JPS5953685B2 - Superconducting toroidal magnet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to improvements in superconducting toroidal magnets that require electrical, thermal, and mechanical protection.

Currently, superconducting toroidal magnets are being considered for use as magnetic field generators for nuclear fusion reactors and electrical energy storage devices, but the size of a practical-scale superconducting toroidal magnet is IOH Joule (in terms of stored energy). This is a gigantic project that has never been realized before.

The main component of a superconducting toroidal magnet is a superconducting toroidal coil, and FIG. 1 shows the concept of a superconducting toroidal coil 1.

That is, as shown in the figure, the superconducting toroidal coil is configured so that a magnetic field B is generated within the coil by a toroidal current 10. However, it is considered that the actual superconducting toroidal coil 1 is almost never wound evenly as shown in FIG.

Because the main radius R of the superconducting toroidal coil is l0m
It is very difficult to make the superconducting toroidal coil 1 as a single coil because the small radius γ is huge, several meters, and it is necessary to supply nuclear fusion fuel, evacuation, measurement, etc. For example, by requiring access to the toroidal magnetic field region. Therefore, as shown in Figure 2,
The superconducting toroidal coil 1 is divided into several parts and formed as a combination of individual superconducting coils 2.

FIG. 3 is a partially cutaway perspective view of a pancake-shaped superconducting coil, which is a type of superconducting coil 2 constituting the superconducting toroidal coil 1. This superconducting coil 2 is made by winding a superconducting wire 3 with a spacer 4 between turns. Rotated pancake coil 2
00 are stacked and fixed in a winding frame 6 via an interlayer spacer 5, and the superconducting wire 3 has an interturn spacer 4 and an interlayer spacer 5 both between turns and between layers.
The interlayer spacer 5 forms a gap 7 through which a cooling medium such as liquid helium flows.

This gap 7 has the role of allowing air bubbles of the cooling medium generated on the surface of the superconducting wire 3 to escape, and the role of supplying the cooling medium. However, such a pancake-shaped superconducting coil cannot be used for superconducting wires due to the huge electromagnetic force generated by the GJ-class coil.
The disadvantage is that the characteristics of the superconductor may deteriorate or the superconducting wire may break.

In order to compensate for the drawbacks of the conventional superconducting coil, a superconducting coil having a structure as shown in FIG. 4 has been considered.

That is, the superconducting coil 2 shown in FIG. 4 is formed by providing a plurality of coil grooves 9 on both sides of a plate-shaped holding member 8 made of metal or an insulator, and storing the superconducting wire 3 in the coil grooves. By stacking a plurality of superconducting disks 100,
It is assembled by tightening bolts 10 and nuts 11. The superconducting coil 2 configured as described above can sufficiently withstand the huge electromagnetic force generated by the coil, so it is suitable for use in superconducting toroidal magnets that are used in nuclear fusion reactors and energy storage devices. Can be used as a coil. Conventionally, the circuit shown in FIG. 5 has been considered as an excitation driving circuit for a toroidal magnet as a magnetic field generator using these superconducting coils.

As shown in the figure, a superconducting toroidal coil 1 is immersed in a cryostat 13 in which a cooling medium 12 is stored, and with a switch 14 closed, a rated operating current of 1 is applied by an excitation power source 15. It is excited up to. By the way, during operation of the superconducting toroidal coil 1, the superconducting toroidal coil 1 may be quenched (superconducting breakdown in which the original superconducting state cannot be restored).

Note that the occurrence of quench in the superconducting toroidal coil 1 is normally detected when the resistive voltage generated in the superconducting toroidal coil 1 reaches a predetermined value, but it is also possible to detect this by measuring the temperature rise. In some cases, it may be more detectable.

When quench occurs in superconducting toroidal coil 1,
It is necessary to rapidly remove the magnetic energy stored in the superconducting toroidal coil 1 and suppress the temperature rise of the superconducting toroidal coil 1 within a certain limit (about room temperature).

The magnetic field generating device shown in FIG. 5 has a common configuration used for protection when quench occurs in the superconducting toroidal coil 1, and a protective resistor 16 is connected in parallel with the superconducting toroidal coil 1. When a quench occurs, the switch] 4 is opened, and the magnetic energy stored in the superconducting toroidal coil 1 is rapidly absorbed by the protective resistor 16.

