JPH0512873B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a superconducting magnet used in a floating railway, etc., for injecting a current into the superconducting magnet or for demagnetizing the current that the superconducting magnet has. , relates to a power lead structure connecting an internal coil and an external power source.

[Technical background of the invention and its problems]

In superconducting magnets such as those used in floating trains, copper conductors are generally used as power leads that connect internal coils and external power sources, directly connecting the superconducting coils and the outside. It is also practiced to supply electricity while cooling with liquid nitrogen and helium gas.

Generally speaking, in order to excite or demagnetize a superconducting magnet by energizing it, it is better to use a good conductor, such as copper with high purity and low electrical resistance, as this will result in less resistance loss during energization. The amount of thermal energy entering the inner tank due to resistance loss can be reduced. However, since the inner tank and the outer tank are always connected through this good conductor, external heat enters through the power lead and vaporizes the liquid helium in the inner tank.

On the other hand, configuring the power lead with a conductor made of copper with poor purity is convenient because it prevents the amount of heat intrusion when no current is applied, but the resistance heats up due to energization during excitation or demagnetization, making it difficult to use a thermal type persistent current switch. If the switch is placed adjacent to the power lead, the heat from the power lead will be transmitted to the persistent current switch, and even if you turn off the heater current to form a persistent current circuit, the heat from the power lead will cause permanent The current switch may no longer turn on, or the persistent current switch that once cooled down to a superconducting state and turned on is gradually warmed up by the power lead, returning to a normal conducting state and turning off at an inconvenient time. There is a risk of malfunction. Such a situation is extremely dangerous and is equivalent to quenching a superconducting magnet, and there is a risk that the persistent current switch may burn out. Conventionally, as a method to prevent this, a large amount of vaporized helium gas was poured into the power lead for cooling purposes while the power lead was energized, thereby cooling the power lead which generated heat.

However, cooling with helium gas as described above increases the consumption of liquid helium, creating the problem that the capacity of the on-vehicle liquid helium reservoir and helium liquid refrigerator must be increased. The drawback was that it was not suitable for miniaturization and weight reduction.

[Purpose of the invention]

The purpose of the present invention was to eliminate these drawbacks, and by constructing the power lead with copper alloy/aluminum alloy, it is possible to prevent heat from entering when no current is applied, and to reduce the consumption of liquid helium. It is an object of the present invention to provide a mechanism that reduces heat intrusion into the interior of a superconducting magnet during excitation or demagnetization.

[Structure of the invention]

An embodiment of the present invention will be described below with reference to FIGS. 1 and 2.
This will be explained using FIG. FIG. 1 is a cross-sectional conceptual explanatory diagram of the basic structure of a conventional superconducting magnet and the present invention.

[Summary of the invention]

The present invention utilizes the thermal conductivity characteristics of the power lead of a superconducting magnet to maintain the superconducting state of the superconducting coil. If the material of the power lead is copper, for example, oxygen-free copper, which has relatively high purity, is used. Since it has good current conductivity and thermal conductivity, it has low electrical resistance during excitation or demagnetization, so it generates little heat and is easy to use. However, once the superconducting coil enters the superconducting state, the current in the power lead disappears, which has the disadvantage that heat easily propagates from the external terminal of the power lead to the superconducting coil, causing the heat-sensitive persistent current switch to malfunction. There is a fear.

On the other hand, when phosphorus-deoxidized copper has low purity and high electrical resistance, it generates a large amount of heat during excitation or demagnetization, and the increased amount of heat must be cooled down. Instead, heat is hardly transmitted from the outside to the superconducting coil through the power lead.

By the way, the time to excite and demagnetize the superconducting state and the time to use it in the superconducting state are of course longer, and during the latter time, if the power lead is a highly pure conductor, the external In order to cool down the total amount of heat transferred from the superconductor to the inside, it is necessary to increase the amount of refrigerant and the size of the liquid helium reservoir.However, if a copper alloy or aluminum alloy is used for the power lead, the power lead will not be exposed to the outside during the superconducting state. Since heat propagation from the terminals is drastically reduced, the refrigerant and liquid helium reservoir can be made smaller and lighter.

In order to achieve the above, special cooling fins are interposed between the power lead and the current switch to prevent malfunctions and conduct heat so that the heat generated during excitation or demagnetization due to the high resistance of the power lead is not transmitted to the current switch. This reduces the size and weight and improves reliability.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIGS. 1 and 2.
This will be explained using FIG.

In FIG. 1, a superconducting coil 1 is provided in an inner tank 2, and is cooled by liquid helium 3 to maintain a superconducting state. A liquid helium reservoir 4 is provided in the upper part of the inner tank 2, and the liquid helium 3 that is vaporized due to heat intrusion into the inner tank 2 becomes gas and collects in the upper part 5 of the liquid helium reservoir 4. These inner tanks 2
etc. are housed in an outer tank 6, which is vacuum insulated and shielded from radiant heat input and kept cool.

A thermal persistent current switch 7 is connected to the superconducting coil 1 and the power lead 8 in the inner tank 2. The power lead 8 is used to send a current to the superconducting coil 1 from the outside to excite or demagnetize it. The power lead 8 has a pair of electrodes, but it is shown as a single line in this figure, which means that even if the electrical resistance is high to a certain extent, the thermal conductivity is low in order to suppress heat intrusion from the outside. It is made of copper alloy or aluminum alloy with low purity, such as copper with relatively low purity such as phosphorus-deoxidized copper, and is kept cooled in an outer cylinder 9 and connected to an external power source with an external terminal 10 of a power lead. Ru. Near the external terminal 10 of the power lead 8, a cooling fluid nitrogen supply pipe 11 and a discharge pipe 12 rise from the cooling section 13, and operating valves 14 and 15 are shown somewhat schematically above the supply pipe 11 and a discharge pipe 12 for cooling the power lead. It is devised to cool the external end portion of the housing 8 and prevent heat from entering from the outside.

When the operation valve 16 is operated, the helium gas accumulated in the upper part of the liquid helium reservoir 4 is taken out through the pipe 17, and the helium gas is made to flow into the position closest to the inner tank of the power reed through the pipe 18, and the helium gas is discharged from the helium gas outlet. 19 and forcibly cools the power lead 8 to cool the heat generated when a large current flows through the power lead 8, and prevents heat from entering the superconducting coil 1 and the persistent current switch 7. There is.

In FIG. 2, the structure of the connecting portion between the power lead 8 and the persistent current switch 7 is shown. The inner tank 2 near the persistent current switch has the power lead end 8
A is electrically insulated from the inner tank 2 or the outer cylinder 9 because it is insulated from the outer cylinders 21 and 22 while maintaining airtightness with the seal of the ceramic insulation 20. Here, the power lead end portion 8a is constituted by a solid copper rod and is connected to the cooling fin 23.

Further, the other end of the cooling fin 23 has a concave groove and is connected to a lead bar 24 which is a curved copper rod, and within this concave curved part, the persistent current switch outlet wire 25 and the superconducting coil outlet are connected. A wire 26 is connected by soldering or the like. The cooling fins 23 and the persistent current switch 7 are mounted on the fixing metal fittings 2.
7, 28 and an insulating material 29 provided concentrically, and the power lead end 8a and lead bar 24 are insulated from the inner tank 2 by bolts and nuts via insulating materials 32, 33, etc. to fixing fittings 30, 31. Stably fixed.

FIG. 3 is a perspective view showing the cooling fin 23 of the present invention, in which the distance between the terminal 23a connected to the power lead end 8a and the other persistent current switch 7 and the connection part is made sufficiently long for effective use of space. In addition, a plurality of fins 23c with an enlarged cooling area are effectively provided between them, and are completely immersed in liquid helium.

Although the above description has shown the parts necessary for the present invention, it goes without saying that various other devices, supporting materials, etc. are arranged to constitute the superconducting magnet.

According to the superconducting magnet structure having the above configuration, power leads made of copper alloy/aluminum alloy, which have high electrical resistance but low thermal conductivity, are used to keep heat intrusion low at all times, and also allow current to flow from an external power source to the power leads. Even if the power reeds generate too much heat due to a lack of cooling gas when energizing, the cooling fins are always cooled by a large amount of liquid helium, so the persistent current switch is kept cool due to the insulation effect between the cooling fins and the power reeds. The persistent current switch can prevent dangerous quenching phenomena by cutting off heat input from the power lead.

Above, we have explained the power lead materials that take advantage of the characteristics of copper due to the difference in purity.
Of course, the same effect can be obtained even if other materials such as copper alloy, aluminum alloy, or other conductive material having similar electrical resistance and thermal conductivity are used.

As a result of the above, conventionally a large amount of helium gas was required for power lead cooling, but according to the present invention, even if the amount of helium gas is significantly reduced, the heat input to the persistent current switch in the inner tank can be reduced. Since this can be effectively prevented, the persistent current switch can be operated stably.

In addition, if this is effectively utilized, it will be possible to operate without any performance problems if the current is below a certain level without using cooling gas, and the structure of the superconducting magnet will make it smaller and lighter, making it more reliable. It will improve.

〔Effect of the invention〕

As explained above, according to the present invention, when power is being supplied to the superconducting magnet, the heat transmitted to the persistent current switch due to the heat generated by the power lead can be absorbed by the cooling fins and cut off.

In addition, when the superconducting magnet is in a superconducting state, it is possible to reduce heat intrusion from the outside due to heat conduction through the power leads, and the cooling fins absorb heat intrusion into the persistent current switch through the power leads. Can be blocked.

[Brief explanation of drawings]

1 is a side view of a superconducting magnet of the present invention, FIG. 2 is an enlarged side view of a portion of FIG. 1, and FIG. 3 is an enlarged perspective view of a cooling fin 23. 1... Superconducting coil, 2... Inner tank, 3... Liquid helium (refrigerant), 7... Persistent current switch, 8
...Power lead, 23...Cooling fin.

Claims (1)

[Claims] 1. In a superconducting magnet device in which a superconducting coil placed in an inner tank is connected to an external power source via a persistent current switch and a power lead, the power lead is made of a copper alloy or an aluminum alloy, and the power lead and A superconducting magnet device characterized in that cooling fins are provided between the persistent current switch and the persistent current switch.