Self-supporting flexible thermal radiation shield for superconducting magnet assemblies

Abstract

A self-supporting flexible shield for positioning between a warm surface (16) and a cold mass (10, 12) so as to substantially surround the cold mass, wherein the self-supporting flexible shield comprises a shaped plastic sheet having a low emissivity coating on both sides thereof.

Description

Technical Field

[0001] The present invention relates to a thermal radiation shield for a superconducting magnet, and in particular to a thermal radiation shield for a superconducting magnet for a magnetic resonance imaging (MRI) system. Background Art

[0002] Figure 1 A conventional arrangement of a superconducting magnet for an MRI system housed within a cryostat is shown, the cryostat including a cryogen vessel 12. The cooled superconducting magnet 10 is disposed within the cryogen vessel 12, which is itself held within an outer vacuum chamber (OVC) 14. In the vacuum space between the cryogen vessel 12 and the outer vacuum chamber 14, one or more thermal radiation shields 16 are disposed. In some known arrangements, a refrigerator 17 is mounted in a refrigerator sock 15, which is located in a turret 18 disposed toward the side of the cryostat for this purpose. An access turret 19 holds an access neck (vent) 20 at the top of the cryostat. In some arrangements, the refrigerator 17 provides active refrigeration to cool the refrigerant gas within the cryogen vessel 12 by recondensing the refrigerant gas into a liquid. The refrigerator 17 may also be used to cool the radiation shield 16. As shown in FIG. Figure 1 As shown, the refrigerator 17 may be a two-stage refrigerator. The first cooling stage is thermally linked to the radiation shield 16 and provides cooling to a first temperature, typically in the range of 40-100 K. The second cooling stage provides cooling of the refrigerant gas to a liquid state, which is at a much lower temperature, typically in the range of 4-10 K. Summary of the invention

[0003] The thermal radiation shield 16 is used to prevent thermal radiation from the external vacuum chamber from reaching the cryogen container. In some arrangements, two or more thermal radiation shields may be provided, one inside the other, to prevent or at least hinder thermal radiation from relatively warm surfaces from reaching relatively cold surfaces. In some arrangements, referred to as "dry" magnets, no cryogen container 12 is provided around the magnet coil 10, and the magnet coil is exposed to the inner surface of the thermal radiation shield 16.

[0004] The thermal radiation shield 16 itself should be thermally conductive so that cooling of the shield by the cryogenic refrigerator 17 at one point serves to remove heat radiated to all portions of the surface of the thermal radiation shield 16 .

[0005] The outer vacuum chamber OVC 14 shown provides a vacuum volume around the cryogen container (if present). The vacuum volume reduces the conduction and convection heat loads from the room temperature shell of the OVC 14 to the cryogen container 12 or the magnet coil 10. The thermal radiation shield 16 is used to reduce the corresponding radiation heat load. The radiation shield 16 is a surface anchored at an intermediate temperature between the temperature of the OVC (about 300K) and the temperature of the magnet coil (e.g., about 4K). The intermediate temperature can be 20K-80K and can be provided by a cryocooler, or by boiling refrigerant gas from the cryogen container. In this specification, the thermal radiation shield 16 will be considered to be at a temperature of about 50K, while the cryogen container or the magnet structure will be considered to be at a temperature of about 4K.

[0006] As a reference, the temperature T h The large relatively hot surface at the temperature T c The thermal radiation power Q of a closed large relatively cool surface at can be expressed as:

[0007] Q=σA(T h 4 -T c 4 ) / (1 / ε1+(1 / ε2)-1)

[0008] in:

[0009] Q is the thermal radiation power;

[0010] σ is the Stefan-Boltzmann constant;

[0011] A is the surface area of ​​each of the two surfaces in question;

[0012] T h is the temperature of the relatively hot surface;

[0013] T c is the temperature of a relatively cool surface;

[0014] ε1 is the emissivity of the relatively hot surface; and

[0015] ε2 is the emissivity of the relatively cool surface.

[0016] Therefore, the radiant heat load is related to T h 4 -T c 4 Proportional, where T h is the temperature of the relatively hot surface (here the inner surface of the OVC), and T cis the temperature of the relatively cold surface (here, the exterior surface of the cryogen container), both expressed in Kelvin. h OVC 14 at T c The intermediate temperature T between the refrigerant container 12 i (temperature of the thermal radiation shield 16), by relatively increasing the temperature T i Extract heat energy from the surface to reduce heat radiation to the cold surface.

