GB2505207A - Displacers to reduce the volume of liquid helium in the cryogen vessel of a superconducting magnet - Google Patents
Displacers to reduce the volume of liquid helium in the cryogen vessel of a superconducting magnet Download PDFInfo
- Publication number
- GB2505207A GB2505207A GB1214949.8A GB201214949A GB2505207A GB 2505207 A GB2505207 A GB 2505207A GB 201214949 A GB201214949 A GB 201214949A GB 2505207 A GB2505207 A GB 2505207A
- Authority
- GB
- United Kingdom
- Prior art keywords
- cryogen
- superconducting magnet
- cryogen vessel
- displacers
- vessel
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
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Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
- G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
- G01R33/38—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field
- G01R33/3804—Additional hardware for cooling or heating of the magnet assembly, for housing a cooled or heated part of the magnet assembly or for temperature control of the magnet assembly
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
- F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
- F17C13/00—Details of vessels or of the filling or discharging of vessels
- F17C13/005—Details of vessels or of the filling or discharging of vessels for medium-size and small storage vessels not under pressure
- F17C13/006—Details of vessels or of the filling or discharging of vessels for medium-size and small storage vessels not under pressure for Dewar vessels or cryostats
- F17C13/007—Details of vessels or of the filling or discharging of vessels for medium-size and small storage vessels not under pressure for Dewar vessels or cryostats used for superconducting phenomena
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F6/00—Superconducting magnets; Superconducting coils
- H01F6/04—Cooling
Abstract
A superconducting magnet e.g. for MRI comprises inner 12 and outer 14 coils partially immersed in liquid helium in a cryogen vessel. Displacers 22 occupy parts of the cryogen vessel below the cryogen fill level 18 and reduce the volume of liquid helium required to fill the vessel to the required level. Support webs 16 may be provided to retain the coils in position and displacers 22 may fill voids between the webs. The displacers may be sized and shaped to accommodate existing equipment 22 within the cryogen vessel. The displacers are made from a non-porous material, such as an epoxy resin with a filler material. The filler may be silane-coated soda glass spheres, sand, gravel, scrap epoxy resin, or scrap composite material. Alternatively, the displacers may be welded hollow metal or a skinned metal foam.
Description
A SUPERCONDUCTING MAGNET WITHIN A CRYOGEN VESSEL
WITH CRYOGEN DISPLACERS
Conventionally, superconducting magnets such as those used in magnetic resonance imaging (MRI) are cooled by partial immersion in a liquid cryogen, such as helium. The magnet itself, typically formed of several coils of superconducting wire, is placed in a cryogen vessel containing a liquid cryogen to a depth sufficient to partially immerse the coils.
Typically, some of the liquid cryogen is lost in use, but a more significant loss is encountered when the magnet is cooled from room temperature.
Once cooled to operating temperature, consumption of cryogen tends to fall to a relatively low rate. A significant quantity of liquid cryogen is stored within each cryogen vessel, and it may be difficult to recover this liquid cryogen at the end of the useful life of the magnet. The material commonly used for making superconducting coils needs to be cooled to a temperature which can only be reached by using liquid helium as the cryogen. A typical superconducting magnet used in an MRI system will consume over 1000 litres of liquid helium before it becomes operational. As is well known, superconducting magnets can suffer quench -where the superconducting coils become resistive, suddenly heating and expelling cryogen from the cryogen vessel. Significant volumes of cryogen must be replaced each time that this happens.
Liquid helium is becoming increasingly scarce and costly. The present invention aims to provide apparatus for reducing the consumption of liquid helium for cooling superconducting magnets, during cooling, during refilling and at the end of their useful life.
The present invention accordingly provides methods and/or apparatus as defined in the appended claims.
The objects, characteristics and advantages of the present invention will become more apparent from the following description of certain embodiments thereof, in conjunction with the accompanying drawings, wherein Fig. 1 shows an axial view of a superconducting magnet structure to which the present invention is applied.
Certain approaches to the problem of reducing cryogen consumption have been attempted in the past. The present invention addresses the problem by reducing the volume of cryogen needed to immerse the superconducting coils to a given depth.
