U.S. patent application number 13/067041 was filed with the patent office on 2011-11-10 for low-loss cryostat configuration.
This patent application is currently assigned to Bruker BioSpin GmbH. Invention is credited to Gerhard Roth, Marco Strobel.
Application Number | 20110271694 13/067041 |
Document ID | / |
Family ID | 44243638 |
Filed Date | 2011-11-10 |
United States Patent
Application |
20110271694 |
Kind Code |
A1 |
Strobel; Marco ; et
al. |
November 10, 2011 |
Low-loss cryostat configuration
Abstract
A cryostat configuration (10), with at least one cryostat (11),
which has at least one first chamber (1) with supercooled liquid
helium having a temperature of less than 4 K and at least one
further chamber (2), which contains liquid helium having a
temperature of approximately 4.2 K, a Joule-Thomson valve (3) being
disposed in the first chamber, wherein the first chamber is
separated from the further chamber by a thermally insulating
barrier (4), wherein helium from the first or the further chamber
expands through the Joule-Thomson valve into a pump-off pipe (13),
which is in thermal contact with the helium of the first chamber
and supercools the latter, and wherein the pump-off pipe is
directly or indirectly in thermal contact with the further chamber
during its further progression and is then connected to the inlet
of a pump (14), is characterized in that the outlet of the pump
and/or an outlet for evaporating helium of at least one of the
cryostats is fluidically connected to the further chamber through a
cryogen pipe (15), and that the cryogen pipe has a branch-off
device (16), which returns a partial current of the helium located
in the cryogen pipe into the further chamber. In this way, the
helium consumption and therefore the operating costs are reduced
while the pressure in the first chamber remains constant.
Inventors: |
Strobel; Marco; (Karlsruhe,
DE) ; Roth; Gerhard; (Rheinstetten, DE) |
Assignee: |
Bruker BioSpin GmbH
Rheinstetten
DE
|
Family ID: |
44243638 |
Appl. No.: |
13/067041 |
Filed: |
May 4, 2011 |
Current U.S.
Class: |
62/51.1 |
Current CPC
Class: |
F25D 19/00 20130101;
H01F 6/04 20130101 |
Class at
Publication: |
62/51.1 |
International
Class: |
F25B 19/00 20060101
F25B019/00 |
Foreign Application Data
Date |
Code |
Application Number |
May 7, 2010 |
DE |
10 2010 028 750.4 |
Claims
1. A cryostat configuration comprising: at least one cryostat, said
cryostat having at least one first chamber disposed, structured and
dimensioned to keep supercooled liquid helium at a temperature of
less than 4 K, said cryostat also having at least one further
chamber disposed, structured and dimensioned to keep helium under
atmospheric pressure at a temperature of approximately 4.2 K, said
cryostat having an outlet for evaporating helium; a Joule-Thomson
valve disposed in said first chamber; a thermally insulating
barrier disposed to separate said first chamber from said further
chamber; a pump-off pipe in thermal contact with helium of said
first chamber, a further progression of said pump-off pipe being in
direct or indirect thermal contact with said further chamber; a
pump, said pump having an inlet connected to said pump-off pipe to
urge helium from said first or said further chamber to expand
through said Joule-Thomson valve into said pump-off pipe, thereby
supercooling helium in said first chamber, said pump also having an
outlet; a cryogen pipe in fluid connection between said further
chamber and said outlet of said pump and/or said evaporating helium
outlet of said cryostat, said cryogen pipe having a branch-off
device, which returns a partial current of helium located in said
cryogen pipe into said further chamber.
2. The cryostat configuration of claim 1, wherein said first
chamber and said further chamber are hydrostatically connected to
each other.
3. The cryostat configuration of claim 1, wherein said further
chamber is disposed above said first chamber.
4. The cryostat configuration of claim 1, further comprising a
pressure regulating device for keeping a constant pressure in said
further chamber.
5. The cryostat configuration of claim 4, further comprising a
heating device disposed in said further chamber.
