JPS5988682A - Electrical discharge bypass structure in nuclear fusion device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a discharge bypass structure that connects divided parts of a device to each other.

Conventionally, for example, in a tokamak-type fusion device, devices that make one circuit in the toroidal direction, except for the boroidal coil, must have a sufficiently large one-circuit resistance in the toroidal direction in order to efficiently start up the plasma current. be. Generally, this one-round resistance value is required to be 0./mΩ or more. One possible method for achieving this is to divide the device into several parts in the toroidal direction and electrically insulate the divided parts (hereinafter the insulated parts will be referred to as insulating parts). Examples of applying this method are shown in FIGS. 1-3.

In FIG. 1, the symbol / is a current transformer iron core for generating a plasma current, and a toroidal magnetic field coil coil for generating an annular toroidal magnetic field is arranged around the central portion /a. An annular vacuum container 3 is disposed within the toroidal magnetic field coil. FIG. 2 is a sectional plan view of the vacuum vessel 3 of FIG. 1. As shown in this figure, the annular vacuum vessel 3 is divided into a plurality of parts (two in the figure), and each divided part 3a, 3b is an insulating part shown in a circle in the figure. They are connected to each other by l. Third
The figure shows an enlarged cross-section of this insulating section. Seven flanges 6 are provided at the ends of the divided parts 3a and 3'o of the vacuum container 3 and project toward the interior j of the vacuum container.
An insulator 7 for electrical insulation is inserted between each flange 4a, xb. Both 7 langes Aa, 4b have connecting holes /9 spaced apart in the voloidal direction, into which the bolt shafts /3 having electrically insulating tubes /g that come into contact with both 7 langes are fitted. Then, through the washer g, insulating ring 9, and washer /θ, the bolt head (fixed part) // and nut (fixed part) /λ cooperate to connect the 9 cars 7 ring A.
a, 4b are connected. , 7. Members other than bolts and nuts may be used as the fixing part as long as both 7 lunges can be fixed.

The device that goes around in the toroidal direction is inside the vacuum container!
When the plasma current changes rapidly, such as during disruption (plasma collapse), a high voltage is generated between the self-dividing parts 3a and 3b. As a result, arcs may fly near the insulation and damage the equipment. In order to prevent damage to equipment due to discharge accompanying the generation of such high voltages, a method of providing a discharge bypass circuit using a discharge gap or a shunt resistor has been considered. In such a bypass circuit, it is said that a negative resistance value of 10 to 0/mΩ is appropriate.

When using conventional shunt resistors, there are the following drawbacks.

(a) During Taylor discharge cleaning (continuous discharge cleaning) At this time, the current flowing through the resistor itself is small, but the pulse interval generated by discharge is short and the pulse generation frequency is high. Joule heat accumulates in the resistor, exposing the resistor to high temperatures for a long period of time (1)) When the plasma current changes rapidly, as in the case of disruption, a large current flows instantaneously through the resistor, and this Due to the Joule heat generated by this, the hot water temperature of the resistor ll'i rapidly rises adiabatically. In order to suppress the generation of Joule heat, the smaller the resistance value of the resistor, the better. However, as described above, this resistance value is limited by the lower limit of the one-round resistance value in the toroidal direction, and the resistance value cannot be made very small. Furthermore, the larger the volume of the resistor, the lower its resistance, but with the conventional resistor as described above, the volume cannot be made sufficiently large. Therefore, the temperature of the resistor becomes extremely high due to Joule heat.

Due to the interaction between the large current that momentarily flows through the resistor and the magnetic field, a strong electromagnetic force acts on the resistor. In order to suppress the current flowing inside the resistor, even if a metal with a large specific resistance value (specific resistance) is selected, Inconel 623's 0.0
0θ/30m is the maximum possible value. Therefore, due to restrictions on the resistance value of the resistor, it is often necessary to limit the resistor to an elongated shape. Seven examples are shown in FIGS. C and 3, in which the resistor /ll is composed of an elongated wire-like or strip-like metal plate. When such a resistor is used, there is a risk that the resistor may break due to strong electromagnetic force.