This is achieved, according to an aspect of the invention, by the provision of cryogen displacers within the cryogen vessel. Using such displacers, a given depth of immersion can be achieved with a reduced volume of liquid cryogen.
Some attempts have been made to achieve a given immersion depth with less liquid cryogen by providing cryogen vessels shaped to more closely match the shape of the magnet structure. However, the provision of such cryogen vessels is complex and costly.
The present invention provides immersion of coils to a certain depth using a reduced volume of liquid cryogen by placement of displacers within a cryogen vessel. Such an arrangement may be easily implemented, and can easily be adapted to changes in the magnet structure by provision of different shapes or combinations of displace rs.
Preferably, the displacers are provided below the usual level of liquid cryogen for the magnet in operation. By avoiding placement of displacers within the cryogen vessel but above this level, an additional quantity of cryogen may be provided, as is conventional, to maintain cooling of the magnet during transport.
The displacers provided by the present invention represent an added cost and assembly effort during manufacture of the magnet, but this is believed to be amply outweighed by the cost saving in liquid cryogen, particularly where that cryogen is helium.
The thermal mass of the magnet structure will be increased by provision of the displacers, and so the thermal capacity and mass of the material used to form the displacers should be considered. Extra thermal mass will require extra cryogen to cool it down, so cancelling a part of the benefit achieved by provision of the displacers.
Care should be taken to ensure that the displacers do not absorb liquid cryogen, either through a leak or due to the use of permeable materials, If a displacer absorbs liquid cryogen, there is a risk that it might burst: explode or fracture if the temperature in the cryogen vessel rises and the cryogen reverts to a gaseous phase.
An example displacer envisaged by the inventors and which may be provided within a cryogen vessel, below an operational cryogen till level, according to an embodiment of the present invention is cuboid, having a volume of -3Ulitres. A number of these displacers would be used dependent on magnet geometry to displace a total volume of -2solitres. The displacers are preferably made of silane coated soda glass spheres vacuum impregnated with an epoxy resin.
Using a vacuum impregnation technique, displacers of complex shapes can be moulded from this material if required.
Fig. 1 schematically represents an axial view of a superconducting magnet structure to which the present invention is applied. The magnet structure 10 is essentially cylindrical, with inner coils 12 and outer coils 14 arranged coaxially about an axis A. Support structures are provided to retain inner coils 12 and outer coils 14 in the required relative positions. Webs 16 are typically provided, as shown, to retain the support structures in required relative positions. An example operational cryogen till level 18 is shown.
Displacers 20 according to an embodiment of the present invention are shown, placed in voids between webs 16 and below the operational cryogen fill level 18. The shapes and sizes of the displacers are preferably adapted to fit the available space.
For example, displacers 20a are shown smaller than the remaining displacers illustrated, to fit around existing equipment 22. Not all voids between webs below the operational cryogen fill level 18 need contain a displacer. Void 24 is shown without a displacer, due to existing equipment within that void. There is no reason that displacers cannot be placed above or at the operational cryogen fill level 18, but the utility of a displacer is much improved by placing it below the operational cryogen fill level 18. Preferably, the displacers should be mounted to the support structure with a minimum of contact points. For example, one or more threaded studs may be moulded in to a displacer and used to attach the displacer to the support structure.
Alternatively, a threaded insert may be moulded into a displacer, with a bolt passing into the insert to attach the displacer to the support structure.
The cost of the example material, silane coated soda glass spheres in epoxy resin, has been estimated to be approximately equal to the cost of an equal volume of liquid helium at current prices (2012). Therefore, by displacing an equal volume of cryogen when a cryogen vessel is filled, the displacers of this example pay for themselves on an initial filling with liquid helium, and cost savings can be made on each later refilling. It is expected that the cost of liquid helium will rise in the future, which will make the economic benefit of using displacers according to the present invention even more attractive.
In addition to the saving in cryogen costs on filling the cryogen vessel, the reduced volume of cryogen within the cryogen vessel may allow for additional cost reductions in vessel design due to reductions in the pressure generated during a quench.