6. The cryostat configuration of claim 4, wherein said pressure
regulating device adjusts a pressure in said further chamber to a
settable target pressure that is greater than or equal to an
ambient pressure of the cryostat configuration.
7. The cryostat configuration of claim 5, wherein said pressure
regulating device adjusts a pressure in said further chamber to a
settable target pressure that is greater than or equal to an
ambient pressure of the cryostat configuration.
8. The cryostat configuration of claim 4, wherein said pressure
regulating device sets a pressure in said further chamber to a
defined positive pressure above atmospheric pressure.
9. The cryostat configuration of claim 5, wherein said pressure
regulating device sets a pressure in said further chamber to a
defined positive pressure above atmospheric pressure.
10. The cryostat configuration of claim 1, wherein said cryogen
pipe has at least one relief valve and/or at least one bursting
disk.
11. The cryostat configuration of claim 1, wherein said cryogen
pipe contains a buffer vessel for provision of an additional volume
for helium located in said cryogen pipe.
12. The cryostat configuration of claim 1, wherein said cryogen
pipe has at least one filtering device for separating off
impurities in flowing helium.
13. The cryostat configuration of claim 1, wherein said partial
flow returned into said further chamber comprises between 20% and
80% of a total helium flow conveyed through said pump.
14. The cryostat configuration of claim 13, wherein said partial
flow returned into said further chamber comprises between 25% and
60% of a total helium flow conveyed through said pump.
15. The cryostat configuration of claim 1, wherein helium is input
into said cryogen pipe from at least one further, physically
separate cryostat.
16. The cryostat configuration of claim 1, further comprising a
superconducting magnet coil disposed in said first chamber.
17. The cryostat configuration of claim 16, wherein the cryostat
configuration is part of NMR, MRI, or FTMS equipment.
18. The cryostat configuration of claim 17, wherein the equipment
comprises an ultrahigh-resolution high-field NMR spectrometer with
a proton resonance frequency .gtoreq.800 MHz.
Description
[0001] This application claims Paris Convention priority of DE 10
2010 028 750.4 filed May 07, 2010 the complete disclosure of which
is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] The invention concerns a cryostat configuration, with at
least one cryostat, which has at least one first chamber with
supercooled liquid helium having a temperature of less than 4 K and
at least one further chamber, which contains liquid helium at
essentially atmospheric pressure having a temperature of
approximately 4.2 K, wherein a Joule-Thomson valve is disposed in
the first chamber, the first chamber being separated from the
further chamber by a thermally insulating barrier, wherein helium
from the first or the further chamber expands through the
Joule-Thomson valve into a pump-off pipe, which is in thermal
contact with the helium of the first chamber and supercools the
latter, and wherein the pump-off pipe is directly or indirectly in
thermal contact with the further chamber during its further
progression and is then connected to the inlet of a pump.
[0003] Such a cryostat configuration is known from DE 40 39 365 C2
(U.S. Pat. No. 5,220,800).
[0004] Magnet systems for magnetic resonance equipment are subject
to the highest achievable demands in terms of the magnetic field
strengths and homogeneity.
[0005] At a resonance frequency of 600 MHz, a field strength of
14.1 T must be achieved. These high magnetic field strengths are
technically best achieved using superconducting magnet coils having
a superconducting short-circuiting switch.
[0006] The superconducting magnet coils only require energy during
the charging phase and produce a high magnetic field in
short-circuited operation for a long time after the power supply
has been disconnected. Decay times until half the original field
strength is reached are around 5000 years for modern
superconducting magnets. This means that, in short-circuited
operation over a period of hours and days, practically no change
occurs in the magnetic field strength.
[0007] High stability over time is above all necessary in long-term
measurements, especially in 2D and 3D measurements. This can only
be achieved in superconducting short-circuited operation. The
magnet coils are usually charged once and then produce a
homogeneous magnetic field for many years once the power cables
have been removed. In routine operation, typical intervals between
helium refills of magnet systems are several months in the case of
"low-loss" cryostats.
