JP2019161060A - Superconducting magnet device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a superconducting magnet device which suppresses a temperature rise of a superconducting coil during PCS control and shortens a recooling time without using a refrigerator having a large refrigerating capacity. A superconducting magnet device 20 having a superconducting coil 5 housed in an adiabatic vacuum vessel 2 and a permanent current switch 10 thermally connected to the superconducting coil 5 and composed of a high-temperature superconductor. The permanent current switch 10 has a structure in which the cooling device 1 is cooled directly or via a superconducting coil 5, the permanent current switch 10 is provided with a heating means 11 for raising the temperature, and the superconducting coil 5 and the permanent current switch 10 are provided. It is connected by a permanent current switch cooling plate 12, and the permanent current switch cooling plate 12 has a cross-sectional area of the heat transfer path of the permanent current switch cooling plate 13 on the superconducting coil side as compared with the permanent current switch cooling plate 14 on the permanent current switch side. It is characterized by being enlarged. [Selection diagram] Fig. 1

Description

  Embodiments described herein relate generally to a superconducting magnet apparatus including a permanent current switch that forms a closed circuit through which a permanent current caused by superconducting flows.

  The superconducting magnet allows a large current to flow through the electromagnet due to the characteristic of zero electric resistance, so that the electromagnet can be greatly reduced in size when compared with a higher magnetic field or the same magnetic field than a permanent magnet or a normal electromagnet. Widespread use in equipment is expected through the development of wire, coiling technology, and cryogenic technology.

  The permanent current switch (hereinafter referred to as PCS) is necessary to form a closed loop inside the magnet after the high temperature superconducting magnet is excited by an external power source or the like, and to stop the current supply from the power source. If the electric resistance is 0, the current is literally a permanent current, but in actuality, it attenuates with a constant time constant because of a very small resistance such as a connection resistance. However, since the resistance is generally on the level of nano Ω, it is possible to energize and generate a magnetic field for several days or more.

The PCS includes a superconductor, a heater that is a heating means for raising the temperature of the superconductor, a refrigerator and a PCS cooling plate for cooling the superconductor. The PCS high-temperature superconductor is connected in parallel to the superconducting coil and the external power supply. When an external power source excitation, so that no current flows through the PCS, PCS heater by raising the temperature to a critical current (T _C) or more, so that no current flows only to the superconducting coil side by normal conductive resistance (OFF resistance). After the rated current is applied, the PCS heater is turned off and the PCS temperature is cooled to Tc or lower. When the power supply current is lowered in this state, the current is shunted to the PCS side, and when the power supply current becomes zero, the closed loop formed by the superconducting coil and the PCS becomes the permanent current mode.

  As described above, when the PCS is heated by the heater in the procedure for setting the permanent current mode, heat is transferred to the refrigerator or the superconducting coil via the PCS cooling plate for cooling the PCS, and the temperature is increased. There is a possibility.

  On the other hand, when the heater energization of the PCS is set to 0 and the PCS is re-cooled to the same temperature range as that of the coil, it is cooled via this cooling plate. Therefore, it takes a long time to recool.

  Therefore, the heat transfer characteristics required for the PCS cooling plate, which is contradictory to the above, are designed so as to have a heat penetration amount commensurate with the refrigerating capacity of the refrigerator and an allowable recooling time.

Japanese Patent No. 459498 Japanese Patent No. 4896620

  In order to satisfy both the contradictory design conditions of the PCS cooling plate, that is, the reduction in temperature rise of the superconducting coil and the shortening of the PCS recooling time, the refrigeration capacity of the refrigerator must be increased. However, excessive refrigerators that are not necessary during normal operation will be installed based on the limited specification conditions when controlling the PCS, resulting in higher costs, larger magnets, increased power consumption, etc. It will be connected.

  The purpose of this patent is to obtain a superconducting magnet device that can suppress the temperature rise of the superconducting coil during PCS control and shorten the recooling time without using a refrigerator having a large refrigerating capacity.

  The present embodiment includes a superconducting coil housed in a heat insulating vacuum vessel, a permanent current switch thermally connected to the superconducting coil and configured by a high-temperature superconductor, and the superconducting coil and the permanent current switch with respect to an excitation power source. A superconducting magnet device having a current lead connected in parallel with each other, wherein the permanent current switch is cooled by a cooling device directly or via the superconducting coil, and the permanent current switch is used for increasing the temperature. A heating means is provided, and the superconducting coil and the permanent current switch are connected by a permanent current switch cooling plate, and the permanent current switch cooling plate is connected to the permanent current switch cooling plate on the high temperature superconducting coil side. The cross-sectional area of the heat transfer path is larger than that of the cooling plate.