In an example, in the order of 200 litres of cryogen may be displaced, to raise the cryogen level to the operational cryogen fill level 18 while including an acceptable volume of liquid cryogen. The mass of 200 litres of displacers of silane coated soda glass spheres in epoxy resin is in the order of 390kg. This is a disadvantage as it adds to the mass of the cryogen vessel, and the mass of the displacers must be cooled along with the superconducting magnet. Preferably, a mechanical or sacficial cooling method may be used to cool the magnet structure including the displacers to a first cryogenic temperature, while cooling to operational temperature may be achieved by addition of liquid cryogen.
While the example of displacers made of vacuum-moulded silane coated soda glass spheres in epoxy resin is believed to be advantageous, displacers according to the present invention may be made of other materials and by other methods. Sealed hollow vessels, such as welded metal structures, can be used but require costly materials, welding, and care must be taken to avoid leaks, to ensure that cryogen does not enter the sealed volume and cause a risk of explosion. Burst discs may be included in a hollow displacer, so that the risk of damage is reduced.
Metal skinned foam may be used. It offers a substantial saving in mass and thermal load as compared to silane coated soda glass spheres in epoxy resin, but there is a risk of cryogen entering the open celled structure. This may cause fracturing of the structure if the cryogen reverts to its gaseous state.
Explosion or fracturing of displacers, or burst discs within the displacers, risks causing mechanical damage to the magnet due to debris propelled within the cryogen vessel.
The present invention provides displacers for displacing liquid cryogen within a cryogen vessel containing a superconducting magnet. In addition to the examples discussed above, the present invention also provides displacers of the following constructions.
The displacers may be made of any suitable solid material, which is non-porous to the cryogen.
The displacers may be moulded from any suitable material, which is non-porous to the cryogen.
Moulded displacers may be formed using hollow microspheres embedded in epoxy resin. The mass and thermal mass of such displacers will be reduced as compared to the silane coated soda glass spheres in epoxy resin example, but with a risk of leakage and fracture of the hollow microspheres.
Other filler materials which may be used for forming the displacers, when embedded in a suitable epoxy resin, include sand; gravel; crushed scrap epoxy resin; crushed scrap composite materials comprising epoxy resin and a tiller material.
In certain embodiments of the invention, displacers of differing materials and/or construction may be employed.
It may be preferred not to fill the cryogen vessel with cryogen before the magnet is shipped to its installation site. Rather, the magnet may simply be cooled by addition of liquid cryogen at its installation site. In such examples, the displacers of the present invention may serve to reduce the volume of liquid cryogen required on-site to fill the cryogen vessel to the operational cryogen fill level 18.
When a magnet is conventionally cooled, or suffers a quench, a significant volume of liquid cryogen is expelled. The present invention reduces the volume of liquid cryogen within the cryogen vessel, and so reduced the volume of liquid cryogen which is available to be expelled.
Claims (16)
- CLAIMS1. A superconducting magnet within a cryogen vessel, characterised in that displacers (20) are provided below an operational cryogen fill level (18) whereby a volume of liquid cryogen required to fill the cryogen vessel to the operational cryogen fill level (18) is reduced.
- 2. An essentially cylindrical superconducting magnet within a cryogen vessel, according to claim 1, comprising inner coils (12) and outer coils (14) arranged coaxially about an axis (A), with support structures provided to retain inner coils (12) and outer coils (14) in required relative positions, webs (16) being provided to retain the support structures in required relative positions, wherein displacers (20) are placed in voids between webs (16) and below the operational cryogen fill level (18).
- 3. A superconducting magnet within a cryogen vessel, according to claim 1, wherein shapes and sizes of the displacers are adapted to fit into available space around existing equipment (22).
- 4. A superconducting magnet within a cryogen vessel, according to claim 1, wherein at least one of the displacers is moulded of a material which is non-porous to the liquid cryogen.
- 5. A superconducting magnet within a cryogen vessel, according to claim 4 wherein the material comprises an epoxy resin containing a filler material.
- 6. A superconducting magnet within a cryogen vessel, according to claim 5 wherein the filler material comprises silane coated soda glass spheres.
