JPH05215876A - Barrier aperture for high frequency heating device - Google Patents

Abstract

PURPOSE:To reduce the dielectric loss of an aperture plate so as to improve plasma heating efficiency. CONSTITUTION:The barrier aperture of a high frequency heating device is provided with short-circuit rings 29 rigidly secured to both outer peripheral side faces of an aperture plate 22; sealing rings 28 holding both sides of the aperture plate 22 airtightly on the inner peripheral side of the short-circuit rings 29; second short-circuit bodies 30, 32 of approximately cylindrical shape containing the aperture plate 22 with the short-circuit rings 29 rigidly fixed thereto and also supporting the sealing rings 28 airtightly through a heat insulating ring 31; a vacuum container 24 containing these and supporting them airtightly through the heat insulating ring 31 while being connected airtightly to a transmission line by a suspensionsupporting member 36; first cooling sources 38, 39 connected to the short-circuit rings 29 so as to cool these rings 29 to the first low temperature; and second cooling sources 40, 41 for cooling the second short-circuit bodies 30, 32 to the second low temperature higher than the first low temperature.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a barrier window of a high-frequency heating device for generating and heating plasma of a fusion reactor by an electromagnetic wave having a high frequency of electron cyclotron frequency (ECRF), for example, several tens GHz to several hundreds GHz. In particular, it relates to improvement of the cooling structure of the barrier window.

[0002]

2. Description of the Related Art In order to operate a fusion reactor, it is necessary to generate and heat a 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 one type of heating apparatus using this high frequency heating method. The heating apparatus shown in the figure is a high-frequency oscillator 1 such as a gyrotron that oscillates a high-power electromagnetic wave, and a waveguide as a transmission line for propagating the output electromagnetic wave of the high-frequency oscillator 1 to the plasma 3 inside the fusion reactor 2. 4 and a barrier window 5 inserted in the middle of the waveguide 4. The fusion reactor 2 and the transmission reactor 4 are kept in high vacuum.

The barrier window 5 prevents the products of nuclear fusion reaction such as tritium from diffusing to the outside.
Specifically, as shown in FIG. 4, window plates 6a and 6b made of a circular ceramic plate inserted in the middle of the circular waveguide 4.
And a cooling box 7 installed so as to surround the window plates 6a and 6b. Among them, the window plates 6a and 6b are made of alumina having high strength and high thermal conductivity, for example, and are circular conductors in a state where they are orthogonal to the propagation direction of the electromagnetic wave D and separated by a predetermined distance d. The cut end surface of the wave tube 4 is hermetically metallurgically bonded, whereby the product of the fusion reaction is sealed. The distance d between the two window plates 6a and 6b
Is set to the optimum size that can cancel the impedance mismatch. The supply port 7a and the discharge port 7b of the cooling box 7 are connected to a cooling source (not shown) so that the cooling medium C flows between the two window plates 6a and 6b. Therefore, the electromagnetic wave for heating the plasma passes through the window plate 6, and the heat generated by the dielectric loss of this plate is removed by cooling the side surface and the outer peripheral surface.

FIG. 5 shows, as another example of the barrier window, a peripheral cooling type barrier window having a simpler structure. The same components as those in FIG. 4 are designated by the same reference numerals. The barrier window 10 shown in the figure is a single circular window plate 11
And a cooling box 7 installed so as to surround the window plate 11, the window plate 11 is provided in the middle of the circular waveguide 4 with a sealing ring 12 such as Kovar or the like using a metallurgical method. It is airtightly joined. The window plate 11 is orthogonal to the propagation direction of the electromagnetic wave D. Therefore, the cooling medium C supplied from the supply port 7a of the cooling box 7 returns to the cooling source from the discharge port 7b while passing through the outer circumference of the sealing ring 12, and cools the outer peripheral surface of the sealing ring 12 in the middle thereof. The temperature of the window plate 11 is lowered. The dielectric loss L that causes the heat generation is expressed by the following equation. _{L = 2πzPtan δfε 0 ε r t} ...... (1)

Here, P is transmission power, f is frequency, and ε ₀
Is the permittivity of a vacuum, and z, tan δ, ε _r , and t are the characteristic impedance of the window, the dielectric tangent, the permittivity, and the plate thickness, respectively.

