JP2009032758A - Conduction cooled superconducting magnet system - Google Patents

Abstract

A conduction-cooled superconducting magnet apparatus is provided that is unlikely to quench a superconducting coil even if a power failure occurs.
A cryogenic refrigerator, a container containing a refrigerant, a superconducting coil immersed in the refrigerant, and both the container and the cryogenic refrigerator are in thermal contact, and heat between the two Heat conduction means for conducting heat, and when the cryogenic refrigerator is in operation, heat conduction between the container and the cryogenic refrigerator is performed via the heat conduction means, When the operation of the cryogenic refrigerator is stopped, the heat conduction between the container and the cryogenic refrigerator is interrupted by the shutting means provided in the heat transfer means, and from the outside The heat is prevented from flowing into the container through the heat transfer means and the refrigerant is evaporated.
[Selection] Figure 3

Description

  The present invention relates to a superconducting magnet device used in a nuclear magnetic resonance apparatus, and more particularly to a conduction-cooled superconducting magnet device for a nuclear magnetic resonance apparatus that cools a superconducting coil with a cryogenic refrigerator.

  In the measurement of nuclear magnetic resonance, it is necessary to apply a strong static magnetic field to the sample in order to observe a nuclide having a nuclear spin in the sample. Therefore, conventionally, a superconducting magnet device using liquid helium as a refrigerant as shown in FIG. 1 has been used.

  In the figure, 1 is a superconducting coil. The superconducting coil 1 is immersed in a helium tank 2 in which liquid helium is stored and maintained at a cryogenic temperature. Further, in order to suppress the liquid helium in the helium tank 2 from being lost by evaporation, a nitrogen tank 3 in which liquid nitrogen is stored for cooling the environment around the helium tank 2 is provided. The helium tank 2 and the nitrogen tank 3 are housed in a vacuum vessel 4 and are thermally shielded from the outside in order to prevent external heat from entering.

  The problem with such a superconducting magnet device using a refrigerant such as liquid helium or liquid nitrogen is that the refrigerant must be replenished periodically. This work is cumbersome and the superconducting coil will quench if it is forgotten to replenish, so it will put a great mental burden on the maintenance personnel of the superconducting magnet device depending on how to replenish the refrigerant during a long vacation or on a business trip. It was.

  In recent years, therefore, a conduction cooling superconducting magnet device that does not use a refrigerant such as liquid helium or liquid nitrogen has been proposed (Non-patent Document 1, Patent Documents 1 and 2). The conduction-cooled superconducting magnet device uses a cryogenic refrigerator to cool the superconducting coil, so that the superconducting state of the superconducting coil can be maintained with only electric power, even without the use of liquid helium or liquid nitrogen. It is designed to be able to.

  FIG. 2 shows an example of a conduction cooling superconducting magnet device for a nuclear magnetic resonance apparatus. In FIG. 2, this conduction cooling superconducting magnet device for nuclear magnetic resonance apparatus has a heat conduction effect in a vacuum vessel 5 that has been evacuated in order to avoid heat penetration from outside. A heat radiation shield chamber partitioned by the radiation shield plate 6 is provided, and the superconducting coil 7 is accommodated in the heat radiation shield chamber.

  Reference numeral 8 denotes a Gifford-McMahon type refrigerator (GM refrigerator) as a cryogenic refrigerator that cools the superconducting coil 7. The GM refrigerator 8 includes a first stage 8a and a second stage 8b. The first stage 8a is in thermal contact with the thermal radiation shield 6 that defines the thermal radiation shield chamber, and cools the thermal radiation shield 6 to 40 to 50K. The two-stage stage 8b is in thermal contact with the heat transfer plate 9, and is also in thermal contact with the superconducting coil 7 in thermal contact with the heat transfer plate 9 via the heat transfer plate 9. From the bottom, it is cooled to about 4K.

  Also, in the heat radiation shield chamber, the superconducting shim coil 10, which is indispensable for correcting the distortion of the static magnetic field generated by the superconducting coil 7, is in thermal contact with the heat transfer plate 9 when measuring nuclear magnetic resonance. , Provided.

  Further, outside the vacuum vessel 5, current is supplied to the refrigerator power source and the compressor 12, the excitation power source 13 for exciting the superconducting coil 7 and the superconducting shim coil 10 necessary for operating the GM refrigerator 8. Is provided with a superconducting shim power supply 14.

