JPH0359565B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field of the Invention The present invention relates to a superconducting electromagnet device in which a component that can serve as a current shunting element during excitation and demagnetization is provided between both ends of a superconducting coil constituting the electromagnet.

Technical Background of the Invention In recent years, superconducting electromagnet devices have been used not only in stationary equipment but also in rotating equipment. As is well known, a superconducting electromagnet device mainly consists of a low-temperature container whose interior is kept at an extremely low temperature, a superconducting coil housed in the low-temperature container, and a DC power supply that excites the superconducting coil. ing. If the superconducting coil can be operated in persistent current mode, a persistent current switch is provided in the low temperature container to selectively short-circuit both ends of the superconducting coil. Further, generally, a protective resistor is connected between a pair of lead wires that connect the superconducting coil and a DC power supply located outside the low temperature container.

FIG. 1 shows an example of a superconducting electromagnet device that can be switched to persistent current mode, in which a variable output DC current is connected to both ends of a superconducting coil 2 housed in a cryogenic container 1 via lead wires 3a and 3b. A thermal persistent current switch 5 connected to the output end of the power supply device 4 and selectively short-circuiting both ends of the superconducting coil 2 is provided in the low temperature container 1, and a protective resistor 6 is provided between the lead wires 3a and 3b. ing. The persistent current switch 5 includes a switch body 11 made of superconducting wire, and a heater that selectively heats the switch body 11 by receiving input from the outside and switches it between a normal conduction mode (off) and a superconductivity mode (on). It consists of 12. In addition, 1 in the figure
3 indicates the equivalent resistance in normal conduction mode.

Therefore, the device configured as described above switches to the persistent current mode (excitation) and eliminates the permanent electromagnetic mode (demagnetization) in the following manner. That is, during excitation, the heater 12 is energized to turn off the switch body 11 of the persistent current switch 5, and in this state, the output current of the DC power supply device 4 is linearly increased at a predetermined current increase rate, Set to a predetermined value. Next, by stopping the power supply to the heater 12, the switch body 11 of the persistent current switch 5 is turned on. Subsequently, the output current of the DC power supply device 4 is lowered to zero. Through such control, the system is switched to a so-called persistent current mode in which a persistent current flows in a closed circuit consisting of the superconducting coil 2 and the switch body 11 of the persistent current switch 5.
Furthermore, during demagnetization, the output current of the DC power supply device 4 is first increased to a value equal to the persistent current flowing through the superconducting coil 2, and then the heater 12 is energized to turn off the switch body 11 of the persistent current switch 5. Switch to In this state, the output current of the DC power supply device 4 is decreased at a predetermined current reduction rate, and finally becomes zero. Then, the power supply to the heater 12 is stopped to complete the demagnetization control.

Problems of the Background Art The above-described control certainly makes it possible to switch to persistent current mode and eliminate persistent current mode. However, in the case of conventional devices, the output current of the DC power supply is continuously changed at a predetermined current increase rate (decrease rate) from zero during excitation and from the persistent current value during demagnetization. Therefore, there was a problem in that the time required for excitation and the time required for demagnetization inevitably became longer. That is, during excitation, for example, the second
As shown by the solid line _I0 in the left half of the figure, the DC power supply 4
When the output current of the superconducting coil 2 is increased, even if this output current reaches the set value at time _t1 , the current actually flowing through the superconducting coil 2 is the result of its own inductance, the protective resistor 6, and the normal conduction of the persistent current switch 5. Due to the resistance associated with the mode, that is, the presence of the shunt element, the current flowing through the superconducting coil 2 coincides with the set value, as shown by the broken line I _L in FIG. 2, at a time t ₂
lags considerably behind time t ₁ . For this reason, not only does excitation take a long time, but it is also necessary to energize the heater 12 of the persistent current switch 5 for that long period of time, resulting in a large loss of refrigerant. Also,
When any of the superconducting coil 2, persistent current switch 5, or protective resistor 6 is replaced with a new one, the self-inductance value and resistance value are almost never exactly the same as the previous one. The period from time t1 to time t2 and from time t4 to time described above
The period up to t5 depends on the self-inductance value and resistance value. Therefore, when some of the components have been replaced, it is necessary to set the duration for which the persistent current switch 5 is energized to the heater 12 for a longer period of time for safety reasons. For this reason, there is a limit to shortening the energization time to the heater 12, and it has been difficult to suppress loss of refrigerant. This was true not only during excitation, but also during demagnetization, as shown in the right half of FIG. During excitation and demagnetization, the rate of increase (rate of decrease) of the current flowing through the superconducting coil 2 is suppressed by the characteristics of the coil.
Therefore, since the conventional device changes the output current of the DC power supply 4 from zero (set value) at an increase rate (decrease rate) determined by the above characteristics, the above-mentioned problems cannot be avoided. . Note that H in FIG. 2 indicates the strength of the magnetic field generated in the superconducting coil 2.

Purpose of the Invention The present invention was made in view of the above circumstances, and its purpose is to excite the superconducting coil in the shortest time determined by the characteristics of the superconducting coil, without wasting time during excitation and demagnetization. Demagnetization can be performed. An object of the present invention is to provide a superconducting electromagnet device.