Since the transmission power P is proportional to the square of the electric field, the loss L is also proportional to the square of the electric field. The electric field distribution in the circular waveguide 4 is, as shown by the dotted lines in FIGS.
Since the electric field strength is higher in the central portion of 6b, the loss L in the central portion also becomes larger. Moreover, since the operating frequency f of the heating device is as high as 100 GHz, for example, the dielectric loss L increases in proportion to this. Furthermore, the electrostatic tangent tan δ is the window plate 6
It is proportional to the 1.96th power of the absolute temperature of a and 6b.

[0008]

However, an example of the above-mentioned dielectric loss L is transmitted power P = 1 MW, temperature =
400 K, frequency f = 110 GHz, permittivity ε _r = 9.
4. Calculated with the plate thickness t = 1.3 mm, L = about 2
Since it also becomes kW and the amount of heat generated by this loss also increases, unless the temperature of the window plates 6a and 6b in FIG. 4 and the window plate 11 in FIG. Fall into a vicious cycle of increase. For this reason, in recent years, the heating power has been increased, that is, the electromagnetic wave energy has been increased and the operating time has been extended, that is, in response to a request for single pulse operation (~ ms) to long pulse operation (~ 10s) or continuous operation, The conventional barrier window cooling structure having a simple structure and a flow path has various problems as described below, and it has been difficult to cope with them.

First, the first problem is due to the shape of the cooling channel. The dielectric loss L increases in proportion to the 1.96th power of the absolute temperature as described above. However, in the conventional cooling structure shown in FIG. 4, a large amount of the cooling medium C supplied from the lower portion of the cooling box bypasses both sides of the window plates 6a and 6b having a smaller flow path resistance. , Window plate 6
There is a problem in that the amount of flow between a and 6b, especially in the central portion thereof, is reduced, which results in low cooling efficiency and large dielectric loss L. On the other hand, in the conventional cooling structure shown in FIG.
Since only the outer peripheral surface of the window plate 11 having a small surface area is cooled, the structure is simple, but there is a problem that the cooling efficiency is further reduced and the dielectric loss becomes larger than that of the structure of FIG. there were.

The second problem is due to the heat generation distribution. As a measure to cover the above low cooling efficiency, the cooling medium C
Although a method of increasing the mass flow rate of A to increase the amount of heat removal and reducing the loss L can be considered, for that purpose, it is necessary to increase the pressure of the cooling medium C. In general, a gas is used as the cooling medium C in order to reduce the dielectric loss of the medium itself, and a pressure of about 1 atm has been sufficient for the conventional low power and single pulse operation. However, in high power, continuous operation, in order to increase the mass flow rate, a pressure of, for example, about 10 atm is required.
The force received by a, 6b, and 11 naturally increases.

In addition to this, since the calorific value (temperature difference) between the central portion and the outer peripheral portion of the window plates 6a, 6b, 11 is large, a large thermal stress difference is generated between the central portion and the peripheral portion, and the window plate 6a. , 6
Bending moment is generated in b and 11, and the window plates 6a, 6b,
There was a problem that 11 was damaged.

The third reason is that the frequency of the electromagnetic wave is high. Since the operating frequency of the high-frequency heating device is as high as 100 GHz as described above, the free space wavelength is as short as 3 mm, and when the pressure of the cooling medium C is increased as described above, the gap between the window plates 6a and 6b caused by the high pressure. There is a problem that d increases, the amount of power reflected increases, and the efficiency of plasma generation and heating decreases.

Fourthly, in order to reduce the bending moment and the amount of deformation due to the above-mentioned stress difference, the above-mentioned (1)
As can be seen from the formula, increasing the plate thickness is also envisaged, but if this is done, then the dielectric loss L will depend on the plate thickness.
However, there is a contradictory problem that the heat generation amount increases.