[0008] To obtain stronger homogeneous magnetic fields and a more
stable superconductor, a publication by Williams et al. in "Rev.
Sci. Instrum." 52 (5), May 1981, American Institute of Physics,
649-656, proposes operating the superconducting magnet coil at a
lower operating temperature than the normal temperature of liquid
helium (T=4.2 K). This lower temperature is usually achieved by
pumping off the liquid helium.
[0009] In the cited publication, a cryostat is proposed that has
two concentric helium tanks, one nesting inside the other. The
outer tank contains liquid helium at T=4.2 K under normal pressure
(1 bar).
[0010] From this outer tank, a filling pipe for liquid helium leads
to the inner tank so that the liquid helium can be moved from the
outer to the inner tank. In the inner tank, in which the
superconducting coil is located, the helium is pumped off down to a
pressure of 40 mbar and thus cooled down to a temperature of 2.3
K.
[0011] One major disadvantage of this configuration is that the
supercooled helium in the inner tank is under vacuum so that the
electrical supply cables, especially those for charging the
superconducting magnet coil, have to be routed through the cold
vacuum system. This gives rise to sealing problems and also
insulation problems due to the heat input into the cold vacuum
reservoir through the supply cables brought in from an environment
at room temperature and under normal pressure, which necessarily
results in much reduced intervals between helium refills.
[0012] A further disadvantage is that no means are provided to
lower the helium consumption required to operate this equipment,
with the result that both enormous operating costs are incurred and
only relatively short intervals between liquid helium refills are
achieved, except in cases where it is in any event necessary to
constantly fill the equipment with fresh helium during
operation.
[0013] DE 40 39 365 C2 and U.S. Pat. No. 5,220,800 propose a system
in which two temperature ranges are provided in a first and in a
further chamber, wherein, in the first chamber, liquid helium,
which enters from the further chamber under normal pressure and a
temperature of T=4.2 K, is cooled by pumping off through a
restrictor in a state of non-equilibrium.
[0014] This equalizes the pressure level in the first chamber with
the pressure level in the further chamber. Because atmospheric
pressure essentially prevails in the first chamber with the
supercooled liquid helium, the problems associated with a vacuum
bushing for the electrical supply cables to the superconducting
magnetic coil do not occur.
[0015] Because of the vertical disposition of the first chamber
underneath the further chamber, gravity counteracts flowback of the
denser and therefore heavier supercooled helium from the lower cold
reservoir into the upper warmer reservoir. This ensures defined
flow conditions and there is no unwanted mixing of cold and warm
helium in the upper reservoir.
[0016] A thermally insulating barrier not only prevents convection
between the two chambers but, to a great extent, also heat transfer
by thermal conduction from one chamber to the other. The barrier
consists of two plates separated by a vacuum and consisting of a
poorly thermally conducting material, such as stainless steel or
plastic. The vacuum insulation prevents heat exchange between the
upper and the lower reservoir.
[0017] To avoid unwanted cooling of the helium in the further
chamber, an electric heating element is disposed in the further
chamber usually in addition to the thermal insulation.
[0018] The vacuum is part of the single vacuum part of the
cryostat, so that the barrier does not have to be separately
evacuated.
[0019] In contrast to continuous tank systems, these measures cause
a drastic reduction in the heat entering from the outside and are a
precondition for a cryostat with low operating losses ("low
loss").
[0020] The electrical supply cables to the magnetic system and the
supply cables for liquid helium are routed inside through the
conduit passing through the tower or towers. This hollow conduit
design results in a dual cryostat that can be used both at 4.2 K
under normal pressure and in vacuum operation in the range, for
example, from 1.8 K to 2.3 K.
[0021] In both operating modes, the cryostat has low-loss
properties because, irrespective of the proportion of the helium
flow that is pumped off and evaporates, the total enthalpy in both
gas flows is essentially passed to the shield system of the
cryostat.