Invention and Summary A superconducting electromagnet device according to the present invention is provided with a magnetic field detection element that detects the strength of the magnetic field generated in a superconducting coil, and detects the rate of change in the strength of the magnetic field detected by the magnetic field detection element during excitation and demagnetization. The present invention is characterized by being provided with a DC power supply device that changes the output current so as to match the permissible maximum rate of change determined by the characteristics of the superconducting coil.

Effects of the Invention If the strength of the magnetic field detected by the magnetic field detection element described above is H, the current flowing through the superconducting coil at that time is I _L , and the constant is K, then I _L = KH ……( 1) The following relationship is established. In other words, the strength H of the magnetic field is proportional to the current flowing through the superconducting coil. Since the device of the present invention is provided with a magnetic field detection element, it is possible to know the strength H of the magnetic field. Therefore, by controlling the output power of the DC power supply by feeding back the magnetic field strength H, a desired magnetic field strength variation pattern can be obtained regardless of the presence of the shunt element. The present invention takes advantage of this relationship. Therefore, according to the present invention, excitation and demagnetization can be performed in the shortest time determined by the characteristics of the superconducting coil without any wasted time during excitation and demagnetization. Therefore, when applied to a device that can be switched to persistent current mode, it is possible to minimize loss of refrigerant during excitation and demagnetization.
Furthermore, even if some of the components are replaced, excitation and demagnetization without wasted time can be achieved.

Embodiment of the Invention FIG. 3 shows a circuit configuration of a superconducting electromagnet device according to an embodiment of the present invention, and the same parts as in FIG. 1 are designated by the same symbols. Therefore, the explanation of the overlapping parts will be omitted.

In this embodiment, a magnetic field detection element 21 such as a Hall element for detecting the strength of the magnetic field generated by the superconducting coil 2 is provided inside the cryogenic vessel 1, and the output signal of this magnetic field detecting element 21 is transmitted outside the cryogenic vessel 1. The signal is introduced as a control signal Z to the DC power supply 23 via an amplifier 22 provided in the DC power supply 23.

The DC power supply device 23 can also send out a negative output current, and when the signal P indicating the start of excitation is introduced, the increase rate of the control signal Z becomes the maximum permissible magnetic field increase rate determined by the characteristics of the superconducting coil 2. Increase the output current I ₀ so that it is equal. This control is performed until the magnitude of the control signal Z reaches a predetermined value. Further, when a signal Q indicating the start of demagnetization is introduced, the output current I ₀ is decreased so that the rate of decrease of the control signal Z becomes equal to the maximum permissible magnetic field decrease rate determined by the characteristics of the superconducting coil 2. This control is continued until the magnitude of the control signal Z becomes zero.

Therefore, according to this device, if a target value that changes linearly is set in the DC power supply 23 so as to obtain the maximum magnetic field increase rate (decrease rate) determined by the wire characteristics of the superconducting coil 2, for example. Then, during excitation, as shown in the left _half of _FIG . , a current I _L flows from zero at an increasing rate determined by the characteristics of this coil. Similarly, during demagnetization, as shown in the right half of FIG. 4, the current flowing through the superconducting coil 2 decreases at a rate determined by the characteristics of this coil. For this reason, the allowable minimum time determined by the characteristics of superconducting coil 2
Excitation and demagnetization can be performed at T ₀ , and the time required for excitation and demagnetization can be significantly shortened compared to conventional devices. Furthermore, since the coil current is controlled by detecting the strength of the magnetic field, the coil current and the strength of the magnetic field can always be adjusted to the target value.

In the above-described embodiment, a DC power supply device capable of outputting a negative output current is used, but a DC power supply device capable of outputting only a positive output current may be used. In this case, the rate of change of the coil current becomes gradual in the final stage of demagnetization, but it does not have much of an effect. Furthermore, the present invention can be applied to cases where a superconducting coil is wound around an iron core, where multiple superconducting coils are connected in series, where a persistent current switch is not present (however, a protective resistor is present), etc. .

[Brief explanation of drawings]

Fig. 1 is a circuit configuration diagram of a conventional superconducting electromagnet device, Fig. 2 is a diagram for explaining waveforms of various parts during excitation and demagnetization of the same device, and Fig. 3 is a superconducting electromagnet device according to an embodiment of the present invention. FIG. 4 is a diagram for explaining waveforms of various parts during excitation and demagnetization of the same embodiment device. 1... Low temperature container, 2... Superconducting coil, 21...
...Magnetic field detection element, 23...DC power supply device.

Claims (1)

[Claims] 1 A superconducting coil constituting an electromagnet, a shunt element connected between both ends of this superconducting coil through which current flows when the superconducting coil is excited and demagnetized, and a magnetic field detection element that detects the strength of the magnetic field generated in the superconducting coil. and its output terminals are connected to both ends of the superconducting coil, and the rate of change in the strength of the magnetic field detected by the magnetic field detection element during excitation and demagnetization matches the allowable maximum rate of change determined by the characteristics of the superconducting coil. 1. A superconducting magnet device comprising: a DC power supply device for excitation/demagnetization that sends out an output current while changing the output current.