JPS6292416A - Superconductive magnet device - Google Patents

Abstract

PURPOSE:To secure fully safe protection for a switch without the switch enlarged with respect to quenching of a permanent-current switch, by installing protective resistors for the switch extremely neighboring a superconductive magnet. CONSTITUTION:Protective resistors 2 for a permanent-current switch 6 are connected in series with diodes 7 which are provided for preventing current from flowing in the protective resistors 2 because of voltage generated at the time of excitation and demagnetization. This circuit is electrically connected in parallel with each of a superconductive magnet 1 and a permanent-current switch 6 and installed neighboring the superconductive magnet 1. The protective resistors 2 for the permanent-current switch are installed so that they are surrounded through the permanent-current switch 6, coming in close contact with the peripheral surface of a superconductive winding 1a which is wound in a solenoid shaped around a cylindrical bobbin 8 having flanges on its both ends. These protective resistors 2 are made of copper, stainless steel, or the like and they are connected so that currents in the protective resistor layers 2a and 2b flow in the reverse directions to each other, so as not to make the protective resistors have inductance.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical field to which the invention pertains] The present invention relates to a protection method when a persistent current switch in a superconducting magnet device quenches fc.

[Prior art and its problems]

Superconducting magnets using superconducting wires can increase the current density, so they can generate a strong magnetic field in a wide space with a compact magnet and with relatively small electric power.The superconducting wires currently in practical use are The temperature of liquid helium (approximately 4.2 K at 1 atm) is sufficient to embed fine wires of superconducting material in pure metals such as copper and aluminum (these properties are referred to as porosity).
However, if the superconducting state is lost due to certain causes and becomes a high resistance state (so-called quench phenomenon), the ratio of the stabilizing material to the superconductor in the superconducting composite superconducting wire (this is generally determined by the copper ratio). ) depends on the cooling condition of the manufactured magnet during use, the size of the magnet, and the operating method.Generally, superconducting magnets with a large stored energy have a large copper ratio in the composite superconducting wire and a small current density. Therefore, it is most preferable to operate a superconducting magnet with a large significant energy at a current density as high as possible.

When the magnet quenches, the accumulated magnetic energy is consumed as the Joule heat generation of the stabilizing material mentioned above.
The temperature of the magnet rises due to this Joule heat generation.The maximum value TM of this temperature is TMOCJ02・τ...
...Slap...Scream...Scream...+
1) where JO is the current density in the stabilizing material.

T is a decay time constant of 7 ml: L/R (L is the inductance of the magnet, R is the resistance value of the circuit, and in this case, the resistance value generated in the superconducting magnet is dominant). This maximum temperature TM is usually designed to be about 300 K for small magnets to protect the magnet, 200 to 100 K for medium-sized magnets, and about 70 K for large magnets that allow quenching. The resistance of the circuit is due to the resistance of the coil itself, or when the maximum temperature of the magnet 1 of the power source is suppressed by opening the circuit breaker 4 after detecting the quench of the magnet 1 as shown in Figure 5, or when it is higher. Protection schemes are often used that allow magnets to be operated at current densities. Note that 3#'i in Figure 5
The current supply lead that supplies excitation current to magnet 1 is shown, and 0
indicates the cryogenic region.

Superconducting magnets operate in so-called persistent current mode, in which both terminals of the superconducting magnet are short-circuited using a persistent current switch using superconducting wire, and the current supply lead is pulled out during normal use except for excitation and demagnetization of the magnet. It is normal to Leads to persistent current mode. Therefore, it is known to use a protective resistor 2 connected in parallel with a switch 6 as shown in FIG. In this case, the resistance value R2 of the protective resistor 2 needs to be sufficiently smaller than the normal conduction resistance value Rs when the switch 6 is in the OFF state, but these values are determined by the stored energy of the magnet and the practical excitation time. Determined by taking into consideration. In addition, the protective resistor 2 must be placed sufficiently away from the operating magnet, for example, in the refrigerant gas space L2, and must be constructed so as not to interfere with magnet excitation. The magnet and switch shall be installed in the refrigerant liquid area.

When designing persistent current switches and their protective resistors,
Letting R be the resistance value when the switch is OFF, that is, during normal conduction, the following must be satisfied. Here, W: enthalpy increase [JA] when switched, and E: stored energy (J) of the superconducting magnet. That is, the energy that can be absorbed by the switch and the maximum temperature θm of the switch must satisfy the equation (2), and it is desirable that 0m exceeds 300K. As the stored energy increases, the problem arises that the persistent current switch must also become larger and the heat-resistant load must also be increased, and the larger switch also requires 0N-OFF
This results in a problem of poor responsiveness.

[Purpose of the invention]

To provide a superconducting magnet device capable of sufficiently safely protecting a persistent current switch without increasing the size of the switch when the superconducting magnet is operated in persistent current mode, without increasing the size of the switch. purpose.

