacuum pump 28 for discharging internal gas of the heat pipe
25 is connected to the narrow tube 26 through a second bulb 27, and
a gas container 30 (gas supplying member) for supplying gas to the
heat pipe 25 is also connected to the narrow tube 26 through a
first bulb 29.
[0039] The both ends of the heat pipe 25 is composed of a material
having high heat conduction such as copper, and the intermediate
portion thereof is composed of a material having low heat
conduction such as stainless steel (SUS).
[0040] As described above, the heat pipe 25 connects the cryocooler
22 with the thermal anchor 18 continued to the radiation shield of
the cryostat which requires the frigidity, and the ultracryostat is
provided with the vacuum pump 28 for discharging internal gas of
the heat pipe 25 and the gas container 30 for supplying gas to the
heat pipe 25. By doing so, when the cryocooler 22 is ON, the first
bulb 29 opens and gas is supplied from the gas container 30 into
the heat pipe 25. Thus, frigidity is provided by repeating
condensation of the gas in the heat pipe 25 by frigidity of the
cryocooler 22 and internal evaporation of the condensed gas by heat
supplied from the thermal anchor 18.
[0041] On the contrary, when the cryocooler 22 is OFF, the first
bulb 29 for supplying gas closes and the second bulb 27 of the
vacuum pump 28 opens, so that the gas inside the heat pipe 25 is
discharged. Thus, even if the temperature of the cryocooler 22
rises, heat does not flow into the thermal anchor 18 by heat
conduction and convection. Further, penetration of heat caused by
heat conduction at the wall of the heat pipe 25 is low, since a
material having low heat conductivity such as stainless steel (SUS)
is used.
[0042] When the cryocooler 22 in ON, although noise is large,
evaporation rate of helium decreases since heat is discharged.
[0043] On the contrary, when the cryocooler 22 is OFF, although
heat is not discharged, the device can be operated with small noise
as same as an ordinal cryostat. Further, evaporation does not
increase needlessly since the cryocooler 22 is not connected
thereto.
[0044] As a result, it becomes possible to provide the
ultracryostat in which the heat pipe connects the cryocooler with
the thermal anchor continued to the radiation shield of the
cryostat which requires the frigidity, and the ultracryostat is
provided with the vacuum pump for discharging internal gas of the
heat pipe and the gas container for supplying gas to the heat pipe.
When the cryocooler is ON, gas is supplied from the gas container
into the heat pipe. Thus, frigidity is provided by repeating
condensation of the gas in the heat pipe by the action of frigidity
of the cryocooler and internal evaporation of the condensed gas by
the action of heat supplied from the thermal anchor. On the
contrary, when the cryocooler is OFF, the bulb for supplying gas
closes and the bulb of the vacuum pump opens, so that the gas in
the heat pipe is discharged. Thus, even if the temperature of the
cryocooler rises, heat does not flow into the thermal anchor by
heat conduction and convection.
[0045] The entire disclosure of Japanese Patent Application No.
2004-164266 filed on Jun. 2, 2004, including specification, claims,
drawings and summary are incorporated herein by reference in its
entirety.
* * * * *