- 7. A superconducting magnet within a cryogen vessel, according to claim 5 wherein the filler material comprises hollow microspheres.
- 8. A superconducting magnet within a cryogen vessel, according to claim 5 wherein the filler material comprises sand or gravel.
- 9. A superconducting magnet within a cryogen vessel, according to claim 5 wherein the filler material comprises crushed scrap epoxy resin.
- 10. A superconducting magnet within a cryogen vessel, according to claim 5 wherein the filler material comprises crushed scrap composite material, said composite material itself comprising epoxy resin.
- 11. A superconducting magnet within a cryogen vessel, according to claim 4 wherein a threaded stud is moulded in to a displacer and is used to attach the displacer to the support structure.
- 12. A superconducting magnet within a cryogen vessel, according to claim 4 wherein a threaded insert is moulded into a displacer, with a bolt passing into the insert to attach the displacer to the support structure.
- 13. A superconducting magnet within a cryogen vessel, according to claim 1, wherein at least one of the displacers is a sealed hollow vessel.
- 14. A superconducting magnet within a cryogen vessel, according to claim 1, wherein a hollow displacer is formed from welded metal.
- 15. A superconducting magnet within a cryogen vessel, according to claim 1, wherein a hollow displacer comprises a burst disc.
- 16. A superconducting magnet within a cryogen vessel, according to claim 1, wherein at least one of the displacers is formed of a metal skinned foam.Amendments to the claims have been filed as followsCLAIMS1. An essentially cylindrical superconducting magnet within a cryogen vessel, comprising inner coils (12) and outer coils (14) arranged coaxially about an axis (A), with support structures provided to retain inner coils (12) and outer coils (14) in required relative positions, webs (16) being provided to retain the support structures in required relative positions, characterised in that displacers (20) are placed in voids between webs (16) and below an operational cryogen fill level (18), whereby a volume of liquid cryogen required to till the cryogen vessel to the operational cryogen fill level (18) is reduced.2. A superconducting magnet within a cryogen vessel, according to claim 1.wherein shapes and sizes of the displacers are adapted to fit into available space around existing equipment (22).3. A superconducting magnet within a cryogen vessel, according to claim 1, C') wherein at least one of the displacers is moulded of a material which is non-porous to the liquid cryogen.LU0 20 4. A superconducting magnet within a cryogen vessel, according to claim 3 0 wherein the material comprises an epoxy resin containing a filler material.5. A superconducting magnet within a cryogen vessel, according to claim 4 wherein the filler material comprises silane coated soda glass spheres.6. A superconducting magnet within a cryogen vessel, according to claim 4 wherein the filler material comprises hollow microspheres.7. A superconducting magnet within a cryogen vessel, according to claim 4 wherein the filler material comprises sand or gravel.8. A superconducting magnet within a cryogen vessel, according to claim 4 wherein the filler material comprises crushed scrap epoxy resin.9. A superconducting magnet within a cryogen vessel, according to claim 4 wherein the filler material comprises crushed scrap composite material, said composite material itself comprising epoxy resin.10. A superconducting magnet within a cryogen vessel, according to claim 3 wherein a threaded stud is moulded in to a displacer and is used to attach the displacer to the support structure.11. A superconducting magnet within a cryogen vessel, according to claim 3 wherein a threaded insert is moulded into a displacer, with a bolt passing into the insert to attach the displacer to the support structure.12. A superconducting magnet within a cryogen vessel, according to claim 1, wherein at least one of the displacers is a sealed hollow vessel.13. A superconducting magnet within a cryogen vessel, according to claim 1, wherein a hollow displacer is formed from welded metal.14. A superconducting magnet within a cryogen vessel, according to claim 1, C') wherein a hollow displacer comprises a burst disc.15. A superconducting magnet within a cryogen vessel, according to claim 1, 0 20 wherein at least one of the displacers is formed of a metal skinned foam.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB1214949.8A GB2505207B (en) | 2012-08-22 | 2012-08-22 | A superconducting magnet within a cryogen vessel with cryogen displacers |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB1214949.8A GB2505207B (en) | 2012-08-22 | 2012-08-22 | A superconducting magnet within a cryogen vessel with cryogen displacers |
