JP3516413B2 - High frequency heating equipment - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to an electron cyclotron frequency (ECRF) band (for example, several tens GHz to several hundreds GHz).
The present invention relates to a high-frequency heating device for heating and generating plasma in a fusion reactor by high-frequency electromagnetic waves, and particularly to improvement of a barrier window suitable for high-frequency high-power transmission.

[0002]

2. Description of the Related Art In order to operate a fusion reactor, it is necessary to generate and heat core plasma, and one of the methods is a high frequency heating method. This heating method is a method of injecting high-frequency electromagnetic wave energy into plasma in the core and raising the plasma temperature by resonance heating of the plasma or current driving.

FIG. 3 shows a conventional example of an ECRF high frequency heating apparatus which is a kind of heating apparatus using this high frequency heating method.
The heating device shown in the figure has a high-frequency oscillator 1 such as a gyrotron that oscillates a high-power electromagnetic wave, and a circular waveguide as a transmission line for causing the output electromagnetic wave of the high-frequency oscillator 1 to enter the plasma 3 inside the fusion reactor 2. Tube 4 and this circular waveguide 4
There is a barrier window 5 inserted in the middle of. The inside of the fusion reactor 2 and the circular waveguide 4 are kept in high vacuum.

The barrier window 5 is provided in order to prevent the products of nuclear fusion reaction such as tritium from diffusing to the outside. As shown in FIG. And a ceramic plate 6 which is inserted orthogonally to the propagation direction 9 of the same, and is hermetically fixed to the outer peripheral surface of the ceramic plate 6 by a metallurgical method, and both ends thereof are hermetically sealed to the circular waveguide 4. And a cooling box 7 having a cooling flow path on the outer peripheral side of the sealing ring 8 and projecting around the circular waveguide 4.

When a high frequency electromagnetic wave is propagated through the barrier window 5 having such a structure, heat is generated in the ceramic plate 6 due to the dielectric loss. This heat is the refrigerant 10 flowing in the cooling box 7.
Is removed by heat. That is, the coolant 10 is supplied from a coolant supply source (not shown) to the supply port 7a attached to the cooling box 7, and removes heat generated in the ceramic plate 6 while flowing through the outer peripheral surface of the sealing ring 8 to cool the cooling box. The discharge port 7b attached to 7 returns to the coolant supply source. By the way, the dielectric loss L which is the cause of the heat generation is expressed by the following equation.

[0006]

## EQU1 ## L = 2πZP tanδfεo εr t (1) where P is the transmission power, f is the working frequency, εo is the permittivity in vacuum, and Z, tanδ, εr, and t are the ceramic plate 6, respectively. Characteristic impedance, dielectric tangent, dielectric constant, and plate thickness.

The dielectric tangent tan δ is the ceramic plate 6
It increases in proportion to the 1.96 power of the absolute temperature of. Since the transmission power distribution in the circular waveguide 4 is larger in the central portion 6a of the ceramic plate 6 as indicated by reference numeral 12 in FIG. 4, the heat generation density due to the dielectric loss is also larger in the central portion 6a.

Recently, there has been a tendency toward higher output and higher frequency of the high frequency heating device in terms of steady operation of the fusion reactor and efficiency of plasma heating, and the barrier window 5 is under severe conditions.

[0009]

When high-power high-frequency transmission is performed in a vacuum using the circular waveguide 4, the circular waveguide 4
The stray electrons inside are accelerated by the high electric field of high frequency, and the electrons hit the wall surface of the ceramic plate 6 to emit secondary electrons. Generally, the secondary electron emission coefficient of the ceramic plate 6 is 1
Because of the above, secondary electrons may increase in an avalanche phenomenon and develop into a multipactor discharge, and eventually high frequency transmission may become impossible.

Further, with respect to the heat generation due to the dielectric loss described above, if the cooling is not sufficiently performed, the dielectric loss L increases with the temperature increase, which causes a vicious cycle of the temperature increase and the dielectric loss increase.

In the conventional cooling structure of the barrier window 5, since the thermal conductivity of the ceramic plate 6 is small, the generated heat cannot be quickly transferred to the outer peripheral portion 6b of the ceramic plate 6 which is the cooling part. Further, since the heat generation distribution increases toward the central portion 6a, a large temperature difference occurs between the central portion 6a and the outer peripheral portion 6b, and as a result, a large thermal stress is generated in the ceramic plate 6 and the ceramic plate 6 may be damaged. It was

The present invention has been made in view of the above circumstances. Multipactor discharge is unlikely to occur, electromagnetic waves are satisfactorily propagated, while cooling performance is improved to suppress the temperature rise of the ceramic plate. Alternatively, a high-frequency heating device that positively lowers the temperature of the ceramic plate to reduce the dielectric loss to improve the plasma heating efficiency and prevents damage to the ceramic plate due to thermal stress and to significantly improve reliability is provided. The purpose is to provide.