[0022] Because the cryostat contains two chambers with helium at
two different temperature levels, there are two exhaust gas flows
at different pressure levels. One exhaust gas flow arises due to
the helium evaporating from the further chamber at atmospheric
pressure; the second exhaust gas flow is formed by the helium
pumped off through the refrigerator under a pressure of approx. 40
mbar.
[0023] Depending on the operating state of the cryostat, the two
exhaust gas flows have different strengths, and the exhaust gas
flow from the further chamber may even cease altogether. For a
low-loss cryostat, it is essential that the enthalpy contained in
the exhaust gas be utilized as-completely as possible. For this
purpose, it is necessary to distribute the two exhaust gas flows
evenly among the various towers and the shields connected to them,
whatever the strength of the two flows.
[0024] The object of this invention is to lower the helium
consumption and therefore the operating costs still further as
compared to prior art, while keeping the pressure in the first
chamber as constant as possible.
SUMMARY OF THE INVENTION
[0025] The object is inventively achieved by fluidically connecting
the outlet of the pump and/or an outlet for evaporating helium of
the or of at least one of the cryostats through a cryogen pipe with
the further chamber, and providing the cryogen pipe with a
branch-off device, which returns a partial current of the helium
located in the cryogen pipe into the further chamber.
[0026] Instead of releasing the total pumped-off helium into the
atmosphere, as was previously the case, the inventive cryostat
configuration leads part of the helium into the first chamber. The
helium is re-condensed in the cryogen pipe, which becomes
increasingly colder inside the cryostat. The thermal energy of the
helium is brought into the further chamber, making a heating
element superfluous.
[0027] The helium for re-condensation can originate from the same
cryostat, into which the partial current is to be returned. This
would be the case, for example, if only one cryostat were present.
However, in a configuration having multiple cryostats, it is
conceivable for the evaporated or pumped-off helium of one or more
further cryostats to be input into one of the cryostats for
re-condensation.
[0028] One especially preferred embodiment is characterized in that
a pressure regulating device is provided, which keeps the pressure
in the further chamber constant. This could be implemented, for
example, using an actively or a passively regulated valve on the
cryogen pipe. A constant pressure is indispensable for an even
temperature distribution and especially important for highly
sensitive NMR measurements.
[0029] In a further embodiment, a heating device is provided in the
further chamber. Although the necessary heat input into the further
chamber can only be achieved by the helium supplied to the
cryostat, embodiments are conceivable in which pressure regulation
is achieved by means of the evaporation rate of the helium from the
further chamber.
[0030] It is advantageous if, in the embodiments stated above, the
pressure regulating device sets the pressure in the further chamber
to a settable target pressure that is greater than or equal to the
ambient pressure of the cryostat configuration.
[0031] Alternatively, the pressure regulating device sets the
pressure in the further chamber to a defined positive pressure
above atmospheric pressure.
[0032] In a further embodiment, the cryogen pipe has at least one
relief valve and/or at least one bursting disk. This ensures
controlled pressure reduction in the event of an unexpected large
increase in pressure.
[0033] An embodiment is also conceivable that is characterized in
that the cryogen pipe contains a buffer vessel for the provision of
an additional volume for the flowing helium. In this way, a reserve
volume is constituted in case more helium has to be supplied to the
cryostat. The buffer volume is also an additional means of keeping
the pressure constant.
[0034] An embodiment is especially preferred in which the cryogen
pipe has at least one filtering device for separating off
impurities in the helium. Impurities that enter the first chamber
can constitute significant heat input. Moreover, solids and frozen
matter can be deposited, narrowing or even blocking pipes and
valves. For that reason, the helium used must be of high
purity.
[0035] It is preferred if the partial flow returned into the
further chamber comprises between 20% and 80%, preferably between
25% and 60% of the total helium flow conveyed through the pump.