[0017] To further reduce the thermal load, the thermal emissivity of both the emitting (hot) and receiving (cold) surfaces should be reduced as much as possible so that the emitting surface emits the least radiation and the receiving surface absorbs the least amount of any radiation that does impinge upon it. Typically, the radiation shield 16 is made of aluminum or copper because they have low emissivity. A thin foil of highly reflective high purity aluminum can be applied to the surface of the thermal radiation shield to provide a low emissivity surface.

[0018] Between the cryogen container and the thermal radiation shield, and / or between the OVC and the thermal radiation shield, a multi-layer insulation (MLI) blanket may be placed. The MLI blanket comprises several layers of aluminized polyester sheets held in place, slightly spaced apart, shaped and mounted to reflect thermal radiation and eliminate line-of-sight paths as much as possible. Such MLI blankets help reduce thermal radiation between surfaces.

[0019] For a magnet system having a cryogen vessel 12 surrounding the magnet coil, the outer surface of the cryogen vessel 12 is the receiving surface for the thermal radiation. Typically, this is stainless steel, which has a high emissivity. Alternatively, impure alloy aluminum may be used, but it also has a relatively high emissivity. A thin foil of highly reflective high purity aluminum, typically 50 μm thick, may be applied to the receiving surface to provide a low emissivity surface which, in this case, tends to reflect incident radiation from the receiving surface.

[0020] Disadvantages of this foil wrapping approach include the time it takes to effectively wrap the cryogen container, the complexity due to the relatively complex shapes that need to be covered, and the assembly complexity due to the fact that the foil must be adhered with double-sided tape and vented with small holes to allow gas to escape as the volume around the cryogen container is evacuated within the OVC. The foil will be relatively conductive, and in an MRI system, this conductivity can cause gradient coil interactions that can increase the thermal load of the system.

[0021] For magnet systems in which the magnet coil 10 is not enclosed within a cryogen container (often referred to as "dry magnets"), the magnet coil and support structure typically provide a receiving surface. Materials such as stainless steel, GRP, resins, such as those used in the magnet coil and support components typically have high emissivity. Some conventional steps have been taken to try to reduce the emissivity. Such surfaces can be coated with a layer of aluminum foil as discussed above, or with a thinner aluminum laminated to a plastic (such as polyester) to give improved tear resistance. An example material is RUAG Space GmbH's COOLCAT 4K. It is a laminate of a double-sided aluminized 12μm polyester foil and a 6μm pure aluminum foil.

[0022] For convenience, the magnet structure within the cryogen container (where provided) and the separate magnet structure (where no cryogen container is provided) may be referred to as a "cold mass", i.e., an item cooled to a minimum temperature (e.g., 4K).

[0023] Such an approach also has disadvantages, including the time it takes to wrap the foil or laminate around a complex shape, to stick the foil or laminate in place with adhesive tape, and to provide enough holes for gas to escape when the OVC is evacuated. The commonly used double-sided adhesive tape only adheres well to metal, not to plastic, resin or GRP, and it may be difficult to arrange the foil or laminate to be adequately attached. The conductivity of the foil means that care must be taken with electrical connectors and surrounding uninsulated wiring to avoid compromising electrical isolation. The foil will be relatively conductive, and in an MRI system, this conductivity can cause gradient coil interactions, which may increase the thermal load of the system. Depending on the thickness of the metal layer, this may also apply to the laminate. If the layer of conductive material in the gradient field is very thin, it has a high square resistance, so eddy currents will not be induced and there is little dissipation; on the other hand, if the conductive material is very thick and conductive, eddy currents will be induced, but the resistance is low, so there is little ohmic heating and the dissipation is also low. If the thickness of the material is between the two, significant eddy currents may be generated and resistive losses will occur, which increases the thermal load of the system.

[0024] An alternative solution that has been proposed is to add an additional thermal radiation shield that is cooled to substantially the temperature of the cryogen container or magnet structure and is located between the cryogen container or magnet structure and the conventional thermal radiation shield. This additional thermal radiation shield may be referred to as a "4K shield", and it may be made of aluminum that is several millimeters thick and coated on the outside with a low emissivity aluminum foil. The outer surface then absorbs very little radiated heat due to its low emissivity coating, and the inner surface is substantially at the temperature of the cryogen container or magnet structure, and therefore does not radiate heat toward the cryogen container or magnet structure.