On the other hand, in order to prevent damage to equipment, shunt resistors are sometimes installed in parts that cannot be easily replaced. For example,
In order to protect the vacuum vessel, it is desirable to provide the shunt resistor on the side closer to the plasma. However, conventional shunt resistors have poor reliability and cannot be used.

The present invention has been made in order to eliminate the above-mentioned drawbacks, and provides a discharge bypass structure in a nuclear fusion device that can prevent damage to equipment even if high voltage is momentarily generated between divided equipment. The main purpose is to.

Next, the discharge bypass structure of the present invention will be explained in detail with reference to the drawings.

FIG. 9 and FIG. There is. Symbol /j is a shunt resistor, which is inserted between a conductive member /A having good conductivity and a washer IO.

This shunt resistor/3 has excellent heat resistance and strength resistance, and is made of a material with good conductivity (for example, silicon carbide 51
0). Shunt resistor/
3. The washer / θ and the conductive member / 6 are fitted into the insulation tube / groove, while the washer (! conductive member) and the conductor nut /
2 and the flange 6b. The conductive member 16 is a shunt resistor/! The main purpose is to dissipate the Joule heat generated within the interior in the voloidal direction, and as shown in Figure S, it is made up of an annular plate (e.g. copper plate) that is long in the voloidal direction. /7 is the only seam of this annular plate. The discharge bypass structures are spaced apart in the voloidal direction.

In the diagram, the plasma current flows from left to right, and the externally applied toroidal magnetic field also points in this direction. Therefore, the insulating part of the vacuum container has a left flange 6a as shown by the arrow in FIG.
, ↑ conductive member / A, shunt resistor l, washer /
Current flows through the discharge bypass circuit toward the right 7 langes 6b through the shaft portion 13 and the washer g. Therefore, even if a high voltage is instantaneously generated in the vacuum vessel 3, such as during disruption, the divided parts 3tJ and 3b of the vacuum vessel are electrically connected via the shunt resistor /j. A current flows through this shunt resistor /S to prevent excessive voltage from being applied between the divided portions 3a and 3b. Also, shunt resistor /j
acts as a conductor, and even if Joule heat is generated within the resistor, it escapes through the conductive member /A, preventing Joule heat from accumulating.

In the embodiments shown in FIGS. 9 and 3, the shunt resistor IS is provided only on the left side of the 7 langes Aa;
It is also possible to provide it on the right side of the lunge 6b. Furthermore, in this embodiment, the discharge bypass structure was placed near the insulating part of the vacuum vessel 3, but other equipment in the fusion device could be damaged due to instantaneous high voltage generation. It may be arranged in a part.

In the above-described embodiment, the shunt resistor has a specific resistance value greater than or equal to a predetermined value (θ, θO/Ωrn), and is elongated in the discharge bypass structure of the present invention like a conventional shunt resistor. Since it is not necessary to have a block-like structure, for example, a block-like structure can be used. Therefore, materials for resistors include, for example, pyrotic graphite, graphite, graphite made by adding a material with poor conductivity, and a material made by adding a conductive material to an insulating material such as aluminum. Conceivable. In addition, if the varistor material has a sufficiently strong structural strength, it will act as a high-resistance element when the applied voltage is low, such as during normal operation or discharge cleaning, and the resistance value will rapidly decrease as the applied voltage increases. Since it becomes a conductor when high voltage is generated, such as when a high voltage is generated, it prevents the generation of high voltage between the divided portions, making it very suitable as a material for the shunt resistor of the present invention.

Recent sintered crystals of silicon carbide have excellent heat resistance and strength properties, and among them, conductive crystals using silicon as a sintering medium have also been developed. Its specific resistance is about 50 times higher than that of metals such as special steel, and its thermal conductivity is sometimes about 10 times higher than that of special steel. Silicon carbide itself has properties similar to that of a varistor material, and if the sintering medium material is appropriately selected, it can be made into a resistor having the properties of a varistor.

