JP2929773B2 - Current lead of superconducting magnet device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current lead for supplying a DC exciting current from an external power supply to a superconducting coil housed in a vacuum insulated container, and more particularly to a current lead using an oxide superconducting conductor for a low-temperature side lead. Cooling structure.

[0002]

2. Description of the Related Art Since a superconducting coil of a superconducting magnet device is cooled by a cryogenic refrigerant such as liquid helium to maintain a superconducting state, a liquid shield is provided in a vacuum shielded container having a radiation shield using liquid nitrogen or a multilayer heat insulating layer. It is stored in a immersed state. In addition, the current leads are cooled by the low-temperature helium gas, which vaporizes liquid helium due to the heat entering the low-temperature side, preventing the heat entering from the room temperature and the Joule heat generated by the current leads from entering the cryogenic part. It is configured to Conventionally, electric current conductors such as copper have been used as conductors for current leads.However, since copper is a good conductor at the same time as a good conductor, the heat that penetrates into the cryogenic part increases,
The vaporization loss of expensive liquid helium increases. Therefore,
A current lead that uses an oxide-based superconductor, which is a high-temperature superconductor, on the low-temperature side of the current lead to reduce the Joule heat to zero and at the same time significantly reduce the heat that penetrates into the cryogenic part by utilizing its low thermal conductivity. It has already been proposed by the present applicant (for example, Japanese Patent Application No. 2-84252). Further, since an oxide-based superconducting conductor exhibits a superconducting phenomenon when cooled to a temperature of liquid nitrogen or lower, a current lead configured to be cooled by liquid nitrogen is also known.

FIG. 4 is a sectional view schematically showing a conventional superconducting current lead of a superconducting magnet device. In the figure,
The superconducting coil 1 contains liquid helium He in a vacuum heat insulating container 2.
And is conductively connected to the low-temperature terminal 5A of the current lead 3 by a lead wire. The current lead 3 is configured as a series connection of a high-temperature side lead 4 having a normal temperature terminal 4A on the upper portion and made of a good conductor and a low-temperature side lead 5 made of an oxide superconductor and controlling the temperature of the oxide superconductor by a liquid. By cooling below the nitrogen temperature (about 77K), the oxide-based superconducting conductor enters a superconducting state, and the Joule heat when current flows is reduced to zero. In addition, since the oxide-based superconducting conductor, which is a thermal insulator, blocks heat entering from the high-temperature side lead by the low-temperature side lead, the low-temperature terminal 5A
This results in a current lead of the superconducting device that has less heat penetrating into the side and thus consumes less liquid helium. Also,
The current lead 3 includes a liquid nitrogen container 6 surrounding the connection between the high-temperature side lead 4 and the low-temperature side lead 5. Liquid nitrogen is supplied through a control valve 7, and the liquid level is detected by a level sensor 8. The liquid level controller 9 controls the opening of the control valve 7 so that the liquid level of the liquid nitrogen in the liquid nitrogen container 6 is always maintained at a constant level.
The nitrogen gas vaporized by the heat of intrusion is discharged outside through a discharge pipe (not shown).

[0004]

In the current lead constructed as described above, the connection between the high-temperature side lead and the low-temperature side lead is cooled to near the temperature of the liquid nitrogen by the heat of vaporization of the liquid nitrogen, and moves toward the low-temperature side lead. And the low-temperature side lead is cooled to a temperature lower than the liquid nitrogen temperature by the low-temperature helium gas to be in a superconducting state, and its Joule heat is reduced to zero. Can be obtained. However, since the supply amount of the liquid helium is controlled so that the liquid level is constant, the liquid nitrogen is supercooled in a state where the flowing current is small, so that the liquid nitrogen is wasted and wasted. Since the service port is required, the service port for accommodating the battery becomes large, and the liquid nitrogen boils when the rated current flows, making it difficult to detect the liquid level by the level sensor 8 and to maintain a constant level. In addition, there is a problem that an expensive level sensor 8 and a liquid level controller 9 are required in order to improve the detection accuracy of the liquid level, which leads to an economic disadvantage.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a small and inexpensive current lead cooling structure capable of accurately controlling the amount of flowing nitrogen in accordance with the flowing current of a current lead, not wasting liquid nitrogen. It is in.

