JPS6286703A - Protecting method for superconductive magnet - Google Patents

Abstract

PURPOSE:To reduce current running in a protective circuit when a magnet is being excited and to reduce the Joule loss by a method wherein a protective circuit, in which a low resistor and a permanent current switch are series-connected, is parallel- connected to a magnet coil, the permanent current switch is maintained in a normal conductive state when a magnet is excited, and the permanent current switch is maintained in a superconductive state after said excitation is finished. CONSTITUTION:The current loss generating in a protective circuit is indicated by the quantity of heat W1=V<2>/(R+r) when the resistance value of a permanent current switch (PCS) 4 is set at (r). Accordingly, if the PCS 4 is maintained in the normal conductive state and allows the resistance (r) in that state when a magnet is excited, the resistance of the protective circuit is brought to (R+r), which is larger than before, and the value of W1 is reduced. Also, in the mode of permanent current, a magnet coil and the PCS 2 can be protected by the desired protective resistor 3 by having the PCS 4 in the superconductive state of r=0 in the same manner as the PCS 2 of a magnet. The permanent current switch usually has the structure wherein an electric heater is wound on a superconductive wire, electric resistance is generated on the superconductive wire or its resistance in brought to zero by turning ON or OFF the heater. This well known switch can be the PCS 4.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention is directed to a superconducting magnet that can reduce current loss when exciting a superconducting magnet having a protective resistance and evaporation loss of a cryogen for cooling the magnet (generally liquid helium). Regarding how to protect magnets.

[Conventional technology]

In superconducting magnets, it has been considered to connect a low resistance in parallel with the magnet coil for the purpose of protecting the coil during quench (transition from superconducting to normal conducting) and protecting the persistent current switch.

Figure 3 shows the equivalent circuit when the coil is excited. In the figure, numeral 1 is a magnet coil, 2 is a persistent current switch (hereinafter referred to as p, c, s), and 3 is a protective resistor.

In this circuit, when a quench occurs in the coil and parts P, C, and S and an abnormal voltage occurs, the current is shunted to the protective resistor 3 with a low resistance value, and the energy accumulated in the coil is consumed by the protective resistor 3. It was designed to let you do so.

[Problem that the invention seeks to solve]

However, in this equivalent circuit, when the inductance of the coil 1 is L, a current loss occurs in the current flowing through the coil, and the amount of evaporation of the cryogen increases due to the heat.

[Means for solving problems]

In order to eliminate the above-mentioned problem, this invention has the structure of the magnet protection circuit shown in FIG.
, C, and S4 are connected in series, and this second p,
By turning c and s 4 ON and OFF, the protection circuit is kept at high resistance during excitation and low resistance during persistent current mode.

That is, in the equivalent circuit during excitation shown in Fig. 1, if the second p, c, s 4 are kept in a normally conductive state and the resistor r is allowed to function as is during excitation, the resistance of the protection circuit becomes The value of Wl is reduced by R0r, which is larger than the conventional value.

In addition, in persistent current mode, the second p, c, s4 are set to superconducting state like p, c, a2 of McNet, and r
=Q, the equivalent circuit in FIG. 1 changes to the equivalent circuit in FIG. 2, and the magnet coil and P, C, S) are protected by the intended protection resistor 3.

A persistent current switch generally has a structure in which an electric heater is wrapped around a superconducting wire, and the heater is turned on and off.
to create resistance in the superconducting wire or reduce the resistance to 0.
However, the second p used in the present invention,
c and s4 may be these well-known switches.

〔effect〕

As described above, according to the method of the present invention, the current flowing through the protection circuit when the magnet is excited is reduced by the second P, C, and S resistors connected in series with the protection resistor, so the Joule loss is reduced. To become, and for that purpose,
The amount of evaporation of the refrigerant is also reduced.

[Brief explanation of drawings]

Figure 1 shows an equivalent circuit when a superconducting magnet is excited by the method of the present invention, Figure 2 shows an equivalent circuit when the magnet is in persistent current mode, and Figure 3 shows an equivalent circuit when a conventional superconducting magnet with a protective resistor is excited. This is the equivalent circuit of 1... Magnet coil, 2... Persistent current switch (P, C, S), 3... Protective resistor, 4... Second persistent current switch (P, C, S) Patent applicant Sumitomo Electric Industrial Co., Ltd. Agent Kama 1) Letter 2 Figure 1

Claims (1)

[Claims] In a superconducting magnet equipped with a persistent current switch, a protection circuit in which a low resistance element and a second persistent current switch are connected in series is connected to the magnet coil in parallel, and the second persistent current switch is normally conductive when the magnet is energized. A method of protecting superconducting magnets that maintains them in a superconducting state after excitation.