[0025] However, due to the amount of material required, such a structure is expensive and bulky. It must be connected to a cryogenic cooling device (such as a refrigerator 17) to keep it at the temperature of the refrigerant container 12 (if any) or the magnet structure 10, which adds complexity. The time and energy required to cool the mass of the 4K shield to the required temperature will increase the time to cool down at startup. The 4K shield requires space in the hole of the magnet coil, which in turn increases the diameter required for the magnet coil, and therefore also increases the amount of wiring required, thereby increasing cost and weight. The outer surface of the 4K shield needs to be coated with foil, so the foil coating still exists as a time-consuming processing step. Depending on the thickness and resistivity of the material used for the 4K shield, significant eddy currents may be generated and resistive losses may occur, which increases the thermal load of the system.

[0026] GB2490478 discloses an example of a 4K shield.

[0027] US7548000 discloses a power generation system comprising a thermal radiation shielding member using a thin double aluminum alloy. sheet, and partially surrounds the superconducting rotor coil.

[0028] The present invention addresses the shortcomings of conventional arrangements and provides a thermal radiation shield that avoids the need to coat the surface of the cryogen container or magnet structure with foil or laminate material. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The above and other objects, features and advantages of the present invention will become more apparent through the following description of certain examples of the present invention, which are given by way of example only, in conjunction with the accompanying drawings, in which:

[0030] Figure 1 A conventional arrangement of wet magnets in a cryostat is schematically shown, showing the electrical connections and refrigeration arrangements;

[0031] Figure 2 Schematically shows an arrangement according to the invention;

[0032] Figure 3 A flexible shield according to one embodiment of the present invention is shown in cross section;

[0033] Figure 4 shows a partial cut pattern of a flexible material for use in forming a portion of a flexible shield according to one embodiment of the present invention;

[0034] Figure 5 shows a folding hood according to the present invention; and

[0035] Figure 6 A folding box according to the invention is shown for enclosing a heat-generating device such as a switch. DETAILED DESCRIPTION

[0036] Figure 2 An embodiment of the present invention is schematically illustrated, which provides a flexible radiation shield 30 between the cryogen container 12 (or when the cryogen container 12 is not provided, the magnet structure 10), which replaces the rigid aluminum 4K shield or foil or laminate coating described with reference to the prior art. A self-supporting shell of a low emissivity flexible material 30, somewhat similar to a tent, is provided, which is located between the cryogen container 12 or the magnet structure 10 and a conventional thermal radiation shield 16. It can then be found that it is not necessary to provide a low emissivity foil coating on the thermal radiation shield or the cryogen container or the magnet structure. Conventional thermal radiation shields 16 are typically at a temperature of about 50K, and often between 20K-80K, and the cryogen container or magnet structure is typically at a temperature of about 4K. However, the present invention can be applied between components of different temperature ranges.

[0037] The flexible material selected for the self-supporting housing is preferably strong enough to allow it to be folded into a self-supporting shape and to maintain a certain tension so that its shape can be controlled. For example, suitable materials include double aluminized polymer sheets, such as polyethylene terephthalate sheets (which may also be referred to as PET, The PET may have a thickness in the range of 125-500 μm, and the aluminum coating may have a thickness in the range of 20-100 nm and may be applied by physical vapor deposition (PVD). The thickness of the aluminum coating should be chosen so that it is sufficient to reflect the expected thermal radiation, but not so thick that it has significant in-plane thermal conductivity, or is subject to eddy currents generated by gradient coil interaction.

[0038] The flexible material is preferably aluminum clad on both sides to ensure low emissivity properties both towards the higher temperature surface and towards the lower temperature surface.

[0039] The flexible material can be formed into a self-supporting structure by one or more assembly methods. Examples of such methods include:

[0040] - Vacuum forming of heated materials, provided that the low emissivity properties of the surface are maintained;

[0041] - Cut with a laser, knife, saw or other means and then folded into a shape that is held in place by taping or by using grooves and barbs formed in the flexible material. Aluminum tape or aluminum-coated polymer tape can be used in the assembly of the flexible material to maintain the low emissivity surface.

[0042] The flexible material is preferably attached to the refrigerant container or magnet structure using non-adhesive fasteners. So-called nylon "fir tree" rivets may be used to removably hold the flexible material in place by passing through corresponding holes in the material of the flexible shield and support structure. Screws or other types of rivets may alternatively be used. Slots or holes and barbs may also or alternatively be used.

