JPS61265805A - Superconducting apparatus - Google Patents

Abstract

PURPOSE:To prevent the burning of a protecting semiconductor element and to display an excellent protecting functions, by arranging the protecting semiconductor element at a position lower than the highest position of a superconducting coil. CONSTITUTION:A diode 4 is arranged at a position, which is lower than the highest position of a superconducting coil 2 by a sufficient distance A. Then, a permanent current switch 3 and the superconducting coil 2 can be protected, under the state the diode 4 is always positioned in liquid helium 10. Before the liquid surface is lowered to the height of the diode 4, the superconducting coil 2 is forcibly quenched. Therefore the burning of the diode 4 can be prevented even if energy stored in the superconducting coil 2 is high.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a superconducting device, and particularly to an improvement in a superconducting device in which a protective semiconductor element is connected in parallel with a superconducting coil.

[Technical background of the invention and its problems]

As is well known, when a superconducting coil, persistent current switch, etc. quench, it is necessary to quickly eliminate the energy stored in the superconducting coil by some means to prevent these from burning out.

As one such protection means, connecting a semiconductor element such as a diode or a thyristor in parallel to the superconducting coil has been attempted and already proven.

FIG. 4 shows an example in which the persistent current switch is protected by a diode. Namely.

In the figure, numeral 1 indicates a cryostat that contains liquid helium inside. Inside this cryostat 1 are a superconducting coil 2, a persistent current switch 3, and a diode 4.
and are housed in immersed relationship in liquid helium. The permanent N-flow switch 3 has a superconducting wire 5 and a superconducting m
The superconducting wire 5 is connected between both ends of the superconducting coil 2, and both ends of the heater wire 6 are connected to the cryostat 1 via lead wires.
being led outside. A diode 4 is connected between both ends of the superconducting coil 2 in the illustrated polarity.

Power leads 7a are provided at both ends of the superconducting coil 2, respectively.
, 7b are connected, and these power leads 7
The other ends of a and 7b are each guided outside the Talaios slat 1 and connected to a power source 8 for excitation and demagnetization.

The superconducting device configured in this manner prevents the persistent current switch 3 from being burnt out in the following manner when the persistent current switch 3 is quenched. In other words, when the superconducting wire 5 quenches while operating a closed loop consisting of the superconducting coil 2 and the superconducting wire 5 of the persistent current switch 3 with a persistent current flowing, the lower side in the figure becomes positive at both ends of the superconducting coil 2. A voltage is generated. When this voltage exceeds a certain level, diode 4 becomes conductive;

The voltage across the superconducting wire 5 is maintained at a value of 2V or less, thereby preventing the superconducting wire, that is, the persistent current switch 3, from burning out. Note that the energy stored in the superconducting coil 2 is mainly consumed by heat radiation from the diode 4.

By the way, in a superconducting device incorporating a semiconductor element for protection as described above, normally, as shown in FIG. 5, a superconducting coil 2 is housed in a cryostat 1,
A configuration is adopted in which a persistent current switch 3 and a diode 4 as a protective semiconductor element are housed above the coil 2, and liquid helium 10 is housed at a level where these are submerged. This arrangement is due to (1) work convenience;
(2) Effective use of the upper space inside the cryostat 1.

(3) This is because during protection, heat is slowly dissipated only by the diode 4, and the coil 2 is kept in a superconducting state. .

However, when the superconducting device is used for industrial electronics or magnetic resonance imaging devices, etc.

The taliostat must be made smaller.

The stored energy of the coil must also be increased.

For this reason, in the case of the above-mentioned applications, it is difficult to protect the superconducting device only by consuming liquid helium during protection.
You must be prepared for a certain amount of temperature rise in the coils, etc. In such a case, if the conventional configuration is adopted, the protective semiconductor element may be positioned above the liquid helium level during protection, and as a result, heat dissipation from the protective semiconductor element is insufficient. There was a strong possibility that the protective semiconductor element would be burnt out and the protection could not be ensured.

[Purpose of the invention]

The present invention has been made in view of the above circumstances, and its purpose is to provide a superconducting device that can reliably prevent burnout of protective semiconductor elements and thereby reliably realize protection during quenching. It's about doing.

[Summary of the invention]

According to the present invention, in a superconducting device comprising a superconducting coil and a protective semiconductor element connected in parallel to the superconducting coil and immersed in a cryogenic liquid together with the superconducting coil, A superconducting device is provided in which a semiconductor element is arranged below the highest position of the superconducting coil.

〔Effect of the invention〕

With the above configuration, burnout of the protective semiconductor element can be reliably prevented and a good protective function can be exhibited. That is, during protection, the semiconductor element is conductive, and heat is radiated from the semiconductor element, which is stored in the superconducting coil and energy is consumed.

