JP2001143922A - Superconducting magnet and circuit for protecting the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To validly use the capability of a freezer. SOLUTION: This superconducting magnet is provided with a helium vessel 4 for storing fluid helium 2, a superconducting coil 1 arranged so as to be immersed in the fluid helium in the helium vessel, a radiation shield 5 arranged so that the helium vessel 4 can be surrounded, a vacuum vessel 6 surrounding the helium vessel and the radiation shield whose inside part is held so as to be vacuum, and a freezer 3 arranged at the vacuum vessel side for cooling gas helium evaporated in the radiation shield 5 and the helium vessel 4. An opening in a proper size is formed at the upper face part of the helium vessel 4, and a condensed bar 15 whose heat conductivity is high is fixed to the opening so as to be projected in the atmosphere of the gas helium 7 in the helium vessel 4, and the condensed bar 15 is thermally connected with the thermal conductive part of the freezer 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid helium immersion cooled superconducting magnet and a protection circuit for the superconducting magnet.

[0002]

2. Description of the Related Art As a superconducting magnet in which a superconducting coil is immersed in liquid helium to cool it, there are a type in which liquid helium evaporated by intrusion heat or the like is released to the atmosphere and a type in which a helium is recondensed by a refrigerator.

FIG. 15 shows an example of a superconducting magnet employing a recondensing type.

[0005] The superconducting magnet shown in FIG. 15 is immersed in liquid helium 2 in a helium container 4 to house the superconducting coil 1, and a radiation shield 5 is provided so as to surround the helium container 4. Radiant heat entering is reduced. A vacuum vessel 6 is arranged so as to surround the helium vessel 4 and the radiation shield 5.

The vacuum vessel 6 is provided with a refrigerator 3. One stage of the refrigerator 3 is brought into thermal contact with the radiation shield 5, and the second stage is brought into thermal contact with the helium container 4. Gives cold.

In the figure, reference numeral 8 denotes a liquid level measuring means for measuring the liquid level of the liquid helium in the helium container 4.

In such a superconducting magnet, the radiation shield 5 is cooled to about 50K by the first stage of the refrigerator 3. The superconducting coil 1 is cooled by liquid helium 2 and is kept at about 4K.

Further, the liquid helium 2 evaporates due to intrusion heat such as heat conduction and radiant heat from the supporting material of the helium container 4,
In order to recondense the gas helium 7 and return it to the liquid helium 2, it is necessary to contact a portion having a temperature lower than the temperature (about 4K) at which the gas helium 7 condenses. This contact is hereinafter referred to as the helium condensation surface.

For this reason, conventionally, as shown in the figure, the refrigerator 3 and the helium container 4 are directly thermally connected, and the helium gas is supplied by applying cold heat so that the inner surface of the helium container 4 becomes a helium condensing surface. Recondensing.

FIG. 16 shows an example of a conventional superconducting magnet and a protection circuit.

The superconducting coil 1 has oxide superconducting current leads 9 connected to both ends thereof, and is housed inside a cryostat. The oxide superconducting current lead 9 is led out of the cryostat and connected to an excitation power supply 10 for exciting the superconducting coil 1 via a circuit breaker 11;
These excitation power supply 10 and circuit breaker 11 are connected to control device 12.

The protection circuit includes a superconducting coil 1
And a series circuit of a diode 13 and a discharge resistor 14 installed inside the cryostat in parallel.

In such a superconducting magnet protection circuit, when a quench of the superconducting coil 1 is detected, the circuit breaker 11 cuts off the circuit by a signal from the control device 12, and the current flowing from the exciting power supply 10 is protected by the protection circuit. To commutate. The reason why the oxide superconducting current lead 9 is not incorporated in the protection circuit is that the oxide superconducting current lead 9 may be quenched, in which case it cannot be continuously energized. This is because it is not suitable.

[0014]

In the superconducting magnet having the above-described structure, the capacity of the refrigerator 3 has a strong dependence on the temperature as shown in FIG. 14, and when the temperature decreases, the cooling capacity sharply increases. It tends to get worse.

However, since the conventional helium container 4 is made of a material having low thermal conductivity such as austenitic stainless steel, the refrigerator 3
Is brought into thermal contact with the inner surface of the helium container 4 as a condensation surface, a large temperature difference ΔT occurs there. FIG.
As can be seen from FIG. 4, since the capacity of the refrigerator 3 is reduced by the amount corresponding to the temperature difference ΔT, there is a disadvantage that the capacity of the refrigerator 3 cannot be fully utilized.