According to the present invention, while maintaining good electromagnetic wave propagation characteristics, the cooling efficiency is improved and the temperature rise of the window plate is suppressed, or the window plate is positively maintained, without lowering the mechanical strength of the window plate. Temperature is reduced, dielectric loss is reduced to improve plasma heating efficiency, and the amount of deformation and bending moment of the window plate is suppressed to prevent damage to the window plate, and the reliability is significantly improved. It is an object of the present invention to provide a barrier window of a high-frequency heating device that can be used.

[0015]

In order to achieve the above object, the present invention has a barrier window of a high frequency heating device in which a window plate is inserted in the middle of a transmission path for propagating a high frequency electromagnetic wave to plasma in a fusion reactor. A first short-circuit body fixed to both outer peripheral side surfaces of the window plate, a sealing ring for hermetically gripping both sides of the window plate on the inner peripheral side of the first short-circuit body, and the first short circuit A substantially tubular second short-circuit body that includes a window plate to which a body is fixed and that hermetically supports the sealing ring via a first heat insulator, and the second short-circuit body that includes the second short-circuit body. The second short-circuit body is airtightly supported via the second heat-insulating body, and is connected to the outer peripheral container air-tightly connected to the transmission line and the first short-circuit body, and the first short-circuit body is connected to the first short-circuit body. And a second cooling source that cools to a second low temperature that is higher than the low temperature of 1.

[0016]

In the barrier window of the high-frequency heating apparatus having such a structure, the window plate receives the radiant heat from the transmission line and the outer container and the conductive heat from the second heat insulator via the second short-circuit body. Since it is cooled in two stages by a so-called cryostat structure which is removed by the second cooling source, the second low temperature (for example, 80
K).

Radiant heat from the second short-circuit body, conductive heat from the first heat insulator, and heat due to dielectric loss generated in the window plate are removed by the first cooling source via the first short-circuit body. Then, it becomes parallel at the first low temperature (for example, 20K). In this way, the temperature of the window plate can be positively reduced to the first low temperature. For example, if the first low temperature is 20K, 400
Dielectric loss is about 1/400 compared to normal temperature operation at K
Can be Moreover, since the first short-circuit body is directly fixed to the window plate, the thermal resistance can be reduced. further,
Since the sealing ring can be thinned, the heat of intrusion can be reduced and the thermal stress generated in the window plate during manufacturing can be reduced.

Therefore, not only the plasma generation heating efficiency is improved, but also the temperature rise and the temperature distribution are remarkably reduced, and the thermal stress can be ignored. Moreover, unlike the conventional case where the cooling medium is caused to flow along the side surface of the window plate, deformation or bending moment due to the pressure of the cooling medium does not occur.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a partially cutaway view of a structural example of a barrier window of a high frequency heating apparatus according to the present invention, and FIG. 2 is a sectional view taken along the line AA of FIG. In FIGS. 1 and 2, reference numeral 20 denotes a circular room temperature waveguide of a high frequency heating device,
A barrier window 21 is attached in the middle of the room temperature waveguide 20,
A window plate 22 made of ceramics is provided as the window.

The barrier window 21 is composed of a cylindrical room-temperature vacuum container 24 as an outer peripheral container attached to the room-temperature waveguides 20 at both ends in the axial direction, and a cooling device 25 attached to the outside of the container 24. A cooling mechanism for cooling the window plate 22 by the cooling device 25 is provided inside the room temperature vacuum container 24.

The window plate 22 is formed of, for example, a circular sapphire having a predetermined thickness. A donut-shaped short-circuit ring 29 is fixed to both outer peripheral sides of the window plate 22 so as to have a low thermal contact resistance, and these two short-circuit rings 29 form a first short-circuit body. Sealing rings 28 are hermetically metallurgically bonded to both sides of the window plate 22 on the inner peripheral side of the short-circuit ring 29.

A low-temperature waveguide 30 is arranged on both sides of the window plate 22 in the axial direction with a predetermined gap therebetween, and the low-temperature waveguide 30 is integrally provided with a flange at a substantially intermediate position on the outer peripheral surface thereof. 1 and the sealing ring 28, which is divided by the flange 30a, is hermetically sealed via a heat insulating ring 31 as a first heat insulating body having a bellows, and in a state in which there is little heat intrusion. It is joined.