[0036] In a further conceivable embodiment, helium is input into
the cryogen pipe from at least one further, physically separate
cryostat. This embodiment is especially advantageous if multiple
cryostats are installed in a place of work, such as a research
institute. In this case, the evaporating helium from one cryostat
can, for example, be input into another cryostat and cooled in the
manner described.
[0037] A preferred embodiment is characterized in that a
superconducting magnet coil is disposed in the first chamber.
[0038] In a variant of this embodiment, the cryostat configuration
is part of NMR, MRI, or FTMS equipment.
[0039] In a further variant of the embodiment, the equipment
comprises an ultrahigh-resolution high-field NMR spectrometer with
a proton resonance frequency .gtoreq.800 MHz.
[0040] The first chamber and the further chamber can be disposed
either one above the other or side by side.
[0041] Further advantages of the invention can be derived from the
description and the drawing. The characteristics stated above and
below can also be used individually or together in any
combinations. The embodiments shown and described are not to be
considered an exhaustive list but are intended as examples to
explain the invention.
[0042] The invention is shown in the drawing and is explained in
more detail using the example of the embodiments. The figures
show:
BRIEF DESCRIPTION OF THE DRAWING
[0043] FIG. 1 Embodiment of an inventive cryostat configuration
with one cryostat with supercooled helium;
[0044] FIG. 2 Embodiment of an inventive cryostat configuration
with one cryostat with supercooled helium and a further cryostat
with helium, which are interconnected through a cryogen pipe;
[0045] FIG. 3 Embodiment of an inventive cryostat configuration
with one cryostat with supercooled helium and a further cryostat
with helium, which are interconnected through a cryogen pipe that
leads to a condenser;
[0046] FIG. 4 Embodiment of an inventive cryostat configuration
with multiple cryostats with supercooled helium and multiple
further cryostats with helium, which are interconnected through a
cryogen pipe;
[0047] FIG. 5 Embodiment of an inventive cryostat configuration
with two cryostats with supercooled helium, which have a shared
pump-off pipe, and a further cryostat with helium, wherein a
cryostat with supercooled helium and the cryostat with helium are
interconnected through a cryogen pipe.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0048] FIG. 1 shows an embodiment of an inventive cryostat
configuration 10 with one cryostat 11 with supercooled helium. The
cryostat 11 consists of a first chamber 1 with supercooled helium
(temperature <4 K) and a further chamber 2 with liquid helium
(temperature approx. 4.2 K), that are separated by a thermally
insulating barrier 4. In the first chamber 1, a Joule-Thomson valve
3 is disposed through which the helium can expand from the further
chamber 2 into the pump-off pipe 13, thus supercooling the first
chamber 1. The helium is pumped off from the pump-off pipe 13 by a
pump 14 and led to a cryogen pipe 15. In the embodiment depicted,
the latter comprises a buffer vessel 18 to provide to the helium an
additional volume that can serve as a pressure reserve and/or
backflow reserve. A relief valve 6 with a bursting disk 7 prevents
an excessive pressure in the cryogen pipe 15 if the pressure
regulating device 17 of the branch-off device 16 fails or if the
pressure cannot be kept constant for any other reason. To remove
impurities through the pump 14, a filter 5 is also disposed in the
cryogen pipe 15.
[0049] FIG. 2 shows a further embodiment of an inventive cryostat
configuration 20. Here, the helium of a further cryostat 22, which
works with liquid helium (4.2 K), evaporates into a cryogen pipe 25
constituted as a manifold, to which a buffer vessel 28 and a
branch-off device 26 with a pressure regulating device 27 are also
connected. The helium evaporated from the further cryostat 22 can
now partially be input into the first cryostat 21 with supercooled
helium, wherein the supercooling is performed by the expansion of
helium in the Joule-Thomson valve 3 as shown in FIG. 1. Also for
the case of the embodiment shown in FIG. 2, the helium expanded
into the pump-off pipe 23 is pumped off by a pump 24. However, it
is not thereby input into the cryogen pipe 25, rather released into
the atmosphere.