[Key points of the invention]

In a superconducting magnet operated using a persistent current switch, this invention prevents the current flowing through the protective resistor from quenching the persistent current switch by installing the protective resistor of the switch very close to the superconducting magnet. KL uses Joule heat to heat the superconducting magnet and quench the magnet itself.
, the energy consumption in the switch is suppressed by consuming the stored energy inside the magnet, thereby reducing the size of the persistent current switch.0 [Embodiment of the Invention] Fig. 1 shows an embodiment of the invention. This is an electrical circuit diagram of a superconducting device showing the same parts as those in the conventional electrical circuits of FIGS. The protective resistor 2 of the permanent current switch 6 is connected in series with a diode 7 provided to prevent current from flowing through the protective resistor 2 due to the voltage generated during excitation/demagnetization, and this circuit connects the superconducting magnet 1 and the permanent They are each electrically connected in parallel to the current switch 6 and positioned close to the superconducting magnet 1. In this case, since the voltage during excitation and demagnetization of the superconducting magnet is extremely small, no current flows through the protective resistor due to the forward breakdown voltage (about several volts) of the diode 7. Further, the reason why the diodes are connected in antiparallel is to be able to cope with either the polarity (+ or -) of the circuit. The combined resistance value R28 (82 g
=H, +4), a voltage is induced between the terminals &f, turning on the diode 7, and in persistent current mode
Most of the current #1 flows through the ac df circuit that includes two protective resistor circuits ◎Therefore, Joule heat is generated in the protective resistor 2, which heats up the superconducting magnet 1 in the vicinity and quenches it. 〇 Figure 2 is a vertical cross-sectional view showing a specific method of installing a protective resistor of a persistent current switch. The protective resistor 2 is connected to the surface through the persistent current switch 6.
This protective resistor 2 is made of copper, stainless steel, etc., but in this case, the direction of the current flowing through the protective resistor itself and the layer 2b is opposite so that the protective resistor does not have inductance. Connect as shown. In addition, the protective resistor installed closely on the outside of the superconducting winding has the advantage of simultaneously suppressing electromagnetic force. Figure 3 shows the protective resistor 2a and 2b layers in Figure 2 when Cooling hole 9 that promotes cooling of electric groove winding 111m
FIG. 3 is a perspective view showing a state in which the

FIG. 4 is a longitudinal sectional view showing another embodiment in which the protective resistor of the switch is installed inside the superconducting winding 1a. Since the structure is such that the protective resistor is placed in close proximity to the superconducting magnet winding, after the switch is quenched, the protective resistor is energized and the superconducting magnet is also quenched due to the heat generated by it, dispersing the released magnetic energy. can be consumed by
Therefore, the heat resistance capacity of the persistent current switch can be reduced. Therefore, a small persistent current switch can handle superconducting magnets that have a large amount of stored energy, and in particular, it is possible to improve the 0N-OFF response in thermal persistent current switches, and to manufacture switches using superconducting wire with less twist. Therefore, the magnetic stability is improved.@Furthermore, by dispersing the energy consuming parts, the protective resistor itself can be made smaller.
In addition, the quench caused by the protective resistor tends to affect the entire magnet in a short period of time, rather than being a local quench of the magnet.

[Brief explanation of drawings]

FIG. 1 is an electric circuit diagram of a superconducting magnet device according to the present invention,
FIG. 2 is a vertical cross-sectional view of a superconducting magnet with a protective resistor installed on the outside as a first embodiment of the present invention, and FIG. FIG. 4 is a perspective view of a superconducting magnet provided with holes, FIG. 4 is a vertical sectional view of a superconducting magnet with a protective resistor installed inside as a third embodiment of the present invention, and FIGS. FIG. 3 is a diagram showing a protection circuit for a superconducting magnet.

Claims (1)

[Claims] 1) In a superconducting magnet operated using a persistent current switch; a protective resistor against quenching of the persistent current switch is provided in close contact with the superconducting winding, and this protective resistor is electrically connected in antiparallel A superconducting magnet device, characterized in that the superconducting magnet device is configured to be connected in series with the superconducting diode and in parallel with the superconducting winding. 2) In the superconducting magnet device according to claim 1; a superconducting winding is wound around a winding frame having flanges at both ends of a cylindrical body, and a protective resistor divided into an even number of layers is wound around the outer periphery of the winding frame. A superconducting magnet device comprising: 3) In the superconducting magnet device according to claim 1; a protective resistor divided into an even number of layers is wound around a winding frame having flanges at both ends of a cylindrical body, and a superconducting winding is wound around the outer periphery of the winding frame. A superconducting magnet device comprising: 4) In the superconducting magnet device according to claims 2 and 3; the protective resistor is divided into an even number of layers and wound so that the current flowing through each layer is connected in the opposite direction. A superconducting magnet device characterized by: 5) A superconducting magnet device according to claim 2, wherein the protective resistor is divided into an even number of layers and wound and has a plurality of cooling holes penetrating each layer. .