In this way, most of the magnetic energy stored in the superconducting toroidal coil 1 is consumed by the protective resistor 16, and only a portion of the magnetic energy is consumed in the cooling medium, so that the temperature of the superconducting toroidal coil 1 does not rise. Not only is this kept below the limit, but the consumption of cooling medium is also reduced.
However, although the protection of the superconducting coil in the conventional magnetic field generating device described above is effective for superconducting coils of approximately 100 KJ or less, it cannot be applied to large superconducting coils having magnetic energy greater than that.

This point will be discussed below. In Fig. 5, when quench occurs in superconducting toroidal coil 1, switch 1
4 is opened to create a closed circuit consisting of the superconducting toroidal coil 1 and the protective resistor 16, the current is 1.

decays with a time constant.

Here, L (H) is the inductance of the superconducting toroidal coil 1, Rp is the resistance value of the protective resistor 16, and Rc (Ω) is the resistance value of the superconducting toroidal coil, which usually increases with time. The smaller the current decay time constant τp is, the smaller the Joule heat generation caused by the superconducting toroidal coil 1 entering the normal conduction state becomes, and the smaller the temperature rise within the superconducting toroidal coil 1 becomes.

In order to reduce the time constant τp, the resistance value R of the protective resistor 16 is
p and the normal conduction state resistance value Rc of the superconducting toroidal coil 1
needs to be made larger. Rc is an amount that changes depending on the coil stabilization method of the superconducting toroidal coil 1, the condition inside the winding, the amount of the normal conductive base material (for example, copper) of the superconducting wire, etc.; We discuss Rc = 0 (this corresponds to the case where the fully stabilized superconducting coil is locally in a normally conducting state and the normally conducting part does not propagate to the surroundings) when the conducting part remains in only one part. do. The time constant τp in this case is longer than τp when Rc>0, and coil protection becomes more difficult, so Rc=
It is sufficient to discuss the case of 0. The current decay time constant τp cannot be made as long as desired, but must be set to be less than or equal to the current decay time constant limit τa.

τa is the temperature T at which when the current attenuates, heat generation is absorbed by the heat capacity of the superconducting wire, and the temperature at time t→1 does not deteriorate the superconductor or insulator. (usually 300K) or less, it is given by the formula.

Here, IO(A) is the coil current before quenching, m
(G4m) is the superposition of normal conducting substrate per unit length, A(m
ri is the cross-sectional area of the base material, and Qc is integrated. C (J/g) is the specific heat of the base material, and ρ (Ω-m) is the resistivity of the normal conductive base material.

For example, I is applied to a superconducting wire with a cross section of 10 mm x 36 mm for a large superconducting coil.

=34. The time constant limit τa when 700A flows is 50 seconds. In the magnetic field generator shown in Fig. 5, it is necessary to keep the current decay time constant τp to 50 seconds or less when a quench is detected and the power is turned off.
For example, if the inductance L of
It has to be more than that.

However, it is assumed that Rc=0. The voltage Vt generated across the superconducting coil 5 during this current attenuation is Vt=IOR
p(v) (3).

Ic=34.700A. Substituting RP=5.2Ω, we get
t=180k. At such high voltages, it is extremely difficult to maintain insulation across the coil. in this way,
In a large superconducting coil, the superconducting toroidal coil 1 cannot be protected with the conventional configuration. In view of the above-mentioned difficulties, a large magnetic field generator has been proposed that can protect a large superconducting coil from being damaged when it is quenched. FIG. 6 shows an example of this prior art. In the figure, 1-1 to 1-n are divided excitation coils, 15-1 to 5-n are excitation power supplies for excitation, 14-1 to 14-n are switches, 16-1 to 16-
n is a protective resistor, and the excitation coils 1-1 to 1n are configured to be excited by independent excitation systems.

In FIG. 6, one of the excitation coils 1-1 to 1-n, for example 1-1, is quenched, and the excitation circuit to which the excitation coil 1-1 belongs is switched.]
4-] is opened to release the energy of the excitation coil 1-1 to the protective resistor 16-1.

The time constant τPn at that time is the one when it is assumed that no resistance is generated in the superconducting coil 5.

Here, Ln(H) is the inductance of each of the divided coils 1-1 to 1-n, and when the n divided coils are attenuated simultaneously, Ln has a relationship with the inductance L of the superconducting coil 5.

The inductance Ln of the excitation coil 1-1 when only one excitation coil 1-1 attenuates the current is only a self-inductance, and is naturally smaller than Ln in equation (5).

Here, as the most severe conditions, excitation coils 1-1 to
1-n are quenched at the same time, each excitation coil 1
-1 to 1-n when each current 10 attenuates, the voltage Vn generated in each exciting coil 1-1 to 1-n is Vn=I
ORpn(V) (6).

