JPH07105529B2 - Superfluid helium generator - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention relates to a superfluid helium generator, and more particularly to improvement of a superfluid helium generator for cooling a large superconducting magnet.

[Prior Art and its Problems] As is well known, liquid helium transforms from a normal liquid, that is, a liquid having a normal flow to a liquid having a superfluidity, at a temperature equal to or lower than a lambda point (2.17k). Such superfluid helium is widely used as a refrigerant for superconducting magnets.

By the way, superfluid helium as a refrigerant for superconducting magnets is classified into two types. One is saturated superfluid helium obtained by decompressing liquid helium with a vacuum pump, and the other is unsaturated superfluid at 1 atmospheric pressure generated by heat exchange with this saturated superfluid helium. Helium (pressurized superfluid helium). The former can be easily generated, but the latter is relatively difficult. However, the latter is far superior in heat transfer characteristics such as critical heat flux. Therefore, pressurized superfluid helium is often used as the refrigerant for the superconducting magnet.

The pressurized superfluid helium generator is generally constructed as shown in FIG. That is, the normal flow helium tank 1 containing 4.2 k of helium H and the superfluid helium tank 2 are always connected via a connecting pipe 3 closed by a valve 3 '. The valve 3'is manufactured so that superfluid helium leaks even when it is closed. A heat exchanger 4 for cooling the tank 2 below the lambda point is arranged in the superfluid helium tank 2, and one end of the heat exchanger 4 is a Joule-Thomson valve (hereinafter abbreviated as JT valve). 5, connected to the suction port of the vacuum pump 7 via the secondary side of the JT heat exchanger 6. The discharge port of the vacuum pump 7 is connected to the refrigeration liquefier 9 via the compressor 8. Then, in the freeze liquefaction machine 9, the helium tank 1
Liquid helium is supplied to. Helium tank 1, helium tank 2, JT heat exchanger 6, JT valve 5 are heat insulating containers 10
It is housed in.

Therefore, this apparatus is designed to superfluidize the liquid helium A in the superfluid helium tank 2 as follows. First, the valve 3'in the connecting pipe 3 is opened, 4.2 k of normal-flowing liquid helium H is introduced into the superfluid helium tank 2 and the normal-flow helium tank 1, and then the valve 3'is closed. In such a state, the vacuum pump 7, the compressor 8 and the freeze liquefaction machine 9 are operated. When the vacuum pump operates, a part of the 4.2k liquid helium H in the helium tank 1 is in the path of the primary side of the JT heat exchanger 6, the JT valve 5, the heat exchanger 4, and the secondary side of the JT heat exchanger 6. Flowing. If the inside of the heat exchanger 4 is exhausted to a saturated vapor pressure corresponding to a temperature Ts lower than the temperature Tb in the superfluid helium tank 2, the helium leaving the helium tank 1
While passing through the primary side of the JT heat exchanger 6, it is pre-cooled to, for example, 2.2 k, and becomes gas and liquid of temperature Ts. This liquid is the heat exchanger 4
Evaporates while passing through, which results in a superfluid helium bath 1
The helium A inside is cooled.

The superconducting magnet 12 is housed in the superfluid helium tank 2 and is excited by the power lead 13 penetrating the insulative filling material 11.

By the way, in such an apparatus, when the superconducting magnet is large, the superfluid helium tank becomes large and the amount of helium used increases. In addition, there is a problem that there is an extra refrigerating power to cool it.

Further, the temperature Tb and the temperature Ts had to be controlled in a constant relationship during the initial cooling from 4.2 k to the magnet operating temperature below the lambda point, and the initial cooling was not always easy.

[Object of the Invention] The present invention has been made in view of such circumstances, and an object of the present invention is to generate superfluid helium that is easy to perform initial freezing with a small amount of superfluid helium required as a refrigerant for a superconducting magnet. To provide a device.

