JP2635165B2 - Forced cooling superconducting coil device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a superconducting coil of a forced cooling type in which a superconducting wire is embedded in a conduit and a refrigerant flows in the conduit, and particularly to a cooling device for a superconducting coil. About.

[Conventional technology]

The method of cooling a superconducting coil is roughly divided into a immersion cooling method in which the coil is directly immersed in a cooling medium and a cooling method, and a coil formed by winding a superconducting conductor with a superconducting wire inserted inside a metal conduit. There is a forced cooling system in which a coolant is forcibly circulated through an internal superconducting wire and a gap for cooling. In the case of immersion cooling, since the coil is immersed in the refrigerant, even if a part of the coil is in the normal conduction state, it is cooled by the surrounding refrigerant, and when the conduction current is reduced, the superconducting characteristics are restored and the coil becomes stable. Although it has high performance, a cryostat for containing a superconducting coil and a refrigerant is required. In addition, the electrical insulation of the superconducting coil is in contact with the outer surface of the superconducting wire, and especially in the case of a large superconducting coil, an intermittent insulating spacer makes contact between bare superconducting conductors, and a high withstand voltage cannot be obtained. There are drawbacks. On the other hand, in the case of the forced cooling coil, since the superconducting conductor itself serves as a coolant flow path, there is no need for a cryostat for storing the coolant. It is possible to increase the withstand voltage by selecting an insulating material, and the cooling characteristics are improved because the refrigerant is forced to flow around the superconducting wires inside the conduit. There are advantages. Therefore, it has a large and complicated shape like a poloidal coil for a fusion reactor, and is most suitable for a superconducting coil that generates AC loss and high voltage.
Attention has been drawn from various fields and development has been made. An example of conventional forced cooling will be described with reference to FIGS. 3 and 4. FIG. Third
The figure is a cross-sectional view of the forced cooling superconductor,
The superconducting wire 3 is disposed inside a coolant passage 4 inside a stainless steel square pipe (conduit) 2 along this passage, and helium is flowed through the cooling passage 4 to cool the superconducting wire 3 until the superconducting wire 3 exhibits a superconducting state. I do.

FIG. 4 shows a general cooling device of a forced cooling coil using such a superconducting conductor 1. The main components are a circulating compressor 5, a liquid nitrogen tank 6, a liquid helium tank 7, a storage container 9 for storing a counter-current heat exchanger 8, etc., a vacuum container 11 for storing a superconducting coil 10, and the like. Transfer pipes 12a, 12b
The cooling is performed in the following manner.
That is, the helium gas serving as the refrigerant is compressed by the circulating compressor 5 and guided to the inside of the heat exchanger storage container 9, cooled to about 80 ° K in the liquid nitrogen tank 6, and returned to the heat exchanger group 8 by the heat exchanger group 8. Exchanges heat with the liquid helium tank 7, where it is cooled to 5K to become supercritical helium, and the helium transfer pipe 12
a, enters the vacuum vessel 11 via the terminal box 13, joins the current lead 14 coming from the excitation power supply 15 at the terminal box 13, cools the superconducting coil 10, and returns the heat gas again through the return helium transfer pipe 12b. After entering into the container housing 9, it is JT-expanded by the Jew-Thomson valve 16 to become a liquid and stored in the liquid helium tank 7. The gas evaporated here and the gas that has not been liquefied return to the circulating compressor 5 through the return pipe while exchanging heat with the incoming gas, and cool it while repeating it.

[Problems to be solved by the invention]

In the above prior art, since the distance between the storage container 9 of the refrigerant generator and the vacuum container 11 storing the superconducting coil is long, the refrigerant temperature rises due to heat leak,
Large heat loss due to heat penetration from a, 14b, large heat loss due to terminal box 13,
At 13, the temperature of the refrigerant to be joined is increased. In addition, when a superconducting coil is used in a conventional apparatus, since the refrigerant flows through a gap in a narrow conduit, the flow resistance becomes extremely high. There was a drawback that it could not flow and required a long time for cooling.

As a method of compensating for such a drawback, a method of providing a refrigerant storage tank in a vacuum vessel and reducing the intrusion of heat from the outside is disclosed in JP-A-59-117281. In addition, although the cooling medium for cooling the coil body can be cooled, the problem that it takes a long time to cool the coil body has not been solved because precooling from room temperature cannot be performed.