Mikami Yukio, Sakuraba Junji, Watazawa Keiichi et al., "Development of 15T Refrigerator Cooling Type Superconducting Magnet", Magazine "Cryogenic Engineering" (Cryogenic Engineering Association / Cryogenic Engineering Society), Vol. 34, No. 5, 1999 Published May 20, 2000, pages 200-205 JP 2001-77434 A JP 2004-259925 A

  Under such circumstances, one of the biggest problems when putting a conduction-cooled superconducting magnet device into practical use is that if the power failure occurs while the device is in operation, the refrigerator stops and the temperature of the superconducting coil rises. Along with this, quenching occurred.

In the nuclear magnetic resonance apparatus, extremely high magnetic field stability of 10 ⁻⁹ / hour or more is required. Therefore, once the superconducting magnet is quenched, it is brought into a stable state again after being excited, We have to wait for a few days to stabilize the magnetic field. Meanwhile, the device becomes unusable and the experiment stops.

  In addition, excitation of the superconducting magnet is a very specialized task and cannot be handled by general users. Therefore, every time a quenching occurred due to a power failure, we had to request a request from an expert.

  Therefore, by using both superconducting coil immersion in liquid helium without relying only on the refrigerator, liquid helium is present in the container even if the refrigerator stops operating due to a long-term power failure, etc. It is important to devise so that quenching does not occur during this period.

  In view of the above points, an object of the present invention is to provide a conduction-cooling superconducting magnet apparatus in which quenching of a superconducting coil hardly occurs even if a power failure occurs.

In order to achieve this object, a conduction cooling superconducting magnet device according to the present invention is:
A cryogenic refrigerator,
A container containing a refrigerant;
A superconducting coil immersed in the refrigerant;
A heat transfer means that is in thermal contact with both the container and the cryogenic refrigerator, and conducts heat between them;
A conduction-cooling superconducting magnet apparatus, comprising: a blocking means provided in the heat transfer means so as to block heat conduction between the container and the cryogenic refrigerator.

  In addition, the shut-off means is configured to use the container and the cryogenic refrigerator when the cryogenic refrigerator is operating based on a signal from a detecting means for detecting an operating state of the cryogenic refrigerator. When the operation of the cryogenic refrigerator is stopped, the heat conduction between the container and the cryogenic refrigerator is operated to be interrupted. .

  The detecting means is a means for monitoring at least one of the temperature rise of liquid helium, the pressure rise of the liquid helium container, or the stop of the refrigerator compressor with a sensor.

Also, a cryogenic refrigerator,
A superconducting coil installed in a vacuum vessel;
A heat transfer means that is in thermal contact with both the superconducting coil and the cryogenic refrigerator, and conducts heat between the two;
It is characterized by comprising a shut-off means provided in the heat transfer means so that heat conduction between the superconducting coil and the cryogenic refrigerator can be cut off.

  Further, the shut-off means is configured to detect the superconducting coil and the cryogenic coil when the cryogenic refrigerator is operating based on a signal from a detecting means for detecting an operating state of the cryogenic refrigerator. Operates to interrupt heat conduction between the superconducting coil and the cryogenic refrigerator when the cryogenic refrigerator is stopped while mediating heat conduction between the refrigerators. It is characterized by.

  Further, the detection means is a means for monitoring at least one of a temperature rise of the superconducting coil, a pressure rise in the vacuum vessel, or a stop of the refrigerator compressor with a sensor.

According to the conduction cooling superconducting magnet device of the present invention,
A cryogenic refrigerator,
A container containing a refrigerant;
A superconducting coil immersed in the refrigerant;
A heat transfer means that is in thermal contact with both the container and the cryogenic refrigerator, and conducts heat between them;
Since it is provided with a blocking means provided in the heat transfer means so that the heat conduction between the container and the cryogenic refrigerator can be blocked,
It has become possible to provide a conduction-cooled superconducting magnet device in which quenching of the superconducting coil hardly occurs even if a power failure occurs.