It can be expressed by substituting equations (4) and (5) into this. On the other hand, the voltage Vt across the coil in the magnetic field generator shown in FIG. 5 is obtained from equations (1) and (3) where Rc: 0.

Since both τP and τPn are τP=τPn and τa (current decay time constant limit), the voltage Vn at the time of quenching of the magnetic field generator of the prior art shown in FIG. 6 is the voltage Vt(7)n of the prior art of FIG. It becomes 1/1. Calculating the appropriate division number n for the superconducting coil (IO = 34.700A.L: 260H) given as an example earlier, assuming Vp = 5kV as the withstand voltage at both ends of each excitation coil, in equation (6), Since Vn=5kV, Rpn=0.14Ω is obtained.

Therefore, by substituting the above value and τPn=50 seconds into equation (4), Ln=7.2H, so from equation (5), n
:36 is obtained. In this way, if the large magnetic field generator is configured as shown in Figure 6, it becomes easy to protect the large superconducting coils used in nuclear fusion reactors, energy storage devices, etc., and the insulation process can be simplified. This is suitable for practical use because only the current in the quenched excitation coil can be reduced to zero, and most of the other parts can be kept excited.

FIG. 7 is a diagram showing still another embodiment of this prior art,
In this example, the middle points of the individual excitation coils 1-1 to 1-n are grounded.

In this case, a voltage of Vn/2 is generated at the positive terminal of the exciting coils 1-1 to 1-n, and a voltage of Vn/2 is generated at the negative terminal, so that the withstand voltage Vp is Vp=Vn/2.
・・・・・・・・・Consider (9).

Assuming VP=5kV as the withstand voltage, (6), (9)
0.29Ω obtained from the formula is the individual excitation coil 1-1~
The protective resistance value is 1-n. did. Therefore, in the case of the excitation coil of the superconducting coil (IO: 34.700A.L = 260H), if Vp = 5kV, the necessary number of divisions n is 18, and in the case of the circuits shown in Figs. 5 and 6. Number of divisions: 36
It has the advantage that only one half of the amount is required. As is clear from the above explanation, in this prior art, one excitation coil is formed by a plurality of superconducting coils, and a protective resistor is connected in parallel to each superconducting coil, and a switch is connected to each of the parallel bodies. The device is equipped with an excitation device that supplies an excitation current through the protective resistor, and by opening a switch of the excitation circuit to which the excitation coil that generated the quench belongs, the magnetic energy of the excitation coil that generated the quench is absorbed by the protective resistor. Since the voltage generated between both terminals of each excitation coil can be suppressed to a low level, a large magnetic field generator can be realized without special insulation treatment. The superconducting toroidal coil 1 is connected to n excitation coils 1-1 to 1.
The simplest way to divide the superconducting toroidal coil into n pieces is to divide the superconducting toroidal coil shown in FIG. ~1-n.

When the number m of superconducting coils 2 is n or more, the number of excitation coils may be m instead of n.

In this case, the voltage generated in each excitation coil (that is, each superconducting coil) is smaller than the value when dividing into n pieces, making it easier to protect the coil electrically and thermally. Furthermore, when the number m of superconducting coils 2 is less than or equal to n, a power lead can be taken out from the middle of one superconducting coil to reduce the number of excitation coils to n.

When adopting the method of dividing the excitation coil as in the above three examples, it is possible to electrically and thermally protect the superconducting toroidal coil during quenching, but mechanical protection becomes considerably difficult.

Figure 8 is a diagram showing the electromagnetic force acting on superconducting coils 2-02 and 2-24 on both sides of superconducting coil 2-01 when #1 of one superconducting coil 2 constituting a superconducting toroidal coil is quenched. be.

However, the number of spatial divisions m of the superconducting toroidal coil is 2
4, and we will discuss the coil specifications given above as an example. In Fig. 8, superconducting coil 2
-01 is quenched and the coil current attenuates to zero, an electromagnetic force F in the θ direction acts on the superconducting coils 2-02 and 2-24 at both ends.

As shown in Figure 8, this electromagnetic force has opposing directions, and its magnitude F is a huge force of about 70,000 tons.
Although it is not impossible to design a support structure that can withstand this force, the increased weight of the support structure and the associated increase in heat penetration are major drawbacks for superconducting toroidal coils. Furthermore, although it is possible to operate 23 of the 24 superconducting coils, it has the disadvantage that the uniformity of the magnetic field distribution deteriorates.