An object of the present invention is to cool a current lead and a superconducting coil main body cooling pipe to prevent a rise in the temperature of the refrigerant due to the intrusion of heat from the outside, and also to cool a pipe that comes into contact with the superconducting coil and pre-cools the pipe. An object of the present invention is to provide a forced cooling superconducting device that shortens a cooling time in cooling.

[Means for solving the problem]

The object is to provide a current lead, and a refrigerant storage tank installed in a vacuum vessel to cool the superconducting coil body, and
This is achieved by branching and supplying from an external refrigerant storage tank both pipes that are in contact with the superconducting coil main body and precool the superconducting coil.

[Action]

In order to solve the problem that the refrigerant flow is poor due to the large pressure loss of the superconducting conductor for the forced cooling coil and the pre-cooling time is prolonged, a refrigerant pipe is installed in contact with the superconducting coil, and the coil is cooled from the outside so that the superconducting conductor is cooled. The flow of supercritical helium in the inside can be made easier to flow, and the cooling time from room temperature can be shortened.

In addition, in order to reduce heat intrusion from the current lead and the cooling pipe, it can be achieved by providing a pipe for efficiently supplying a refrigerant from the outside to the current lead and a refrigerant storage tank for cooling the cooling pipe. In addition, this operation can be effectively cooled by providing and adjusting the flow rate control valves on the upstream side of the refrigerant storage tank and on the upstream side of the superconducting coil of the pipe that pre-cools in contact with the coil. .

〔Example〕

Hereinafter, an embodiment of the present invention will be described with reference to FIG. This device is equipped with supercritical helium 18
19a for transferring the superconducting coil to the forced cooling superconducting coil 10, a power supply 15 for supplying a current to the superconducting coil, and current leads 14a, 14
b, a refrigerant storage tank 20 through which the current lead and the refrigerant pipe 19a penetrate, and a pre-cooling pipe 27 that contacts the superconducting coil 10 and cools from outside.

The supply of liquid helium to the refrigerant storage tank 20 and the pre-cooling pipe 27 is guided from the external liquid helium dewar 21 by a pipe 23, branched in a vacuum vessel, and the flow rate is controlled by a flow control valve 25 in each pipe. , Adjusted at 26.

On the other hand, the refrigerant storage tank 20 and the evaporative gas after the coil pre-cooling are connected to a helium recovery device 30 via a valve 29.

Next, the operation of the present embodiment will be described. The helium gas supplied from the refrigerant generator 17 enters the terminal box 13 through the pipe 19a, and after cooling the superconducting coil, returns to the refrigerant generator 17 through the return pipe 19b.
Repeat this. However, initial cooling from room temperature takes a long time due to pressure loss in the coil, etc., so up to about 20K, close the valve 26 to the refrigerant storage tank and open the pre-cooling valve 25 to cool the coil conductor from the outside. Then, the supercritical helium in the superconducting coil is made to flow easily to promote cooling.

When the temperature of the superconducting coil drops below 20K, the magnet pre-cooling valve 25 is closed and the valve 26 to the refrigerant storage tank is opened to open the storage tank 20.
Liquid helium is stored in the helium to suppress heat intrusion from the current lead and temperature rise due to heat leak from the outside of the supercritical helium.

When the coil temperature reaches a superconducting state, excitation is performed by supplying power from the excitation power supply 15. The temperature rise of the current lead during the excitation is suppressed by the liquid helium and gas helium in the storage tank 20.

A superconducting coil with a superconducting wire inserted at a void rate of 50% in a square stainless steel conduit with a side length of 7 mm and wound in a bobbin shape with an inner diameter of 100 mm was manufactured. And circulates liquid helium from the external liquid helium dewar 21 to the internal storage tank.
20 and a pipe 27 in contact with the superconducting coil 10 for cooling.

As a result, in the method of the present invention, the flow rate of the helium gas flowing in the superconducting coil conductor can be increased by about 20 times compared to the case where there is no pipe 27 in contact with the conventional superconducting coil, and the cooling until the superconducting state is reached. The time could be reduced to about 10% under the same conditions as above.

