JPH11329114A - Forced cooling superconductive conductor and superconducting coil using the conductor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To heighten stability of a forced cooling superconductive conductor, by setting the flow rate of a cooling medium in the twisted wire part parallel to a high-resistance channel part to be larger than the flow rate in the twisted wire part parallel to a low-resistance channel part, therefore by enlarging the amount of heat removed by the cooling medium, in the twisted part where the flow rate of the cooling medium is larger. SOLUTION: In this forced cooling superconductive conductor, perforated holes 4 are formed in the wall surface of a channel 3 to permit replacement of a cooling medium in a conduit 1 containing a twisted wire part 2 and a channel part 3. Although the outside diameter of the channel part 3 is constant over the length of it, the inside diameter of the channel 3 is lessened in the portions where higher stability is required.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a forced cooling superconductor in which the superconductor is cooled by a refrigerant such as supercritical helium circulating in the superconductor, and more particularly to a twisted wire portion of the superconductor and a coolant flow path. And a superconducting coil using the same.

[0002]

2. Description of the Related Art Methods for improving the stability of a supercooled superconducting conductor are disclosed in Japanese Patent Application Laid-Open Nos. 7-46137 and 8-8
No. 3620 is disclosed. In each case, the superconducting wire is number 1
Cable-in-conduit conductor (Cable-In-con) in which 0 to several hundred strands are twisted, bundled and put in a metal sheath
duit conductor). The stability of a superconducting conductor (ie, the property that a phenomenon called quench, in which a normal conduction transition region spreads over the entire conductor due to local thermal disturbance, is unlikely to occur) occurs when a superconducting conductor locally becomes a normal conducting state. Can be improved by removing the heat generated by the cooling medium.

In Japanese Patent Application Laid-Open No. 7-46137, a superconducting wire is twisted around a conductor having a high thermal conductivity, and the heat generated from the superconductor which has undergone a normal conduction transition is conducted to the conductor and quickly removed. Japanese Patent Application Laid-Open No. 8-83620 discloses a method for promoting heat transfer to a refrigerant by providing a projection or the like on the surface of a stranded wire of a superconducting conductor, or by thinning the stranded wire and increasing the surface area of the stranded wire of the superconducting conductor. It is assumed that.

[0004]

However, in the above prior art, since the superconducting stranded wire needs to be processed, the number of man-hours for manufacturing the stranded wire increases, the wire material price increases, and the superconducting stranded wire itself is damaged. It will be easier. On the other hand, it is also possible to improve the heat transfer from the superconducting stranded wire to the refrigerant by increasing the flow rate of the refrigerant without taking the above method.
However, the pressure loss increases in proportion to the square of the flow rate of the refrigerant, and the flow rate of the refrigerant also increases, thereby increasing the capacity of the refrigerant circulation pump. An object of the present invention is to provide a forced cooling superconducting conductor having higher stability and a superconducting coil using the same.

[0005]

SUMMARY OF THE INVENTION To achieve the above object, the present invention is characterized in that the channel is a low-resistance channel having the smallest flow resistance of the refrigerant, and the flow resistance of the refrigerant is larger than that of the low-resistance channel. And a high-resistance channel portion.

[0006] Since the flow path resistance of the refrigerant is large in the high resistance channel portion, the flow rate of the refrigerant is smaller than that in the low resistance channel portion. Since the flow rate of the refrigerant is small, the flow rate of the refrigerant flowing through the stranded wire section parallel to the high-resistance channel section is larger than that of the stranded wire section parallel to the low-resistance channel section. Therefore, the flow rate of the refrigerant is higher in the stranded wire section parallel to the high-resistance channel section than in the stranded wire section parallel to the low-resistance channel section. In the stranded portion where the flow rate of the refrigerant is increased, the heat removed by the refrigerant is increased, so that the stability of the forced cooling superconducting conductor is improved.

If the flow resistance of the channel is increased over the entire length of the forced cooling superconducting conductor, the flow rate of the refrigerant is greatly reduced. However, if the flow resistance of the channel where stability is desired to be improved is increased, In addition, a decrease in the flow rate of the refrigerant can be suppressed to a small value, and the stability can be improved.

