JPH031807B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical field to which the invention pertains] The present invention relates to an indirect cooling superconducting electromagnetic coil used for detecting particles in high-energy physics.

[Prior art and its problems]

This type of superconducting electromagnetic coil has a diameter and length of several meters, and generally includes a cylindrical cooling body with a cooling tube fixed to the outer circumference for passing a cooling medium such as liquefied helium, and the inside of this cooling body. An indirect cooling type electromagnetic coil is used, which consists of a single-layer inner-wound superconducting coil that is closely wound around the circumferential surface of the coil. In order to strengthen the coil and the cooling body mechanically, an insulating layer containing an adhesive resin is interposed between the coil and the cooling body to fix and integrate the two. Therefore, the coil is cooled through the insulating layer, so the insulating layer is required to have high insulation performance and adhesive strength, as well as good thermal conductivity and resistance to severe cooling cycles. Cryogenic resistance and heat cycle resistance without deterioration of the above-mentioned performance are required.

FIG. 1 is a schematic cross-sectional view of an internally wound superconducting electromagnetic coil. In the figure, reference numeral 2 denotes a cylindrical cooling body made of a good thermal conductor such as aluminum or copper, and a cooling pipe 5 is welded to the outer peripheral surface of the cooling body. 3 is an insulating layer containing adhesive resin applied to the inner peripheral surface of the cooling body 2;
is an inner-wound superconducting coil, in which a superconducting wire formed into a rectangular cross section and insulated by a protective conductor such as aluminum or copper is closely wound around an insulating layer 3 while applying force in the tangential direction of the cylinder. The thus formed superconducting electromagnetic coil 1 is placed in a heat curing furnace at a predetermined temperature with distributed loads indicated by arrows in the figure being applied by an axial pressure device and a radial pressure device (not shown). By heating and hardening the adhesive resin that has been carried in and applied to the insulating layer, the cooling body 2 and the inner-wound superconducting coil 4 are firmly bonded and integrated via the insulating layer 3.

In the superconducting electromagnetic coil formed as described above, if the coil is a large coil with a diameter and length of several meters, the voltage required to flow a large current through the coil is several thousand volts. The insulation between the superconducting coil 4 and the cooling body 2 is required to withstand the above voltage. Furthermore, based on the weak point theory, the breakdown voltage of an insulator decreases in inverse proportion to the increase in the area of the insulator, so for large coils such as those mentioned above, the breakdown voltage generally measured as a material is tens of thousands of volts. Certain things are required.
Therefore, glass-reinforced plastic laminates have conventionally been used as an insulating material that can withstand such voltages, but since the thickness of the insulating layer that can withstand such voltages needs to be approximately 1 mm, for example, 0.5 mm is required.
It was used by bonding two layers of millimeter-thick laminates together. However, due to the high rigidity of the laminate, it is difficult to attach it to the inner circumferential surface of the cylindrical cooling body without any gaps, and the air bubbles sealed by the highly viscous adhesive may pass through the coil. It is difficult to expel the insulating layer even if a pressing force is applied, and the thermal conductivity of the insulating layer formed in this way is poor due to the serial interposition of the thermal resistance of the thick insulating layer and the thermal resistance of the void. Therefore, there was a problem in that it became difficult to indirectly cool the superconducting coil 4 to a predetermined temperature near zero absolute temperature. Another drawback is that voids remain in the butt parts of the laminates, and the insulation strength of these parts is low, so even if the butt parts of different layers are laminated with the butt parts shifted from each other, the withstand voltage value will drop by almost half. It was hot.

On the other hand, it is also known that the insulating layer is formed using an insulating film such as polyimide film. Polyimide film has excellent electrical insulation properties, as well as excellent heat and cold resistance, and is thinner and softer than glass-reinforced plastic laminates, making it relatively easy to form an insulating layer that tightly adheres to the inner circumferential surface of a cylindrical cooling body. Since the thickness of the insulating layer can be reduced to a fraction of that of the laminated plate method, it has the advantage of providing excellent cooling performance. However, polyimide film has poor adhesion with adhesives such as epoxy resins and is easily damaged mechanically, so it may damage the insulating layer during coil winding of superconducting wire or be damaged by electromagnetic mechanical force acting on the coil. However, there were drawbacks such as peeling of the insulating layer.

[Purpose of the invention]

The present invention was made in view of the above-mentioned situation, and
The purpose of the present invention is to provide an indirect cooling type superconducting magnet coil with a thin insulating layer, few voids and voids in the adhesive layer, excellent insulation performance and thermal conductivity, and an insulating layer with high adhesive strength. do.