In FIG. 15, the positional relationship between the refrigerator 3 and the helium container 4 is relatively shifted between when the apparatus is assembled and when the cooling is completed due to the difference in the heat shrinkage.
And the helium container 4 are in thermal contact with each other, and if they are fixed so that their positional relationship does not shift, a large load is applied to the fixed portions, and the performance of the refrigerator 3 deteriorates,
It causes structural destruction.

Further, referring to FIG.
The internal pressure is determined by the balance between the amount of heat entering and the cooling capacity of the refrigerator 3. If the internal pressure becomes lower than the atmospheric pressure, the air is sucked into the helium container 4 and freezes, causing a pipe jam. .

In FIG. 15, when the superconducting coil 1 is excited, if the liquid amount of the liquid helium 2 is small, it may be quenched. Therefore, it is important to grasp the liquid level.
Therefore, the liquid level measuring means 11 for measuring the liquid level is usually provided. However, since the heat load of the liquid level measuring means 11 is large enough to be equal to the capacity of the refrigerator 3, one minute measurement and one hour The heat load is reduced by intermittent operation such as suspension.

However, this operation method is sufficient because it hardly changes in the case of a normal liquid level, but when there is a temporary large heat generation such as during demagnetization, the liquid level may change suddenly. Yes, if the demagnetization operation is performed during the measurement interval of the liquid level measurement, that is, when the liquid level measurement is not performed, the liquid level cannot be monitored.

On the other hand, in the superconducting magnet protection circuit shown in FIG. 16, it is not preferable in terms of reliability to use a semiconductor element such as a diode 13 as a component of the protection circuit in the cryostat. If any failure occurred in the diode 9, the cryostat had to be disassembled and replaced.

In a superconducting magnet in which the superconducting coil 1 is disposed inside the cryostat, a current introduction terminal for supplying electricity to the superconducting coil 1 is provided on the outer surface of the cryostat. However, since the current introduction terminal is cooled by conduction cooling from the inside, water droplets adhere to the outer surface,
Ground insulation performance deteriorates. When the excitation voltage is as low as several volts, the current can be supplied as it is, but when the excitation voltage is high, there is a risk of electric leakage.

The present invention has been made in view of the above circumstances, and provides a superconducting magnet which can effectively utilize the capacity of a refrigerator and can absorb a displacement caused by cooling of the refrigerator and a helium container. The purpose is to do.

In addition, the superconducting coil can be protected without installing a semiconductor element such as a diode inside the cryostat, and the integrity of the ground insulation is maintained by preventing water droplets from adhering to the outer surface of the current introduction terminal. It is an object of the present invention to provide a protection circuit for a superconducting magnet that can be used.

[0024]

According to the present invention, a superconducting magnet and a protection circuit therefor are constituted by the following means in order to achieve the above object.

The invention corresponding to claim 1 is a helium container storing liquid helium, a superconducting coil immersed and disposed in liquid helium in the helium container,
A radiation shield provided so as to surround the helium container, a vacuum container surrounding the helium container and the radiation shield, and the inside of which is held in a vacuum, and provided on the vacuum container side, the radiation shield and the radiation shield. In a superconducting magnet equipped with a refrigerator for cooling gas helium evaporated in the helium container, an opening of an appropriate size is provided on the upper surface of the helium container, and a condensing rod having a high thermal conductivity is provided in the opening. The condensing rod is protruded and fixed into the gas helium atmosphere in the helium container, and the condensing rod is thermally connected to the cold heat conduction part of the refrigerator.

According to the superconducting magnet of the invention corresponding to the first aspect, the condensing rod having a high thermal conductivity brought into thermal contact with the refrigerator has a sufficient area cooled to a temperature lower than the condensation temperature of liquid helium. Since a condensing surface is obtained, the recondensing efficiency can be increased.

According to a second aspect of the present invention, there is provided the superconducting magnet according to the first aspect of the present invention, wherein the condensing rod and the refrigerator are generated by a difference in heat shrinkage between the condensing rod and the opening of the helium container. The condensing rod is fixed to the helium container with an elastic body capable of absorbing the displacement amount on the surface facing the thermal conduction part interposed therebetween.

According to the superconducting magnet of the invention corresponding to the second aspect, since the condensing rod is fixed to the helium container with an elastic body capable of absorbing displacement interposed therebetween, the refrigerator and the helium container due to differences in heat shrinkage. Can be absorbed, and the refrigerator does not deteriorate in performance or break down the structure.