[0006]

According to the present invention, there is provided, in accordance with the present invention, a method of passing an exciting current from an external power supply through a superconducting coil housed in a vacuum insulated container and immersed in liquid helium. A lead comprising a series connection of a high-temperature side lead made of a good conductive metal and a low-temperature side lead made of an oxide-based superconducting conductor. A nitrogen cooling passage for supplying liquid nitrogen into the side lead and discharging vaporized nitrogen gas from the room temperature terminal side of the high temperature side lead;
And a control means for monitoring the cooling state of the high-temperature side lead and controlling the amount of nitrogen flowing through the nitrogen cooling passage.

Further, the control means is formed so as to monitor the cooling state of the high-temperature side lead based on the temperature of the high-temperature side lead and to control the amount of nitrogen flowing through the nitrogen cooling passage.

Further, it is assumed that the control means is configured to monitor the cooling state of the high-temperature side lead based on the potential drop of the high-temperature side lead and control the amount of nitrogen flowing through the nitrogen cooling passage.

[0009]

In the structure of the present invention, a nitrogen cooling passage for supplying liquid nitrogen into the high-temperature side lead from near the connecting portion between the high-temperature side lead and the low-temperature side lead and discharging the vaporized nitrogen gas from the room temperature terminal side of the high-temperature side lead. And the control means monitors the cooling state of the high-temperature side lead and controls the amount of nitrogen flowing through the nitrogen cooling passage. For example, the high-temperature side lead changes mainly due to the Joule heat caused by the flowing current. By detecting the temperature at the normal temperature terminal side, the cooling state of the high-temperature side lead can be monitored, and the flow rate of liquid nitrogen or its vaporized gas can be controlled according to the difference between the detected temperature and the reference temperature. To maintain a constant temperature to reduce the heat entering the low-temperature side lead, and to control the flow-through nitrogen amount stably with good load following ability without being bothered by boiling of liquid nitrogen. It can, thereby also eliminating wasteful consumption of liquid nitrogen. Further, since the current lead can be cooled by using the inside of the high-temperature side lead as a liquid nitrogen container and a heat exchanger, a liquid nitrogen container and a level sensor are not required, and the configuration of the apparatus can be simplified.

Further, if the control means is configured to monitor the cooling state of the high-temperature side lead by the potential drop of the high-temperature side lead and control the amount of nitrogen flowing through the nitrogen cooling passage, the potential drop due to the increase and decrease of the flowing current can be achieved. , And the flow rate of liquid nitrogen or its vaporized gas can be controlled in accordance with the change in Joule heat, so that the temperature of the high-temperature side lead can be kept constant and the heat entering the low-temperature side lead can be reduced. At the same time, it is possible to stably control the flowing nitrogen amount with good load following ability without being bothered by boiling of the liquid nitrogen, thereby eliminating wasteful consumption of the liquid nitrogen. Further, since the current lead can be cooled by using the inside of the high-temperature side lead as a liquid nitrogen container and a heat exchanger, a liquid nitrogen container and a level sensor are not required, and the configuration of the apparatus can be simplified.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on embodiments. FIG. 1 is a configuration diagram schematically showing a current lead of a superconducting device according to an embodiment of the present invention. The same components as those in the prior art are denoted by the same reference numerals, and redundant description will be omitted. In the figure, a current lead 3 has an insulative joint 1 near a connection between a high-temperature side lead 4 and a low-temperature side lead 5.
2A, a supply pipe 12 for liquid nitrogen, and an outlet pipe 13 for nitrogen gas vaporized inside the high-temperature side lead.
And a nitrogen cooling passage 11 composed of a liquid nitrogen control valve 12B. Further, the control means 15 includes a temperature sensor 16 for detecting the temperature of the normal temperature terminal 4A of the high temperature side lead 4,
The control circuit 17 is configured to compare the detected temperature with a reference value and control the opening of the control valve in accordance with the difference.