A cylindrical low-temperature shield body 32 is mounted between the flanges 30a on both sides of the low-temperature waveguide 30 in a state of being thermally connected, whereby the window plate 22, the first short-circuit body, and the first short-circuit body. The heat insulator 1 and the like are included.

The low-temperature shield body 32 holds the short-circuit ring 29, the window plate 22 and the like via the suspension member 33.
The low-temperature waveguide 30 and the low-temperature shield 32 form a second short-circuit body.

A heat insulating ring 35 having a bellows as a second heat insulating member is formed between the left side surface of FIG. 1 and the inner peripheral surface of the room temperature vacuum chamber 24, which are divided by the flange 30a of the low temperature waveguide 30.
Are joined in an airtight manner and with little heat penetration. The room temperature vacuum container 24 holds the heat insulating ring 35 and the second short-circuit body from the upper part of the inner wall on both ends thereof via the suspending member 36. Both axial ends of the room temperature vacuum container 24 are hermetically connected to the room temperature waveguide 20.

The room temperature vacuum container 24 and the suspension member 36 form an outer peripheral container. The cooling device 25 includes a first cooling unit 38 having a first low temperature (here, about 20K), and a first thermal anchor 39 that thermally connects the first cooling unit 38 and the short-circuit ring 29. A two-stage stage including a second cooling unit 40 having a second low temperature (here, about 80K) higher than the first low temperature and a second thermal anchor 41 that thermally connects the low temperature shield body 32. Constitutes a refrigerator.
Here, the 1st cooling part 38 and the 1st thermal anchor 39 form the 1st cooling source, and the 2nd cooling part 40 and the 2nd thermal anchor 41 form the 2nd cooling source. .. Further, in this embodiment, a heater 42 for heating the window plate 22 during precooling is attached to the short-circuit ring 29. Next, the operation of the barrier window of the high-frequency heating device configured as described above will be described.

Most of the conduction heat from the room-temperature waveguide 20 and the room-temperature vacuum container 24 is cut off by the heat insulating ring 35, and most of the radiation heat from the waveguide 20 and the room-temperature vacuum container 24 is conducted at low temperature. It is absorbed by the wave tube 30 and the low-temperature shield body 32, and the absorbed heat is removed by the second cooling section 40 via the second thermal anchor 41.

Further, the heat insulating ring 31 and the suspension member 3
The conduction heat from 3 is transferred to the first thermal anchor 39 via the short-circuit ring 29 and removed. For this reason, the heat that reaches the window plate 22 from the outside becomes a slight amount of heat that is almost only the radiant heat from the low-temperature waveguide 30.

Therefore, the radiant heat and the heat generated by the dielectric loss are directly transmitted to the first thermal anchor 39 through the short-circuit ring 29 and removed by the first cooling unit 38, so that the window plate 22 and the heat are cooled. Are balanced and the temperature of the window plate 22 is maintained at a first low temperature value of about 20 ° K. For this reason, the dielectric loss generated in the window plate 22 is about 1/400 of that at room temperature, which is a few W, which is much smaller than the conventional value. In this way, the so-called cryo structure is adopted in which the window plate 22 is one and the outer peripheral portion is cooled to an extremely low temperature (about 20 K), so that the dielectric loss is remarkably reduced and the plasma generation heating efficiency is increased. You can

At the same time, since the window plate 22 is made of sapphire, the temperature change of the thermal conductivity of the sapphire can be well captured. That is, the maximum thermal conductivity of sapphire is 300W / cmK at 30K and 100W / cmK at 20K, which is much higher than 0.4W / cmK at 300K. By cooling to a low temperature, the heat generated in the central portion of the window plate 22 is efficiently transmitted to the outer peripheral portion, and the temperature difference in the radial direction of the window plate 22 becomes extremely small. Therefore, even if the dielectric loss or the thermal stress increases due to the temperature rise, the increase can be offset. Further, since the outer peripheral portion of the window plate 22 is cooled and not the surface cooling by the pressurized cooling medium, the stress difference in the radial direction hardly occurs.