According to a third aspect of the present invention, in the superconducting magnet according to the first aspect of the present invention, the condenser rod and the refrigerator are generated by a difference in heat shrinkage between the condenser rod and a cold conduction part of the refrigerator. The condensing rod and the cold conduction section of the refrigerator are thermally connected with a flexible body interposed therebetween that can absorb the amount of displacement on the surface facing the cold conduction section.

According to the superconducting magnet of the invention corresponding to the third aspect, a flexible body is interposed between the refrigerator and the condensing rod to obtain thermal contact. The same effect as the invention can be obtained.

According to a fourth aspect of the present invention, in the superconducting magnet according to the first aspect of the present invention, a convection preventing member is inserted into the opening of the helium container such that one end reaches near the liquid surface of liquid helium. The condensing rod is disposed so as to be surrounded by the convection preventing member.

According to the superconducting magnet of the invention corresponding to the fourth aspect, by installing the convection preventing member on the outer periphery of the condensing rod, only the gas having a temperature close to the liquid temperature gathers near the condensing rod, so that the reconducting rod can be efficiently recycled. Can be condensed.

According to a fifth aspect of the present invention, there is provided a helium container containing liquid helium, a superconducting coil immersed in liquid helium in the helium container, and
A radiation shield provided so as to surround the helium container, a vacuum container surrounding the helium container and the radiation shield, and the inside of which is held in a vacuum, and provided on the vacuum container side, the radiation shield and the radiation shield. In a superconducting magnet including a refrigerator that cools gas helium evaporated in the helium container, a heater provided to be immersed in liquid helium in the helium container,
A pressure measuring unit that is provided in a gas helium atmosphere in the helium container and measures a pressure in the helium container, and controls the heater in accordance with the pressure in the helium container measured by the pressure measuring unit. A pressure controller for maintaining the pressure in the helium container at a predetermined pressure.

According to the superconducting magnet of the invention corresponding to the fifth aspect, the heater installed inside the helium container is heated to control the pressure inside the helium container, so that the atmosphere is sucked into the helium container. Disappears.

According to a sixth aspect of the present invention, there is provided a helium container in which liquid helium is stored, a superconducting coil immersed in liquid helium in the helium container, and
A radiation shield provided so as to surround the helium container, a vacuum container surrounding the helium container and the radiation shield, and the inside of which is held in a vacuum, and provided on the vacuum container side, the radiation shield and the radiation shield. In a superconducting magnet having a refrigerator for cooling gas helium evaporated in a helium container, a liquid level measuring means for measuring a liquid level of liquid helium in the helium container and an excitation voltage of the superconducting coil are measured. Voltage measurement means,
The timing of measurement by these measuring means is controlled, and the liquid level is measured by the liquid level measuring means at a preset time interval, and when the excitation level measured by the voltage measuring means is sensed, the liquid level measuring means may control the liquid level at any time. A control device for measuring the liquid level.

According to the invention corresponding to claim 6, the intermittent operation of the liquid level measuring means minimizes the thermal load on the liquid helium 2 container, and automatically detects the excitation to detect the liquid level as needed. Since the surface is measured, there is no occurrence of quench due to lack of liquid helium, and it can be made highly safe.

According to a seventh aspect of the present invention, there is provided a superconducting coil housed in a cryostat, an exciting power source installed outside the cryostat for exciting the superconducting coil, and installed in the cryostat,
A superconducting magnet comprising: a current lead made of an oxide superconductor inserted between the excitation power supply and the superconducting coil; and a protection circuit connected in parallel to the superconducting coil. One end is connected between the pair of auxiliary leads, and a pair of auxiliary leads is introduced outside the cryostat, and a discharge resistor is connected between the pair of auxiliary leads in series outside the cryostat.

According to an eighth aspect of the present invention, in the superconducting magnet according to the seventh aspect of the present invention, a current control unit controlled by a control device is provided between the auxiliary lead in series with a discharge resistor.

According to the seventh and eighth aspects of the present invention, since the auxiliary lead is provided, the discharge resistor can be installed outside the cryostat, so that there is no need to install a semiconductor such as a diode inside the cryostat. And a highly reliable protection circuit.

According to a ninth aspect of the present invention, in the superconducting magnet according to the seventh aspect of the present invention, a self-control type current controller is provided between the auxiliary leads in series with a discharge resistor.

According to the invention corresponding to the ninth aspect, by connecting the self-control type current control unit in series between the auxiliary leads, during normal excitation, the current is not shunted to the protection circuit and the response is reduced. Can be fast.