In the current lead constructed as described above, the cooling state of the current lead is constantly monitored by the control means 15, and the opening of the control valve 12B is controlled in accordance with the difference between the detected temperature and the reference value. Thus, the heat exchange between the liquid nitrogen supplied into the high-temperature side lead and the current lead is performed using the inside of the high-temperature side lead as a heat exchange chamber. Further, the low-temperature side lead 5 is cooled to the liquid nitrogen temperature or lower by the nitrogen cooling of the high-temperature side lead and the low-temperature helium gas in which the liquid helium is vaporized to be in a superconducting state, so that heat entering the low-temperature terminal 5A side is reduced. . The reference temperature is determined by previously measuring the normal terminal temperature when the temperature of the connection with the low-temperature side lead is cooled to near the liquid nitrogen temperature. Therefore, when the temperature of the room temperature terminal falls to the reference temperature, the supply of liquid nitrogen is shut off, and wasteful consumption of liquid nitrogen is avoided.

On the other hand, a change in Joule heat due to an increase or decrease in the supply current to the superconducting cable 1 is detected by the control means 15 as a change in the room temperature terminal temperature, and is sent to the nitrogen cooling passage 11 by opening the control valve. Is controlled according to the change in the flowing current, the cooling state of the high-temperature side lead 4 changes following the change in the flowing current, and the temperature of the high-temperature side lead is substantially constant. Is controlled. As a result, the low-temperature side lead 5 is maintained at a constant temperature regardless of the increase or decrease of the flowing current, so that the invasion heat of the low-temperature side lead 5 is always kept at a low value regardless of the increase or decrease of the flowing current. A superconducting magnet device with low consumption of expensive liquid helium and low running cost can be provided by utilizing the effect of using the system superconducting conductor.

Further, since the high-temperature side lead also functions as a liquid nitrogen container and a heat exchanger, a liquid nitrogen container is not required, and the apparatus can be made compact and simple. Furthermore, by monitoring the cooling state of the current lead with a temperature sensor, the supply of liquid nitrogen can be controlled stably in response to changes in the flowing current without being bothered by the boiling of liquid nitrogen, and the control means can be simplified. Since it can be configured using a temperature switch, there is an advantage that the control means can be formed small and inexpensively as compared with the liquid level controller.

FIG. 2 is a structural view showing a modification of the above-described embodiment. A control valve 12B is provided on the nitrogen gas outlet pipe 13 side of the nitrogen cooling passage 11 so that the nitrogen exchanged in the high-temperature side lead is completed. This embodiment differs from the above-described embodiment in that the amount of released gas is controlled in accordance with the flowing current.
Since the amount of liquid nitrogen vaporized in the high-temperature side lead can be controlled by the opening degree of 2B, the same operation and effect as in the above-described embodiment can be obtained.

FIG. 3 is a block diagram showing another embodiment of the present invention. The control means 21 compares a voltage detector 22 for detecting a potential drop of the high-temperature side lead 4 with a reference voltage value. The difference from the above-described embodiment is that the control circuit 23 controls the opening of the control valve 12B in accordance with the difference. In the control means 21 configured as described above, the electric resistance of the good conductor such as copper constituting the high-temperature side lead changes according to the temperature, and the potential drop changes in accordance with the increase and decrease of the flowing current. Therefore, the cooling state of the high-temperature side lead is detected by replacing it with a potential drop, and the supply amount of liquid nitrogen or the release amount of nitrogen gas can be controlled in the same manner as in the above-described embodiment. The effect of is obtained.

