JPS622474B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a persistent current switch used when switching and maintaining a superconducting coil in persistent current mode. Methods for supplying current to a superconducting coil and switching to persistent current mode are broadly divided into two methods: a method using lead wires and a method using a flux pump. The method using lead wires involves supplying current from an external power source through the lead wires, and when implementing this method, the circuit configuration shown in FIG. 1 is usually employed. That is, cryogenic container 1
A persistent current switch 3 made of a superconductor is connected in parallel between both ends of the superconducting coil 2, and both ends of the persistent current switch 3 are connected to one terminal of the switches 4a and 4b, respectively.
The other terminals of these switches 4a, 4b are connected to the output end of an external DC power supply 5 via a lead wire. Therefore, in order to actually supply current and shift to persistent current mode, first turn on persistent current switch 3.
Turn off the switch 4a, 4 in this state.
b is turned on to allow a desired DC current to flow from the external DC power supply 5 to the superconducting coil 2. In this state, the persistent current switch 3 is turned on, and then, after the output current of the external DC power supply 5 is reduced to zero, the switches 4a and 4b are turned off. When the persistent current switch 3 is turned on, the energy that has been stored in the inductance of the superconducting coil 2 is stored through the persistent current switch 3. At this time, the persistent current switch 3 and the superconducting coil 2 are in a superconducting state. , the persistent current due to the storage continues to flow, and a persistent current mode is formed here. By the way, the persistent current switch 3 necessary to carry out the method using lead wires as described above is a mechanical one made of a superconductor and installed so that it can be turned on and off from outside the cryogenic container 1. A heater 12 is wrapped around the outer periphery of the superconductor 11 as shown in FIG.
The superconductor 11 is heated by the heater 12 and transferred to a normal conductive state to be turned off, and the superconductor 11 is turned off by stopping heating by the heater 12 and returned to the superconducting state. A switch or the like is used that is turned on by turning the switch on. However, the conventional persistent current switch constructed as described above and connected as shown in FIG. 1 has the following problems. That is, after turning on the persistent current switch 3,
If a noise current flows from the external DC power supply 5 side before the switches 4a and 4b are turned off, this noise current will flow through the persistent current switch 3 which has no impedance. Therefore, depending on the level of the noise current, it may exceed the critical current value of the superconductor constituting the persistent current switch 3, and if it exceeds the critical current value, the superconductor will transition to a normal conductive state and become permanently There was a problem where the current mode was destroyed. This undesirable phenomenon also occurs due to electromagnetic induction current induced in the superconducting coil 2,
Therefore, the reality is that it is desired to develop a persistent current switch that does not cause this phenomenon. The present invention has been made in view of the above circumstances, and its purpose is to prevent the superconducting state of the switch from being destroyed by this noise even when noise enters from the external DC power supply side. The object of the present invention is to provide a persistent current switch for superconducting coils that has a simple structure and has no structure. Another object of the present invention is to provide a superconducting coil with a simple structure, in which even if noise enters from both the external DC power supply side and the superconducting coil side, there is no risk of the superconducting state of the switch being destroyed by this noise. The purpose of the present invention is to provide a persistent current switch for use in the present invention. That is, in order to achieve the above-mentioned object, the present invention constitutes a persistent current switch by connecting an inductance element made of a superconductor in series to a switch element formed with a superconductor. Here, the switch element represents a mechanical switch formed of a superconducting wire or superconductor with a heater that can be selectively switched between a superconducting state and a normal conducting state.
Furthermore, the inductance element represents a superconducting wire simply wound into a coil shape. Therefore, connecting a switch element and an inductance element in series means that a superconducting wire equipped with a heater is wound into a coil and the superconducting wire itself is used as the switch element and inductance element. is also included. With a persistent current switch configured like this,
When incorporated into a circuit that implements the excitation method using lead wires, even if noise enters from the external power supply side, the blocking function of the inductance element works well and prevents large noise current from flowing to the persistent current switch. . Therefore, the persistent current switch can be prevented from transitioning to the normal conduction state due to noise entering from the external power source side, and the persistent current mode can be maintained well. In this case, the simple structure of simply winding the superconducting wire into a coil and adding an inductance element has the advantage of preventing the entire structure from becoming complicated or complicated to manufacture. In addition, in order to achieve the other objects mentioned above, the present invention provides a switch element formed of a superconductor and an inductance element made of the superconductor connected in series to the switch element. A persistent current switch is constructed by connecting resistance elements made of electrical conductors. Here, the switch element and the inductance element have the same structure as described above. With a persistent current switch configured like this,
When the inductance element constituting the switch body blocks the intruding noise, this noise current can flow through the resistance element. Therefore, even if noise enters from the external power supply side, or if noise is generated in the superconducting coil by electromagnetic induction, etc., it is possible to prevent the noise current from flowing into the switch body.