This invention was made in order to eliminate the above-mentioned drawbacks, and provides a superconducting toroidal magnet that can be protected from electrical, thermal, and mechanical damage when the superconducting toroidal coil is quenched. The purpose is to provide

The present invention will be explained below with reference to the drawings.

FIG. 9 is a partial diagram showing a schematic configuration of an embodiment of the present invention, showing only three of the plurality of superconducting coils 2-01 to 2-m constituting the superconducting toroidal coil 1.

In the figure, 21-1 to 2m-n are partial coils, and each superconducting coil 2-01 to 2-m is a plurality of partial coils 2.
1-1 to 2m-n.

Moreover, the exciting coils 1-1 to 1-n are each superconducting coil 2-0.
Partial coils 21-1 with equal relative positions within 1-2-m
It is constructed by electrically connecting 2m-n. That is, for each superconducting coil, a plurality of partial coils 21-]~2m-n
The excitation coils 1-1 to 1-n are constructed by sequentially numbering the partial coils having the same number among the partial coils constituting each of the superconducting coils 2-0] to 2-m and electrically connecting them one after another. Although not shown in the figure, the excitation coils 11 to 1-
The circuit shown in FIG. 6 or 7 is provided for n, and is configured to have the effect described above, that is, protection against electrical and thermal damage.

The configuration as described above has the following advantages.

(1) When one excitation coil is quenched, the current in one partial coil in one superconducting coil is attenuated, so the repulsive force generated between the partial coils on both sides of the quenched partial coil is 1 This is a small value that is several tenths of the repulsion force when three superconducting coils are used as one excitation coil.

Therefore, there is no need to provide a special support structure that takes quenching into consideration. (2) Since the current in the partial coils having the same number among all the superconducting coils constituting the superconducting toroidal coil is attenuated, the non-uniformity of the toroidal coil magnetic field distribution can be reduced.

In the above explanation, the partial coil may be a pancake coil for a pancake-shaped superconducting coil as shown in FIG. It may also be used as a superconducting disk for a superconducting coil.

In addition, in the above explanation, one partial coil is electrically connected to each superconducting coil as a component of each excitation coil, but each A plurality of partial coils may be used as constituent elements of the excitation coil for the superconducting coil.

As is clear from the above description, in this invention, among the partial coils constituting each superconducting coil of a superconducting toroidal coil, partial coils having the same relative position are electrically connected to constitute one excitation coil, and each excitation coil is It is equipped with a protective resistor connected in parallel and an excitation device that supplies excitation current to each of the parallel bodies through a switch, and generates the quench by opening a switch of the excitation circuit to which the excitation coil that generated the quench belongs. The current in the excitation coil is absorbed by the protective resistor, which reduces the electromagnetic force in the toroidal axis direction due to the extinction of the current in the partial coil, and also reduces the non-uniformity of the toroidal magnetic field distribution. A superconducting toroidal magnet that suppresses the voltage generated between both terminals can be realized.

[Brief explanation of drawings]

Fig. 1 is a conceptual diagram of a toroidal coil, Fig. 2 is an actual toroidal coil configuration diagram, Fig. 3 is a partially cutaway perspective view of a pancake-shaped superconducting coil, and Fig. 4 is a partially sectional view of a disk-shaped superconducting coil. , FIG. 5 is a circuit diagram of a conventional superconducting toroidal magnet, FIGS. 26 and 7 are circuit diagrams of a superconducting toroidal magnet of the present invention, and FIG. 8 is a circuit diagram of a superconducting toroidal magnet according to the present invention. Distribution of electromagnetic force generated in the toroidal 'j direction. FIG. 9 is a partial diagram of seven components showing electrical connections in the toroidal magnet of the present invention. In the figure, 1 is a superconducting toroidal coil, 2 and 2
-01 to 2-m are superconducting coils, 200 is a pancake coil, 100 is a superconducting disk, 1-] to 1-n are excitation coils, 14-1 to 14-0n are switches, 15-1 to
15-n is an excitation power supply, 16-1 to 16-n are protection resistors,
21-1 to 2m-n are partial coils.

Claims (1)

[Scope of Claims] 1. A plurality of superconducting coils formed by dividing a superconducting toroidal coil, a plurality of partial coils formed by dividing each superconducting coil, and the partial coils having equal relative positions within each of the superconducting coils. an excitation coil configured by electrically connecting the excitation coils, a protection resistor connected in parallel to each of the excitation coils, and an excitation power source that supplies power to the parallel body of each of the excitation coils and the protection resistor via a switch. Superconducting toroidal magnet. 2. The superconducting toroidal magnet according to claim 1, wherein the middle point of each exciting coil is grounded.