  Embodiment of this invention can suppress the temperature rise of the superconducting coil at the time of permanent current switch control, and can shorten recooling time, without making it a refrigerator with big freezing capacity.

1 is a schematic longitudinal sectional view of a superconducting magnet device showing Example 1. FIG. The graph which shows the calculation result of the temperature change of the PCS cooling plate in the PCS recooling which assumed the prior art example. The graph which shows the calculation result of the temperature change of the PCS cooling plate at the time of PCS recooling by Example 1. FIG. The graph which shows the calculation result of the temperature change of the PCS cooling plate of the other shape at the time of PCS recooling by Example 1. FIG. The graph which compares and shows the calculation result of the recooling time shortening effect of PCS by Example 1 by cross-sectional area ratio. The graph which compares and shows the calculation result of the recooling time shortening effect of PCS by Example 1 by the length ratio of a low temperature side / high temperature side cooling plate. The PCS cooling plate in Example 2 is shown compared with a prior art example, (a) is a schematic diagram which shows a prior art example, (b) shows Example 2, respectively. FIG. 10 is a schematic view of a permanent current switch cooling plate according to a sixth embodiment.

  Embodiments of a superconducting magnet apparatus according to the present invention will be described below with reference to the drawings.

Example 1
Hereinafter, Example 1 will be described with reference to FIG.

  FIG. 1 is a schematic longitudinal sectional view of a superconducting magnet device 20 having a permanent current switch (PCS) 10 and capable of a permanent current mode.

  In FIG. 1, a cryogenic refrigerator cold head 1 is attached to an adiabatic vacuum vessel 2 and is composed of a high-temperature superconducting wire through a radiation shield plate 3 in a first stage cooling section and a superconducting coil cooling plate 4 in a second stage cooling section. The superconducting coil 5 is cooled to a very low temperature. A current is connected and supplied from an external power source (not shown) to the vacuum introduction terminal 6, and the superconducting coil 5 and the PCS 10 can be energized through the current lead 7 in the adiabatic vacuum vessel 2.

  Superconducting coil 5 and permanent current switch heater (PCS heater) 11 are connected in parallel to the power source. A superconducting coil 5 to a superconducting coil connecting line 8 and a permanent current switch (PCS) connecting line 9 from the PCS 10 side are connected in parallel to the low temperature side tip of the current lead 7. Although not shown in the figure, the current lead 7 is insulated and thermally connected to the first-stage cooling unit and the second-stage cooling unit of the refrigerator and cooled to suppress the temperature rise of the superconducting coil 5 and the PCS 10. . In addition, a high-temperature superconductor is usually used for the current lead 7 between the first-stage and second-stage cooling sections, and the current lead 7 has a design that combines high current, low resistance, and heat insulation. The PCS 10 composed of a high-temperature superconductor is configured such that the cooled superconducting coil 5 can be cooled to the same level as the temperature of the superconducting coil 5 through a permanent current switch (PCS) cooling plate 12 thermally. The PCS cooling plate 12 is provided with a permanent current switch (PCS) heater 11 for raising the temperature in order to change the PCS from a superconducting state (resistance 0) to a normal state (having normal resistance). Although not shown in the figure, the heater is energized through the superconducting coil connection line 8 by an external power supply for the heater, and the temperature is increased to a predetermined temperature by a predetermined heat generation.

  After the temperature rises, the PCS heater 11 cools the PCS 10 to the same level as the superconducting coil 5, and the closed loop of the superconducting coil 5 and the PCS 10 (the current lead 7 for connection and the superconducting connection line 8 are also configured in the closed loop. However, in this series of cooling, temperature rise, and recooling, the PCS cooling plate 12 must be designed in consideration of the coil temperature rise and shortening of the recooling time as described above. It becomes.

The PCS cooling plate 12 is controlled so that the temperature of the PCS 10 is equal to or higher than the critical temperature of the PCS 10 while suppressing the maximum heat penetration amount Q _max or less which is the upper limit value of the temperature rise of the superconducting coil 5 when the PCS heater 11 is applied. The PCS cooling plate 12 represented by the formula (1) is used.