The high-resistance channel portion may have a smaller refrigerant flow path size than the low-resistance channel portion. Further, an obstacle that hinders the flow of the refrigerant may be provided in the refrigerant channel.

Another feature of the present invention resides in that the forced cooling superconducting conductor wound first or second time from the inside of the superconducting coil has a high resistance channel portion. The superconducting coil has a strong magnetic field on the inner peripheral side, and if the forced cooling superconducting conductor in this portion has a high resistance channel portion, the stability of the superconducting coil is further improved.

Another feature of the present invention is that the limit current value for each winding of the superconducting coil is three times from the inside,
The point is to have a break from high to low. Since the superconducting coil has a strong magnetic field on the inner circumference side, the current limit value of the conventional superconducting coil is smaller on the inner circumference side, but if the current limit value on the inner circumference side of the superconducting coil is increased, each winding of the superconducting coil has The limiting current value has a break point from high to low.
Since the limiting current value at the hip break point is higher than the conventional limiting current value on the inner peripheral side, the stability of the superconducting coil can be further improved.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the relationship between the flow rate of refrigerant in a superconducting coil and the current limit will be described. The stability of the superconducting coil is sensitive to the local magnetic field and temperature where the superconducting conductor is placed. Regarding a superconducting coil made of a long superconducting conductor, stability is low in a portion where the refrigerant temperature is high or a portion where the magnetic field is large.

[0012] Since the stability of the superconducting coil is evaluated at the portion where the stability is the lowest, if the stability is low locally, the stability of the superconducting coil is improved by improving the stability there. Increase.

One of the quantitative indicators of the stability of the superconducting coil is described in "Kiyoshi Yoshida, Study on stability and protection of large superconducting coil by forced cooling system, JAERI-M 92-11."
9, p. 77, Japan Atomic Energy Research Institute (1992) ".

[0014]

## EQU1 ## I _lim = { ^{ph A} _Cu (T _c −T _b ) / ρ} ^0.5 p: cooling perimeter of stranded wire (m) h: heat transfer coefficient from stranded wire to refrigerant (w / m ² K) ∝v
^0.8 v: Refrigerant flow rate (m / s) A _Cu : Cross-sectional area of stabilized copper (m ³ ) T _c : Critical temperature (K) T _b : Refrigerant temperature (K) ρ: Resistivity of copper (Ωm) (number) The limiting current shown in 1) indicates a current value at which the amount of Joule heat generated by the normal conduction transition in the stranded wire becomes equal to the amount of cooling due to heat transfer to the refrigerant. If the current flowing through the superconducting coil is smaller than the limited current, the heat generated by the superconducting conductor is sufficiently removed by the refrigerant. In other words, the superconducting coil having a larger limiting current has higher stability of the superconducting conductor.

As is apparent from (Equation 1), the limiting current is proportional to the heat transfer coefficient to the power of 0.6.
Superconductivity Engineering Revised Edition, p.116, Ohmsha, Tokyo, 19
According to 1988, the heat transfer coefficient is proportional to the 0.8th power of the refrigerant flow rate. Therefore, the limiting current is proportional to the coolant flow rate to the power of 0.4.

In the case of a forced cooling superconducting conductor having a channel at the center of the conductor cross section and flowing through both the stranded portion and the channel, the refrigerant flow rate in the stranded portion contributes to the stability of the superconducting coil, and the refrigerant flow rate in the channel is controlled by the operation. It contributes to the removal of heat generated inside and the shortening of the cooling time from room temperature to extremely low temperature.

The channel and the stranded portion can be regarded as a parallel circuit through which the refrigerant flows. When the inner diameter of the channel is narrowed or an obstacle is locally provided to increase the flow path resistance of the channel, the flow resistance of the stranded wire portion becomes relatively small, so more refrigerant flows through the stranded wire portion. Become like
Therefore, the flow velocity of the refrigerant in the stranded portion increases. Since the heat transfer from the stranded wire to the refrigerant increases in proportion to the refrigerant flow velocity to the power of about 0.4, at the stranded wire portion where the flow velocity of the refrigerant is increased, the stability of the superconducting conductor is increased, and it is difficult to quench. .