[0043] In certain embodiments, the part of the flexible material can be in close contact with the refrigerant container or the magnet structure, and therefore can be locally cooled to the temperature of the component. In use, such a part will play a role similar to the above-mentioned foil or laminated coating. In other positions, the flexible material will be positioned away from the refrigerant container 12 (if any) or the magnet structure 10. The flexible material is intended to have low in-plane thermal conductivity and electrical conductivity, so the incident radiant heat will not be easy to flow to the magnet structure in the plane. The incident radiant heat on the flexible material of the shield 30 of the present invention will make the temperature of the relevant part of the flexible material float to an intermediate value, which is between the temperature of the magnet (e.g., 4K) and the temperature of the conventional thermal radiation shield (e.g., 50K). Since the flexible material of the shield of the present invention has a low specific emissivity on both sides, it reflects most of the radiation emitted by the 50K shield, and also emits very little towards the refrigerant container or magnet at about 4K. The incident radiation flux onto the cryogen vessel or magnet will be significantly less than a conventional arrangement which has thermal radiation from a 5OK shield to the cryogen vessel or magnet at approximately 4K.

[0044] Using the formula discussed above, if T h =50K, T c =4K, ε1=0.1, ε2=0.02, then the heat radiation to the cooler surface is about 6mW / m 2 This may be the case when a conventional 50K shield of a low emissivity surface surrounds a cryogen container covered in a low emissivity layer.

[0045] With a flexible shield as described above, even with a cryogen container or magnet having a worst case emissivity value of 1.00, the flexible shield floats to an intermediate temperature such as about 41 K, and the thermal radiation emitted to the cryogen container or magnet is only about 3 mW / m even under these worst case conditions. 2 .

[0046] In certain locations, the flexible shield may physically contact components at the temperature of the 50K shield, and therefore locally heat up to the temperature of the shield. This may occur around suspension penetrations, for example. Even if the flexible shield heats up to 50K at such locations, the low in-plane thermal conductivity of the flexible shield means that the rest of the flexible shield will not heat up to 50K. The 50K region of the flexible shield of the present invention acts very similarly to the region of the 50K shield covered with a low emissivity coating.

[0047] In such areas, even with a cryogen container or magnet having a worst-case emissivity value of 1.00, and with a flexible shield at a temperature of 50 K, the thermal radiation emitted onto the cryogen container or magnet for these areas is approximately 7 mW / m even under these worst-case conditions. 2 .

[0048] The low in-plane thermal conductivity of the flexible shield means that areas of the flexible shield can be in contact with a 50K thermal shield, while other areas can be in contact with a cryogen vessel or magnet structure at a temperature of about 4K, without significant heat conduction between areas at such different temperatures. Such low in-plane thermal conductivity is achieved by using very thin metal layers to provide a low emissivity surface without providing appreciable in-plane thermal conductivity.

[0049] The material chosen for the flexible shield should be of sufficient thickness, and therefore resilient, that it does not need to be supported at very regular intervals, and can span large gaps without support. It can therefore be mounted in relatively few places from the magnet structure or mounting structure for the 50K thermal radiation shield. The mounting point can be chosen to be away from the electrical components, which means that special measures to provide electrical isolation of the flexible shield can be minimized.

[0050] In certain embodiments, the inventors have found that a 250 μm thick sheet of PET aluminized on both sides is strong enough to be self-supporting and can be formed into suitable shapes. Such material is available at a reasonable price.

[0051] The proposed flexible shield of, for example, 250 μm PET is low in mass, which means that the initial cool down time is kept short.

[0052] In areas where the shield is self-supporting, the thermal performance of the flexible shield of the present invention is found to be superior to the thermal performance of conventionally applied low emissivity layers to cryogen vessels or magnets.

[0053] The flexible shield of the present invention is quicker to assemble than using conventional arrangements of low emissivity foils.

[0054] The flexible shield of the present invention requires very little additional radial space. The material thickness of the shield is much less than 0.5 mm. As discussed above, it can tolerate contact with higher or lower temperature components. Therefore, it does not need to be located in a continuous annular area and can be assembled around other components of the magnet system as appropriate.

[0055] There is no need to provide a cooling path to the shield, as the temperature of the shield is allowed to float and stabilize at a value between the temperature of the cryogen vessel (eg, 4K) and the temperature of the thermal radiation shield (eg, 50K).

