JP2009267273A - Superconducting electromagnet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a superconducting electromagnet that detects a faulty state where pressure control does not operate normally to prevent a negative pressure from being produced in a helium bath, thereby avoiding freezing and blockage due to inflow of air. <P>SOLUTION: A superconducting electromagnet includes a pressure controller 13 that controls the amount of heat of a heater 14 according to the pressure in a helium bath 3 measured by a pressure sensor 12 so that the pressure in the helium bath 3 does not fall below atmospheric pressure. The superconducting electromagnet includes a state detecting means of determining whether the pressure controller 13 normally controls the pressure in the helium bath 3, and stops the operation of a refrigerator 9 when the detecting means detects a faulty state where the pressure controller does not work normally. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a superconducting electromagnet used for, for example, a magnetic resonance diagnostic imaging apparatus, a single crystal pulling apparatus, and an NMR analyzer.

  In general, in a superconducting electromagnet, it is essential to cool the superconducting coil and maintain it in a superconducting state. A liquid helium immersion type superconducting electromagnet maintains a superconducting state by immersing a superconducting coil in liquid helium and keeping it at a very low temperature. Liquid helium immersion type superconducting electromagnets include a type in which helium evaporated by heat intrusion is opened to the atmosphere, and a type in which helium is recondensed by a refrigerator. FIG. 9 shows a conventional recondensing type superconducting electromagnet.

  In the superconducting electromagnet shown in FIG. 9, the superconducting coil 1 is housed in a helium tank 3 and immersed in liquid helium. A heat shield 4 is disposed so as to surround the helium tank 3 to reduce heat intrusion due to radiation from the outside. Furthermore, the heat shield 4 is housed in a vacuum chamber 5 whose inside is kept in a vacuum, and prevents heat intrusion due to gas convection and conduction. A cryogenic container composed of the helium tank 3, the heat shield 4 and the vacuum tank 5 is called a cryostat 6.

  The cryostat 6 is designed to suppress the heat intrusion to the helium tank 3 as much as possible, but the heat intrusion to the helium tank 3 cannot be made completely zero. Therefore, the superconducting electromagnet has the refrigerator 9, and while cooling and recondensing the evaporated helium, the heat balance of the cryostat 6 can be made zero, and the consumption of liquid helium can be made zero. As the refrigerator 9, for example, a cryogenic refrigerator having an ability to liquefy helium, such as a Gifford-McMahon refrigerator (hereinafter referred to as a GM refrigerator) or a pulse tube refrigerator, is used. The refrigerator 9 has an expander 7 and a compressor 8 and is driven by an AC power supply 10.

  However, the refrigerating capacity of the refrigerator 9 and the amount of heat intrusion into the helium tank 3 are not necessarily balanced, and when the refrigerating capacity of the refrigerator 9 exceeds the amount of gas helium generated by evaporation The amount of gas helium condensed by the machine 9 exceeds the pressure, and the pressure inside the helium tank 3 decreases. When the pressure inside the helium tank 3 is below atmospheric pressure (hereinafter referred to as negative pressure), air is sucked in and freezes, which causes clogging of the piping. When the piping is clogged, for example, when the superconducting coil 1 in the helium tank 3 is quenched, the gas helium cannot be exhausted when the internal pressure suddenly rises, and in the worst case, the cryostat may be ruptured.

  For this reason, in the conventional superconducting electromagnet, the pressure sensor 12 for measuring the pressure in the helium tank 3 and the heater 14 attached to the inside of the helium tank 3 are interlocked by the pressure control device 13, and when the pressure decreases, the heater 14 is supplied with current. The helium tank 3 was evaporated by flowing and heated to increase the internal pressure of the helium tank 3 and controlled to maintain a constant pressure (hereinafter referred to as positive pressure) equal to or higher than the atmospheric pressure. Related technical documents include the following patent documents.