According to a tenth aspect of the present invention, in the superconducting magnet protection circuit according to the ninth aspect, the current control unit is a current control element or a current control circuit controlled by a voltage generated at both ends thereof. is there.

According to the ninth aspect of the present invention, the current control unit provided between the auxiliary leads is a current control element or a current control circuit controlled by a voltage generated at both ends, so that signal processing failure can be prevented. There is no erroneous operation due to the above, and safety can be improved.

According to an eleventh aspect of the present invention, in the superconducting magnet protection circuit according to the seventh aspect of the present invention, a current control element controlled by a controller in series with a discharge resistor between the auxiliary leads is provided at both ends. A plurality of current control elements or current control circuits controlled by the generated voltage are connected in parallel.

According to the invention corresponding to claim 11,
Precise control and passive safety are achieved by paralleling a current control element controlled by the control device and a current control circuit that short-circuits when the voltage exceeds a certain set voltage in a current control unit installed between the auxiliary leads. It will have both.

According to a twelfth aspect of the present invention, in a superconducting magnet having a superconducting coil disposed inside a cryostat, a current introducing terminal for supplying a current to the superconducting coil in the cryostat is penetrated from inside the cryostat to outside. It is installed, and a blowing means is provided so as to be able to blow air toward the outside of the current introduction terminal.

According to the invention corresponding to claim 12,
By providing the air blowing means, it is possible to prevent water droplets from being attached to the current introduction terminal, and to maintain good ground insulation.

[0048]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view showing a first embodiment of a superconducting magnet according to the present invention, and the same parts as those in FIG.

In FIG. 1, reference numeral 4 denotes liquid helium 2 inside.
Is a helium container in which a cylinder 4a is attached to an opening of an appropriate size opened in the upper surface, and the superconducting coil 1 is immersed in liquid helium and stored in the helium container 4. ing.

Reference numeral 5 denotes a radiation shield provided so as to surround the helium container 4, and reference numeral 6 denotes a vacuum container in which a radiation shield 5 surrounding the helium container is disposed.

On the other hand, reference numeral 3 denotes a refrigerator mounted on the upper surface of the vacuum vessel 6, and this refrigerator 3 has a one-stage and a two-stage cold conductor. Then, the first-stage cold conductor is brought into thermal contact with the radiation shield 5 and the second-stage cold conductor is inserted into the cylindrical body 4a on the helium container 4 side with its tip end facing the helium container 4. The heat is brought into thermal contact with the condensing rod 15. Since the condensing rod 15 is kept at a temperature lower than the temperature at which the gas helium 7 condenses (about 4K), the gas helium 7 is brought into thermal contact with this portion to provide cold heat.

In this case, the radiation shield 5 is cooled and held at about 50K by the cold conductor at the first stage of the refrigerator 3. The condensing rod 15 is made of a high thermal conductivity material such as oxygen-free copper so that there is almost no temperature difference from the refrigerator 3.

According to the first embodiment having the above-described structure, the helium gas 7 in the helium container 4 and the contact portion thereof are maintained at a temperature not higher than the condensation temperature of the liquid helium 2, and the condensation surface having a sufficient area is formed by the helium container 4 The gas helium 7 evaporated by the heat of intrusion is efficiently recondensed.

FIG. 2 is a sectional view showing a second embodiment of the superconducting magnet according to the present invention. The same parts as those in FIG. 1 are denoted by the same reference numerals, and the description thereof will be omitted.

In the second embodiment, as shown in FIG. 2, a condensing rod which is in thermal contact with the periphery of an opening of an appropriate size opened on the upper surface of the helium container 4 and the two-stage portion of the refrigerator 3. Fifteen
An elastic body 16 such as a bellows capable of absorbing a displacement caused by a positional shift caused by a difference in heat shrinkage between the refrigerator 3 and the helium container 4 is interposed between the head and the condensing rod 15. It is fixed to the helium container 4.

According to the second embodiment having the above structure, the displacement between the refrigerator 3 and the helium container 4 caused by the difference in heat shrinkage can be absorbed by the elastic body 16, so that the performance of the refrigerator 3 is deteriorated. And no structural destruction.

FIG. 3 is a cross-sectional view showing a third embodiment of the superconducting magnet according to the present invention. The same parts as those in FIG. 1 are denoted by the same reference numerals, and the description thereof will be omitted.

In the third embodiment, as shown in FIG. 3, between the two-stage portion of the refrigerator 3 and the head of the condensing rod 15 inserted and held in the cylinder 4a on the helium container 4 side. The thermal contact is obtained by interposing the flexible body 17. The flexible body 17 is desirably made of a flat wire or a thin plate of oxygen-free copper, which is a high thermal conductivity material.