If the flow resistance of the channel is increased over the entire length of the superconducting coil, the flow rate of the refrigerant is greatly reduced. However, if the flow resistance is locally increased, the decrease in the flow rate of the refrigerant is reduced. Can be suppressed.

Next, an embodiment of the present invention will be described.

FIG. 1 shows a forced cooling superconductor according to an embodiment of the present invention. The forced cooling superconducting conductor of the present embodiment has a stranded wire portion 2 in which a superconducting wire is stranded and a channel 3 through which supercritical helium as a refrigerant flows, inside a conduit 1 covering the outer periphery. The wall of the channel 3 is provided with through holes 4 so that the refrigerant can be exchanged between the stranded wire portion 2 and the channel 3.
Is emptied, and the refrigerant flows through the stranded wire portion 2 and the channel 3
Flow through both. The outer diameter of the channel 3 is the same over the entire length, but the inner diameter differs depending on the required stability of the superconductor. In a portion where higher stability is required, the inner diameter of the channel 3 is reduced.

For the channel 3, two kinds of pipes 3a and 3b having the same outer diameter and different inner diameters as shown in FIG. 2 are used. A pipe 3a having a large inner diameter is used for a portion where the stability of a normal superconducting conductor is required, and a pipe 3b having a small inner diameter is used for a portion where higher stability of the superconducting conductor is desired, and these are connected by welding or the like. Since the outer diameters are substantially equal, if the surface of the connection portion is smoothly worked after the connection operation by welding or the like, there is no danger of mechanically damaging the superconducting stranded wire.

Further, as shown in FIG.
What wound a and 5b in the shape of a spiral may be used.
The gap 6 plays the same role as the through hole 4. If the strip-shaped materials 5a and 5b having different thicknesses are wound so as to have the same outer diameter, pipes having different inner diameters can be manufactured. Further, as shown in FIG. 4, a flow path resistance of the channel 3 may be increased by inserting a bar-shaped obstacle 8 across the channel 3. The bar-shaped obstacle 8 is fixed to the wall surface of the channel 3 by welding or the like. After welding, smooth the outer surface of the channel.

A method for manufacturing a forced cooling superconductor according to this embodiment will be described with reference to FIG. The superconducting stranded wire 2 is twisted from the stranded wire drum 10 around the channel 3 fed out from the channel drum 9, the conduit 1 is wound from the conduit drum 11, and the forming roller 12 is wound.
, And then welded and integrated by the welding machine 13.
This is stretched by a wire drawing machine 14 to obtain a product shape. The internal shape of the channel 3 is inspected by an inspection device 15 such as a non-destructive inspection, a position where the internal shape is changed is marked, and then wound around a product drum 16. At the time of coil production, the conductor region in which the channel shape is changed can be specified by the marking, and the region can be arranged at a desired position of the superconducting coil.

Next, the improvement in stability by the present embodiment will be quantitatively described.

FIG. 6 shows a single pancake coil 7
A pancake-wound coil in which 0 pieces are stacked is shown. FIG. 7 shows a cross-sectional structure of the single pancake coil 7. The single pancake coil 7 is formed by winding the forced cooling superconducting conductor of this embodiment for 9 turns. The supercritical helium of the refrigerant is
Each single pancake 7 flows in from the innermost turn of the coil and flows out from the outermost turn.

FIG. 8 shows an equivalent circuit of the refrigerant flow path of the single pancake coil 7. In each turn, the flow path resistance R ₃ of the flow resistance of the twisted portion 2 R ₂ and channel 3 are installed in parallel, the pressure V of the refrigerant circulation pump, the coolant flow rate I ₂ and I ₃ is generated.

In the single pancake coil 7, the inner diameter of the channel 3 in the first turn is reduced, and is increased in the second to ninth turns. The ratio of the channel resistance R ₃₁ of the first flow path resistance of the turns of stranded wire section 2 R ₂₁ and channel 3 R _21: R
₃₁ = r: 2r = 1: 2. The ratio of the flow path resistance R _2n of the stranded wire portion 2 to the flow resistance R _3n of the channel 3 in the second to ninth turns is R _2n : R _3n = r: r = 1: 1.