Japanese Patent Laid-Open No. 01-159576 JP 2006-165209 A JP 2001-143922 A JP 2006-352146 A JP 2007-019520 A

  In the prior art, the heater 14 is controlled by the pressure control device 13 according to the internal pressure of the helium tank 3 measured by the pressure sensor 12 so that the pressure inside the helium tank does not become atmospheric pressure or less, and the inside of the helium tank 3 is corrected. By maintaining the pressure, the inflow of air is prevented and icing is prevented. However, even if the pressure control does not work properly, such as a failure of the power supply that supplies power to the heater 14, a connection error, or an operation error. The refrigerator 9 has a problem of continuing operation. In such a case, unless the operator notices that, the inside of the helium tank 3 has a negative pressure, and air is sucked in, resulting in freezing.

  The present invention has been made to solve the above-mentioned problems, and when the pressure control is not operating normally, this is detected to prevent the inside of the helium tank from becoming negative pressure in advance. However, it is intended to prevent icing and blockage due to air inflow.

  A superconducting electromagnet according to the present invention includes a helium tank in which liquid helium is stored, a superconducting coil disposed by being immersed in the liquid helium in the helium tank, and a heat provided so as to surround the helium tank. Measures the pressure inside the helium tank, the vacuum tank surrounding the shield, the helium tank and the heat shield, the inside of which is kept in vacuum, the refrigerator that condenses the gas helium evaporated in the helium tank, and The amount of heat of the heater is determined according to the pressure inside the helium tank measured by the pressure sensor so that the pressure inside the helium tank and the pressure inside the helium tank are not less than atmospheric pressure. In a superconducting electromagnet equipped with a pressure control device to control, the pressure control device is in a state of controlling the pressure inside the helium tank Provided condition detecting means for detecting whether said is obtained so as to stop the operation of the refrigerator when not detected to control does not work.

  According to the superconducting electromagnet of the present invention, when the control of the pressure inside the helium tank does not work, this is detected and the operation of the refrigerator is stopped, so even if the pressure control is not working, By not creating a situation where only the refrigerator works, it is possible to prevent the inside of the helium tank from becoming negative pressure in advance, and it is possible to prevent icing and blockage due to air inflow.

Embodiment 1 FIG.
FIG. 1 is a block diagram showing a superconducting electromagnet according to Embodiment 1 of the present invention, and shows its internal pressure control device and internal pressure control method. In the drawings of the specification, the same reference numerals indicate the same or corresponding parts, and the description thereof may be omitted. In FIG. 1, 1 is a superconducting coil immersed in liquid helium, 2 is liquid helium for cooling the superconducting coil, 3 is a helium tank in which liquid helium is stored, and 4 is provided so as to surround the helium tank 3. The heat shield 5 is a vacuum tank that surrounds the helium tank 3 and the heat shield 4 and is kept in a vacuum, 6 is a cryostat, 7 is an expander, 8 is a compressor, 9 is gas helium evaporated in the helium tank 3 10 is an AC power supply, 11 is a refrigerator ON / OFF switch, 12 is a pressure sensor for measuring the pressure inside the helium tank 3, 13 is a pressure control device, and 14 is for heating the inside of the helium tank 3. Indicates a heater.

The superconducting coil 1 is formed by winding a superconducting wire using, for example, niobium titanium (NbTi), niobium 3 tin (Nb ₃ Sn) or the like as a superconducting material. The superconducting electromagnet obtains a desired magnetic field by passing a current through the superconducting coil 1, but in MRI or NMR, the strength of the output magnetic field is required to be spatially highly uniform, and the superconducting electromagnet external The superconducting coil 1 is not a single coil, but a plurality of divided superconducting coils (not shown) including those having opposite polarities are arranged so as to satisfy desired magnetic field characteristics. It becomes.

  In order to cool the superconducting coil 1, the superconducting coil 1 is immersed in liquid helium 2 and stored in a stainless steel helium tank 3. In order to reduce heat intrusion from the outside, the helium tank 3 is entirely surrounded by an aluminum heat shield 4 and further housed in a stainless steel vacuum tank 5, and the inside of the vacuum tank 5 is evacuated. The helium tank 3 is supported by a resin support material (not shown) such as glass epoxy having a small thermal conductivity. A cryogenic container designed to suppress heat penetration into these liquid helium tanks is called a cryostat 6.