Q _max = (S / L) × ∫λdT (1)

  Here, S is the cross-sectional area of the PCS cooling plate 12, L is the length of the PCS cooling plate 12, λ is the thermal conductivity of the PCS cooling plate 12, integral is related to temperature, and the lower limit value is the temperature rise of the PCS 10 The temperature and the upper limit value are the temperatures on the superconducting coil 5 side.

  The maximum S / L allowed is determined by the above equation (1). Therefore, the subsequent recooling time is shortest when the PCS cooling plate 12 having the maximum S / L value is used, but it cannot be recooled in a shorter time. The normal design is to suppress the temperature rise of the superconducting coil as much as possible, and considering the safety factor, it is necessary to make the PCS cooling plate 12 with a smaller S / L, in which case the recooling time increases. .

  Therefore, in FIG. 1, in the temperature dependence of the thermal conductivity of the PCS cooling plate 12, the characteristic that the thermal conductivity peaks at the 10 K level is used as the characteristic of the high purity metal, and half the PCS on the superconducting coil side. The cooling plate (coil side PCS cooling plate) 13 is configured to have a larger cross-sectional area S than the PCS 10 side half PCS cooling plate (PCS side PCS cooling plate) 14.

  In the state where the temperature of the PCS 10 is raised, most of the thermal resistance is handled by the PCS cooling plate 14 on the PCS side, and together with the small thermal resistance of the PCS cooling plate 13 on the coil side, Set to have the same or similar thermal resistance.

  When the coil-side PCS cooling plate 13 and the PCS-side PCS cooling plate 14 having different cross-sectional areas are re-cooled, the coil-side PCS cooling plate 13 is heated more than the coil-side temperature of the PCS cooling plate in the conventional example. Since the resistance is small, the PCS 10 is cooled while the temperature is transiently kept low. At this time, the thermal conductivity of the PCS cooling plate 12 becomes a high value due to the temperature dependence of the thermal conductivity of the metal. If the temperature difference is the same, the PCS 10 can be cooled with a large amount of heat.

  Here, the examination result in the specific example which shows an actual effect is shown.

The superconducting coil 5 is kept at 20K and the PCS 10 is kept at 100K (when a heater is applied), and a pure aluminum plate having a residual resistance ratio (RRR) = 3000 is used as a PCS cooling plate assuming a connected conventional example. The PCS cooling plate 12 was shaped as shown in FIG. 7A so that the intrusion amount was 4 W.
PCS cooling plate 12 shape: t0.5mm × W10mm × L200mm

  Note that the heat capacity of the PCS 10 varies depending on the design, and is calculated here as 2 g of aluminum. FIG. 2 shows a time course in which the PCS 10 cools to about 20 K (here, 25 K) of the superconducting coil temperature immediately after the heater is turned off.

  The horizontal axis of the graph indicates time (seconds), and the vertical axis indicates temperature (K). In the graphs, the maximum temperature is PCS10, the minimum temperature (20K) is the superconducting coil 5, and the interval This graph shows the temperature change of the PCS cooling plate 12 every 25 mm. In this example, re-cooling takes 11.6 seconds.

On the other hand, FIG. 3 shows the examination results when the coil-side PCS cooling plate 13 and the PCS-side PCS cooling plate 14 have the following shapes.
PCS cooling plate 13 shape on the coil side: t2mm x W10mm x L100mm
PCS cooling plate 14 shape on the PCS side: t0.29mm x W10mm x L100mm

  Even in this case, when the PCS side is kept at 100K by the heater 11, the heat penetration amount into the 20K superconducting coil is 4 W, and the same calculation result as in the case of the PCS cooling plate assuming the conventional example is obtained. . On the other hand, the calculation result of the temperature change of each part immediately after turning off the heater 11 is shown in FIG. The time required for the PCS 10 to reach 25K is 10.7 seconds, which shortens the recooling time by 7% in terms of time.

Furthermore, the examination result at the time of setting it as the following cooling plate structure is also shown in FIG.
PCS cooling plate 13 shape on the coil side: t2mm x W10mm x L175mm
PCS cooling plate 14 shape on the PCS side: t0.08mm x W10mm x L25mm

  In this case, the time required for the PCS to reach 25K was 10.1 seconds, which was 13% shorter than the case of the PCS cooling plate assuming the conventional example.