In the third embodiment having the above structure, the same operation and effect as in the second embodiment can be obtained.

FIG. 4 is a cross-sectional view showing a fourth embodiment of the superconducting magnet according to the present invention. The same parts as those in FIG. 1 are denoted by the same reference numerals, and the description thereof will be omitted.

In the fourth embodiment, as shown in FIG. 4, one end of a cylindrical convection preventing member 18 is inserted into an opening of an appropriate size opened on the upper surface of the helium container 4 so that the liquid level of the liquid helium 2 is increased. It is inserted and attached so as to reach the vicinity, and the tip of the convection preventing member 18 faces the inside of the helium container 4, and the condensing rod 15 inserted and held is thermally connected to the two-stage cold conductor of the refrigerator 3. The contact is made.

In the superconducting magnet having the above structure, the gas helium 7 is more likely to be re-condensed into the liquid helium 2 as the temperature is closer to the condensation temperature, that is, the liquid temperature. On the other hand, in the gas helium 7, convection is generated due to the gas temperature distribution formed by the distribution of the penetrating heat, and a warm gas may flow near the condensing rod 15.

According to the fourth embodiment, the convection preventing member 18 allows the helium gas 7 near the liquid surface to be close to the liquid temperature.
Since only the particles gather near the condensing rod 15, recondensing can be performed efficiently.

FIG. 5 is a sectional view showing a fifth embodiment of a superconducting magnet according to the present invention. The same parts as those in FIG. 1 are denoted by the same reference numerals, and the description thereof will be omitted.

In the fifth embodiment, as shown in FIG. 5, a heater 19 is provided in the helium container 4 so as to be immersed in the liquid helium, and the gas pressure is set in the atmosphere of the helium gas 7 in the helium container 4. Is provided, a heater 19 is connected to a heater power supply 21 via a lead wire led out of the vacuum vessel 6, and a measuring section of the pressure measuring means 20 is led out of the vacuum vessel 6. And a heater power supply 21 and a pressure controller 22 respectively.

In this case, when the pressure measured by the pressure measuring means 20 becomes equal to or less than the preset pressure, the pressure controller 22 activates the heater power supply and activates the heater 19 until the pressure reaches a separately preset pressure. Is to be heated.

According to the fifth embodiment having the above-described structure, the heater 19 is heated to evaporate the liquid helium, and the helium container 4 is adjusted so as not to be lower than the atmospheric pressure. It can be a superconducting magnet that can be operated for a long time.

FIG. 6 is a cross-sectional view showing a sixth embodiment of the superconducting magnet according to the present invention. The same parts as those in FIG. 1 are denoted by the same reference numerals, and the description thereof will be omitted.

In the sixth embodiment, a liquid level measuring means 8 for measuring a helium liquid level is provided inside a helium container 4 as shown in FIG. Input to a level gauge 23, and both ends of the superconducting coil 1 are connected to an excitation power supply 24 outside the vacuum vessel 6, and a voltmeter 25 for measuring the excitation voltage is provided.
3. An excitation power supply 24 and a voltmeter 25 are connected to a control device 26.

Here, the controller 26 causes the liquid level measuring means 8 to measure the liquid level through the liquid level meter 23 at a preset time interval, and when the exciting voltage is detected by the voltmeter 25, The liquid level measurement means 8 is operated as needed. Further, when the liquid level measured by the liquid level measuring means 8 falls below a certain set value, an interlock signal can be sent to the excitation power supply 24.

According to the sixth embodiment having the above-described structure, the excitation is automatically sensed while the heat load in the helium container 4 is minimized by intermittently operating the liquid level measuring means 8. The liquid level can be measured at any time, and the occurrence of quenching due to lack of liquid helium 2 can be suppressed.

FIG. 7 is a circuit diagram showing a seventh embodiment of the superconducting magnet according to the present invention. The same parts as those in FIG.

In the seventh embodiment, superconducting coil 1 has oxide superconducting current leads 9 connected to both ends thereof and is housed inside a cryostat. The oxide superconducting current lead 9 is led out of the cryostat and is connected via a circuit breaker 11 to an excitation power supply 10 for exciting the superconducting coil 1.

The excitation power supply 10 and circuit breaker 11 are connected to a control device 12.

As the protection circuit, the superconducting coil 1
One end of the auxiliary lead 27 is connected between both ends of the auxiliary superconducting current lead 9 and the other end thereof is led out of the cryostat. A discharge resistor 14 is connected between the lead terminals to form a protection circuit. I have.