  A cryostat 9 including an expander 7 and a compressor 8 is attached to the cryostat 6. The refrigerator 9 shown here is a cryogenic Gifford-McMahon refrigerator (GM refrigerator) for refrigerating by repeatedly compressing and expanding helium gas, but if it has the ability to liquefy helium, a pulse tube Other types of refrigerators such as refrigerators may be used. The expander 7 has two cooling stages having an absolute temperature of 4K and 40K, and is attached to an opening provided in the cryostat 6. The 4K cooling stage at the tip is inserted into the helium tank 3, and the 40K cooling stage in the middle is in thermal contact with the heat shield 4 to cool the heat shield 4. The refrigerator 9 receives power from the AC power supply 10 and operates.

  The refrigerator 9 and the AC power source 10 are connected to each other with a refrigerator ON / OFF switch 11 interposed therebetween, and the power supply to the refrigerator 9 is turned ON / OFF as necessary. The refrigerator ON / OFF switch 11 includes a relay (A contact) that is closed only when a relay drive signal is received. If there is no relay drive signal from the outside, the refrigerator ON / OFF switch 11 is connected to the refrigerator 9. The power supply is turned off. The pressure sensor 12 detects the pressure difference between the gas helium inside the helium tank 3 and the atmosphere, and sends a signal to the pressure control device 13. The heater 14 is installed on the surface of the refrigerator inside the helium tank 3, and heats the surface of the expander 7 under the control of the pressure control device 13. Although the heater 14 is installed on the surface of the refrigerator, the same effect can be obtained regardless of where the heater 14 is installed in the helium tank 3. Moreover, although the refrigerator ON / OFF switch 11 is represented as a device independent of the refrigerator, even if the function is incorporated in the refrigerator, the same effect is produced.

  Next, details of the pressure controller 13, the refrigerator ON / OFF switch 11, the pressure sensor 12, and the heater 14 will be described with reference to FIG. 2 showing a block diagram of the pressure controller 13. In FIG. 2, the signal from the pressure sensor 12 is input to the pressure control device 13, and then input to the A / D converter 21 and the heater current control circuit (heater heat amount control device) 22 inside the pressure control device 13. . Further, a pressure value display unit 24 and a communication control unit 25 are connected to the A / D converter 21, and the pressure value measured by the pressure sensor 12 is displayed on the pressure value display unit 24, and the computer system 26 is passed through the communication control unit 25. Sent to. The heater current control circuit 22 controls the current flowing from the DC power source 23 to the heater 14. The output of the DC power source, that is, the output of the first state detecting means 27 is output from the pressure control device 13 as a drive signal for the refrigerator ON / OFF switch 11.

Next, the operation will be described separately when the pressure control device 13 is powered on and off.
(1) When the power supply of the pressure control device 13 is in the ON state Since the DC power supply 23 operates, the drive signal of the refrigerator ON / OFF switch 11 that is the output of the first state detection means 27 is the direct current of the pressure control device 13. Output from the power source 23. Accordingly, the relay of the refrigerator ON / OFF switch 11 is closed, power is supplied to the refrigerator 9, and the refrigerator 9 operates.

(2) When the power supply of the pressure control device 13 is in an OFF state When the DC power supply 23 is not normal due to a power failure, failure, voltage drop or human error, etc. A drive signal for a certain refrigerator ON / OFF switch 11 is not output from the DC power supply 23 of the pressure control device 13. For this reason, the relay of the refrigerator ON / OFF switch 11 is opened, power is not supplied to the refrigerator, and the refrigerator 9 does not operate.

