JPH05343224A - Superconducting magnet circuit - Google Patents

Abstract

PURPOSE:To improve the stability of a permanent current mode by providing a by-pass circuit having a second permanent current switch in parallel with a permanent current switch, and making the resistance value of the by-pass circuit higher than that of the permanent current switch. CONSTITUTION:An emergency loop is formed by providing a by-pass circuit composed of a permanent current switch 3 and a series circuit of a microresistor 6 and a permanent current switch 7 connected in parallel to the permanent current switch 3, or a by-pass circuit 8 having a semiconductor switch or contactor as a switch connected in parallel to the permanent current switch 3. And permanent current is caused to flow in this emergency loop, when the permanent current switch 7 is quenched. By adopting constitution like this, the permanent current switch 7 is cooled with liquid helium while the permanent current is flowing in the emergency loop, and returns to a superconductive state by itself. Consequently, it becomes possible to keep the superconducting magnet 2 at a permanent current mode always stably, and increase the reliability of the superconducting magnet.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exciting circuit for a cryogenic superconducting magnet.

[0002]

2. Description of the Related Art A conventional superconducting circuit for exciting a superconducting magnet operating in a cryogenic state will be described with reference to FIG.

In general, the superconducting magnet device 1 includes a superconducting magnet 2
In order to cool the permanent current switch 3 to a cryogenic temperature, the inner tank 4 is dipped in liquid helium to be housed therein, and the inner tank 4 is further covered with a radiation shield plate cooled by liquid nitrogen, and these are vacuumed. It is configured to be housed in the outer tub 5 which is a heat insulating container.

The permanent current switch 3 is a switch used to excite or demagnetize the superconducting magnet 2 in a permanent current mode, and is composed of one or a plurality of switches. It is used.

[0005]

When the permanent current switch 3 is quenched due to some factor or disturbance, it becomes a normal conducting state and it becomes impossible to maintain the persistent current mode of the superconducting magnet.

Therefore, there is a demand for a permanent current switch that can quickly and automatically recover the quenched permanent current switch when the permanent current switch reaches the quench state, and maintain the persistent current mode of the superconducting magnet.

[0007]

In order to solve this problem, a bypass circuit including a second permanent current switch 7 in which a minute resistor 6 is connected in parallel with the permanent current switch 3 or in parallel with the permanent current switch 3 is provided. A bypass circuit having a semiconductor switch or a contactor as a second switch is provided to form an avoidance loop, and a permanent current flows through the avoidance loop when the persistent current switch is quenched.

[0008]

With this structure, the permanent current of the superconducting magnet maintained in the permanent current mode flows through the permanent current switch in the normal state (when the permanent current switch is ON).
When a quench occurs in the persistent current switch, the electrical resistance of the persistent current switch becomes larger than the electrical resistance of the parallel bypass circuit, and the persistent current flows through the bypass circuit.

While the permanent current is flowing through the bypass loop by the bypass circuit, the permanent current switch is cooled by liquid helium, its electric resistance becomes zero, the permanent current flows through the permanent current switch again, and self-recovers to the superconducting state. To do.

[0010]

EXAMPLES The present invention will be described based on the example shown in FIG.

In the superconducting magnet device 1, a superconducting magnet 2 and a first permanent current switch 3 formed of one or a plurality of switches are immersed in liquid helium and housed in an inner tank 4, which is then stored in a liquid. It is covered with a radiation shield plate cooled with nitrogen and accommodated in the outer tank 5 of the vacuum heat insulating container.

In such a superconducting magnet device 1, a minute resistor (resistance value r) 6 is connected in series to the permanent current switch 3 connected to operate the superconducting magnet 2 in the permanent current mode. The bypass circuit 8 including the second persistent current switch 7 is connected in parallel to the persistent current switch 3 to form a current avoidance loop.

The application of such a persistent current switch is as follows.

Normally, when the permanent current switches are used in parallel, a balance resistor for impedance balancing is inserted in each of the permanent current switches so that the shared currents of the parallel permanent current switches are balanced. In such a case, a voltage drop occurs due to the current flowing through the balance resistance, which causes a problem such as a decrease in the current decay time constant or heat generation. However, in the case of the permanent current switch of the present invention, when the permanent current switch is in the normal state, current flows through the permanent current switch without a balance resistor, so that voltage drop and heat generation hardly occur. It can be said that this system is more effective than conventional switches, because voltage drop and heat generation occur only in the abnormal situation of quenching of the persistent current switch.

With such a structure, the superconducting magnet 2 is excited as follows.

Open (OFF) the permanent current switches 3 and 7
Exciting current is supplied from the power supply 9 to the superconducting magnet 2.
Next, the permanent current switch 3 is closed (ON), a permanent current is caused to flow in a closed circuit formed by the superconducting magnet 2 and the first permanent current switch 3, and a permanent current mode is obtained.

After entering the permanent current mode, the bypass circuit 8
The second permanent current switch (pcs-2, resistance value R _Pcs-2 ) 7 is closed. At this time, the resistance value R _Pcs-1 of the first permanent current switch 3 is zero, and the electric resistance of the bypass circuit 8 having the minute resistance 6 of the resistance value r is higher,
The persistent current mode through the first persistent current switch 3 remains maintained.