In the end, it is possible to prevent the persistent current switch from transitioning to the normal conduction state no matter what kind of noise enters, and it is possible to obtain a device with a simple structure and high reliability. Embodiments of the present invention will be described below with reference to the drawings. FIG. 3 shows a persistent current switch 21 according to an embodiment of the present invention.
21 has a coil 23 formed by winding the superconducting wire 22 into a simple coil shape, and this coil 2.
3, and a resin layer (not shown) provided so as to cover the surface of the heater 24 and the surface of the coil 23. With the above configuration, when the coil 23 is cooled to a temperature close to absolute zero, the impedance of the coil 23 has zero resistance and only inductance. In addition, in the above state, the heating heater 24
When the superconducting wire 22 is energized and heated, the superconducting wire 22 transitions to a normal conductive state, and the impedance of the coil 23 at this time becomes a value that is a combination of a relatively high resistance component and an inductance component. Therefore, this persistent current switch 21 is substantially composed of a switch element A and an inductance element B connected in series. Therefore, the persistent current switch 21 with the above configuration
When this is incorporated into a circuit implementing the lead wire method, the equivalent circuit at that time becomes as shown in FIG. This figure corresponds to FIG. 1, and the same parts are designated by the same reference numerals. In addition, C in the figure is a normal conduction state,
In other words, it shows the equivalent resistance when the persistent current switch 21 is turned off. Therefore, the persistent current switch 21 with the above configuration
If the circuit is built in, the persistent current switch 2
1 is turned off, switches 4a and 4b are turned on, and after passing DC current through the superconducting coil 2,
Even if noise intrudes from the external DC power supply 5 side after turning on the persistent current switch 21 and then reducing the output current of the external DC power supply 5 to zero and before turning off the switches 4a and 4b, this Due to the blocking effect of the inductance element B, only a small amount of current accompanying the noise flows through the persistent current switch 21 . Therefore, the persistent current switch 21 does not transition to a normal conductive state due to the intrusion of noise, and since it has a simple induction winding configuration, the above-mentioned effects are not achieved. You will get it. FIG. 5 shows the appearance of a persistent current switch 21a according to another embodiment of the present invention, and the same parts as in FIG. 3 are designated by the same reference numerals. Note that the resin layer covering the surface of each element is also omitted in this figure. In this embodiment, a normally conductive resistor 25 is connected in parallel between both ends of the coil 23. That is, in this embodiment, a switch body is formed by connecting a switch element A and an inductance element B in series with a coil 23, and the resistor 25 is connected between both ends of this switch body. When the persistent current switch 21a having the above structure is incorporated into a circuit implementing the lead wire method, the equivalent circuit at that time becomes as shown in FIG. Therefore, in the above circuit, when noise enters from the external DC power supply 5 side while the persistent current switch 21a is on and the switches 4a and 4b are on, the noise current is suppressed by the blocking function of the inductance element B. It does not flow into the switch body, but instead flows into the resistor 25. Further, even if noise is generated in the superconducting coil 2 due to electromagnetic induction or the like, this noise current will not flow to the switch body but to the resistor 25. Therefore, no matter what kind of noise enters, this noise will cause the persistent current switch 21a to
There is no risk of transitioning to a normal conducting state, and the above-mentioned effect can be obtained after all. Also, resistor 2
5 also functions as a protective resistor when the superconducting coil 2 is quenched. Although each of the above-mentioned embodiments is an example in which the present invention is applied to a type equipped with a heating heater, the present invention is not limited to this, and the present invention is applicable to a machine configured with a superconductor as a switch element. A target switch may also be used. Further, the inductance value of the inductance element is set to an appropriate value depending on expected noise. As described in detail above, according to the present invention, it is possible to provide a so-called persistent current switch for superconducting coils that is strong against noise despite having an extremely simple configuration.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram for exciting a superconducting coil using a lead wire, Fig. 2 is an external view of an example of a conventional persistent current switch, and Fig. 3 is a diagram of a persistent current switch according to an embodiment of the present invention. 4 is an excitation circuit diagram incorporating the same switch, FIG. 5 is an exterior diagram of a persistent current switch according to another embodiment of the present invention, and FIG. 6 is an excitation circuit incorporating the same switch. It is a diagram. 21 , 21a ... Persistent current switch, 22...
Superconductor, 23... Coil, 24... Heater, 25... Resistor, A... Switch element, B...
...Inductance element.

Claims (1)

[Claims] 1. A persistent current switch for a superconducting coil, comprising a switch element made of a superconductor and an inductance element made of the superconductor connected in series to the switch element. 2. A switch body consisting of a switch element made of a superconductor, an inductance element made of a superconductor connected in series to the switch element, and a resistance element made of a normal conductor connected between both ends of this switch body. A persistent current switch for a superconducting coil, characterized by comprising: