JPS632122B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a superconducting magnet structure used in a superconducting magnetically levitated vehicle, and particularly to a cooling structure thereof.

Superconducting magnets are made of special materials such as Nb and Ti alloys, which have zero electrical resistance when cooled to extremely low temperatures, and are made of multi-core wires, placed in a stabilizing metal such as copper, and then drawn.The superconducting wire is wound many times. The turned coil is used. This coil is fixed in an inner tank for superconducting magnets, cooled to an extremely low temperature with liquid helium, maintained in a superconducting state, and energized for operation.

Extreme care must be taken to maintain this superconducting state. In other words, cooling at extremely low temperatures may not be sufficient, the coil may be unstable and move, or vibrations may cause unnecessary external force or deformation to the coil or the inner tank for the superconducting magnet that fixes the coil. When the superconducting state is destroyed, the superconducting state becomes normal conducting state. Alternatively, during a cooling transition, a vapor lock phenomenon may occur due to the generation of a large amount of helium gas, resulting in insufficient cooling. In this case, electrical resistance occurs in the coil, and the energy from the large current flowing through the coil is instantly dissipated as heat, causing local heat generation that may damage the coil or damage the liquid helium that was cooling the coil. There is a risk that the superconducting magnet may be evaporated, causing high pressure in the inner tank for the superconducting magnet, causing mechanical damage, and deteriorating the performance of the superconducting magnet.

In FIG. 1, normally, during cold storage, since the amount of gas is small, liquid helium descends as the bubbles rise in the connecting pipe 4, and the coil 2 is replenished with sufficient liquid. However, when the coil is energized or demagnetized, a large amount of helium gas is generated to cool down the heat generated at the persistent current switch section, power lead connection section, etc.

The helium gas generated in large quantities in this manner becomes a mass of bubbles that moves upward due to buoyancy and escapes into the tank 3 through the connecting pipe 4. The helium gas accumulated in the upper part of the tank 3 is discharged to the outside through a discharge pipe 11.

On the other hand, the evaporated amount of liquid helium in the inner tank 1 needs to be replenished from the tank 3 through the connecting pipe 4 into the inner tank 1, but if the helium gas rising inside the connecting pipe 4 becomes large, The liquid cannot descend with the force of the gas rising. This is the so-called vapor lock phenomenon.

In particular, the specific gravity of liquid helium is 7.4 times that of helium gas near its boiling point, and that of liquids with high boiling points, such as nitrogen.
Even compared to 183 times, the difference in specific gravity between gas and liquid is extremely small.
The vapor lock phenomenon described above is likely to occur.

For this reason, helium gas accumulates in the upper part of the inner tank for superconducting magnets (hereinafter referred to as the inner tank), and if the upper part of the coil 2 is exposed to the gas and becomes insufficiently cooled, it may lead to superconductor destruction as described above. There is a fear.

In order to solve the vapor lock phenomenon, conventionally, a pipe for ascending gas and a pipe (or passage) for descending liquid are prepared separately, and the pipe for descending liquid (hereinafter referred to as supply pipe) is connected to the bottom of tank 3. By configuring from the bottom of the inner tank 1 to the lower part of the inner tank 1 (at least the part not in contact with the evaporating helium gas), the helium gas moves upward in the inner tank 1, and in the connecting pipe 4 it flows upward in one direction. A series of convection paths are formed in which the liquid in the tank passes through the supply pipe and descends to the lower part of the inner tank.

Note that the injection pipe 10 in FIG. 1 is cooled by introducing a refrigerant from the outside, and then liquid helium is injected into the injection pipe 10.
It is installed for the purpose of storing liquid helium in the tank, and has no function after that, so it cannot be used as the supply pipe.

In addition to the above, there are other ways to prevent this, such as installing a dedicated helium gas recovery pipe from the switch box 7, which is the part where a large amount of helium gas is generated, to the tank 3, or installing another helium gas recovery pipe inside the connecting pipe 4. It is conceivable to create a tube and extend it to one part of the coil to use it as a liquid helium supply tube. However, in the former case, the number of pipes maintained in a high vacuum increases, which increases the risk of vacuum leaks, requires space, and complicates the structure. On the other hand, in the latter case, the inside of the connecting pipe becomes complicated, making it difficult to assemble, and the diameter of the connecting pipe becomes large.

An object of the present invention is to provide a cooling structure that can smoothly remove a large amount of helium gas generated in a coil portion and also supply new liquid helium without installing special piping.

That is, the present invention provides a structure in which the injection tube 10B of the coil portion of the injection tube 10 used for injecting liquid helium from the outside can also be used as the supply tube.

The present invention will be explained in detail below with reference to FIGS. 2 and 3.

The inner tank 1 is composed of a container made of stainless steel or the like, and the coil 2 is fixed therein using a special fixture (not shown). A liquid helium tank 3 is provided on the upper side, and both are connected by a connecting pipe 4.
The upper and lower liquid helium 5 are in communication.

A switch box 7 containing a persistent current switch 6 is attached to the inner tank 1, and a power lead 8 is further connected thereto. The current supplied from the external connection part 9 of the power lead 8 passes through the power lead 8 and a lead wire (not shown) to the persistent current switch 6.
and flows into coil 2. On the other hand, piping for cooling is an injection pipe 10 serving as a liquid helium injection port 10.
A and 10B are provided, and a discharge pipe 11 for discharging evaporated helium gas to the outside is provided.

These cryogenic parts 12 are built into an outer tank (not shown) configured as a vacuum container, are heated and shielded by a heat shield plate and a super-insulating material, and are thermally supported by a load support material so that the inside of the cryogenic part 12 is It is designed to be able to maintain extremely low temperatures. The superconducting magnet also has a liquid helium injection port 10, a helium gas discharge port 13, and a power lead connection port 9 shown here.
In addition, various piping and ports are provided.

In FIG. 2, the injection pipe 10A is piped into the inside of the tank 3, the injection pipe 10B is piped into the inner tank 1, and the junction of both is connected to the receiving pipe 10C in the connecting pipe 4.
engage with.

As shown in FIG. 3, the receiving pipe 10C is connected and fixed to one end of the inner tank injection pipe 10B, and is fitted with the tank injection pipe with an annular gap 4B, so that the upper end is flush with the bottom of the tank 3. Install it so that it opens in a shape. This gap 4B is 0.5~
2 mm (standardly, less than 1 mm is preferred), and the fitting length is set to 30 to 100 mm (standardly, 50 mm or more is preferred).

In this superconducting magnet cooling method, first, cold helium gas is sent through the injection port 10 to cool the inner tank 1, coil 2, etc.
It is fed into the inner tank 1 through the opening 14 through B, and the device is cooled from room temperature to a cryogenic temperature. This is to efficiently cool the coil section, which has a large heat capacity.The cold helium gas that has cooled the coil 2 cools the tank 3, passes through the discharge pipe 11 from the tank outlet 15, and is sent to the recovery device from the discharge port 13. It will be returned.

After pre-cooling to an extremely low temperature in this way, liquid helium is sent from the injection port 10 into the inner tank 1 and the tank 3.
is stored.

In this state, current is supplied to the coil 2 and the coil 2 is excited, but during such energization, the persistent current switch 6 and the power lead 8 generate heat due to electrical resistance, and a large amount of helium gas is generated.

This large amount of helium gas is transferred between the connecting pipe 4 and the receiving pipe 1.
It rises through an annular gap 4A surrounded by 0C. On the other hand, the supplementary liquid helium passes through the receiving tube 10C and descends to the bottom of the inner tank 1 through the injection tube 10B, thereby enabling smooth gas-liquid exchange. It can also be used as a tube for initial cooling and liquid helium injection.

In FIG. 3, if this gap 4B is wide and the fit is short, the refrigerant gas sent from the inlet 10 leaks out from the coil 2 in the inner tank 1.
On the other hand, if the gap is made too narrow or the fit is made too long, the above-mentioned function as a supply pipe will not be obtained. Note that the same applies to the case of injection of liquid helium.

On the other hand, in this configuration, the injection pipes 10A, 1
Compared to 0B, the pipe diameter required for the receiving pipe 10C is only slightly increased, and these connections are simple fits, so assembly around the connecting pipe 4 can be performed very easily.

As explained above, in the connecting pipe for connecting the liquid helium tank and the inner tank, a receiving pipe is provided at the upper end of the inner tank side injection pipe, and the tank side injection pipe is inserted.
By forming a tube structure in which the gap and fitting length are selected to predetermined values, it is possible to use the liquid helium supply tube that prevents vapor lock phenomenon as well as the inner tank side injection tube, without creating a complicated structure by adding a separate tube. It becomes possible to provide an excellent superconducting magnet cooling structure that is easy to assemble and does not need to be assembled.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of the internal structure of a conventional superconducting magnet.
FIG. 2 is a sectional view of the internal structure of the superconducting magnet of the present invention,
Fig. 3 is a detailed view of the part shown in Fig. 2. DESCRIPTION OF SYMBOLS 1... Inner tank for superconducting magnet, 2... Coil, 3... Tank, 4... Connecting pipe, 4A... Annular gap, 4B... Gap, 5... Liquid helium, 6... Current switch, 7...
Switch box, 10A, 10B...Injection tube, 10C...
Receiving tube.

Claims (1)

[Claims] 1. In a superconducting magnet equipped with a connecting pipe that connects the superconducting magnet inner tank and the tank, a receiving pipe of a specified length is installed inside the connecting pipe, and an injection pipe is connected to this receiving pipe and the superconducting magnet inner tank. 10B, the injection pipe 10A is fitted into the receiver pipe, and the fitting gap and fitting length are set to predetermined values.