[0013]

In order to achieve the above object, the present invention forms a diamond coating on at least one surface of a ceramic plate by a vapor phase synthesis method. Further, the diamond coating is formed thicker in the central portion than in the outer peripheral portion of the ceramic plate in accordance with the power distribution in the transmission line.

[0014]

In the barrier window of the high-frequency heating device constructed as described above, the diamond coating has a secondary electron emission coefficient of 1 or less, so that multipactor discharge does not occur even when a high-power high-frequency wave is transmitted.

Since diamond has a thermal conductivity about 10 times that of ceramics such as quartz and alumina, the heat generated in the ceramic plate is efficiently transferred to the outer peripheral portion and cooled, so that the cooling performance is improved. As a result, the temperature rise of the ceramic plate and the temperature difference in the radial direction can be reduced, and thermal stress and dielectric loss can be suppressed low.

Further, the heat generation due to the dielectric loss of the ceramic plate increases as it goes to the central portion, but by increasing the thickness of the diamond coating toward the central portion, the heat conduction in the central portion increases, and the central portion of The high fever is properly removed. Thereby, the temperature difference in the radial direction of the ceramic plate becomes smaller, and the thermal stress caused by this temperature difference can be further suppressed.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 and FIG. 2 show the main configuration of a barrier window of a high frequency heating apparatus according to the present invention, and in the figures, 4 shows a circular waveguide in the high frequency heating apparatus. A barrier window 5 is provided in the middle of the circular waveguide 4 to prevent out-diffusion of the product of the nuclear fusion reaction.

The barrier window 5 is a disk-shaped ceramic plate 6 which is inserted in the circular waveguide 4 so as to be orthogonal to the transmission direction of an electromagnetic wave 9 which propagates in the circular waveguide 4, and this ceramic. The cooling box 7 is formed so as to project from the circular waveguide 4 so as to cover 6 and the sealing ring 8 that seals the ceramic plate 6 to the waveguide 4.

A diamond coating 11 is formed on at least one surface of the ceramic plate 6, and the thickness of the diamond coating 11 is in the central portion 11a.
It is thicker and corresponds to the mountain-shaped electric field distribution 12 in the waveguide 4. Although the thickness of the diamond coating 11 is emphasized in the drawing, it is, for example, 1 compared with the thickness of the ceramic plate 6.
It is about / 10 and thin enough.

A predetermined position on the outer peripheral side of the ceramic plate 6 and the end of the circular waveguide 4 are metal-tightly metal-bonded to each other via a sealing ring 8. The sealing ring 8 is made of a material such as Kovar having a thermal expansion coefficient close to that of the ceramic plate 6. The outer peripheral portion 6b of the ceramics plate 6 thus joined is in a state of protruding from the sealing ring 8 to the outside, as shown in the figure.

The cooling box 7 is formed in an axially short cylindrical shape having a predetermined capacity, and the ceramic plate 6 is provided therein.
Is provided so as to project from the end of the circular waveguide 4 and is hermetically joined. At the lower end and the upper end of the cooling box 7, a supply port 7a and a discharge port 7b which are connected to a coolant supply source (not shown) are provided in a protruding manner, and a coolant 10 such as liquid nitrogen or Freon is supplied from the supply port 7a. It flows through the outer peripheral portion of the plate 6 and returns from the discharge port 7b to the refrigerant supply source.

As described above, the circular waveguide 4 is formed by forming the diamond coating 11 on the side surface of the ceramic plate 6.
Even if a high output high frequency is transmitted to the
Since the secondary electron emission coefficient is 1 or less, stable high frequency transmission can be realized without causing multipactor discharge.

On the other hand, the high frequency energy is the circular waveguide 4
Through the ceramic plate 6 and is incident on the plasma 3 of the fusion reactor 2. Further, the product of the fusion reaction from the fusion reactor 2 is sealed by the barrier window 5.