[0017]

As described above, according to the present invention, liquid nitrogen is supplied into the high-temperature side lead from the vicinity of the connection between the high-temperature side lead and the low-temperature side lead, and the vaporized nitrogen gas is discharged from the room temperature terminal side of the high-temperature side lead. A nitrogen cooling passage is provided, and the control means monitors the cooling state of the high-temperature side lead to control the amount of nitrogen flowing through the nitrogen cooling passage. As a result, the cooling state of the high-temperature side lead is monitored by, for example, a change in the temperature of the high-temperature side lead due to a flowing current or a change in the potential drop of the high-temperature side lead. Unlike the conventional technology that maintains the liquid level of the liquid nitrogen container at a constant level, the temperature of the connection with the low-temperature lead is close to the liquid nitrogen temperature regardless of the increase or decrease of the flowing current. It is possible to provide a current lead of a superconducting magnet device which can be maintained at a constant temperature and can greatly reduce heat entering a low-temperature side lead using an oxide superconducting conductor.

Further, the problem of the prior art that liquid nitrogen is wasted in an area where the current is small is avoided by controlling the amount of flowing nitrogen in accordance with the current value.
A current lead with low consumption of liquid nitrogen and low operating cost can be provided. Furthermore, the problem of the prior art that the liquid level is difficult to detect due to the boiling of liquid nitrogen is avoided by monitoring the temperature or potential drop of the high-temperature side lead, and the cooling state of the current lead can be accurately and stably determined. It is possible to provide a current lead that can detect and appropriately control the amount of flowing nitrogen. Furthermore, the large size and economic disadvantage of the apparatus are that the high-temperature side lead also serves as a liquid nitrogen container and a heat exchange chamber, which eliminates the need for a liquid nitrogen container, which has been a problem in the prior art, and an expensive liquid level controller. Can be avoided by replacing the control means with inexpensive temperature switches and over / under voltage switches. Therefore, almost all of the problems of the prior art are improved, the amount of flowing nitrogen can be controlled accurately in accordance with the flowing current, and the consumption of liquid nitrogen is small, inexpensive, and the consumption of liquid nitrogen is small. A superconducting magnet device having a small number of current leads can be provided.

[Brief description of the drawings]

FIG. 1 is a configuration diagram schematically showing a current lead of a superconducting device according to an embodiment of the present invention.

FIG. 2 is a configuration diagram schematically illustrating a modification of the above-described embodiment.

FIG. 3 is a block diagram schematically showing a different embodiment of the present invention.

FIG. 4 is a cross-sectional view schematically showing a conventional superconducting current lead of a superconducting magnet device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Superconducting coil 2 Vacuum insulated container 3 Current lead 4 High temperature side lead 5 Low temperature side lead (using oxide superconducting conductor) 6 Liquid nitrogen container 7 Control valve 8 Level sensor 9 Liquid level controller 11 Nitrogen cooling passage 12 Supply of liquid nitrogen Piping 12B Control valve 13 Outlet piping for vaporized nitrogen gas 15 Control means 16 Temperature sensor 17 Control circuit 21 Control means 22 Voltage detector 23 Control circuit

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H01L 39/04 ZAA H01F 6/00

Claims (3)

(57) [Claims] 1. A current lead for passing an exciting current from an external power supply to a superconducting coil housed in a vacuum insulated container and immersed in liquid helium, wherein the high-temperature side lead is made of a highly conductive metal; Liquid nitrogen is supplied into the high-temperature side lead from the vicinity of the connection portion between the high-temperature side lead and the low-temperature side lead, and the low-temperature side lead is connected to the normal-temperature terminal side of the high-temperature side lead. A superconducting magnet, comprising: a nitrogen cooling passage for discharging nitrogen gas vaporized from the fuel cell; and control means for monitoring a cooling state of the high-temperature side lead and controlling an amount of nitrogen flowing through the nitrogen cooling passage. Equipment current leads. 2. The control device according to claim 1, wherein the control means monitors the cooling state of the high-temperature side lead based on the temperature of the high-temperature side lead to control the amount of nitrogen flowing through the nitrogen cooling passage. Current lead of superconducting magnet device. 3. The control device according to claim 1, wherein the control means monitors a cooling state of the high-temperature side lead based on a potential drop of the high-temperature side lead to control the amount of nitrogen flowing through the nitrogen cooling passage. The current lead of the superconducting magnet device as described.