Publications (3)
| Publication Number | Publication Date |
|---|---|
| GB201214949D0 GB201214949D0 (en) | 2012-10-03 |
| GB2505207A true GB2505207A (en) | 2014-02-26 |
| GB2505207B GB2505207B (en) | 2014-12-10 |
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Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB1214949.8A Expired - Fee Related GB2505207B (en) | 2012-08-22 | 2012-08-22 | A superconducting magnet within a cryogen vessel with cryogen displacers |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2505207B (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2508061A (en) * | 2012-09-05 | 2014-05-21 | Gen Electric | Warm bore cylinder assembly of cryostat |
| GB2530537A (en) * | 2014-09-25 | 2016-03-30 | Siemens Healthcare Ltd | Cryostat for actively-shielded superconducting magnet with reduced cryogen requirement |
| GB2547581A (en) * | 2014-11-04 | 2017-08-23 | Shenzhen United Imaging Healthcare Co Ltd | Displacer in magnetic resonance imaging system |
Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS63192281A (en) * | 1987-02-04 | 1988-08-09 | Japan Atom Energy Res Inst | Cryogenic equipment |
| JPH061876A (en) * | 1992-06-22 | 1994-01-11 | Japan Gore Tex Inc | Production of porous hydrophilic fluororesin material |
| US20110136671A1 (en) * | 2009-12-03 | 2011-06-09 | General Electric Company | Displacer and superconducting magnet |
-
2012
- 2012-08-22 GB GB1214949.8A patent/GB2505207B/en not_active Expired - Fee Related
Patent Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS63192281A (en) * | 1987-02-04 | 1988-08-09 | Japan Atom Energy Res Inst | Cryogenic equipment |
| JPH061876A (en) * | 1992-06-22 | 1994-01-11 | Japan Gore Tex Inc | Production of porous hydrophilic fluororesin material |
| US20110136671A1 (en) * | 2009-12-03 | 2011-06-09 | General Electric Company | Displacer and superconducting magnet |
Cited By (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2508061A (en) * | 2012-09-05 | 2014-05-21 | Gen Electric | Warm bore cylinder assembly of cryostat |
| GB2508061B (en) * | 2012-09-05 | 2014-11-19 | Gen Electric | Warm bore cylinder assembly |
| US10281538B2 (en) | 2012-09-05 | 2019-05-07 | General Electric Company | Warm bore cylinder assembly |
| GB2530537A (en) * | 2014-09-25 | 2016-03-30 | Siemens Healthcare Ltd | Cryostat for actively-shielded superconducting magnet with reduced cryogen requirement |
| GB2547581A (en) * | 2014-11-04 | 2017-08-23 | Shenzhen United Imaging Healthcare Co Ltd | Displacer in magnetic resonance imaging system |
| US9835701B2 (en) | 2014-11-04 | 2017-12-05 | Shanghai United Imaging Healthcare Co., Ltd. | Displacer in magnetic resonance imaging system |
| GB2547581B (en) * | 2014-11-04 | 2019-01-09 | Shenzhen United Imaging Healthcare Co Ltd | Displacer in magnetic resonance imaging system |
| US10670675B2 (en) | 2014-11-04 | 2020-06-02 | Shanghai United Imaging Healthcare Co., Ltd. | Displacer in magnetic resonance imaging system |
| US10996298B2 (en) | 2014-11-04 | 2021-05-04 | Shanghai United Imaging Healthcare Co., Ltd. | Displacer in magnetic resonance imaging system |
| US11573279B2 (en) * | 2014-11-04 | 2023-02-07 | Shanghai United Imaging Healthcare Co., Ltd. | Displacer in magnetic resonance imaging system |
Also Published As
| Publication number | Publication date |
|---|---|
| GB201214949D0 (en) | 2012-10-03 |
| GB2505207B (en) | 2014-12-10 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| 732E | Amendments to the register in respect of changes of name or changes affecting rights (sect. 32/1977) |
Free format text: REGISTERED BETWEEN 20160211 AND 20160217 |
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| PCNP | Patent ceased through non-payment of renewal fee |
Effective date: 20160822 |