In the superconducting magnet circuit maintained in this permanent current mode state, the first permanent current switch (pcs-1) 3
Is quenched, the electric resistance value R _Pcs-1 becomes higher than the electric resistance value (r + R _Pcs-2 ) of the bypass circuit 8, so that the permanent current flows into the bypass circuit 8. While the permanent current is flowing in this bypass circuit, the quenched permanent current switch 3 is cooled by the liquid helium in the inner tank and again returns to the superconducting state by itself, and the electric resistance of the permanent current switch 3 becomes zero and the bypass circuit The permanent current flowing through the circuit flows through the circuit of the original permanent current switch 3.

To demagnetize the superconducting magnet 2, a demagnetizing current is passed through the permanent current switch 3, the permanent current switch 7 of the bypass circuit is turned off, and then the permanent current switch 3 is turned off.
A degaussing current flows through the superconducting magnet 2, and when the degaussing current is swept, the superconducting magnet 2 is degaussed.

Another embodiment of the present invention will be described based on the example shown in FIG.

The bypass circuit in the above is formed only by the semiconductor switch 10 such as a thyristor.

The ON / OFF of this semiconductor switch 10 is the outer tank 5.
It is performed by the switch 11 provided outside the.

In the above structure, the permanent current switch 3
Is maintained in the superconducting state, the excitation of the superconducting magnet 2 is as follows.

First, the permanent current switch 3 is turned off, and an exciting current is passed through the superconducting magnet 2.

Next, when the permanent current switch 3 is turned on, a permanent current flows in the closed loop of the superconducting magnet 2 and the permanent current switch 3 to realize the permanent current mode.

After the permanent current mode is realized, the semiconductor switch 10 is turned on. Even when the semiconductor switch 10 is turned on, the electric resistance of the permanent current switch is zero, so that the permanent current mode formed between the superconducting magnet 2 and the permanent current switch 3 is still maintained.

When the permanent current switch 3 is quenched due to some factor or disturbance to the circuit maintained in the permanent current mode state, the electric resistance of the permanent current switch 3 exceeds the electric resistance of the semiconductor switch 10, so that the superconductivity is increased. The permanent current flowing in the closed loop of the magnet 2 and the permanent current switch 3 flows in the avoidance loop of the semiconductor switch 10 connected in parallel as a protection circuit. While the persistent current is flowing through the semiconductor switch 10 as described above, the quenched persistent current switch 3 is cooled by the liquid helium in the inner tank 4 and returns to the superconducting state again. As a result, the electric resistance of the permanent current switch 3 becomes zero and becomes smaller than the electric resistance of the semiconductor switch 10 again, so that the permanent current flowing through the semi-electric switch 10 again flows through the permanent current switch 3.

To demagnetize the superconducting magnet 2, a demagnetizing current is passed through the permanent current switch 3, and the permanent current switch 3 is OF
When the semiconductor switch 10 is turned off as well as F, a degaussing current flows through the superconducting magnet 2. Sweeping this degaussing current completes the demagnetization of the superconducting magnet 2.

As described above, even if the permanent current switch 3 is quenched, by supplying an exciting / demagnetizing current to the semiconductor switch 10, it is possible to always maintain the superconducting magnet 2 in the permanent current mode state. Quench resistance and stability. , It is possible to provide a highly reliable persistent current switch.

In another embodiment of the present invention, shown in FIG. 3, a contactor 12 is used in place of the above semiconductor switch to form an avoidance loop in the event of a quench of the persistent current switch 3.

The contactor 12 is turned on and off by opening and closing a pneumatic valve 13 provided outside, and the opening and closing of the pneumatic valve 13 is performed by turning on and off a compressed gas.

Also in the above configuration, since the permanent current flows through the contactor 7 even when the permanent current switch 3 is quenched during the excitation / demagnetization, the same effect as that of the above embodiment can be obtained.

[0033]

According to the present invention, even if the persistent current switch is quenched in the circuit of the superconducting magnet at cryogenic temperature,
Immediate self-recovery allows the superconducting magnet to always be stably maintained in the permanent current mode, thereby improving the reliability of the superconducting magnet.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a superconducting magnet circuit according to the present invention.

FIG. 2 is a circuit configuration diagram of another embodiment of the present invention.

FIG. 3 is a circuit configuration diagram of still another embodiment of the present invention.

FIG. 4 is a circuit diagram of a conventional superconducting magnet circuit.

[Explanation of symbols]

 2 ... Superconducting magnet 3 ... (First) permanent current switch 4 ... Inner tank 6 ... Micro resistance 7 ... (Second) permanent current switch 10 ... Semiconductor switch 12 ... Contactor

Claims (3)

[Claims] 1. A superconducting magnet circuit having a first permanent current switch (pcs-1) for switching a superconducting magnet to a superconducting mode in a cryogenic state, wherein a second permanent current switch is provided in parallel with the permanent current switch. A superconducting magnet circuit, wherein a bypass circuit including (pcs-2) is provided, and the resistance value of the bypass circuit is larger than the resistance value of the first permanent current switch. 2. The bypass circuit is formed by adding a minute resistance (resistance value r) to a second permanent current switch (resistance value R _Pcs-2 ), and the resistance value (r + R _Pcs-2 ) of this bypass circuit.
And the resistance value (R _Pcs-1 ) of the _first persistent current switch is normal (when the persistent current switch is ON)
Is R _Pcs-1 <(r + R _Pcs-2 ), and R _Pcs-1 > (r + R _Pcs-2 ) when the first persistent current switch (pcs-1) is quenched. 1. The superconducting magnet circuit according to 1. 3. A superconducting magnet circuit having a permanent current switch for switching a superconducting magnet to a superconducting mode in a cryogenic state, wherein a bypass circuit having a switch is provided in parallel with the permanent current switch. Superconducting magnet circuit.