In such a superconducting magnet protection circuit, when a quench is detected, the circuit breaker disconnects the excitation circuit by a signal from the control device 12, and the current flowing from the excitation power supply 10 is commutated to the protection circuit. . In the case of normal excitation, of the current supplied from the excitation power supply 10, the protection circuit has a shunt of I = V / R corresponding to the excitation voltage (V) and the discharge resistor 14 (R). It generates heat at 14,
Since the discharge resistor 14 is outside the cryostat, there is no particular problem.

According to the present embodiment, by connecting the auxiliary leads 27 to both ends of the superconducting coil 1, the discharge resistor 14 can be installed outside the cryostat. It is not necessary to install the protection circuit, and a highly reliable protection circuit can be obtained.

FIG. 8 is a circuit diagram showing an eighth embodiment of a superconducting magnet according to the present invention. The same parts as those in FIG. 7 are denoted by the same reference numerals, and the description thereof will be omitted.

In the eighth embodiment, as shown in FIG. 8, a protection circuit is formed by connecting a current controller 28 in series with the discharge resistor 14 between the lead terminals of the auxiliary lead 27 led out of the cryostat. , The current controller 28 can be controlled by the controller 12.

In this case, the current control section 28 is an element or a circuit for controlling the current by a signal from the control device 12, and is constituted by a one-way current control element such as a thyristor.

In the superconducting magnet protection circuit having the above-described configuration, when a quench is detected while the superconducting coil 1 is energized, the current control unit 28 is short-circuited by a signal from the control device 12. Thereafter, the circuit breaker 1 disconnects the excitation circuit by a signal from the control device 12, and the current flowing from the excitation power supply 10 to the superconducting coil 1 is diverted to the protection circuit. Energy is consumed by heat generation.

According to the eighth embodiment, since the current control unit 28 is provided, the current does not shunt to the protection circuit during normal excitation.
The current actually flowing in the superconducting coil 1 always coincides, and the superconducting magnet can have a fast response.

FIG. 9 is a circuit diagram showing a ninth embodiment of the superconducting magnet according to the present invention. The same parts as those in FIG. 8 are denoted by the same reference numerals, and the description thereof will be omitted.

In the ninth embodiment, as the current control unit 28 connected in series with the discharge resistor 14, a one-way current control element such as a diode, or a thyristor 19 when the voltage exceeds a certain set voltage as shown in FIG. The self-ignition type circuit designed so that the ignition signal is automatically input to the control circuit 12 eliminates the control by the control device 12.

According to the ninth embodiment having the above-described configuration, there is no malfunction due to failure of the signal processing in the control device 12 or the like, and a protection circuit with high safety can be provided.

In the above, the current control unit 28 having the circuit configuration as shown in FIG. 10 which is not controlled by the signal from the control device 12 is used. However, in the ninth embodiment, the current control unit 28 is As shown in FIG. 11, a current control element such as a thyristor 29 that controls the current by a signal from the control device 12 and a current control circuit that short-circuits when the voltage exceeds a certain set voltage are used in parallel. Is also good.

In the superconducting magnet protection circuit having the above-described configuration, when a quench is normally detected in the same manner as in the eighth embodiment, the current control unit 28 is short-circuited. The self-ignition type current control circuit is short-circuited by the voltage generated at both ends of the current control unit 28, so that the function as the protection circuit is not lost.

The use of the current control unit 28 having such a configuration makes it possible to duplicate the precise control in which the current control is performed by the signal of the control device 12 and the control in which the current control is performed passively such as a self-ignition type current control circuit. Thus, a protection circuit having safety can be obtained.

Further, a current control unit 28 having a circuit configuration as shown in FIG. 12 may be used in which the current control units having the circuit configuration shown in FIG.

If the current control unit having such a configuration is used,
A protection circuit for the superconducting magnet that can cope with both forward and reverse excitation directions can be provided.

FIG. 13 shows a tenth embodiment of the superconducting magnet according to the present invention.
It is sectional drawing which shows the structure of the electric current introduction terminal part in embodiment.

In the tenth embodiment, as shown in FIG. 13, a current introduction terminal 30 for penetrating the inside and outside of the cryostat to introduce a current into the superconducting coil inside the cryostat is provided. A cover 31 for preventing electric shock is provided on the atmosphere side of the introduction terminal 30.
And the cover 31 is provided with a blower 32.

