JPS6249598B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a discharge bypass structure that connects toroidally divided parts of a device in a nuclear fusion device.

Conventionally, for example, in a tokamak-type nuclear fusion device, devices that make one circuit in the toroidal direction, except for the poloidal coil, need to have a sufficiently large one-circuit resistance in the toroidal direction in order to efficiently raise the plasma current. Generally, this one-round resistance value is required to be 0.1 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, reference numeral 1 denotes a current transformer iron core for generating a plasma current, and a toroidal magnetic field coil 2 for generating an annular toroidal magnetic field is arranged around the central portion 1a. An annular vacuum vessel 3 is disposed within the toroidal magnetic field coil 2. 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 the divided parts 3a and 3b are mutually connected to each other by an insulating part 4 shown in a circle in the figure. It is connected. FIG. 3 shows an enlarged cross section of this insulating portion 4. As shown in FIG. The ends of the divided parts 3a and 3b of the vacuum container 3 are provided with flanges 6a and 6b that protrude toward the interior 5 of the vacuum container.
An insulator 7 for electrical insulation is inserted between a and 6b. Both flanges 6a, 6b have connection holes 19 spaced apart in the poloidal direction, into which the bolt shaft 13 having an electrically insulating tube 18 in contact with both flanges is fitted. Then, through the washer 8, insulating ring 9, and washer 10,
Bolt head (fixed part) 11 and nut (fixed part) 1
Both flanges 6a and 6b are connected by cooperation between the two flanges 6a and 6b. Note that members other than bolts and nuts may be used as the fixing part as long as both flanges can be fixed.

The equipment circulating in the toroidal direction interacts with the plasma current generated inside the vacuum container 5,
When the plasma current changes rapidly, such as during disruption (plasma collapse), a high voltage is generated between the divided portions 3a and 3b. Therefore, an arc may fly near the insulating section 4 and damage the equipment. In order to prevent damage to equipment due to discharge accompanying the generation of such high voltages, methods have been considered in which a discharge bypass circuit is provided using a discharge gap or a shunt resistor. In such a bypass circuit, it is said that a one-round resistance value of 10 to 0.1 mΩ is appropriate.

When using a conventional shunt resistor, there are the following drawbacks.

(a) At the time of Taylor discharge cleaning (continuous discharge cleaning) At this time, although the current flowing through the resistor itself is small, the pulse interval generated by discharge is short and the pulse generation frequency is high. Joule heat accumulates in the resistor and the resistor is exposed to high temperatures for a long time (b) When the plasma current changes suddenly, such as during disruption.At this time, a large current flows instantaneously through the resistor, and as a result The temperature of low antibodies rapidly rises adiabatically due to the fever. 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 described above, the volume cannot be made sufficiently large.
Therefore, the temperature of the resistor becomes extremely high due to Joule heat.

Furthermore, due to the interaction between the large current instantaneously flowing through the resistor and the magnetic field, a strong electromagnetic force acts on the resistor. Even if a metal with a large specific resistance value (specific resistance) is selected to suppress the current flowing inside the resistor, the maximum possible value is 0.00013 Ωcm for Inconel 625. Therefore, due to restrictions on the resistance value of the resistor, it is often necessary to limit the resistor to an elongated shape. An example is shown in FIGS. 2 and 3, where resistor 14
It is made up of a thin 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 cannot be used because of their poor reliability.

The present invention was 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 instantaneously generated between divided equipment. The main purpose is to.

In order to achieve this object, the present invention is designed to be inserted into connecting holes provided at intervals in the poloidal direction in both adjacent flanges at the divided ends of a device divided into a plurality of parts in the toroidal direction. A discharge bypass structure in a nuclear fusion device, comprising: a shaft portion having an electrically insulating tube; and fixing portions disposed at both ends of the shaft portion and working together to fix both flanges to each other via an electrical insulator. In the body, a conductive member is inserted between the fixed part and both flanges, and a specific resistance value of 0.001 Ωcm or more is provided between at least one of the conductive members and the fixed part associated with the conductive member. A shunt resistor is disposed, and a discharge bypass circuit runs from one flange to the other flange through one conductive member, the shunt resistor, one fixed part, the shaft part, and the other conductive member. It is characterized by the fact that it has been formed.

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

Figures 4 and 5 show examples in which the discharge bypass structure of the present invention is applied to the vacuum vessel insulation part of a tokamak-type nuclear fusion device, and the same components as in Figures 1 to 3 are given the same reference numerals. There is. Reference numeral 15 denotes a shunt resistor, which is inserted between a conductive member 16 having good conductivity and the washer 10. This shunt resistor 15 has excellent heat resistance and strength resistance, and is made of a material with good conductivity (for example, silicon carbide).
It is preferable to be composed of SiC). The shunt resistor 15, the washer 10, and the conductive member 16 are fitted onto the insulating tube 18, while the washer (conductive member) 8 is in contact with the nut 12 and the flange 6b. The conductive member 16 is disposed with the main purpose of dissipating the Joule heat generated within the shunt resistor 15 in the poloidal direction, and as shown in FIG. ), and reference numeral 17 is the only joint of this annular plate. The discharge bypass structures are poloidally spaced apart.