  In the case of (1), when the cooling capacity of the refrigerator 9 exceeds the amount of heat intruding into the helium tank 3, a heater current control circuit (heater) is used so that the pressure inside the helium tank 3 does not become below atmospheric pressure. The operation of the heat quantity control device) 22 causes an appropriate current to flow from the DC power source 23 to the heater 14, so that the refrigeration capacity of the refrigerator 9 is canceled by the heat generated by the heater 14, and the evaporation of the liquid helium 2 becomes dominant. The internal pressure of the tank 3 increases. On the contrary, when the pressure inside the helium tank 3 is high, the current flowing from the DC power source 23 to the heater 14 is reduced by the operation of the heater current control circuit 22, so that heat input by the heater 14 is reduced. Condensation becomes dominant, and the pressure inside the helium tank 3 decreases. As an operation of the heater current control circuit 22, for example, by defining a response of an energization current to the heater 14 with respect to a helium tank pressure value (positive pressure with respect to atmospheric pressure) as shown in FIG. Safe operation of the superconducting magnet is realized by maintaining a slight positive pressure of about 500 to 1000 Pa, which is about 1% of the atmospheric pressure.

  In the case of (2), since the refrigerator 9 is not operated in advance before the negative pressure is reached, the gas helium is not condensed and the inside of the helium tank 3 does not become a negative pressure. The conditions assumed here, “when the pressure control device 13 is not operating”, that is, when the control of the pressure inside the helium tank 3 does not work, are the cases where the DC power supply 23 does not operate or the pressure control device. There can be 13 failures.

  According to the present invention, even if the control of the pressure inside the helium tank 3 does not work, this is detected and the refrigerator automatically stops, and the inside of the helium tank 3 is prevented from becoming negative pressure in advance. Thus, the system of the pressure control device 13 and the refrigerator 9 can be provided with a function as a so-called interlock.

Embodiment 2. FIG.
FIG. 4 is a block diagram showing the configuration of the pressure control apparatus according to the second embodiment. The configuration diagram corresponding to FIG. 1 in the second to sixth embodiments is the same as that in the first embodiment. The second embodiment is different from the first embodiment in the internal configuration and operation of the pressure control device 13. In FIG. 4 showing the pressure control device, a signal from the pressure sensor 12 is inputted to the pressure control device 13 and then inputted to the A / D converter 21 and the heater current control circuit 22 inside the pressure control device 13. The heater current control circuit 22 controls the current flowing from the DC power source 23 to the heater 14. The output of the DC power source, that is, the output of the first state detection means 27 is output from the pressure control device 13 via the relay 42 as a drive signal for the refrigerator ON / OFF switch 11.

  The relay 42 is a relay (A contact) that is closed only when a drive signal is received, and maintains an open state in other cases. A heater connection confirmation circuit (second state detection means) 41 is connected to the heater 14 in parallel with the heater current control circuit 22, and an output from the heater connection confirmation circuit 41 becomes a drive signal for the relay 42. The heater connection confirmation circuit 41 measures the resistance value of the heater 14 and monitors the connection state. When the resistance of the heater 14 measured by the heater connection confirmation circuit 41 is within the specified value range, the heater 14 is determined to be in a normal connection state, and the heater connection confirmation circuit 41 outputs a signal for driving the relay 42. Therefore, even if the power supply of the pressure control device is in the ON state, if the connection of the heater 14 is not normal, the relay 42 is opened by the output of the heater connection confirmation circuit (second state detection means) 41, and the refrigerator ON / OFF The drive signal for the OFF switch 11 is not output.

  In the first embodiment, the relay of the refrigerator ON / OFF switch 11 is always turned on when the power supply of the pressure control device 13 is turned on. In the second embodiment, in addition to the above conditions, If the connection of the heater 14 is not in a normal state, the relay drive signal of the refrigerator ON / OFF switch 11 is not output from the pressure control device 13, and the refrigerator does not operate.

  As described above, according to the second embodiment, not only when the pressure control device 13 is not turned on, there is a mistake in the connection of the heater 14 that controls the pressure, or the heater 14 itself is damaged. Then, even when the heater 14 is not normal, the refrigerator is automatically stopped, and the function as a so-called interlock that prevents the inside of the helium tank 3 from becoming negative pressure is the heater 14, the pressure control device 13, and the freezer. The system of the machine 9 can be provided.