FIG. 9 shows the refrigerant flow rate of the single pancake coil 7 in which the inner diameter of the channel 3 is reduced only in the first turn, and the refrigerant flow rate of the conventional single pancake coil in which the inner diameter is large from the first turn to the ninth turn. The difference is shown.

In the single pancake coil 7, the total flow rate I is reduced by 6.3% as compared with the conventional pancake coil ((6/19) /
(1/3) = 0.947), the flow rate I _2n of the stranded portion 2 after the second turn is also reduced by 6.3%, but the flow rate I ₂₁ of the stranded portion 2 in the first turn is 42.1. % Increase ((3 /
19) / (1/9) = 1.421).

FIG. 10 shows the temperature, magnetic field, and limiting current of each turn for the single pancake coil 7 and the conventional single pancake coil. The refrigerant temperature is lowest in the first turn, and increases as it goes downstream, but does not have a significant effect. The magnetic field created by the coil is the highest on the first turn,
It decreases as it moves to the outer circumference and increases again slightly.
The critical temperature of the superconductor strongly depends on the magnetic field distribution, and becomes the lowest at the first turn. In the conventional type, the limiting current is the lowest in the first turn and 1.13 times the operating current, which defines the stability of the coil.

In the single pancake coil 7, the limiting current of the first turn is 1.29 times the operating current, the limiting current of the second turn is slightly reduced to 1.20 times, and the stability of the coil is limited by the limiting of the second turn. Defined by current. Therefore, the margin of the superconducting coil stability is increased from 13% to 20% as follows: 1.
It can be increased 6 times or more. For a coil having a sufficient margin of 13%, the cross-sectional area of the stabilized copper shown in (Equation 1) can be reduced by 11%, so that the square of (1.13 / 1.20) = 0.886), the coil size can be reduced, and the superconducting stranded wire can be inexpensive. Alternatively, the 11% resistivity of the stabilized copper can be increased, and the cost of copper is reduced. Alternatively, since the refrigerant flow rate can be reduced by 14% ((1.13 / 1.20) to the 2.6th power = 0.860),
The pressure loss can be reduced by 26% (the square of (1.13 / 1.20) to the power of 2.6 = 0.740), and the capacity of the refrigerant circulation pump can be reduced.

Further, processing the channel 3 to increase the flow rate of the refrigerant in the stranded wire portion 2 can be performed easily and inexpensively as compared with processing the stranded wire portion 2 of the superconductor.

Further, in this embodiment, the case where the channel resistance of the channel 3 has two levels of high and low has been described. However, a plurality of levels may be used according to the required stability.

[0034]

According to the present invention, the flow rate of the refrigerant is greater in the stranded portion parallel to the high-resistance channel portion than in the stranded portion parallel to the low-resistance channel portion. In the stranded portion where the flow rate of the refrigerant is increased, the heat removed by the refrigerant is increased, so that the stability of the forced cooling superconducting conductor is improved.

The superconducting coil has a strong magnetic field on the inner peripheral side. If the forced cooling superconducting conductor in this portion has a high resistance channel portion, the stability of the superconducting coil is further improved.

Further, if the current limiting value on the inner peripheral side of the superconducting coil is increased, the current limiting value for each winding of the superconducting coil has a waist break point from high to low. Since the current value is higher than the conventional limit current value on the inner circumference side, the stability of the superconducting coil can be further improved.

According to the present invention, a superconducting coil having high stability can be provided without increasing the refrigerant flow rate and pressure loss. Therefore, the stability margin against disturbance causing coil quench can be increased, and the high performance superconducting coil can be provided. A superconducting coil can be provided. Alternatively, if the stability is the same as that of the prior art, the amount of stabilized copper can be reduced, the coil size can be reduced, and the superconducting conductor can be inexpensive. Or,
The resistivity of the stabilized copper can be increased, or the flow rate of the refrigerant can be reduced to reduce the capacity of the refrigerant circulation pump.

[Brief description of the drawings]

FIG. 1 is a diagram showing a forced cooling superconductor according to an embodiment of the present invention.

FIG. 2 is a view showing pipes 3a and 3b constituting a channel 3.