[0056] The cold mass is substantially surrounded by the flexible shield of the invention.

[0057] In addition to the intermediate flexible shield 30 located between the cold mass (including the cryogen vessel 12 (where present) or the magnet structure 10) and the thermal radiation shield 16, or as part of the flexible shield 30, the above materials and techniques can be used for in-box components to prevent thermal radiation from those components from reaching other components such as the magnet 10 or cryogen vessel 12. For example, a superconducting switch that must be warmed to change to an open state can be surrounded by a box-like housing made of the materials discussed above for the flexible shield, folded into a self-supporting box to block thermal radiation from the superconducting switch to the magnet coils. This prevents thermal radiation from reaching the magnet coils and also reduces heat losses from the switch, thereby requiring less total heating power input to open the superconducting switch, which has benefits for the entire cryogenic system.

[0058] The present invention provides a self-supporting thermal floating radiation shield. The material selected is suitably strong to be able to be formed into a shape and maintain its position unaided over a relatively large distance. The flexible radiation shield can be a plastic layer (such as 250μm PET) with a low emissivity coating on both sides. The plastic layer gives sufficient strength and rigidity to the shield, while the metallic low emissivity coating (such as 20-100nm PVD aluminum) provides the required low emissivity properties while maintaining low in-plane thermal conductivity and electrical conductivity. This low in-plane thermal conductivity allows the shield to contact both relatively low temperature surfaces and relatively high temperature surfaces without causing thermal shorts, which involve unwanted heat flow to or from the flexible shield. The assembly of the flexible shield of the present invention reduces complexity and assembly time compared to applying low emissivity foil to the surface of the refrigerant container or magnet structure and the thermal radiation shield.

[0059] Preferably, the flexible shield is formed from a plastic sheet treated by application of a low emissivity layer on both sides. In particular, the flexible shield may be formed from a double aluminised PET sheet of sufficient thickness to be self-supporting and capable of being formed into a self-supporting structure.

[0060] A method for assembling a flexible shield may include the following steps, all of which allow for the creation of a lightweight and substantially light-impermeable shield that is easy to manufacture.

[0061] The material of the flexible shield is formed into the required shape by folding, vacuum forming, using barbed tabs and slots to give structural strength to the required shape and allow the material to wrap around complex shapes. The shape so formed is mounted to the support structure by means such as attachment by rivets (such as fir tree rivets) or barbs to require minimal taping, thereby reducing assembly time and reliance on adhesive bonding at low temperatures.

[0062] The material of the flexible shield of the present invention can be cut and folded to form the desired shape. Grooves, barbs and lugs can be used to enable the material to be assembled into the desired shape without the use of adhesives or fasteners. Such cutting features can be formed by the use of a knife, hot wire cutting, laser cutting, die stamping, etc. Since labor costs can be reduced through a simple assembly process, such parts can be assembled neatly and inexpensively. By reducing the reliance on adhesives in assembly, it can be found that the assembly is more reliable at low temperatures and the possibility of the adhesive bond loosening in use is correspondingly reduced.

[0063] Flexible shielding material may be used as described to form a shield to surround heating components to reduce heat loss by radiation from such components.

[0064] Figure 3 A magnet system is schematically represented which is substantially rotationally symmetric about a magnet axis AA, wherein the magnet structure is enclosed in a flexible shield according to an embodiment of the invention. Figure 3The shield shown is made by wrapping a flexible sheet of material having two low emissivity surfaces (such as double aluminized PET) around the magnet to form a shell 24. The shell is attached to a corresponding end piece 28 by a slot and barb fastener 26, each end piece 28 also formed of a flexible sheet of material having two low emissivity surfaces (such as double aluminized PET). Such slots and barb fasteners 26 can be repeated at certain intervals around the periphery of the magnet system. An aperture piece 30, also made of a flexible sheet of material having two low emissivity surfaces (such as double aluminized PET), is placed around the inner hole of the magnet and can be attached to the magnet structure 10 (e.g., a magnet former) using a fir tree rivet 32 ​​or some other suitable fixing device. The aperture piece 30 is attached to the corresponding end piece 28 by a slot and barb fastener 26. Such slots and barb fasteners 26 can be repeated at certain intervals around the periphery of the magnet system. Alternatively or additionally, the radial ends 34 of the end piece 28 may be formed by cutting the radial ends of the material into wings and bending the wings parallel to the magnet axis. The wings may then be held in place by adhesive tape, or (preferably) by the interlocking grooves and barbed lugs mentioned above. Alternatively or additionally, the axial ends 34 of the shell piece 24 and the orifice piece 30 may be formed by cutting the axial ends of the material into wings and bending the wings perpendicular to the magnet axis. The wings may then be held in place by adhesive tape, or (preferably) by the interlocking grooves and barbed lugs mentioned above.