[Key points of the invention]

The present invention provides a superconducting electromagnetic coil in which a superconducting coil is fixed on the surface of a cooling body through an insulating layer with an adhesive resin, in which the insulating layer is placed on the surface of the cooling body using a roughened polyimide film and a glass-reinforced plastic sheet. By forming a composite insulating layer by laminating a composite sheet with a heat-sensitive adhesive layer (hereinafter referred to as a heat-sensitive adhesive film) that does not contain bubbles etc. on at least one side of a laminate,
This achieves the above objective.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 2 is a structural sectional view of a composite sheet according to the present invention. In the figure, a composite sheet 11 is made by firmly adhering a polyimide film 6 whose surface has been roughened by sandblasting or the like and a glass reinforced plastic sheet 7 with, for example, an epoxy resin adhesive layer 8 to form a composite insulating sheet. A heat-sensitive adhesive film 9 is attached to one surface of the composite sheet by, for example, a transfer method, and an anti-adhesion sheet 10 is adhered to the surface of the heat-sensitive adhesive film 9, which is removed when the composite sheet is used. The thickness of the polyimide film that mainly maintains the withstand voltage of the composite sheet 11 configured in this way can be selected in the range of 0.01 to 0.5 mm, and the thickness of the polyimide film can be selected in the range of 0.01 to 0.5 mm, and the mechanical protection of the polyimide film and the adhesiveness of the insulating sheet can be selected. As a glass-reinforced plastic sheet whose main purpose is to improve the surface resistance, a thin glass cloth impregnated with, for example, epoxy varnish and cured is used, and its thickness is suitably slightly thinner than that of a polyimide film.
The composite sheet constructed in this manner has appropriate flexibility, high electric strength and mechanical strength. The heat-sensitive adhesive film has a particularly important function in forming the insulating layer. That is, the heat-sensitive adhesive film 9 is made of, for example, a semi-cured epoxy resin, and the degree of semi-curing is such that it has a moderate adhesive strength at room temperature and can easily maintain its state when attached to, for example, a cylindrical cooling body. A semi-cured material that does not peel off, has a suitable level of softness, and has the ability to form a passageway between the bonded surface and the adhesive layer to allow residual air to escape when pressure is applied to the adhesive layer through the coil. The state of the adhesive resin is determined, and when heated to a predetermined temperature, it melts and becomes fluid, and the excess adhesive resin containing air bubbles flows out of the insulating layer. It is preferable to use a material having melting temperature characteristics and curing temperature characteristics such that an adhesive layer with no adhesive layer is formed.

FIG. 3 is a schematic sectional view of an internally wound superconducting electromagnetic coil for explaining the insulating layer of the superconducting electromagnetic coil of the present invention, and FIG. 4 is a partially enlarged view of the superconducting electromagnetic coil. In the figure, a composite insulating layer 30 is formed by bonding two layers of composite sheets 11 configured as shown in FIG. coil 4
are fixed via the adhesive resin layer 12 applied to the surface of the composite insulating layer 30 or the superconducting coil 4.

The adhesive resin layer 12 may be made of either a heat-cured resin or a room-temperature cured resin, and the heat-curing temperature of the heat-sensitive adhesive film 9 in the composite sheet 11 may be appropriately selected depending on the type of heat-sensitive adhesive.

The structure of the composite insulating layer 30 is, as shown in FIG. 4, by abutting a plurality of composite sheets each having a width of, for example, 0.5 meters so that the ends of adjacent sheets do not overlap each other, and then forming the first layer. The abutting portions 11A and the abutting portions 11B of the second layer are shifted in position in the circumferential direction of the coil cylinder so that they do not overlap, and are attached so as to extend in the axial direction of the coil cylinder. The composite insulating layer 30 is not limited to the above-mentioned two-layer configuration, and the sheets may be overlapped along the axial direction at multiple locations in the circumferential direction without providing the abutting portion, or It is also possible to wrap the composite sheet in a spiral manner in the circumferential direction.

Further, when manufacturing a superconducting coil having an insulating layer according to the present invention, the following characteristics are provided. That is, after forming the adhesive resin layer 12 by applying an adhesive with an appropriate viscosity to the surface of the composite insulating layer 30, a pressing force is applied to the composite insulating layer 30 by applying force to the superconducting wire in the tangential direction of the cylinder. When the coil 4 is formed by winding the superconducting wire as shown in FIG. Similarly, when a distributed load is applied to the coil 4 in the axial direction, a predetermined surface pressure can be equally applied between each winding of the coil 4 without damaging the composite insulation layer 30 due to the lubricating action of the adhesive resin layer. It has the advantage of being able to Next, when a radial pressing force is applied to the insulating layer through the coil 4, the adhesive of the adhesive resin layer 12 fills the gap between the coils and the coil can be firmly fixed.

The heat-sensitive adhesive film 9 in a semi-cured state (see FIG. 2) gradually adheres to the surface to be bonded due to the pressing force, and at this time, residual air interposed between the heat-sensitive adhesive film 9 and the surface to be bonded is expelled. Therefore, at this time, by shifting the positions of the butting parts of the sheets so that they do not overlap each other as shown in FIG.
A small gap extending in the axial direction of the coil serves as a passage for the remaining air, making it easier to expel the remaining air. Next, when the whole is placed in a heat-curing furnace and gradually heated to a predetermined temperature, the heat-sensitive adhesive film 9 flows when the melting temperature of the heat-sensitive adhesive is reached, and the excess heat-sensitive adhesive film 9 entrains the remaining air. The adhesive flows out through the abutting portions 11A and 11B, and the gap between the abutting portions is filled with the flowing heat-sensitive adhesive. Therefore, when the adhesive resin is heated and cured, there are few voids or voids in the resulting insulating layer, making it possible to obtain a superconducting electromagnetic coil that has high insulation performance and heat transfer performance, and is strongly integrated. can.