Also, after the superconducting coil has reached a temperature at which superconductivity is reached, supercritical helium with a pressure of 5 atm and a mass flow rate of 3 g / s is passed through the superconducting coil, and the liquid helium is stored in the internal liquid helium storage tank. In the state where no power was supplied, the DC stabilized power supply 15 was excited. As a result, when liquid helium is not stored, the temperature of the current lead rises and the refrigerant temperature also rises, and the mass of the refrigerant flowing through the coil decreases by 5 g.
Even when the current is increased to / s, the superconducting coil 10 undergoes normal conduction transition at an exciting current of 110A. On the other hand, when excited with liquid helium stored, when the flow rate of 3 g / s was passed through the superconducting coil, even when excited to 200 A, the temperature of the current lead did not rise and the normal conduction transition did not occur. Excitation was stable.

Another embodiment of the present invention will be described with reference to FIG. FIG. 2 shows only the main parts, and the parts not shown are the same as those in FIG. In this embodiment, two automatic valves 31 and 32 are provided on the upstream side of the pipe entering the refrigerant storage tank 20, and a valve 32 close to the storage tank is provided.
Is opened and closed by detecting the liquid level by a liquid level sensor 33 installed in the storage tank. In this embodiment, the tank is closed at 90% of the effective height of the tank and opened at 70%.

In addition, the automatic valve 31 far from the storage tank opens and closes by detecting the temperature of the temperature sensor 35 installed on the superconducting coil, together with the automatic valve 34 installed on the pipe that branches off from the main pipe and cools the superconducting coil from the outside. However, in this embodiment, the temperature of the superconducting coil is set to 20K, and when it is higher than that, the automatic valve 34 is opened,
31 was closed and vice versa when low.

As a result, during pre-cooling and during excitation, there was no need to operate the valve, and stable and economical operation was possible.

It is needless to say that the present invention is not limited to these embodiments, and various modifications such as setting of a detector can be considered without departing from the scope of the present invention.

〔The invention's effect〕

According to the present invention, a liquid helium refrigerant storage tank in a vacuum vessel reduces heat intrusion from outside the vacuum vessel through supercritical pressure helium piping and current leads, and uses liquid helium for pre-cooling of a superconducting coil. Since supercritical pressure helium is not used and the absolute amount and consumption of supercritical pressure helium can be reduced, the supercritical pressure helium generator can be downsized. In addition, a sufficient amount of liquid helium can be used for pre-cooling the superconductor regardless of the capability of the supercritical pressure helium generator.

Further, according to the present invention, the supply of the refrigerant for pre-cooling can be automated in conjunction with the liquid level sensor and the temperature sensor, so that stable and economical operation is possible.

[Brief description of the drawings]

FIG. 1 is a system diagram of a superconducting coil device showing one embodiment of the present invention, FIG. 2 is a system diagram showing another embodiment of the present invention, and FIG. 3 is a typical forcing used in the present invention. FIG. 4 is a system diagram showing an example of a conventional forced cooling system. 1 ... forced cooling superconducting conductor, 2 ... metallic conduit,
3 ... superconducting wire, 4 ... refrigerant channel, 5 ... circulating compressor,
6 ... liquid nitrogen tank, 7 ... liquid helium tank, 8 ... heat exchanger.

Claims (2)

(57) [Claims] 1. A generator for generating supercritical helium, a vacuum vessel, a superconducting coil provided in the vacuum vessel and wound by a forced cooling superconductor, and from the generator to the forced cooling superconductor. A pipe for supplying the supercritical pressure helium; a current lead for supplying a current to the superconducting coil; a refrigerant storage tank provided in the vacuum vessel to cool the pipe and the current lead; A forced cooling type superconducting coil device, comprising: a precooling pipe having a branch pipe for supplying to the refrigerant storage tank and precooling the superconducting coil using liquid helium in contact with the superconducting coil. 2. The forced cooling type superconducting coil device according to claim 1, wherein two valves provided on the branch pipe of the precooling pipe, and a valve provided on the superconducting coil side of the branch pipe of the precooling pipe. A valve on the branch pipe close to the refrigerant storage tank, which opens and closes based on the liquid level of the refrigerant storage tank, and a valve on the branch pipe far from the cooling storage tank and the pre-cooling. A forced cooling type superconducting coil device, wherein a valve provided on the side of the superconducting coil from the branch pipe of the pipe opens and closes based on a temperature of the forced cooling superconducting conductor.