[0065] The end pieces 28, shell piece 24 and aperture piece 30 may all be attached to the magnet coil 10 or support structure by fir tree rivets 32 or other suitable fasteners.

[0066] Figure 4 One example of a slit and barbed lug arrangement for creating a folded structure in the flexible shield material is shown.A sheet of material 61 is cut to define wings 62,63.

[0067] One of the wings, referenced 62, has a slit 64 cut into it. The other wing, referenced 63, has a barbed tab 65 attached thereto. During the assembly step, the flexible material is folded along a fold line 66, which may be defined by scoring or partially cutting through the flexible material. The barbed tab 65 is pressed through the slit 64 so that the barb 67 engages the end of the slit 64 to hold the assembly together. Figure 4 The structure shown can be assembled into a box shape.

[0068] Figure 5 A complex folded cowl is shown for placement around a component that must penetrate the shield. In use it will be in mechanical contact with a part at a temperature of about 50 K. The barbed lugs 65 and wings 71 can be seen.

[0069] Figure 6 An example of a folding box cover 42 is shown, and this folding box cover 42 is assembled by wings, slits, barbed lugs as described. As illustrated here, such a folding box cover can be used to pack heat-generating components 38 such as switches into a box to prevent the heat radiation from those components from reaching other components such as magnets 10 or refrigerant containers 12. The assembled box 42 is shown as being attached to a supporting structure 40 by fir tree rivets 32. In use, this folding box cover is attached to a part cooled to a temperature of about 4K, which part can be a supporting structure 40. Grooves and barb fixings 26 are shown, where one side of the box is slightly folded over the adjacent side to improve the light tightness of the box.

[0070] Although the invention has been described with particular reference to a superconducting magnet having an OVC and a thermal radiation shield placed between the OVC and the magnet structure or cryogen vessel (if any), the invention can be applied to other cooling equipment and thus generally the thermal radiation shield of the invention can be located between a warm surface and a cold mass, the term "warm" being relative here and simply meaning that it is at a higher temperature than the cold mass. Although described in terms of cryogenically cooled superconducting magnets, the invention can be applied to any cooling equipment within a housing at a different temperature.

Claims

1. A superconducting magnet assembly comprising a cold mass within an outer vacuum chamber (14), the cold mass itself comprising a superconducting magnet coil (10), wherein a thermal radiation shield (16) is located around the cold mass but within the outer vacuum chamber (14), wherein the superconducting magnet assembly further comprises a self-supporting flexible shield so as to substantially surround the cold mass, wherein the self-supporting flexible shield comprises a shaped plastic sheet having a low emissivity coating on both sides thereof, the shaped plastic sheet being located between the cold mass and the thermal radiation shield, the self-supporting flexible shield comprising a folded structure of the shaped plastic sheet having the low emissivity coating on both sides thereof, the folded structure being attached to the cold mass, The folded structure includes a slit and a barbed lug arrangement. 2 . The superconducting magnet assembly of claim 1 , wherein the self-supporting flexible shield thermally floats at an intermediate temperature between the temperature of the cold mass and the temperature of the thermal radiation shield.

3. A superconducting magnet assembly according to claim 1 or claim 2, wherein the folding structure comprises a folding box cover (73).

4. A superconducting magnet assembly according to claim 1 or claim 2, wherein the folded structure comprises a folded hood.

5. A superconducting magnet assembly according to any one of the preceding claims, wherein the folded structure comprises a polymer sheet that is aluminised on both sides. 6 . The superconducting magnet assembly of claim 5 , wherein the polymer sheet comprises a PET sheet having a thickness of 125-500 μm. 7 . The superconducting magnet assembly according to claim 6 , wherein the polymer sheet comprises a PET sheet having a thickness of 250 μm.

8. The superconducting magnet assembly according to any one of claims 5 to 7, wherein the polymer sheet is aluminized on both sides with respective aluminum layers, each aluminum layer having a thickness of 20-100 nm.

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