JPH0727815B2 - Superconducting device - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention relates to a normal conduction transition (quenching) of a superconducting magnet.
The present invention relates to a superconducting device having a protection function against.

[Technical background of the invention and its problems]

As is well known, when the superconducting magnet is quenched, the excessive electromagnetic energy stored in the superconducting coil is consumed in the coil that has changed to the normal conducting state. Therefore, the superconducting coil changes its composition or burns due to heat generation due to energy consumption.

Therefore, in order to prevent such accidents, the coil of the superconducting device is protected by various methods. FIG. 7 shows an example thereof.

That is, generally, a superconducting device accommodates a superconducting magnet 1 and a permanent current switch 2 forming a closed loop in a cryogenic region A at a liquid helium temperature level, and the power leads 3a, 3b from outside the cryogenic region A. The power supply 4 can be connected to the superconducting magnet 1 via the. Then, in order to protect the superconducting magnet 1, the superconducting magnet 1, a plurality of unit superconducting coil 5
The unit superconducting coil 5a, 5b is divided into a and 5b.
The protection resistors 6a and 6b are connected in parallel with the above.

With such a configuration, when one of the unit superconducting coils 5a, 5b is quenched, the energy stored in the coil is consumed by the protection resistors 6a, 6b, so that the unit superconducting coils 5a, 5b Energy consumption in the can be suppressed, and the coil can be protected.

However, in the conventional superconducting device having such a configuration, when the power source 4 excites and demagnetizes, a current also flows through the protective resistors 6a and 6b. Therefore,
The conventional superconducting device provided with the above-mentioned protection means has a problem that the protective resistances 6a and 6b generate heat during excitation and demagnetization, resulting in large heat loss in the cryogenic region and poor economic efficiency. .

[Object of the Invention]

The present invention has been made in view of the above-mentioned conventional drawbacks, and an object thereof is to further ensure the protective performance of a superconducting magnet in the case of quenching, and further, in an extremely low temperature region during excitation and demagnetization of the superconducting magnet. An object of the present invention is to provide a superconducting device that suppresses heat loss in the interior and is excellent in economy.

[Summary of the Invention] A superconducting device of the present invention includes a superconducting magnet having a superconducting coil housed in a cryogenic region and cooled to a cryogenic temperature, and a diode or thyristor housed in a cryogenic region and cooled to a cryogenic temperature. And a protection circuit connected in parallel to the superconducting coil so as to form a current path parallel to the superconducting coil.

That is, as a result of investigating the behavior of a semiconductor device, for example, a diode in the cryogenic region of the liquid helium temperature level, the present inventor found that the forward characteristic is represented by the curve shown in FIG. That is, as is clear from this figure, the voltage Vs (hereinafter, referred to as “switching voltage”) at which the current in the forward characteristic sharply increases is extremely low at 10 to 20V for the diode cold-cooled to an extremely low temperature. high,
Further, once turned on, it exhibits a negative resistance characteristic and settles to an on-voltage Vo of about 2V. This is because the impurities in the diode are hardly activated in the extremely low temperature state, and the forward current of the diode does not increase so much because the carriers are extremely small, and when a certain amount of current flows in the diode, It is considered that this is caused by abrupt increase of carriers due to heat generation of the diode itself.
Note that such a phenomenon can be similarly observed in other semiconductor elements, for example, thyristors.

That is, the present invention was made by paying attention to the characteristics peculiar to such a semiconductor element such as a diode or a thyristor cooled to an extremely low temperature.

〔The invention's effect〕

As described above, a semiconductor element such as a diode or a thyristor cooled to an extremely low temperature has a high switching voltage Vs in the forward direction, so that the voltage generated at both ends of each unit superconducting coil when exciting the superconducting magnet. If it is set to be lower than the switching voltage Vs, no current will flow through a semiconductor element such as a diode or a thyristor during excitation. Of course, when the unit superconducting coil is changed to the normal conducting state, a voltage higher than the switching voltage is generated at both ends of the coil, so that a semiconductor element such as a diode or a thyristor conducts and the coil protecting function is exerted. Further, during degaussing, a reverse voltage is applied to the semiconductor element such as the diode or thyristor, so that no current flows through the semiconductor element such as the diode or thyristor in this case as well.