[Summary of the Invention] The present invention connects the first and second helium tanks containing liquid helium therein, the first helium tank and the second helium tank, and is always closed to close the first helium tank. A connecting pipe that is opened when liquid helium is replenished from the helium tank to the second helium tank, and the liquid helium in the second helium tank is set to a lambda point by using the liquid helium in the first helium tank. Cooling means utilizing the Joule-Thomson expansion effect for cooling, a superconducting magnet having a cooling channel inside, a conduit for communicating the cooling channel of the superconducting magnet with the cooling means, and the superconducting First and second installed in the conduit between the cooling means and the inlet side and the outlet side of the cooling flow path of the magnet, respectively.
And a connecting pipe for connecting the cooling passage inlet side of the superconducting magnet to the second helium tank, a third valve arranged in the connecting pipe, and the initial cooling of the superconducting magnet. The first and second valves are opened, the third valve is closed, and the mist-like saturated helium generated by the Joule-Thomson expansion by the cooling means is passed through the cooling passage of the superconducting magnet. Then, when the initial cooling is completed, the pressurized superfluid helium cooled from the inside of the second helium tank below the lambda point by closing the first and second valves and opening the third valve. And a valve control means for controlling so as to be introduced into the cooling flow path of the superconducting magnet.

Further, the present invention is characterized by including a pipe for initial cooling that bypasses the cooling flow path in the middle thereof.

[Effect of the invention] If the mist-like helium is made to flow through the cooling passage of the superconducting magnet for the initial refrigeration from 4.2k as in the device of the present invention, JT
The opening of the valve is easy to adjust, and it is sufficient to adjust the opening of the JT valve so that the temperature of the expanded Joule-Thomson mist is slightly lower than the temperature of the magnet. Further, when the superconducting magnet is excited, the pressurized superfluid helium, which has good heat transfer characteristics, is filled in the cooling passage, so that stable excitation and demagnetization are possible. In particular, if the superconducting magnet is composed of bundle conductors, the thin wires of the superconducting wires that compose the bundle conductor will be directly cooled, so a high cooling effect is expected to recover the superconducting state even if the superconducting state is partially broken. it can.

Further, structurally, the amount of superfluid helium required as a refrigerant can be minimized.

Embodiments of the Invention Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a main part of a superfluid helium generator according to an embodiment of the present invention, and the same parts as those in FIG. 2 are designated by the same reference numerals. Therefore, the description of the overlapping portions will be omitted.

The main difference of this embodiment from the conventional apparatus shown in FIG. 2 is that the immersion cooling type superconducting magnet 12 housed in the superfluid helium tank 2 in FIG. The superconducting magnet 14 is replaced with a superconducting magnet 14 at the time of cooling.
The mist-like saturated helium generated by Thomson expansion is caused to flow through the cooling passage of the superconducting magnet 14, and when the initial cooling is completed, the pressurized supercooled inside the second helium tank 2 is cooled to the lambda point or lower. The point is that a plurality of valves are used to introduce the flowing helium into the cooling passage of the superconducting magnet 14.
That is, specifically, one end of the internal cooling flow path of the superconducting magnet 14 is connected to one end of the heat exchanger 4 via the insulating joint 15 and the valve 16, and is also connected to the superfluid helium tank 2 via the valve 17. There is. The other end of the internal cooling flow path of the superconducting magnet 14 is also connected to the secondary side of the JT heat exchanger 6 via an insulating joint 15 and a valve 18. Besides, a valve 19 for bypassing the internal cooling flow path of the superconducting magnet 14 and valves 20, 20 'vacuum pump 7 for bypassing a part of the internal cooling flow path when precooling the superconducting magnet 14.
A valve 21 for bypassing the valve is provided.

Therefore, this apparatus is designed to cool the superconducting magnet 14 to below the lambda point as follows. First, the valve 3'of the connecting pipe 3 is opened, the valves 19, 20 ', 18 are closed, the JT valve 5, valves 16, 17, 20, 21 are opened, and the compressor 8 and the refrigerating liquefier 9 are operated. Precool the superconducting magnet 14. When the internal flow path between the valves 16 and 20 of the superconducting magnet 14 has cooled and the pressure loss has decreased, the valve 20 'is opened and the valve 20 is closed. valve
When the internal cooling passage between 20 and the valve 20 'has also cooled, the valve 18 is opened and the valve 20' is closed to cool the whole to 10 k or less. Thereafter, the JT valve 5 and the valve 17 are closed, the refrigeration liquefier 9 is switched to the liquefaction mode, and liquid helium is stored in the helium tank 1 and the superfluid helium tank 2. Then valve 21, valve 19, valve 18,
The valve 17 and the valve 3 are closed, the vacuum pump 7, the compressor 8 and the freeze liquefaction machine 9 are operated to start cooling to a temperature of 4.2 k or less. When the temperature Ts of the JT valve 5 is changed to the superconducting magnet 14
If the temperature is adjusted to be slightly lower than the temperature of, the mist-like saturated helium generated by the Joule-Thomson expansion effectively evaporates in the internal cooling passages of the heat exchanger 4 and the superconducting magnet 14, and the superfluid helium tank 2 , Cool the superconducting magnet 14. When the superconducting magnet 14 has cooled and the pressure loss in the internal cooling passage has become small, the return passage of helium is sequentially switched from the valve 20 to the valve 20 'and the valve 18. In this way, the superconducting magnet 14 can be easily cooled to the magnet operating temperature.
When the magnet operating temperature below the lambda point is reached, the helium return flow is switched to valve 19, valve 16, valve 20, valve 20 ',
The valve 18 is closed. At the same time, the valve 17 is opened, and pressurized superfluid helium is introduced into the internal cooling passage of the superconducting magnet 14.
In this state, the heat that has entered the superconducting magnet 14 is removed via the superfluid helium A and the heat exchanger 4, and stable excitation and demagnetization are possible.