According to experimental studies by the inventors, an insulating film mold with a thickness of 0.5 mm and the structure shown in Figure 4 was made.
As a result of determining its breakdown voltage, a value of 70KV was obtained. This value is more than twice the breakdown voltage determined for an insulating film type with a thickness of 1 mm using a conventional method using a glass-reinforced plastic laminate, and it shows that the thickness of the insulating layer can be significantly reduced compared to the conventional method. It became clear. The adhesive shear strength of the two was also compared, and the values were almost the same, approximately 3 Kg/mm ² (at room temperature).

Note that the thermal expansion coefficient of the composite sheet constructed as shown in Figure 2 is approximately equal to that of aluminum over a wide temperature range, so if the cooling body 2 and the protective conductor of the superconducting wire are constructed of aluminum, the thermal expansion The thermal stress caused by this is small, and the adhesive strength of the insulating layer can be stably maintained even when the insulating layer is cooled to an extremely low temperature.

Although the above explanation was given only to a superconducting electromagnetic coil having an insulating layer wound inwardly, it is clear from the above description that it is also applicable to a superconducting electromagnet coil having an insulating layer wound outwardly. Furthermore, the object of application of the present invention is not limited to so-called solenoid-type superconducting electromagnetic coils in which a superconducting coil is fixed on the circumferential surface of a cylindrical cooling body through an insulating layer, but a pancake of cylindrical superconducting coils. It can also be applied to shaped or saddle-shaped superconducting electromagnetic coils. FIG. 5 shows a cross-sectional view of the pancake-shaped superconducting electromagnetic coil, and FIG.
The same parts as those in the figures are given the same symbols and the explanation will be omitted. In the case of a pancake shape or a saddle shape, although the coil winding operation is slightly different, the same effects can be obtained by applying the insulating layer of the present invention as explained above.

〔Effect of the invention〕

The present invention provides a superconducting electromagnetic coil in which a superconducting coil is fixed on the surface of a cooling body with an adhesive resin via an insulating layer, in which at least one of a laminate of a polyimide film and a glass-reinforced plastic sheet with a roughened insulating layer is provided. A composite insulating layer was formed by laminating a composite sheet on which a heat-sensitive adhesive film containing no air bubbles was adhered.

As a result, the high insulation strength of the composite insulation layer allows the thickness of the insulation layer to be reduced to a fraction of that of conventional insulation layers using glass-reinforced plastic laminates, improving insulation and cooling performance. . Furthermore, when forming the insulating layer of the superconducting coil of the present invention, adhesion to the cooling body can be made easier by appropriately selecting the adhesive strength and softness at room temperature and the melting temperature at high temperatures of the heat-sensitive adhesive film on the composite sheet. This makes it easy to save labor, and the remaining air can be almost completely exhausted. Furthermore, the composition of the composite sheet of the insulating layer of the present invention is such that the easily damaged polyimide film is protected by a glass-reinforced plastic sheet with high mechanical strength, and an adhesive resin layer is interposed between the composite insulating layer and the superconducting coil. By doing so, it becomes possible to improve the slippage between the two during winding and pressure tightening, and also has the effect of preventing damage to the composite insulating layer. Furthermore, although the structure relies mainly on polyimide film for the withstand voltage of the insulating layer, the glass-reinforced plastic layer functions as an aggregate, so its coefficient of thermal expansion is close to that of aluminum, and even at extremely low temperatures. The occurrence of thermal stress is small, and the adhesive strength of the insulating layer can be stably maintained.

By combining the above effects, insulation performance, cooling performance,
It is possible to provide a superconducting electromagnetic coil that has excellent adhesive strength, cryogenic resistance performance, and heat cycle resistance performance, and requires less insulation space.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view of an inner-wound superconducting electromagnetic coil, FIG. 2 is a cross-sectional view of a composite sheet used in the present invention, FIG. 3 is a plan view of the superconducting electromagnetic coil illustrating the insulating layer of the present invention, and FIG. The figure is a partially enlarged sectional view of FIG. 3, and FIG. 5 is a sectional view of a pancake-shaped superconducting electromagnetic coil to which the present invention is applied. 1: superconducting electromagnetic coil, 2: cooling body, 3: insulating layer, 4: superconducting coil, 5: cooling tube, 6: polyimide film layer, 7: glass reinforced plastic layer, 8: adhesive layer, 9: heat-sensitive adhesive film, 11: Composite sheet, 12: Adhesive resin layer, 11A, 11B: Butt portion, 30: Composite insulating layer.

Claims (1)

[Claims] 1. In a superconducting electromagnetic coil in which a superconducting coil is fixed on the surface of a cooling body with an adhesive resin via an insulating layer, the insulating layer is a heat-sensitive adhesive film on at least one surface of a laminate of a polyimide film and a glass-reinforced plastic sheet. A superconducting electromagnetic coil characterized by having a composite insulating layer formed by laminating composite sheets coated with.