Also, a cryogenic refrigerator,
A superconducting coil installed in a vacuum vessel;
A heat transfer means that is in thermal contact with both the superconducting coil and the cryogenic refrigerator, and conducts heat between the two;
Since it is provided with a blocking means provided in the heat transfer means so that the heat conduction between the superconducting coil and the cryogenic refrigerator can be blocked,
It has become possible to provide a conduction-cooled superconducting magnet device in which quenching of the superconducting coil hardly occurs even if a power failure occurs.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 3 shows an embodiment of a conduction cooling superconducting magnet device for a nuclear magnetic resonance apparatus according to the present invention. In FIG. 3, this conduction cooling superconducting magnet device for a nuclear magnetic resonance apparatus has a heat conduction effect in a vacuum vessel 5 that has been evacuated in order to avoid heat penetration from outside. A heat radiation shield chamber partitioned by the radiation shield plate 6 is provided, a liquid helium container 21 is provided in the heat radiation shield chamber, and the superconducting coil 7 is accommodated.

  Reference numeral 8 denotes a Gifford-McMahon type refrigerator (GM refrigerator) as a cryogenic refrigerator that cools the superconducting coil 7. The GM refrigerator 8 includes a first stage 8a and a second stage 8b. The first stage 8a is in thermal contact with the thermal radiation shield 6 that defines the thermal radiation shield chamber via the first stage heat transfer plate 22, and cools the thermal radiation shield 6 to 40 to 50K. In addition, the second stage 8b is in thermal contact with the second stage heat transfer plate 23, and also with the liquid helium container 21 in thermal contact with the second stage heat transfer plate 23 via the second stage heat transfer plate 23. In thermal contact, the liquid helium container 21 is cooled to about 4K.

  Further, outside the vacuum vessel 5, a refrigerator power source and a compressor (not shown) necessary for operating the GM refrigerator 8, an excitation power source (not shown) for exciting the superconducting coil 7 and the like are provided. ing.

  In the superconducting magnet device having such a configuration, when the refrigerator is stopped, the heat flow into the superconducting coil section is such that the first stage heat transfer plate 22 connecting the refrigerator 8 and the liquid helium vessel 21 and the second stage. The heat transfer plate 23 is the main path. It is estimated that about 80% of the inflow heat amount flows through the refrigerator.

  The stoppage of the refrigerator can be detected by monitoring the temperature rise of the liquid helium, the pressure increase in the liquid helium container, the stoppage of the refrigerator compressor, and the like with a sensor. Usually, a conduction cooling superconducting magnet apparatus equipped with a refrigerator is operated at 4K or lower, and when an abnormality occurs, the temperature rises to 4K or higher. The superconducting magnet device provided with the liquid helium container is provided with a safety valve 24 so that a slight pressure is applied to the liquid helium. When an abnormality occurs, the pressure in the liquid helium container becomes 1 This is because it rises above atmospheric pressure.

  Therefore, in order to block the main heat inflow path when the refrigerator is stopped, the first stage heat transfer switch is connected to the first stage heat transfer plate 22 connecting the first stage 8a of the refrigerator and the heat radiation shield 6. 25, and a two-stage heat transfer switch 26 is installed on the two-stage heat transfer plate 23 connecting the second stage 8b of the refrigerator and the liquid helium container 21. Both the switches are normally brought into thermal contact with each other so that the superconducting coil 7 is cooled.

  When an abnormality is detected by the sensor, for example, the two heat transfer switches 25 and 26 are thermally separated using a heat transfer switch drive mechanism 27 installed on the upper part of the conduction cooling superconducting magnet device. As a method of separation, the two heat transfer switches 25 and 26 may be moved upward by several millimeters.

  As a specific structure of the heat transfer switch, two plates on a flat plate as shown in FIG. 3 may be simply brought into contact, but a cup-like structure having an inclination as shown in FIG. A method of giving a stronger contact by utilizing the spring property of metal is also conceivable.

  Usually, since the heat transfer switch drive mechanism 27 (motor, etc.) is provided in the room temperature atmosphere, the heat transfer switch is driven by a cylindrical rod made of glass epoxy resin or the like having high heat insulation so as not to transmit heat from the outside. Turn on / off using.

  Since the superconducting coil 7 is housed in the vacuum vessel 5, substantially no heat is transferred unless a heat transfer switch is connected. If the heat transfer switch is turned off, the inflow of heat from the outside can be suppressed, so that the consumption of liquid helium can be suppressed and the superconducting state retention time can be extended by about five times. It corresponds to 10-25 days in terms of days. With this number of days, additional replenishment of liquid helium and repair of the refrigerator can be sufficiently performed, and quenching can be prevented.