[0050] In this way, the helium consumption of the entire cryostat
configuration 20 is reduced from around 230 ml/h without helium
return to around 170 ml/h.
[0051] FIG. 3 shows a further embodiment of an inventive cryostat
configuration 30. In this case, the helium of a further cryostat
32, which works with liquid helium (4.2 K), evaporates into a
cryogen pipe 35 constituted as a manifold, which leads to an
external condenser 39 (not explicitly depicted). A buffer vessel 38
and a branch-off device 36 with a pressure regulating device 37 are
also connected to the cryogen pipe 35. The helium evaporated from
the further cryostat 32 can now partially be input into the first
cryostat 31 with supercooled helium. The partial flow input into
the first cryostat 31 now no longer has to be condensed by the
condenser 39, whereby the latter is offloaded and can be rated for
a smaller capacity. Also in this embodiment, the helium expended
into the pump-off pipe 33 is pumped off by a pump 34 and released
into the atmosphere.
[0052] FIG. 4 illustrates an embodiment of an inventive cryostat
configuration 40, in which multiple further cryostats 42 are
connected to a cryogen pipe 45 constituted as a manifold. A
branch-off device 46 with a pressure regulating device 47 regulates
the pressure in the cryogen pipe 45 and releases excess helium into
the atmosphere. Part of the helium evaporated by the cryostat 42 is
now supplied to the first cryostat 41 and condensed therein. The
helium of the first cryostat 41 expanded into the pump-off pipe 43
is released into the atmosphere through a pump 44. The total
consumption of such a configuration is thus reduced from approx.
460 ml/h without helium return to a minimum of approx. 340
ml/h.
[0053] Finally, FIG. 5 shows an embodiment of an inventive cryostat
configuration 50, in which a further cryostat 52 is connected
through a cryogen pipe 55 to a first cryostat 51. A branch-off
device 56 with a pressure regulating device 57 controls the
quantity of the helium input into the first cryostat 51. The first
cryostat 51 shares the pump-off pipe 53 with a further cryostat
51', which also works with supercooled helium. A pump 54 pumps the
helium of the two cryostats 51, 51' out of the pump-off pipe 53
into the atmosphere.
LIST OF REFERENCE SYMBOLS
[0054] 1 First chamber (2 K He) 32 Cryostat (4.2 K helium) [0055] 2
Further chamber (4.2 K He) 33 Pump-off pipe [0056] 3 Joule-Thomson
valve 34 Pump [0057] 4 Thermally insulating barrier 35 Cryogen pipe
[0058] 5 Filter 36 Branch-off device [0059] 6 Relief valve 37
Pressure regulating device [0060] 7 Bursting disk 38 Buffer vessel
[0061] 10 Cryostat configuration 39 Condenser [0062] 11 Cryostat
(2K helium) [0063] 13 Pump-off pipe 40 Cryostat configuration
[0064] 14 Pump 41 First cryostat (2 K helium) [0065] 15 Cryogen
pipe 42 Further cryostat [0066] 16 Branch-off device 43 Pump-off
pipe [0067] 17 Pressure regulating device 44 Pump [0068] 18 Buffer
vessel 45 Cryogen pipe [0069] 46 Branch-off device [0070] 20
Cryostat configuration 47 Pressure regulating device [0071] 21
First cryostat (2 K helium) [0072] 22 Further cryostat 50 Cryostat
configuration [0073] 23 Pump-off pipe 51 First cryostat (2 K
helium) [0074] 24 Pump 51' Further cryostat (2k helium) [0075] 25
Cryogen pipe 52 Further cryostat [0076] 26 Branch-off device 53
Pump-off pipe [0077] 27 Pressure regulating device 54 Pump [0078]
28 Buffer vessel 55 Cryogen pipe [0079] 56 Branch-off device [0080]
30 Cryostat configuration 57 Pressure regulating device [0081] 31
Cryostat (2 K helium)
* * * * *