When the semiconductor element becomes conductive, the cryogenic liquid evaporates due to heat radiation from the semiconductor element, and the liquid level of the cryogenic liquid gradually decreases due to this evaporation. In this case, even if the liquid level drops to the highest position of the superconducting coil, the semiconductor element still exists in the cryogenic liquid. therefore,
Compared to conventional devices, the time it takes for the semiconductor element to reach the surface of the cryogenic liquid can be lengthened, so the semiconductor element can be cooled more reliably and burnout of the semiconductor element can be prevented. Note that if the energy stored in the superconducting coil is large, the liquid level may further drop and a portion of the superconducting coil may come out above the liquid level. When a part of the superconducting coil protrudes above the liquid level in this way, the superconducting coil is forcibly quenched, and the energy stored in the superconducting coil is consumed by the superconducting coil itself. At this point, most of the energy has already been consumed through the semiconductor element, so the superconducting coil will not burn out. In this way, it is possible to reliably prevent the protective semiconductor element from being burnt out, and as a result, it is possible to prevent the occurrence of a situation in which the protective function cannot be performed.

[Embodiments of the invention]

Hereinafter, nine embodiments of the present invention will be described with reference to the drawings.

FIG. 1 schematically shows a superconducting device according to an embodiment of the present invention. In addition, this example.

This corresponds to FIG. 5 and is an example in which the present invention is applied to a superconducting device in which a persistent current switch 3 is protected by a diode 4. therefore.

The same parts as in FIG. 5 are denoted by the same reference numerals, and detailed explanation of the overlapping parts will be omitted.

This embodiment differs from the conventional one in the arrangement of the diode 4. That is, in this example.

A diode 4 is placed a sufficient distance A below the highest position of the superconducting coil 2.

With such a configuration, if the persistent current switch 3 is turned ON and the persistent current switch 3 is quenched while operating in the persistent current mode.

A voltage is generated across the persistent current switch 3, which causes the diode 4 to conduct. When the diode 4 is conductive, the voltage across the persistent current switch 3 is maintained at a value of 2V or less. Therefore, forever! The current flowing through the current switch 3 is suppressed to a sufficiently small value, thereby preventing the persistent current switch 3 from burning out.

When diode 4 is conductive and in a protected state.

What is the energy stored in superconducting coil 2?

It is gradually consumed by the heat dissipation of the diode 4.

Therefore, the liquid helium evaporates, and the liquid level of the liquid helium 10 gradually decreases. When the energy stored in the superconducting coil 2 is large, the liquid level of the liquid helium 10 may be lower than the upper surface of the superconducting coil 2. In this way, when a part of the superconducting coil 2 protrudes above the liquid level, that part is quenched due to natural temperature rise or a slight disturbance, and the quench propagates throughout the coil in an extremely short period of time. Therefore, energy is consumed throughout the superconducting coil 2. The energy at this point is the remaining energy after subtracting the energy that has already been consumed. Therefore, this quenching will not cause the superconducting coil 2 to burn out. And at this point, the diode 4 is still in liquid helium 10.

In this way, since the diode 4 is placed below the highest position of the superconducting coil 2, the persistent current switch 3 and the superconducting coil 2 can be protected while the diode 4 is always placed in the liquid helium 10. I can do it. Since the superconducting coil 2 is forcibly quenched before the liquid level drops to the level of the diode 4,
parable.

Even when the energy stored in the superconducting coil 2 is large, burning out of the diode 4 can be prevented.

FIG. 3 shows a typical example of the current flowing through the superconducting coil 2 during protection.

Time point 1. When a quench occurs in the persistent current switch 3, a current flows through the diode 4, and as a result, the current gradually attenuates. Then, at the second time point t1, when a part of the superconducting coil 2 protrudes above the liquid surface and quenching occurs in the superconducting coil 2, the current rapidly attenuates. Therefore, the protection diode 4 can be prevented from being burnt out, so the reliability of protection can be improved, and the above-mentioned effects can be achieved after all.

Note that the present invention is not limited to the embodiments described above. That is, in the embodiment described above, only the diode that protects the persistent current switch is incorporated;
It goes without saying that the present invention can also be applied to a device incorporating a semiconductor element that protects a superconducting coil or a semiconductor element that protects a Yabawa lead.

In addition, if the superconducting coil 2 is housed in a cryostat with its axial center line horizontal, as shown in FIG. A diode 4 may be placed.

[Brief explanation of the drawing]

FIG. 1 is a schematic block diagram of a superconducting device according to an embodiment of the present invention, FIG. 2 is a schematic diagram of a main part of a superconducting device according to another embodiment of the present invention, and FIG. 3 is a schematic diagram of a superconducting device according to another embodiment of the present invention. Diagram for explaining an example of changes in current flowing through superconducting coils during protection,
FIG. 4 is a circuit diagram showing an example of a superconducting device incorporating a semiconductor element for protection, and FIG. 5 is a schematic diagram showing the actual configuration of the device. 1... Cryostat, 2... Superconducting coil. 3... Persistent current switch, 4... Diode. 7a, 7b...Power lead, 10...Liquid helium. Applicant's agent Patent attorney Takehiko Suzue Figure 1 Figure 2 Figure 3 Figure 4 Figure 5

Claims (1)

[Claims] A superconducting device comprising a superconducting coil and a protective semiconductor element connected in parallel to the superconducting coil and immersed in a cryogenic liquid together with the superconducting coil,
A superconducting device characterized in that the protective semiconductor element is arranged below the highest position of the superconducting coil.