JPS6028150B2 - Thermal persistent current switch - Google Patents

Description

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

A general schematic diagram of a superconducting device is shown in FIG.

That is, a superconducting coil 3, a superconducting gate wire 8, and an electrothermal generator 10 are placed in a container 2 containing cold soot 1 such as liquid helium.
The coil 3 is connected to an external power source 6 via superconducting lead wires 4, 4' and a copper lead wire 5. On the other hand, the superconducting gate wire 8 in the persistent current switch 7 is connected in parallel to the superconducting lead wires 4 and 4' via the superconducting lead wires 9 and 9', and the heating wire 10 is connected to the heater power source 12 via the lead wire 11. It is connected. When a voltage is applied from the switch power supply 12 to the electric heating hot spring in the thermal persistent current switch 7 to generate heat, the superconducting gate wire 8 is heated above the critical temperature and becomes a normal conduction state, and at this time, the external power supply 6 When , current flows through the superconducting coil 3 because the resistance of the coil is zero.

After generating a desired magnetic field in the superconducting coil 3, when the electric current of the electrothermal annular go 10 in the switch is cut off, the superconducting coil 3, lead wire 4', lead wire 9', superconducting gate 8,
A closed circuit formed by the lead wire 9, the lead wire 4, and the superconducting coil 3 is created, and even if the external power source 6 is temporarily cut off, a current flows in the superconducting coil and it continues as a permanent magnet. Therefore, a thermal persistent current switch transitions from a superconducting state to a normal conducting state or from a normal conducting state to a superconducting state by intermittent current flowing through a heating wire, and opens and closes a persistent current circuit by utilizing a large change in electrical resistance. It is something. In order to ensure current carrying capacity, the conventional persistent current switch 7 uses a plurality of superconducting wires as an east gate wire, and as shown in FIG. 2, a heating wire is wound around the gate wire in a helical shape. For this reason, the contact area between the heating wire and the superconducting wire is small, and it takes a large heat capacity and time to make the gate wire normal conductive, which has the disadvantage of increasing the evaporation loss of liquid helium and worsening the heating characteristics of the switch. was. In addition, conventional switch winding frames are made of bakelite, epoxy, stainless steel, etc., but these winding frames have poor thermal conductivity at extremely low temperatures, so it takes a long time for the gate wire to return to the superconducting state. This has disadvantages in that it impairs the cooling characteristics of the switch and cannot stably secure current carrying capacity due to the resulting instability. An object of the present invention is to provide a thermal persistent current switch that reduces the amount of evaporation of cold soot such as liquid helium, has little heat loss, is stable, and has a fast response speed.

The present invention aims to increase the contact area between a plurality of superconducting gate wires and a heating wire by removing the copper matrix of a plurality of ultrafine multi-core wires in which a large number of superconducting wires are embedded in a copper matrix. First, a heating wire was wound around each of the multiple superconducting gate wires, and the wires were assembled to produce 0.1 cal at room temperature.
A thermal persistent current switch is characterized in that it is wound non-inductively around a bobbin having a thermal conductivity of 1/sec/°C or higher.

That is, the bobbin is made of aluminum or copper at room temperature.
We improved the cooling properties by using a material with good thermal conductivity of 1 cal/sec/°C or more, and in order to further improve the heating properties of the superconducting gate wires, we installed electrically insulated heating wires for each gate wire. It has been found that it is extremely advantageous to create a structure in which the heating wires are connected in parallel circuits to increase the contact area depending on the number of gate wires, such as by winding them. Aluminum or copper as a material for the winding frame has a thermal conductivity of 0.1 cal/skin·sec·°C or more at room temperature, so it has great cooling properties and a fast response speed from a normal conductive state to a superconducting state, but other metals It was found that the response speed of the material from the normal conductive state to the superconducting state is extremely slow. Example 1 The superconducting gate wire has 271 superconducting wires made of Nb-Ti-Zr alloy with a wire diameter of 54 mm embedded in a copper matrix, an outer diameter of 1.45 ribs, and a cross-sectional area ratio of steel to superconducting wire of 2. Six ultra-fine multi-core wires are used, and the copper matrix of the ultra-fine multi-core wires is partially removed with nitric acid.

Next, as shown in FIG. 3, six nichrome wires with an outer diameter of 0.25 insulated from each gate line are turned around in an IJ direction and a glass tape is wrapped over them. The completed gate wire is wound one after another from the inner layer of the aluminum bobbin without guidance, and is finally fixed with glass tape. At the end of the winding, I attached a copper terminal to the bobbin and soldered all six terminals together. The outer layer of the switch was fixed by soaking it in paraffin in a vacuum chamber.

The switch manufactured as described above was immersed in liquid helium, and the current carrying capacity and response speed of the switch were measured.

As a result, a current carrying capacity of 1500 to 170 M could be stably secured in an external magnetic field of 0 to 1 Oersted. In addition, regarding the time from turning on the heater to the occurrence of resistance during normal conduction, that is, the heating characteristics, as shown in FIG. 4, the switch 14 according to the present invention is superior to the conventional switch 13 manufactured by the method shown in FIG. Compared to this, the response time was reduced to about 1/2. In addition, as for the time required for returning to the superconducting state after supplying the same heater capacity as above and shutting off the heater, that is, the cooling characteristics, as shown in FIG. For example, when the heater capacity is 5 watts, it is reduced to about 1'10, and the effect of the aluminum bobbin is remarkable.

As explained in the above embodiments, the thermal persistent current switch was manufactured by winding heating wire around each gate wire and using an aluminum bobbin, using a Bakelite bobbin,
Compared to a conventional switch that wraps a heating wire around the entire gate wire, the heating characteristics of the switch shorten the response time to 1'2, and the cooling characteristics shorten the time to return to the superconducting state to about 1/10. be shortened.

As a result, the evaporation loss of liquid helium is greatly reduced, and an ideal and economical effect is exhibited. In addition, its good cooling properties reduce heat generated by instability within the gate line.
It can be removed quickly and stability can be improved. In addition, because the response speed is fast, even if the superconducting device transitions to a normal conductive state for some reason, it is possible to quickly absorb magnetic energy into the external resistance, which prevents destruction due to rapid evaporation of cold soot such as liquid helium. Accidents and burnouts of superconducting equipment can be completely prevented, and the effects are significant in terms of performance and stability. In addition, similar effects can be obtained by using aluminum alloys, copper, copper alloys, magnesium, magnesium alloys, beryllium, and beryllium alloys, which have a thermal conductivity of 0.1 cal/sec/°C or higher at room temperature, as bobbin materials. was gotten.

Furthermore, epoxy resin or other resins may be used as the impregnating material for the completed switch. Brief Description of the Drawings Fig. 1 is a schematic diagram of a superconducting device, Fig. 2 is a structural diagram of a gate line used in a conventional switch, Fig. 3 is a structural diagram of a gate line of the present invention, Figs. FIG. 5 is a diagram comparing the response speed of the switch between the product of the present invention and a subordinate switch.

1...Liquid helium, 2...Container, 3
...Superconducting coil, 4...Superconducting lead wire, 5...Copper IJ-wire, 6...External power supply, 7...Thermal type Persistent current switch, 8...
...Superconducting gate line, 9...Superconducting leader line, 1
0... Heating wire, 11... Lead wire, 12.
. . . Power supply for switch, 13 . . . Conventional switch, 14 . . . Switch of the present invention.

Dance diagram Figure 2 Figure 3 Figure 4 Tsutomata diagram

Claims (1)

[Claims] 1. The copper matrix is partially removed from an ultra-fine multi-core wire material in which many superconducting wires are embedded in a copper matrix, and each of the multiple superconducting gate wires is insulated and heated by being wound around each wire and integrated. A thermal persistent current switch, characterized in that the integrated superconducting gate wire is wound around a bobbin having a thermal conductivity of 0.1 cal/cm·sec·°C or more at room temperature.