[Brief description of drawings]

FIG. 1 is a basic block diagram of a superfluid helium generator showing a typical embodiment of the present invention, and FIG. 2 is a basic block diagram showing a conventional superfluid helium generator. 1 ... Normal fluid helium tank (first helium tank), 2 ...
Superfluid helium tank (second helium tank), 3 ... connecting pipe, 4 ... heat exchanger, 5 ... JT valve (cooling means), 6 ...
JT heat exchanger, 14 ... Superconducting magnet with cooling passage inside, 16 ... Valve (first valve), 17 ... Valve (third valve), 18
... valve (second valve), 19 ... valve (fourth valve), 20 ... valve (fifth valve), 20 '... valve (fifth valve).

Claims (4)

[Claims] 1. A first and a second helium tanks for accommodating liquid helium therein, and a first helium tank and a second helium tank, which are connected to each other and are closed at all times from the first helium tank. A connection pipe opened when replenishing the second helium tank with liquid helium, and using the liquid helium in the first helium tank to cool the liquid helium in the second helium tank to a temperature below the lambda point. Cooling means utilizing the Joule-Thomson expansion effect, a superconducting magnet having a cooling flow passage therein, a conduit for communicating the cooling flow passage of the superconducting magnet with the cooling means, and the cooling of the superconducting magnet. First and second valves respectively installed in the conduits between the inlet side and outlet side of the flow passage and the cooling means; the cooling flow passage inlet side of the superconducting magnet and the second helix. A connection pipe for connecting to the tank, a third valve arranged in the connection pipe, and when initially cooling the superconducting magnet, the first and second valves are opened and the third valve is closed. Then, the mist-like saturated helium generated by the Joule-Thomson expansion by the cooling means is caused to flow through the cooling flow path of the superconducting magnet, and when the initial cooling is completed, the first and second valves are turned on. When closed, the third valve is opened and the second valve is opened.
And a valve control means for controlling so as to introduce pressurized superfluid helium cooled to a temperature below the lambda point from the helium tank into the cooling passage of the superconducting magnet. Superfluid helium generator. 2. The superfluid helium generator according to claim 1, wherein the superconducting magnet is a bundle conductor. 3. A bypass flow passage, which bypasses the inside of the cooling flow passage of the superconducting magnet from the cooling means and is connected to an outlet side, and a fourth valve disposed in the bypass flow passage, The valve control means closes the fourth valve during the initial cooling to cause the mist-like saturated helium to flow through the cooling passage of the superconducting magnet, and when the initial cooling is completed, the fourth valve is closed. The superfluid helium generator according to claim 1, wherein the mist-like saturated helium is controlled so as to be bypassed so as not to pass through the cooling flow path of the superconducting magnet. 4. A bypass flow passage provided in the middle of the cooling flow passage of the superconducting magnet and a fifth valve arranged in the bypass flow passage, the control means for the valve controlling the initial cooling. In the first half, the fifth valve is opened, the second valve is closed, and the mist-like saturated helium is allowed to flow from the first valve of the superconducting magnet to the cooling flow passage to provide the fifth valve. Is discharged from the bypass passage to be initially cooled, and in the latter half of the initial cooling, the fifth valve is closed and the second valve is opened so that the mist-like saturated helium is discharged from the superconducting magnet. The superfluid helium generator according to claim 1, wherein the superfluid helium generator is controlled so as to flow through the entire cooling flow path.