In FIG. 4, the plasma current flows from left to right, and the toroidal magnetic field applied from the outside is also directed in this direction. Therefore, the insulating part 4 of the vacuum container includes a left flange 6a, a conductive member 16, a shunt resistor 15, a washer 10, a bolt head 1, as shown by the arrow in FIG.
1, the current flows through the discharge bypass circuit passing through the shaft portion 13 and the washer 8 toward the right flange 6b. Therefore, even if a high voltage is instantaneously generated in the vacuum vessel 3, such as during disruption, the divided portions 3a and 3b of the vacuum vessel are connected to the shunt resistor 15.
Since the shunt resistor 15 is electrically connected to the divided portion 3 through the shunt resistor 15, a current flows through the shunt resistor 15.
This prevents excessive voltage from being applied between a and 3b. Further, the shunt resistor 15 functions as a conductive member, and even if Joule heat is generated within the resistor, it escapes through the conductive member 16, thereby preventing accumulation of Joule heat.

In the embodiments shown in FIGS. 4 and 5, the shunt resistor 15 is provided only on the left side of the flange 6a, but it can also be provided on the right side of the flange 6b. Furthermore, in this embodiment, the discharge bypass structure was disposed in the insulating part 4 of the vacuum vessel 3, but other equipment of 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 equal to or higher than a predetermined value (0.001 Ωcm), and in the discharge bypass structure of the present invention, it is necessary to make it elongated like a conventional shunt resistor. Since there are no holes, it is possible to have a block-like structure, for example. Therefore, as a material for a resistor,
For example, pyrotechnic graphite, graphite, graphite made by adding a material with poor conductivity and hardened, and something made by adding a conductive material to an insulating material such as aluminum and hardened, etc. can be considered. In addition, varistor materials, whose resistance value rapidly decreases as the applied voltage increases, will act as a high-resistance element when the applied voltage is low, such as during normal operation or discharge cleaning, if the structural strength is large enough, and during disruption, etc. When a high voltage is generated, as shown in FIG.

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

As described above, in the discharge bypass structure in the fusion device of the present invention, there is a gap between at least one fixed part and the conductive member around the shaft part.
A shunt resistor with good conductivity is disposed, and this creates a discharge bypass circuit from one flange to the other flange through one conductive member, the shunt resistor, one fixed part, the shaft part, and the other conductive member. Therefore, even if a high voltage momentarily occurs between the divided portions, current flows through the bypass circuit, thereby eliminating arcing and preventing damage to equipment.

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 of the resistor due to Joule heat can be suppressed to a very low level when the plasma current changes rapidly, such as during disruption. (2) Special steel The overall length of the resistor can be shortened compared to those using metals such as metals as the resistor, and the resistor can be installed easily. The total electromagnetic force acting on the resistor becomes smaller, making it easier to support the resistor against the electromagnetic force (4) Since the overall length of the resistor can be shortened and its thermal conductivity is high, temperature differences within the resistor are less likely to occur ( (Especially when silicon carbide is used as the resistor) (5) By shortening the length of the resistor, the 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, a resistor can be installed even in a place where a shunt resistor cannot be easily replaced, such as inside a vacuum container. Furthermore, the bypass structure of the present invention can also be applied to fusion devices other than tokamak type (for example, stellarator type) under specific conditions (for example, during Joule heating).
Can be used under.

[Brief explanation of the drawing]

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. 4 is an enlarged sectional view of an insulating section similar to that in FIG. 3, which is equipped with a discharge bypass structure of the present invention, and FIG. 5 is an enlarged sectional view of an insulating section showing only two discharge bypass structures of the present invention. FIG. 3 is a partially cutaway plan view. 1... Current transformer iron core, 2... Toroidal magnetic field coil, 3... Vacuum container, 4... Insulation section, 6a, 6b
... Flange, 7 ... Electrical insulator, 8 ... Washer (conductive member), 9 ... Insulation ring, 11 ... Bolt head (fixing part), 12 ... Nut (fixing part), 1
3... Shaft portion, 15... Shunt resistor, 16...
Conductive member, 18... electrical insulation tube, 19... connection hole.

Claims (1)

[Claims] 1. An electrical insulating tube is inserted into connecting holes provided at intervals in the poloidal direction in both adjacent flanges at the divided ends of a device divided into a plurality of parts in the toroidal direction, and electrically insulating tubes are provided around the entire outer periphery. and fixing parts disposed at both ends of the shaft part and cooperating to fix both flanges to each other via an electrical insulator,
In the discharge bypass structure in a nuclear fusion device, a conductive member is inserted between the fixed part and both flanges, and a distance of 0.001 between at least one of the conductive members and the fixed part associated with the conductive member is A shunt resistor having a specific resistance value of Ωcm or more is disposed, and the shunt resistor is connected from one flange through one conductive member, the shunt resistor, one fixed part, the shaft part, and the other conductive member. A discharge bypass structure in a nuclear fusion device, characterized in that a discharge bypass circuit directed toward a flange is formed. 2. The discharge bypass structure in a nuclear fusion device according to claim 1, wherein the shunt resistor is made of a sintered silicon carbide material.