Since the cover 31 is provided with an exhaust outlet 33 and forms a ventilation passage, air can be efficiently blown to the current introduction terminal 30. The current introduction terminal 30 is cooled by heat transfer from the inside of the cryostat, and may have a temperature lower than the dew point.
2 keeps the temperature close to the ambient temperature, so that no water drops are formed.

According to the tenth embodiment having the above structure,
By preventing water droplets from attaching to the current introduction terminal 30,
Good ground insulation.

[0096]

As described above, according to the superconducting magnet of the present invention, the capacity of the refrigerator can be effectively used, and
Safety and reliability can be improved, and the displacement caused by cooling the refrigerator and the helium container can be absorbed.

According to the superconducting magnet protection circuit of the present invention, it is possible to protect the superconducting coil without installing a semiconductor such as a diode in the cryostat and to prevent water droplets from adhering to the outer surface of the current introducing terminal. Thus, the soundness of the ground insulation can be maintained.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a first embodiment of a superconducting magnet according to the present invention.

FIG. 2 is a sectional view showing a second embodiment of a superconducting magnet according to the present invention.

FIG. 3 is a sectional view showing a third embodiment of the superconducting magnet according to the present invention.

FIG. 4 is a sectional view showing a fourth embodiment of a superconducting magnet according to the present invention.

FIG. 5 is a sectional view showing a superconducting magnet according to a fifth embodiment of the present invention.

FIG. 6 is a sectional view showing a superconducting magnet according to a sixth embodiment of the present invention.

FIG. 7 is a circuit diagram showing a superconducting magnet according to a seventh embodiment of the present invention.

FIG. 8 is a circuit diagram showing an eighth embodiment of a superconducting magnet according to the present invention.

FIG. 9 is a circuit diagram showing a ninth embodiment of a superconducting magnet according to the present invention.

FIG. 10 is a circuit diagram showing a configuration example of a current control unit in the embodiment.

FIG. 11 is a circuit diagram showing another configuration example of the current control unit in the embodiment.

FIG. 12 is a circuit diagram showing still another example of the configuration of the current control unit according to the embodiment;

FIG. 13 is a cross-sectional view showing a configuration of a current introducing terminal in a superconducting magnet according to a tenth embodiment of the present invention.

FIG. 14 is an explanatory diagram of cooling characteristics of a refrigerator used for a superconducting magnet employing a recondensing type.

FIG. 15 is a sectional view showing an example of a superconducting magnet employing a conventional recondensing type.

FIG. 16 is a circuit diagram showing an example of a superconducting magnet provided with a conventional protection circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Superconducting coil 2 ... Liquid helium 3 ... Refrigerator 4 ... Helium container 5 ... Radiation shield 6 ... Vacuum container 7 ... Gas helium 8 ... Liquid level measuring means 9 ... Oxide superconducting current lead DESCRIPTION OF SYMBOLS 10 ... Excitation power supply 11 ... Circuit breaker 12 ... Control device 13 ... Diode 14 ... Discharge resistance 15 ... Condensing rod 16 ... Elastic body 17 ... Flexible body 18 ... Convection prevention member 19 ... Heater 20 pressure measuring means 21 heater power supply 22 pressure controller 23 liquid level gauge 24 excitation power supply 25 voltmeter 26 control device 27 auxiliary lead 28 current control unit 29 ...... thyristor 30 ... current introduction terminal 31 ... cover 32 ... blowing means

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Mamoru Shimada 2-4-4 Suehirocho, Tsurumi-ku, Yokohama-shi, Kanagawa Prefecture Inside the Toshiba Keihin Plant (72) Inventor Tsutomu Kurusu 2--4, Suehirocho, Tsurumi-ku, Yokohama-shi, Kanagawa Address Toshiba Keihin Works Co., Ltd. (72) Inventor Takahiro Dobashi 2-4, Suehirocho, Tsurumi-ku, Yokohama-shi, Kanagawa Prefecture F-term (reference) 4M114 AA14 AA17 AA18 AA31 CC03 CC05 CC11 CC13 CC16 DA07 DA09 DA10 DA12 DA45 DA51 DB02 DB67

Claims (12)