  Combine the above considerations with the results of other cooling plate designs, and the horizontal axis is the cross-sectional area ratio of the cooling plates on the low temperature side / high temperature side (the length of each cooling plate is a constant condition of 100 mm), and the vertical axis FIG. 5 shows the calculation result when the recooling time up to 25K (when the conventional design is 100%) is taken. Further, FIG. 6 shows the result of assuming that the thickness of the cooling plate on the low temperature side is constant, the length ratio of the cooling plate on the low temperature side / high temperature side is taken on the horizontal axis, and the time reduction rate is similarly taken on the vertical axis.

  In Example 1, aluminum having a residual resistance ratio (RRR) of 3000 is used, and the results of study on the PCS cooling plate between the operating temperature of 20K and 100K are used to reduce the time even with the PCS cooling plate having the same heat penetration amount. It was shown that 13% can be achieved. This means that the temperature dependence of the thermal conductivity of the aluminum used as the PCS cooling plate is such that the lower the temperature, the higher the thermal conductivity in this temperature range, and the lower the temperature distribution of the PCS cooling plate during recooling. Thus, the re-cooling can be performed in a state of high thermal conductivity.

  Therefore, even if a metal such as copper, silver, indium, gold or the like having high purity (residual resistance ratio is higher than 100) having the same tendency as the above aluminum in the temperature dependence of the thermal conductivity is used as the cooling plate. The effect is obtained.

(Example 2)
In the first embodiment, the cross-sectional area of the PCS cooling plate is differentiated between the PCS cooling plate 13 on the coil side and the PCS cooling plate 14 on the PCS side. It was shown that the cooling characteristics can be improved. At that time, as a specific example, the calculation results are shown with a configuration in which the thickness of the cooling plate is changed. As the same technique, the width of the cooling plate may be changed, and the width of the coil side PCS cooling plate (low temperature side) may be increased. According to this configuration, the same effect as that shown in FIG. 4 can be obtained with respect to the conventional example. FIG. 7 shows a comparison of the shapes of PCS cooling plates with different widths.

  The thermal characteristics of the PCS cooling plate at this time indicate the same temperature change of the PCS cooling plate as long as the cross-sectional area is the same as in the first embodiment.

  Therefore, the same effect as in the first embodiment can be obtained.

(Example 3)
In Example 3, the thermal conductivity of the cooling plate is changed, and in particular, the thermal conductivity of the PCS side PCS cooling plate (high temperature side) 14 is lower than that of the coil side PCS cooling plate (low temperature side) 13. It is good also as a structure using these materials. According to this configuration, the same effect as that shown in FIG. 4 can be obtained with respect to the conventional example.

  The thermal characteristics of the PCS cooling plate at this time indicate the same temperature change of the PCS cooling plate as long as the cross-sectional area is the same as in the first embodiment.

  Therefore, the same effect as in the first embodiment can be obtained.

Example 4
In the fourth embodiment, the number of cooling plates having the same cross-sectional area is changed, and in particular, the number of PCS side PCS cooling plates (high temperature side) 14 is made smaller than the number of coil side PCS cooling plates (low temperature side) 13. It is good also as a structure to keep. According to this configuration, the same effect as that shown in FIG. 4 can be obtained with respect to the conventional example.

  The thermal characteristics of the PCS cooling plate at this time indicate the same temperature change of the PCS cooling plate as long as the cross-sectional area is the same as in the first embodiment.

  Therefore, the same effect as in the first embodiment can be obtained.

(Example 5)
In Example 5, the purity of the metal used for the PCS cooling plate 12 is changed, and in particular, the purity of the PCS cooling plate (high temperature side) 14 on the coil side is higher than that of the PCS cooling plate (low temperature side) 13 on the PCS side. It is good also as a structure using a material of purity. According to this configuration, the same effect as that shown in FIG. 4 can be obtained with respect to the conventional example.

  If the thermal characteristics of the PCS cooling plate at this time are the same as those of the first embodiment, the same temperature change of the PCS cooling plate is shown.

  Therefore, the same effect as in the first embodiment can be obtained.

(Example 6)
In the embodiments so far, in order to show the effect, the sectional area of the PCS cooling plate 13 on the coil side and the sectional area of the PCS cooling plate 14 on the PCS side are changed in two stages. It can be obtained even when the cross-sectional area is changed stepwise in the above-described steps or the cross-sectional area is continuously changed. FIG. 8 shows the width shape of the PCS cooling plate 12 shown in this example.

  FIG. 8 shows a schematic plan view or a longitudinal sectional view of the permanent current switch cooling plate according to the sixth embodiment.