Furthermore, the electromagnetic wave 9 causes a dielectric loss in the ceramic plate 6 based on the above equation (1), the loss is converted into heat, and this heat is transmitted to the outer peripheral portion 6b of the ceramic plate 6 for cooling. Heat is removed by the medium 10. The thermal conductivity of diamond is about 10 times that of quartz or alumina, and the diamond film 11 is formed on the surface of the ceramic plate 6 by the vapor phase synthesis method.
By the formation of the
transmitted to b. For example, when the thickness of the diamond coating 11 is 1/10 of the thickness of the ceramic plate 6, the amount of heat conduction is doubled, and the temperature rise of the ceramic plate 6 and the temperature difference between the central portion 6a and the outer peripheral portion 6b are 1 / It becomes 2.

The heat is applied to the central portion 6a of the ceramic plate 6.
Cross-section area that conducts heat from the
Is the thickness. Therefore, by increasing the thickness in the vicinity of the central portion 6a, the cross-sectional area through which heat passes can be made constant in the vicinity of the central portion 6a and the outer peripheral portion 6b, and heat conduction to the outer peripheral portion 6b is effectively performed. . In the vapor phase synthesis method, since the diamond coating 11 is generally formed thick in the central portion 6a of the ceramic plate, more heat can be conducted in the central portion 6a, and heat transfer can be performed in a shorter step than thickening the whole. Suitable diamond film formation can be performed.

Since the diamond coating 11 is sufficiently thinner than the thickness of the ceramic plate 6, it is not necessary to consider the increase in dielectric heat generated by the volume increase due to the formation of the coating.

Since the cooling performance is remarkably improved in this way, the temperature rise of the ceramic plate 6 and the temperature difference in the radial direction are reduced, and the dielectric loss and the thermal stress can be suppressed low. Although it is not possible to obtain a large-diameter natural diamond plate, a ceramic plate having a performance comparable to that of the diamond plate can be realized by forming the diamond film by the vapor phase synthesis method.

Further, in the present invention, the diamond film 11 is formed on the ceramic plate 6, but there is also a method of forming the diamond film 11 on the silicon substrate by the vapor phase synthesis method and etching the silicon with hydrofluoric nitric acid solution to form the diamond plate. is there.

[0029]

As described above, according to the present invention, by forming the diamond coating on the ceramic plate, the cooling performance is remarkably improved, and the temperature rise of the ceramic plate and the temperature difference in the radial direction can be reduced. Therefore, not only is it possible to improve the plasma heating efficiency by reducing the dielectric loss or prevent the ceramic plate from being damaged by reducing the thermal stress, but it is possible to provide a high-quality high-frequency heating device that does not cause multipactor discharge.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of a barrier window of a high-frequency heating device according to the present invention.

FIG. 2 is a sectional view taken along the line AA of FIG.

FIG. 3 is a configuration diagram showing an outline of a general high-frequency heating device.

FIG. 4 is a cross-sectional view showing a configuration example of a barrier window of a conventional high frequency heating device.

[Explanation of symbols]

4 ... Waveguide, 5 ... Barrier window, 6 ... Ceramic plate, 7 ... Cooling box, 8 ... Sealing ring, 11 ... Diamond coating,
12 ... Transmission power distribution.

Claims (5)

(57) [Claims] 1. A transmission line extended for injecting high frequency electromagnetic wave energy into plasma in a fusion reactor,
A ceramic plate that is inserted orthogonal to the propagation direction of electromagnetic waves, and is sealed to the transmission line via a sealing ring,
A fusion box provided so as to project from the transmission path so as to cover the ceramic plate and the outer periphery of the sealing ring, and a cooling box for forming a cooling passage on the outer peripheral side of the ceramic plate and the sealing ring; A high-frequency heating device having a barrier window for suppressing outward diffusion of products by a reaction, wherein a diamond coating is formed on at least one surface of the ceramic plate. 2. The high frequency heating apparatus according to claim 1 , wherein the diamond coating is formed by a vapor phase synthesis method. 3. The high-frequency heating device according to claim 1, wherein the diamond coating is formed so that the thickness of the central portion of the diamond film is thicker than that of the outer peripheral portion of the ceramic plate in correspondence with the electric field distribution in the transmission line. 4. The high-frequency heating device according to claim 1, wherein the ceramic plate is arranged such that a part of the outer peripheral side thereof projects outside the sealing ring. 5. A ceramic plate, a diamond film is formed by vapor-phase synthesis method on a silicon substrate, it is diamond plate silicon was etched in aqueous nitric acid Tsu Fu high-frequency heating apparatus according to claim 1, wherein.