Therefore, according to the present invention, without impairing the reliable protection performance of the superconducting magnet in the case of quenching, and further suppressing the heat loss in the cryogenic region during the excitation and demagnetization of the superconducting magnet, it is excellent in economic efficiency. It is possible to provide a superconducting device.

Example of Invention

An embodiment of the present invention will be described below with reference to the drawings. In FIGS. 1 to 5, the same parts as those in FIG. 7 are designated by the same reference numerals, and the description of the overlapping parts will be omitted.

FIG. 1 is a diagram showing an embodiment in which a diode is used in a semiconductor protection circuit.

That is, this superconducting device differs from the conventional superconducting device shown above in that the diode 11 is replaced by the protection resistors 6a and 6b.
The point is that a and 11b are added. The diodes 11a, 11b are respectively connected in parallel with the coils 5a, 5b with the direction of the current flowing through the unit superconducting coils 5a, 5b as the forward direction, and together with the coils 5a, 5b, for example, in the cryogenic region A of the liquid helium temperature level. is set up.

When exciting the superconducting device having such a configuration, the power source 4 is connected to the terminals 12a and 12b of the superconducting magnet 1 through the power leads 3a and 3b, and the permanent current switch 2 is turned off to make the superconducting magnet 1 Supply current. At this time, the rate of increase in the supply current is set so that the voltage across each of the unit superconducting coils 5a and 5b does not exceed the switching voltage Vs of the diodes 11a and 11b (for example, about 8V).
The forward current flowing through a and 11b is so small that it can be ignored.
If a plurality of diodes 11a and 11b are connected in series to raise the switching voltage Vs, the above current increase rate can be set higher. When the value of the current flowing through the superconducting magnet 1 reaches a predetermined value, the permanent current switch 2 is turned on. As a result, a permanent current that circulates through the unit superconducting coil 5a to the unit superconducting coil 5b to the permanent current switch 3 flows.

Of the unit superconducting coils 5a and 5b that have reached the superconducting state, for example, the coil 5a is assumed to be quenched due to some cause. When the coil 5a is quenched, the resistance of the coil 5a rapidly increases and the electromagnetic energy accumulated in the superconducting magnet 1 is released. If this energy is consumed only by the coil 5a, the coil 5a will be burned. However, when a resistance value is generated in the coil 5a, the terminal 12a side of the coil 5a is added to both ends of the coil 5a and the coil 5b of the coil 5a is added.
A negative voltage is generated on the side connected to. Normally, this voltage is much higher than the switching voltage Vs of the diode 11a. Therefore, the diode 11a is turned on when a high forward voltage is applied, and the superconducting magnet
1 will contribute to the consumption of the energy released.

When demagnetizing this superconducting device,
Since a reverse bias voltage is applied to 11a and 11b, they do not conduct.

Thus, according to the present embodiment, the unit superconducting coils 5a, 5
It is possible to suppress the consumption of helium during excitation and demagnetization without any loss of the protection function of b. In this example, even if the diodes 11a and 11b are connected in opposite directions, the circuit configuration does not substantially change in a state where both ends of the superconducting magnet 1 are short-circuited. Demonstrate. However, in this case, the coil 5a (5
When b) is quenched, a current flows through the diode 11b (11a).

By the way, the ON voltage of the diodes 11a and 11b is about 2V. At such a voltage, it may take a considerable time from the quench to the completion of the protection operation. In such a case, as shown in FIG. 2, each diode 11a, 11b
The protective resistances 13a and 13b may be respectively connected in series with and to increase the resistance value of the semiconductor protection circuit and reduce the time constant of the circuit.