  In this embodiment, a conduction-cooling superconducting magnet device of a type that uses a refrigerator and a liquid helium container has been described. However, the present invention is a type of conduction that further includes a liquid nitrogen container in the outer layer of the liquid helium container. The present invention can also be applied to a cooling superconducting magnet device or a type of conduction cooling superconducting magnet device that is cooled only by a refrigerator and does not have a liquid helium container itself.

  Also, in the case of a conduction-cooled superconducting magnet device that is cooled only by a refrigerator and does not have a liquid helium container itself, the operation of the refrigerator is stopped when the temperature of the superconducting coil itself rises and the superconducting coil is stored What is necessary is just to detect by the sensor monitoring the rise in pressure in the vacuum vessel or the stop of the refrigerator compressor.

  Moreover, although the case where the GM refrigerator was used was described in the said Example, it cannot be overemphasized that other refrigerators, such as a pulse tube refrigerator, can be substituted similarly.

  Can be widely used in nuclear magnetic resonance apparatus.

It is a figure which shows an example of the conventional superconducting magnet apparatus. It is a figure which shows an example of the conventional superconducting magnet apparatus. It is a figure which shows one Example of the superconducting magnet apparatus concerning this invention. It is a figure which shows one Example of the heat-transfer switch concerning this invention.

Explanation of symbols

1: superconducting coil, 2: nitrogen tank, 3: helium tank, 4: vacuum vessel, 5: vacuum vessel, 6: thermal radiation shield plate, 7: superconducting coil, 8: refrigerator, 8a: one stage, 8b: two-stage stage, 9: heat transfer plate, 10: superconducting shim coil, 11: refrigerator power supply, 12: compressor, 13: superconducting coil excitation power supply, 14: superconducting shim coil excitation power supply, 21: liquid helium container 22: 1 stage heat transfer plate, 23: 2 stage heat transfer plate, 24: safety valve, 25: 1 stage heat transfer switch, 26: 2 stage heat transfer switch, 27: heat transfer switch drive mechanism

Claims (6)

A cryogenic refrigerator,
A container containing a refrigerant;
A superconducting coil immersed in the refrigerant;
A heat transfer means that is in thermal contact with both the container and the cryogenic refrigerator, and conducts heat between them;
A conduction-cooling superconducting magnet apparatus, comprising: a blocking means provided in the heat transfer means so as to block heat conduction between the container and the cryogenic refrigerator. When the cryogenic refrigerator is operating based on a signal from the detecting means for detecting the operating state of the cryogenic refrigerator, the blocking means is provided between the container and the cryogenic refrigerator. The heat conduction between the container and the cryogenic refrigerator is operated when the operation of the cryogenic refrigerator is stopped, and the heat conduction between the container and the cryogenic refrigerator is interrupted. 2. The conduction-cooling superconducting magnet device according to 1. 3. The conduction according to claim 2, wherein the detection means is means for monitoring at least one of a temperature increase of liquid helium, a pressure increase of the liquid helium container, or a stop of the refrigerator compressor with a sensor. Cooling superconducting magnet device. A cryogenic refrigerator,
A superconducting coil installed in a vacuum vessel;
A heat transfer means that is in thermal contact with both the superconducting coil and the cryogenic refrigerator, and conducts heat between the two;
A conduction-cooling superconducting magnet apparatus, comprising: a blocking means provided in the heat transfer means so as to block heat conduction between the superconducting coil and the cryogenic refrigerator. When the cryogenic refrigerator is operating based on a signal from a detecting means for detecting an operating state of the cryogenic refrigerator, the shut-off means is configured to use the superconducting coil and the cryogenic refrigerator. When the operation of the cryogenic refrigerator is stopped, the heat conduction between the superconducting coil and the cryogenic refrigerator is operated to be interrupted. The conduction cooling superconducting magnet device according to claim 4. 6. The detecting means according to claim 5, wherein at least one of the temperature rise of the superconducting coil, the pressure rise in the vacuum vessel, or the stop of the refrigerator compressor is monitored by a sensor. Conductive cooling superconducting magnet device.

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