Embodiment 3 FIG.
FIG. 5 is a block diagram showing the configuration of the pressure control apparatus according to the third embodiment. The third embodiment is different from the first embodiment in the internal configuration and operation of the pressure control device 13. In FIG. 5 showing the pressure control device, a signal from the pressure sensor 12 is inputted to the pressure control device 13 and then inputted to the A / D converter 21 and the heater current control circuit 22 inside the pressure control device 13. The heater current control circuit 22 controls the current flowing from the DC power source 23 to the heater 14. The output of the DC power source, that is, the output of the first state detection means 27 is output from the pressure control device 13 via the relay 52 as a drive signal for the refrigerator ON / OFF switch 11.

  The relay 52 is a relay (A contact) that is closed only when a drive signal is received, and maintains an open state in other cases. A sensor connection confirmation circuit (third state detection means) 51 is connected to the pressure sensor 12, and an output from the sensor connection confirmation circuit 51 becomes a drive signal for the relay 52. The sensor connection confirmation circuit 51 monitors the connection state of the sensor 12. When the sensor connection confirmation circuit 51 determines that the connection state of the sensor 12 is normal, the sensor connection confirmation circuit 51 outputs a signal for driving the relay 52. Therefore, even if the power supply of the pressure control device is in the ON state, if the connection of the sensor 12 is not normal, the relay 52 is opened by the output of the sensor connection confirmation circuit (third state detecting means) 51, and the refrigerator ON / OFF The drive signal for the OFF switch 11 is not output.

  In the first embodiment, the relay of the refrigerator ON / OFF switch 11 is turned on whenever the power supply of the pressure control device 13 is turned on. In the third embodiment, in addition to the above conditions, If the connection of the pressure sensor 12 is not normal, the relay control signal of the refrigerator ON / OFF switch 11 is not output from the pressure control device 13, and the refrigerator does not operate.

  As described above, according to the third embodiment, not only when the power supply of the pressure control device is not turned on, there is a mistake in the connection of the pressure sensor 12 that controls the pressure, or the pressure sensor 12 is broken. Thus, even when the pressure sensor 12 is not normal, the refrigerator is automatically stopped, and the function as a so-called interlock for preventing the inside of the helium tank 3 from becoming negative pressure is the pressure sensor 12, the pressure control device 13, and The system of the refrigerator 9 can be provided.

Embodiment 4 FIG.
FIG. 6 is a block diagram showing the configuration of the pressure control apparatus according to the fourth embodiment. The fourth embodiment differs from the first embodiment in the internal configuration and operation of the pressure control device 13. In FIG. 6 showing the pressure control device, a signal from the pressure sensor 12 is inputted to the pressure control device 13 and then inputted to the A / D converter 21 and the heater current control circuit 22 inside the pressure control device 13. The heater current control circuit 22 controls the current flowing from the DC power source 23 to the heater 14. As in the first, second, and third embodiments, the DC power source 23 has a first state detection means, the heater 14 has a heater connection confirmation circuit (second state detection means) 41, and the pressure sensor 12 has a sensor connection confirmation. A circuit (third state detecting means) 51 is connected.

  Reference numeral 61 denotes a refrigerator ON / OFF control circuit that outputs a drive signal for the refrigerator ON / OFF switch. The refrigerator ON / OFF control circuit 61 receives three signals of the output voltage of the DC power source 23 (output of the first state detection means), the output of the heater connection confirmation circuit 41, and the output of the sensor connection confirmation circuit 51. Yes. The output of the refrigerator ON / OFF control circuit 61 is output to the refrigerator ON / OFF switch 11 and the refrigerator stop state warning display LED 62.

  The refrigerator ON / OFF control circuit 61 has all three input signals ON, that is, [1] DC power is ON, [2] heater 14 is connected normally, and [3] pressure sensor 12 is connected normally. The relay drive signal is output to the refrigerator ON / OFF switch 11 only when all the three conditions are satisfied. Thereby, the refrigerator does not operate except for the state in which all of the pressure control device 13, the heater 14, and the pressure sensor 12 related to the pressure control operate normally.

