JPS5856985B2 - Thermal persistent current switch - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thermal persistent current switch using a superconductive coil provided in a cryostat.

Generally, in order to operate a supercurrent coil in a cryostat, it is sufficient to supply current to the superconducting coil from the outside using a lead wire, and then set the superconducting coil to persistent current mode.

A thermal persistent current switch is used as one of the switches for switching between a charging mode that supplies current to the superconducting coil, a persistent current mode, and a discharging mode that releases energy from the superconducting coil when the superconducting coil is quenched.

Normally, a thermal persistent current switch with a heater attached to a superconducting wire is installed in a cryostat containing liquid helium and containing a superconducting coil.

When supplying current to the superconducting coil housed in the cryostat, the thermal persistent current switch is turned off.

To turn off this thermal persistent current switch, turn on the heater provided on the superconducting wire to bring the superconducting wire into a normal conducting state.

Also, to put the superconducting coil in persistent current mode, turn on the thermal persistent current switch.

To turn on this thermal type water-filled current switch, it is sufficient to turn off the heater of the superconducting wire and bring the superconducting wire into a superconducting state.

When the superconducting coil quenches, the thermal persistent current switch must be turned off to quickly release the energy within the superconducting coil.

In the thermal persistent current switch operated as described above, when the thermal persistent current switch is turned off, the heater installed in the superconducting wire is turned on to raise the temperature of the superconducting wire and bring it into a normal conducting state. However, since a considerable amount of heat from the heater is transferred to the liquid helium in the cryostand, the amount of heat transferred to the superconducting wire decreases, resulting in losses due to vaporization of the liquid helium and power loss in the heater.

Therefore, we wrapped a switch element consisting of a superconducting wire and a heater around a winding frame made of an insulating material such as F, R, P, epoxy resin, or frest, which has a low thermal conductivity. By covering it with a small insulating material to prevent heat from escaping from the heater, the superconducting wire of the switch element can be maintained in a normal conductive state with a small amount of heat, increasing the efficiency of the heater and reducing losses due to vaporization of liquid helium. was.

However, when the superconducting coil quenches, an excessive current flows through the thermal persistent current switch, and the superconducting wire of the switch element enters a normal conducting state, suddenly generating a large amount of Joule heat.

If this heat is not dissipated quickly, the thermal persistent current switch will be destroyed.

However, since the switch element is covered with an insulating material having low thermal conductivity, the efficiency of heat release is poor, leading to destruction of the thermal persistent current switch.

SUMMARY OF THE INVENTION An object of the present invention is to provide a thermal persistent current switch which eliminates the above-mentioned drawbacks and can quickly release heat without being destroyed even if a superconducting coil is quenched.

The present invention utilizes the property of superconducting materials having a small thermal conductivity in a superconducting state and a small thermal conductivity in a normal conducting state, and covering a switch element composed of a superconducting wire and a heater with a superconducting material. As a result, when the switch is off, the Joule heat of the heater is efficiently conducted to the superconducting wire, and when the superconducting coil quenches, the superconducting material covering the switch element becomes normal conductive, and the heat generated inside the switch element is quickly generated. It is designed to release heat.

Hereinafter, typical embodiments of the present invention will be described using the drawings.

The figure shows a section of a thermal persistent current switch 1.

The superconducting wire constitutes a switch element 2 together with a heater, and the superconducting wire is wound around a winding frame 3 made of a superconducting material via an electrically insulating material 4.

Further, the front side of the switch element 3 is covered with a cover 5 made of a superconducting material with an insulating material 4 interposed therebetween.

A refrigerant flow hole 6 is bored in the axial center of the winding frame.

When the thermal water-filled current switch is configured as described above, under normal conditions, the winding frame 3 and cover 5 are cooled by liquid helium in the cryostand (not shown), become superconducting, and have low thermal conductivity. ing.

Therefore, when the heater of the switch element 2 of the thermal persistent current switch 1 is turned on and the thermal persistent current switch 1 is turned off, the Joule heat of the heater of the switch element 2 is transferred to the winding frame 3. Since the cover 5 is in a superconducting state with low thermal conductivity, most of the heat is conducted to the superconducting wire of the switch element 2.

Therefore, almost no Joule heat from the heater is conducted to the liquid helium in the cryostat (not shown), and the heater works efficiently.

On the other hand, when quenching occurs in the superconducting coil (not shown) connected to the thermal persistent current switch 1, an excessive current flows through the superconducting wire of the switch element 2 due to the energy in the superconducting coil, and the superconducting wire becomes normal. condition, resulting in abnormal fever.

However, the winding frame 3. The abnormal heat generation is also conducted to the cover 5, which becomes a normal conductive state with high thermal conductivity, and the abnormal heat generation generated in the superconducting wire within the switch element 2 is quickly released.

Note that the insulating material 4 preferably has a thickness that maintains electrical insulation and allows rapid thermal conduction.

Also, the winding frame 3. The material of the cover 5 may be any superconducting material, but the effect is particularly significant when using a superconducting material composed of a single element.

Furthermore, if a flow hole 6 through which a refrigerant can flow is provided at the center of the axis of the winding frame 3, the cooling effect can be further improved.

Further, the communication hole 6 may be used for attaching the switch element 1 using a screw.

As is clear from the above explanation, according to the present invention, in the thermal persistent current switch, quenching occurs in the superconducting coil and an excessive current flows through the superconducting wire of the thermal persistent current switch. Even if abnormal heat generation occurs, this abnormal heat generation can be quickly released.

Furthermore, since the switch element composed of the superconducting wire and the motor is covered with a superconducting material, changing magnetic fields from the outside can be shielded, and the superconducting wire inside the switch element is prevented from being quenched by the external changing magnetic field.

[Brief explanation of the drawing]

The figure shows a schematic cross-sectional view of the thermal persistent current device 2-te according to the present invention. DESCRIPTION OF SYMBOLS 1... Thermal persistent current switch, 2... Switch element, 3... Winding frame, 4... Insulating material,
-16... Refrigerant flow hole. 5...Hippo

Claims (1)

[Claims] 1. A thermal persistent current switch comprising a switch element comprising a superconducting wire and a heater, the switch element being brought into thermal contact with a superconducting material. 2. The thermal water-filled current switch according to claim 1, characterized in that the superconducting wire is wound around a winding frame. 3. The thermal persistent current switch according to claim 2, wherein the winding frame is made of a conductive material. 4. The thermal persistent current switch according to claim 2, wherein the winding frame is provided with a cover made of a superconducting material. 5. The thermal water-filled current switch according to claim 2, wherein the winding frame is provided with a refrigerant flow hole in the axial direction of the winding frame. 6. The thermal persistent current switch according to claim 1, wherein the superconducting material is composed of a single element superconductor.