JPS6230509B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thermal persistent current switch used in a superconducting coil.

In order to excite superconducting coils for long periods of time and operate them stably, a highly reliable persistent current switch is required. Furthermore, since the superconducting coil is cooled and excited by liquid helium, unnecessary heat generation must be avoided. In response to these demands, thermal persistent current switches have been created that utilize the property of superconducting wires to transition between normal conductivity and superconductivity by giving and receiving heat at the transition temperature.

A thermal persistent current switch generally includes a superconducting wire as a switching element, a heating device for transitioning the wire between normal conductivity and superconductivity, and an appropriate heat insulating layer. However, if a superconducting wire is used bare, it becomes unstable and cannot flow a sufficient current. To remove this instability,
Usually, a composite wire is used, in which a superconducting wire is embedded in a normal temperature good conductor such as copper. For thermal persistent current switches, matrix materials whose resistivity does not decrease even at extremely low temperatures, such as Cypronickel (trademark), a type of copper-nickel alloy, are used to increase the switch resistance during normal conduction transition.

However, in order to have a sufficiently large resistance when the circuit is open, a long superconducting wire is required as the switching element. Therefore, in order to perform the switching operation efficiently, a method has been adopted in which superconducting wire is wound around a winding frame.

FIG. 1 is a sectional view of a conventional thermal persistent current switch employing such a winding method, and FIG. 2 is a perspective view thereof. In the thermal persistent current switch shown in FIGS. 1 and 2, a superconducting wire 1 as a transition temperature switching element is wound around a cylinder of a winding frame 2 made of a material with good heat insulation properties such as FRP, and an electric insulating layer 4 A heater 3 for switching energization is wound around the winding frame 2 between the superconducting wires 1 with the superconducting wires 1 separated from each other, and then the electric insulating layer 4 is impregnated with an insulating varnish to form a heat insulating layer. Such a conventional thermal persistent current switch is only used in which the heat from the heater 3 to the superconducting wire 1 flows toward the inner diameter side of the coil 2, resulting in poor heat utilization.

As mentioned above, thermal persistent current switches usually
Since it is used while being immersed in liquid helium, the heat generated in the liquid helium consumes the liquid helium. Although heat is required to open and close a thermal persistent current switch, the poor heat utilization rate of the conventional thermal persistent current switch described above means that excess heat is generated, and this should be avoided as much as possible. It is something that must be avoided. Therefore, a thermal persistent current switch with high heat utilization efficiency is desired.

SUMMARY OF THE INVENTION An object of the present invention is to provide a thermal persistent current switch that eliminates the above-mentioned conventional drawbacks, avoids excessive heat generation, and performs proper switching with a minimum amount of heat.

In the thermal persistent current switch according to the present invention, as shown in FIGS. 3 to 5, the superconducting wire 1 is provided in a spiral shape on the side surfaces of two winding frames 2 to form a double layer (a fourth
), between the opposing surfaces is a heating device 6 (a fifth
(Fig.) is sandwiched between them, and then the whole is impregnated with an insulating varnish or the like as a heat insulating material to form a heat insulating layer 4 and fixed together.

With this configuration, when the heater 3 generates heat, a heat flow occurs according to the temperature gradient, and since the superconducting wire 1 is arranged so as to surround the heater 3, all the heat generated by the heater 3 is effectively used. This has the effect of reducing heat capacity to less than half that of conventional thermal persistent current switches.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing the structure of a conventional thermal persistent current switch, FIG. 2 is a perspective view of the thermal persistent current switch shown in FIG. 1, and FIG. 3 is a partial cross-sectional view showing an embodiment of the present invention. 4 is a perspective view showing the winding portion in FIG. 3, and FIG. 5 is a plan view showing the heating device in FIG. 3. In the figure, 1 is a superconducting wire, 3 is a heater, 4 is a heat insulating layer, 5 is an electric insulator thin plate, and 6 is a heating device.
Note that the same reference numerals in the figures indicate the same or corresponding parts.

Claims (1)

[Claims] 1 a first winding frame that spirally accommodates the first half of the superconducting wire for temperature switching connected to the superconducting coil; a second winding frame that spirally accommodates the second half of the superconducting wire; A thermal persistent current switch which is held between coils and includes a heating device which is opposed to the first half of the spiral superconducting wire on one side and the second half of the spiral superconducting wire to the other side. The heating device is a permanent thermal type in which a heating wire is wound around a doughnut-shaped electrical insulating thin plate, and the superconducting wire portion and the heating device portion are impregnated and fixed with a heat insulating material made of insulating varnish. current switch.