[Claims] 1. A helium container storing liquid helium, a superconducting coil immersed in liquid helium in the helium container, and a radiation shield provided so as to surround the helium container. A vacuum vessel surrounding the helium container and the radiation shield and maintaining the inside thereof at a vacuum, and a refrigerator provided on the vacuum vessel side for cooling gas helium evaporated in the radiation shield and the helium container, respectively. In the superconducting magnet provided with the above, an opening of an appropriate size is provided on the upper surface of the helium container, and a condensing rod having a high thermal conductivity is fixed to the opening by projecting into a gas helium atmosphere in the helium container. A superconducting magnet, wherein the condensing rod is thermally connected to the cold conduction part of the refrigerator. 2. The superconducting magnet according to claim 1, wherein an amount of displacement of the condensing rod and a cold conduction part of the refrigerator caused by a difference in thermal contraction between the condensing rod and the opening of the helium container. A superconducting magnet characterized in that a condensing rod is fixed to a helium container with an elastic body capable of absorbing water interposed therebetween. 3. The superconducting magnet according to claim 1, wherein a displacement of the condensing rod and a cold conduction part of the refrigerator caused by a difference in heat shrinkage between the condensation rod and the cold conduction part of the refrigerator. A superconducting magnet characterized in that the condensing rod and the cold conduction part of the refrigerator are thermally connected to each other with a flexible body capable of absorbing an amount. 4. The superconducting magnet according to claim 1, wherein a convection preventing member is inserted into the opening of the helium container such that one end reaches near the liquid surface of the liquid helium, and is surrounded by the convection preventing member. A superconducting magnet, wherein the condensing rod is disposed on the superconducting magnet. 5. A helium container in which liquid helium is stored, a superconducting coil immersed in liquid helium in the helium container, and a radiation shield provided so as to surround the helium container. A vacuum vessel surrounding the helium container and the radiation shield and maintaining the inside thereof at a vacuum, and a refrigerator provided on the vacuum vessel side for cooling gas helium evaporated in the radiation shield and the helium container, respectively. A superconducting magnet comprising: a heater provided to be immersed in liquid helium in the helium container; and a pressure measurement provided in a gas helium atmosphere in the helium container to measure a pressure in the helium container. Means, controlling the heater in accordance with the pressure in the helium container measured by the pressure measuring means, Superconducting magnet, characterized in capital provided with the pressure regulator to maintain a pressure in the helium vessel to a predetermined pressure. 6. A helium container in which liquid helium is stored, a superconducting coil immersed in liquid helium in the helium container, and a radiation shield provided so as to surround the helium container. A vacuum vessel surrounding the helium container and the radiation shield and maintaining the inside thereof at a vacuum, and a refrigerator provided on the vacuum vessel side for cooling gas helium evaporated in the radiation shield and the helium container, respectively. A superconducting magnet comprising: a liquid level measuring means for measuring a liquid level of liquid helium in the helium container, a voltage measuring means for measuring an excitation voltage of the superconducting coil, and controlling a measurement timing by these measuring means. The liquid level is measured by the liquid level measuring means at a preset time interval, and the liquid level is measured by the voltage measuring means. Superconducting magnet, characterized by comprising a control device for measuring the needed liquid level was as sensitive to the excitation voltage by the liquid level measuring means. 7. A superconducting coil housed in a cryostat, an exciting power source installed outside the cryostat for exciting the superconducting coil, and an exciting power source installed in the cryostat and between the exciting power source and the superconducting coil. In a superconducting magnet composed of a current lead made of an oxide superconductor inserted in and a protection circuit connected in parallel to the superconducting coil, one end is connected between the superconducting coil and the current lead, A protection circuit for a superconducting magnet, comprising: a pair of auxiliary leads introduced outside the cryostat; and a discharge resistor connected in series outside the cryostat between the pair of auxiliary leads. 8. The superconducting magnet protection circuit according to claim 7, wherein a current control unit controlled by a control device is provided between said auxiliary lead in series with a discharge resistor. 9. The superconducting magnet protection circuit according to claim 7, wherein a self-control type current control section is provided between said auxiliary lead in series with a discharge resistor. 10. The superconducting magnet protection circuit according to claim 9, wherein the current control unit is a current control element or a current control circuit controlled by a voltage generated at both ends thereof. circuit. 11. The protection circuit for a superconducting magnet according to claim 7, wherein a current control element controlled by a control device in series with a discharge resistor between the auxiliary lead and a current control element controlled by a voltage generated at both ends. Alternatively, a protection circuit for a superconducting magnet, wherein a plurality of current control circuits are connected in parallel. 12. A superconducting magnet having a superconducting coil disposed inside a cryostat, wherein a current introducing terminal for passing a current through the superconducting coil in the cryostat is installed so as to penetrate from the inside of the cryostat to the outside. A superconducting magnet characterized in that a blowing means is provided so as to be able to blow toward the outside of the superconducting magnet.