As described above, in the discharge bypass structure in the fusion device of the present invention, a shunt resistor with good conductivity is arranged between at least one fixed part and the conductive member around the shaft part. , thereby connecting one conductive member from one 7-lunge.

A discharge bypass circuit is formed that passes through the shunt resistor, one fixed part, the shaft part, and the other conductive member to the other 7 lunges, so even if a high voltage momentarily occurs between the divided parts, the bypass circuit will not work. Since current flows through the wire, arcing is eliminated and damage to equipment can be prevented.

Furthermore, when the discharge bypass structure of the present invention is applied to a tokamak type nuclear fusion device, it has the following advantages compared to the conventional structure.

(1) Since the total volume of the resistor can be increased, the temperature rise in the resistor due to Joule heating can be kept to a very low level when the plasma current changes rapidly, such as during disruption. (2) Compared to those using special steel or other metal as the resistor, the overall length of the resistor can be shortened and the resistor can be easily installed. (3) Since the entire resistor length can be shortened, The total electromagnetic force acting on the entire body is small, making it easier to support the resistor against magnetic force (e.g., the length of the entire resistor can be shortened and its thermal conductivity is high, so temperature differences within the resistor are less likely to occur). (Especially when silicon carbide is used as the resistor) (3) By shortening the length of the resistor, Joule heat generated during continuous discharge cleaning can be easily removed. (6) The structure is simpler than conventional ones. It is.

Since the discharge bypass structure of the present invention has the above-mentioned advantages, the resistor can be installed even in places where the shunt resistor cannot be easily replaced, such as inside a vacuum container. Further, the bypass structure of the present invention can be used in nuclear fusion devices other than tokamak type (for example, stellarator type) under specific conditions (for example, during Joule heating).

[Brief explanation of drawings]

Figure 1 is a partial cross-sectional view of the main components of a tokamak-type fusion device, Figure 2 is a cross-sectional plan view of the annular vacuum vessel shown in Figure 1, and Figure 3 is an enlarged view of the insulating section in Figure 2. cross section,
FIG. 4 is an enlarged sectional view of an insulating part similar to that in FIG. 3 equipped with the discharge bypass structure of the present invention, and FIG. 3 is a partially broken plane of the insulating part showing only two discharge bypass structures of the present invention. It is a diagram. l... Current transformer iron core, a... Toroidal magnetic field coil, 3...
- Vacuum container, 41... Insulation section, 4a. 6b11-Flange, 7. Red military insulator, φ washer (conductive member), Insulation ring, // Bolt head (fixed part), / Co. Nut (fixed part), 13... Shaft, /3... Shunt resistor, /6... Conductive member, 1g
...Electrical insulation tube, /q...Connection hole. Patent applicant: Japan Atomic Energy Research Institute Mitsubishi Atomic Crab Industry Co., Ltd. Figure 2 Figure 5

Claims (1)

[Claims] (1) A shaft part that is inserted into connecting holes provided at intervals in the voloidal direction in both adjacent flanges at the divided ends of a device that is divided into a plurality of parts in the toroidal direction, and has an electrically insulating tube around the entire outer periphery. . A fixing part is provided at both ends of each shaft part and works together to fix both flanges to each other via an electrical insulator, and a conductive member with good conductivity is inserted between the fixing part and the flange. In the device of the nuclear fusion device, a shunt resistor with good conductivity is arranged between at least one fixed part and the conductive member around the shaft part, so that one of the 7 langes From the conductive member on one side, the shunt resistor, and the fixed part on the other. A discharge bypass structure for a nuclear fusion device, characterized in that a discharge bypass circuit is formed passing through the shaft portion and the other conductive member to the other flange. (2) A discharge bypass structure in a nuclear fusion device according to claim 1, wherein the shunt resistor is made of a sintered silicon carbide material.