  The refrigerator ON / OFF control circuit 61 is in the state where any one of the three input signals is OFF, that is, [1] DC power supply is ON, [2] heater 14 is connected normally, and [3] pressure sensor 12 is connected. The refrigerator stop state warning display LED 62 is turned on when any of the normal conditions is not satisfied. Therefore, when there is an abnormality in any of the pressure control device 13, the heater 14, and the pressure sensor 12 related to the pressure control and the refrigerator is stopped, the refrigerator stop state warning display LED 62 is turned on, The situation can be notified to the operator and the investigation and resolution of the abnormal state can be promoted.

As described above, according to the fourth embodiment, when an abnormality occurs in any of the pressure control device 13, the heater 14, and the pressure sensor 12, the refrigerator can be automatically stopped, An abnormal condition can be notified to the operator, and prompt investigation and resolution of the cause can be promoted.
If the refrigerator is stopped for a long time, the liquid helium that cools the superconducting coil 1 evaporates, and eventually the superconducting coil 1 may develop into a superconducting breakdown (quenching) due to insufficient cooling. In the operation of the electromagnet, an alarm function that allows an operator to quickly notice that the refrigerator is stopped is important. In the fourth embodiment, a method is disclosed in which an LED is used to inform the operator of the refrigerator stop state. However, if the refrigerator stop state can be communicated to the operator, for example, a light bulb or a liquid crystal display device is used. Even if other display devices or alarm devices using sounds such as a buzzer are used, similar effects can be obtained.

Embodiment 5 FIG.
FIG. 7 is a block diagram showing the configuration of the pressure control device and the computer system in the fifth embodiment. The fifth embodiment is different from the first embodiment in the internal configuration and operation of the pressure control device 13 and the computer system 26. In FIG. 7, the signal from the pressure sensor 12 is input to the pressure control device 13 and then input to the A / D converter 21 and the heater current control circuit 22 inside the pressure control device 13. The A / D converter 21 is connected to the pressure value display unit 24 and the communication control unit 25.

  Reference numeral 61 denotes a refrigerator ON / OFF control circuit that outputs a drive signal for the refrigerator ON / OFF switch 11. The refrigerator ON / OFF control circuit 61 receives three signals: the output voltage of the DC power supply 23 (the output of the first state detecting means), the output of the heater connection confirmation circuit 41, and the output of the sensor connection confirmation circuit 51. Yes. The output of the refrigerator ON / OFF control circuit 61 is connected to the refrigerator ON / OFF switch 11 and the communication control unit 25. The communication control unit 25 is connected to a computer system 26 outside the pressure control device 13. A console 71 for operation by an operator is connected to the computer system 26.

  The refrigerator ON / OFF control circuit 61 is in the state where any one of the three input signals is OFF, that is, [1] DC power supply is ON, [2] heater 14 is connected normally, and [3] pressure sensor 12 is connected. A signal is output to the communication control unit 25 when any one of the normal conditions is not satisfied. The communication control unit 25 receives a signal from the refrigerator ON / OFF control circuit 61 and transmits it to the computer system 26 using a predetermined protocol. Therefore, when there is an abnormality in any of the pressure control device 13, the heater 14, and the pressure sensor 12 related to the pressure control and the refrigerator is stopped, the situation is indicated to the operator through the computer system 26 and the console 71. To help investigate and resolve abnormal conditions.

  As described above, according to the fifth embodiment, when an abnormality occurs in any of the pressure control device 13, the heater 14, and the pressure sensor 12, the refrigerator can be automatically stopped, and the abnormality The state can be notified to the operator through the operation console 71 of the computer system 26, and an early cause investigation and solution can be promoted.

Embodiment 6 FIG.
FIG. 8 is a block diagram showing the configuration of the pressure control device and the computer system in the sixth embodiment. The sixth embodiment differs from the first embodiment in the internal configuration and operation of the pressure control device 13 and the computer system 26. 7 is the same as FIG. 7 showing the fifth embodiment except for the computer system portion, and the description thereof will be omitted. In FIG. 8, the communication control unit 25 is connected to the computer system 26. The computer system 26 is connected to an external network 81 such as the Internet, for example, and a maintenance remote host 82 is connected to the end of the network.