  In the sixth embodiment, the cross-sectional area of the heat transfer path is continuously changed. In particular, the cross-sectional area of the heat transfer path of the PCS side PCS cooling plate (high temperature side) 14 is continuously changed to the coil side PCS cooling plate (low temperature). (Side) It is good also as a structure made smaller than the cross-sectional area of the heat-transfer path | route of 13th. According to this configuration, the same effect as that shown in FIG. 4 can be obtained with respect to the conventional example.

  The thermal characteristics of the PCS cooling plate at this time indicate the same temperature change of the PCS cooling plate as long as the cross-sectional area is the same as in the first embodiment.

  Therefore, the same effect as in the first embodiment can be obtained.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention.

  These embodiments can be implemented in various other forms, and various omissions, replacements, changes, and combinations can be made without departing from the scope of the invention.

  These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and the equivalents thereof.

DESCRIPTION OF SYMBOLS 1 ... Cryogenic cold machine 2 ... Heat insulation vacuum vessel 3 ... Radiation shield board 4 ... Superconducting coil cooling plate 5 ... Superconducting coil 6 ... Current introduction terminal 7 ... Current lead 8 ... Superconducting coil connection line 9 ... Permanent current switch (PCS) ) Connection line 10 ... Permanent current switch (PCS)
DESCRIPTION OF SYMBOLS 11 ... Permanent current switch (PCS) heater 12 ... Permanent current switch (PCS) cooling plate 13 ... Permanent current switch cooling plate (PCS cooling plate on the coil side)
14 ... Permanent current switch cooling plate (PCS cooling plate on the PCS side)
20 ... Superconducting magnet device

Claims (9)

A superconducting coil housed in an insulated vacuum vessel;
A permanent current switch thermally connected to the superconducting coil and constituted by a high-temperature superconductor;
A superconducting magnet device having a current lead for connecting the superconducting coil and the permanent current switch in parallel to the excitation power source,
The permanent current switch is structured to be cooled directly by a cooling device or via a superconducting coil, and the permanent current switch is provided with heating means for increasing the temperature,
The superconducting coil and the permanent current switch are connected by a permanent current switch cooling plate, and the permanent current switch cooling plate is connected to the permanent current switch cooling plate on the superconducting coil side than the permanent current switch cooling plate on the permanent current switch side. A superconducting magnet device having a larger cross-sectional area.   2. The superconducting magnet device according to claim 1, wherein a plate thickness of the permanent current switch cooling plate on the high temperature superconducting coil side is made thicker than a plate thickness of the permanent current switch cooling plate on the permanent current switch side.   3. The superconducting magnet device according to claim 1, wherein a plate width of the permanent current switch cooling plate on the superconducting coil side is wider than a plate width of the permanent current switch cooling plate on the superconducting permanent current switch side.   The thermal conductivity of the permanent current switch cooling plate on the superconducting permanent current switch side is made lower than the thermal conductivity of the permanent current switch cooling plate on the superconducting coil side. The superconducting magnet device according to item.   2. The superconducting magnet device according to claim 1, wherein the number of permanent current switch cooling plates on the superconducting permanent current switch side is smaller than the number of permanent current switch cooling plates on the superconducting coil side. The cross-sectional area of the heat transfer path of the permanent current switch cooling plate is continuously increased, or the heat transfer path cross-sectional area of the permanent current switch cooling plate on the superconducting coil side is increased by two or more steps. The superconducting magnet device according to any one of claims 1 to 4, wherein   2. The superconducting magnet device according to claim 1, wherein the permanent current switch cooling plate is made of a metal having a residual resistance ratio higher than 100.   8. The superconducting magnet device according to claim 7, wherein the metal having a residual resistance ratio higher than 100 is copper, aluminum, indium, silver, or gold. A superconducting coil housed in an insulated vacuum vessel;
A permanent current switch thermally connected to the superconducting coil and constituted by a high-temperature superconductor;
A superconducting magnet device having a current lead for connecting the superconducting coil and the permanent current switch in parallel to the excitation power source,
The permanent current switch is structured to be cooled directly by a cooling device or via a superconducting coil, and the permanent current switch is provided with heating means for increasing the temperature,
The superconducting coil and the permanent current switch are connected by a permanent current switch cooling plate, and this permanent current switch cooling plate is used as a permanent current switch cooling plate on the permanent current switch side. A superconducting magnet device characterized in that it is made of a metal having a purity higher than that of the metal.

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