Further, instead of using the diodes 11a and 11b in the semiconductor protection circuit, thyristors 14a and 14b as shown in FIG. 3 may be used. In this case, the gate terminals of the thyristors 14a and 14bb are connected to the corresponding unit superconducting coils 15a and
Connected to the middle tap of 15b, coil 5a, when quenched,
The gate trigger may be given by the voltage generated at 5b.

4A to 4D show still another modified example of the present invention.

First, in FIG. 1A, the diode 11a and the unit superconducting coil 5b in FIG. 1 are thermally coupled, and the diode 11b and the unit superconducting coil 5a are thermally coupled.

That is, for example, when the coil 5a is quenched, the energy accumulated in the superconducting magnet 1 is intensively consumed by the coil 5a and the diode 11a, so that the amount of heat generated by the coil 5a and the diode 11a is large. However, with the above configuration, when the coil 5a is quenched, the diode 11a generates heat due to the current flowing through the diode 11a,
Since the coil 5b thermally coupled to this is also immediately quenched, the energy of the superconducting magnet 1 is dispersed and consumed by the diodes 11a, 11b and the coils 5a, 5b. Therefore, the loads on the diodes 11a and 11b and the coils 5a and 5b are reduced.

In the above embodiment, the diodes 11a and 11b and the coils 5a and 5b are directly and thermally coupled. However, for example, as shown in FIG. Protective resistors 15a and 15b may be connected in series between P and the common connection point Q of the coils 5a and 5b, and these protective resistors 15a and 15b and the coils 5a and 5b may be thermally coupled. .
Further, as shown in FIG. 2C, the protection resistor 13a and the coil 5b of the circuit of FIG. 2 may be thermally coupled to each other, and the protection resistor 13b and the coil 5a may be thermally coupled to each other. Furthermore, as shown in FIG. 4 (d), the thyristors 14a, 14b shown in FIG. 3 may be thermally coupled to the coils 5b, 5a, respectively.

Further, the present invention is not limited to the above-mentioned embodiment, and for example, as shown in FIG. 5, a diode 16 is connected in parallel with the permanent current switch 2 to add a protection function when the permanent current switch 2 is quenched. It can also be applied to the superconducting device described above.

Further, the present invention can be applied not only to a device in which three or more unit superconducting coils are connected in series to configure the superconducting magnet 1 , but also to a device including the superconducting magnet 1 including one coil having a plurality of intermediate taps. It is also applicable to.

In short, the present invention can be implemented with various modifications without departing from the scope of the invention.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a configuration of a superconducting device according to an embodiment of the present invention, FIGS. 2 to 5 are circuit diagrams showing other embodiments of the present invention, and FIG. 6 is a main view of the present invention. FIG. 7 is a characteristic diagram showing characteristics of a semiconductor protection circuit forming a part, and FIG. 7 is a circuit diagram showing a conventional superconducting device. 1 ... Superconducting magnet, 2 ... Permanent current switch, 3
a, 3b …… Power lead, 4 …… Power supply, 5a, 5b …… Unit superconducting coil, 6a, 6b, 13a, 13b, 15a, 15b …… Protection resistance, 11
a, 11b, 16 ... Diode, 14a, 14b ... Thyristor.

Claims (5)

[Claims] 1. A superconducting magnet having a superconducting coil housed in a cryogenic region and cooled to a cryogenic temperature, and a diode or thyristor housed in a cryogenic region and cooled to a cryogenic temperature. And a protection circuit connected in parallel to the superconducting coil so as to form a parallel current path. 2. The superconducting magnet is configured by connecting a plurality of unit superconducting coils in series, and the protection circuit is connected in parallel to each of the unit superconducting coils. The superconducting device according to item 1. 3. The superconducting device according to claim 1, wherein the protection circuit includes a resistor connected in series. 4. The superconducting magnet comprises one superconducting coil having one or more intermediate terminals, and the unit superconducting coil is a divided body of the superconducting coils divided by the intermediate terminals. The superconducting device according to claim 2. 5. The protection circuit is thermally connected to a unit superconducting coil other than the unit superconducting coil connected in parallel with the protection circuit among the plurality of unit superconducting coils. The superconducting device according to claim 2.