FIG. 3 shows a channel 3 formed by spirally winding a band-shaped material.
FIG.

FIG. 4 is a diagram showing an example in which a channel 3 is structured by inserting a bar-shaped obstacle 8 into a channel flow channel.

FIG. 5 is a diagram illustrating a method for manufacturing the forced-cooled superconducting conductor of the present embodiment.

FIG. 6 is a diagram showing a pancake-wound coil.

FIG. 7 is a diagram showing a cross-sectional structure of a single pancake coil 7;

FIG. 8 is a diagram showing an equivalent circuit of a refrigerant flow path of the single pancake coil 7.

FIG. 9 is a table showing the refrigerant flow rates of the single pancake coil 7 and the conventional single pancake coil.

FIG. 10 is a diagram showing distributions of the temperature, the magnetic field, and the limiting current of the single pancake coil 7 and the conventional single pancake coil.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Conduit, 2 ... Stranded wire part, 3 ... Channel, 3a,
3b: pipe, 4: through hole, 5a, 5b: band-shaped material,
6 gap, 7 single pancake coil, 8 obstacle, 9 drum for channel, 10 drum for stranded wire, 1
DESCRIPTION OF SYMBOLS 1 ... Conduit drum, 12 ... Forming roller, 13 ... Welding machine, 14 ... Drawing machine, 15 ... Inspection device, 16 ... Product drum.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Katsuhiko Asano, Inventor Katsuhiko Asano 3-1-1, Sachimachi, Hitachi-shi, Ibaraki Pref. Hitachi, Ltd. Hitachi Plant (72) Inventor Kenkichi Ushigusa 801 Mukoyama, Nakamachi, Naka-gun, Naka-gun, Ibaraki Prefecture No. 1 in the Japan Atomic Energy Research Institute, Naka Research Laboratory (72) Inventor Yoshikazu Takahashi 801 Mukaiyama, Naka-machi, Naka-gun, Ibaraki Prefecture Inside of Japan Nuclear Research Institute Naka Research Laboratory (72) Inventor Mitsuru Kikuchi, Naka-machi Naka-machi, Ibaraki Prefecture 801 Mukoyama 1 Atomic Research Institute, Naka Research Institute of Japan

Claims (5)

[Claims] 1. A stranded wire having a plurality of superconducting wires, and a refrigerant flow passage disposed in parallel with the stranded wire and penetrated in a longitudinal direction for allowing a refrigerant to pass therethrough. A forced cooling superconducting conductor comprising a channel having a passage for supplying the refrigerant from the path to the stranded wire portion, wherein the channel is smaller than the low-resistance channel portion having the smallest flow path resistance of the refrigerant, and A forced-cooled superconductor having a high-resistance channel portion having a large flow path resistance of a refrigerant. 2. The forced cooling superconducting conductor according to claim 1, wherein said high-resistance channel portion has a smaller size of said refrigerant flow path than said low-resistance channel portion. 3. The forced-cooled superconducting conductor according to claim 1, wherein the high-resistance channel portion has an obstacle in the coolant flow path that impedes the flow of the coolant. 4. A stranded wire having a plurality of superconducting wires, and a refrigerant flow passage disposed in parallel with the stranded wire and penetrated in a longitudinal direction for allowing a refrigerant to pass therethrough. In a superconducting coil in which a forced cooling superconducting conductor comprising a channel having a passage for supplying the refrigerant from the path to the stranded wire is wound a plurality of times, the channel portion is a low-resistance channel portion having the smallest flow path resistance of the refrigerant. A high-resistance channel portion having a larger flow path resistance of the refrigerant than the low-resistance channel portion, and wherein the forcibly cooled superconducting conductor wound first and second times from the inside has a high-resistance channel portion. Features superconducting coil. 5. A superconducting coil in which a forcedly cooled superconducting conductor containing a stranded superconducting wire and a channel through which a cooling medium for cooling the superconducting wire passes is wound a plurality of times. A superconducting power supply characterized in that a limiting current value, which is a current value at which a heat value and a cooling amount due to heat transfer to a refrigerant become equal, is set from a high point to a low point by three turns from the inside. coil.