Further, the short-circuit ring 29 is directly fixed to both outer peripheral side surfaces of the window plate 22, and the sealing ring 28 for airtightness is airtightly joined to the heat insulating ring 31 to form a heat insulating path. There is no problem in cooling even if the ring 28 is made thin or lengthened to reduce the rigidity, and it is rather effective in reducing the intrusion heat due to conduction. Further, by reducing the rigidity of the sealing ring 28, it is possible to reduce the residual stress generated in the window plate when the window plate 22 and the sealing ring 28 are metallurgically bonded.

Further, in this embodiment, the heater 42 is precooled.
Since the window plate 22 is heated to a temperature equal to or higher than the second low temperature of the low-temperature waveguide 30 by the above, water is prevented from freezing on the window plate 22,
It is possible to eliminate such an increase in dielectric loss due to freezing and perform stable and efficient plasma generation and heating during the main operation. As a measure for preventing the freezing, preheating may be performed while transmitting microwaves from a high frequency oscillator. The first and second heat insulators 31 and 35 of the present invention may be multiple cylinders. Further, the window plate 22 may be made of glass as long as it has high strength and low dielectric loss.

[0034]

As described above, according to the present invention, the first
Using a so-called cryostat structure composed of a first short-circuit body connected to the cooling source and a second short-circuit body connected to the second cooling source, for example, a window plate that encloses the window plate at a temperature of 20 K (first Since it is cooled to a low temperature of 1, the dielectric loss can be reduced to several hundredth, for example, as compared with a structure in which a conventional cooling medium is used to cool it to around room temperature, and plasma generated by electromagnetic waves is reduced. It is possible to remarkably improve the heating efficiency of (1) to meet the recent demand for higher power and continuous operation. In addition, since the window plate does not receive the pressure of the cooling medium as in the conventional case and has a uniform temperature throughout, it is almost free from bending and deformation due to the stress difference, and mechanical damage can be eliminated. Furthermore, by separating the cooling path and the airtight part of the window plate, the rigidity of the sealing ring can be lowered, so that the stress generated during manufacturing can be reduced, and high performance,
It is possible to provide a highly reliable barrier window for a high frequency heating device.

[Brief description of drawings]

FIG. 1 is a partially cutaway front 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 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.

FIG. 5 is a cross-sectional view showing another configuration example of the barrier window of the conventional high-frequency heating device.

[Explanation of symbols]

20a, 20b ... Waveguide, 21 ... Barrier window, 22 ...
Window plate, 24 ... Vacuum container, 25 ... Cooling device, 28 ...
Sealing ring, 29 ... Short-circuit ring, 30 ... Low temperature waveguide, 31, 35 ... Insulator, 32 ... Low temperature shield,
33, 36 ... Suspension member, 38, 40 ... First and second cooling parts, 39, 41 ... First and second thermal anchors, 42 ... Heater.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Takashi Nagashima, Takashi Nagashima, 80-1, Komuyama, Naka-machi, Naka-gun, Ibaraki Prefecture Inside the Naka Institute, Japan Atomic Energy Research Institute (72) Keiji Sakamoto, 801, Mukaiyama, Naka-machi, Naka-gun, Ibaraki Prefecture No. 1 Naka Institute of Japan Atomic Energy Research Institute (72) Inventor Koji Ito 2-4 Suehiro-cho, Tsurumi-ku, Yokohama-shi, Kanagawa Toshiba Keihin Office

Claims (1)

[Claims] 1. A barrier window of a high-frequency heating device, wherein a window plate is inserted in the middle of a transmission path for propagating a high-frequency electromagnetic wave to plasma in a fusion reactor. And a sealing ring for hermetically gripping both sides of the window plate on the inner peripheral side of the first short circuit body, and the sealing ring containing the window plate to which the first short circuit body is fixed. The first
Second tubular short-circuit body that is airtightly supported via the heat insulating body, and the second short-circuit body is enclosed and the second short-circuit body is airtightly supported through the second heat insulating body. At the same time, a second container, which is connected to the outer peripheral container airtightly connected to the transmission line and the first short-circuit body, cools the first short-circuit body to a second low temperature higher than the first low temperature. A barrier window of a high-frequency heating device, comprising: a cooling source.