  In the sixth embodiment, similarly to the fifth embodiment, the refrigerator is stopped in conjunction with abnormal operation of the DC power supply 23, the heater 14, and the pressure sensor 12, and the negative pressure in the helium tank 3 is prevented. Furthermore, in the sixth embodiment, when an abnormal state that stops the refrigerator 9 occurs, the pressure control device 13 causes the remote host 82 for maintenance via the communication control unit 25, the computer system 26, and the external network 81. Is notified that the refrigerator 9 has stopped. As a result, even when the operator or maintenance engineer is not near the superconducting electromagnet, the abnormal state of the superconducting electromagnet or the pressure control device 13 can be detected, and the cause can be investigated and solved early. it can.

It is a block diagram which shows the superconducting electromagnet in Embodiment 1 of this invention. 2 is a block diagram illustrating a configuration of a pressure control device in Embodiment 1. FIG. It is a figure which shows the heater current output of the pressure control apparatus in Embodiment 1. FIG. 6 is a block diagram illustrating a configuration of a pressure control device according to Embodiment 2. FIG. FIG. 10 is a block diagram illustrating a configuration of a pressure control device according to Embodiment 3. FIG. 10 is a block diagram illustrating a configuration of a pressure control device in a fourth embodiment. FIG. 10 is a block diagram illustrating a configuration of a pressure control device and a computer system in a fifth embodiment. It is a block diagram which shows the structure of the pressure control apparatus in Embodiment 6, and a computer system. It is a block diagram which shows the conventional superconducting electromagnet.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Superconducting coil 2 Liquid helium 3 Helium tank 4 Heat shield 5 Vacuum tank 6 Cryostat 7 Expansion tank 8 Compressor 9 Refrigerator 10 AC power supply 11 Refrigerator ON / OFF switch 12 Pressure sensor 13 Pressure control device 14 Heater 21 A / D conversion 22 Heater current control circuit

23 DC power supply 24 Pressure display unit 25 Communication control unit 26 Computer system 27 First state detection means
41 Heater connection confirmation circuit (second state detection means)
42 relay 51 sensor connection confirmation circuit (third state detection means)
52 Relay 61 Refrigerator ON / OFF control circuit 62 Refrigerator stop status warning LED 71 Console 81 External network 82 Remote host

Claims (6)

A helium tank in which liquid helium is stored;
A superconducting coil disposed by being immersed in liquid helium in this helium tank;
A heat shield provided to surround the helium bath;
A vacuum chamber that surrounds these helium baths and heat shield, and the inside is kept in vacuum;
A refrigerator that condenses the gas helium evaporated in the helium tank;
A pressure sensor for measuring the pressure inside the helium tank;
A heater for heating the inside of the helium tank;
In a superconducting electromagnet comprising a pressure control device that controls the amount of heat of the heater according to the pressure inside the helium tank measured by the pressure sensor so that the pressure inside the helium tank does not become atmospheric pressure or lower,
Provided with a state detecting means for detecting whether or not the control of the pressure inside the helium tank by the pressure control device works, and stops the operation of the refrigerator when it is detected that the control is not working A superconducting electromagnet characterized by being made to cause.   The superconducting electromagnet according to claim 1, wherein the operation of the refrigerator is stopped when it is detected by the state detection means that the power source for heating the heater is not normal.   The superconducting electromagnet according to claim 1 or 2, wherein the operation of the refrigerator is stopped when the state detecting means detects that the heater is not normal.   The superconducting electromagnet according to any one of claims 1 to 3, wherein the operation of the refrigerator is stopped when the state detection means detects that the pressure sensor is not normal.   The superconducting electromagnet according to any one of claims 1 to 4, further comprising means for warning the stop state of the refrigerator when the operation of the refrigerator is stopped by the output of the state detection means.   6. The system according to claim 1, wherein when the operation of the refrigerator is stopped by the output of the state detection means, the refrigerator stop state is reported to a computer system or a remote host through a network from the computer system. The superconducting electromagnet according to any one of the above.

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