JPS6241400B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a nuclear fusion device, and more particularly to a nuclear fusion device equipped with plasma heating means using high-frequency electromagnetic waves.

In a nuclear fusion device, plasma generated in a vacuum vessel is heated to cause a nuclear fusion reaction, and one known method for heating the plasma is to inject high-frequency electromagnetic waves into the plasma. There are several types of incident high-frequency electromagnetic waves depending on the propagation direction and frequency of the waves, and the location where the high-frequency electromagnetic waves are incident on the plasma also differs depending on the type of high-frequency electromagnetic waves. For example, in a tokamak type nuclear fusion device, the normal wave of an electron cyclotron is input from the outside of the torus, and the structure in this case is shown in FIG.

In FIG. 1, 1 is a vacuum vessel usually made of stainless steel, 2 is a plasma, 3 is a waveguide for high frequency oscillation, 4 is a lid, and TC is the center axis of the torus. In other words, a waveguide 3 attached to a vacuum vessel 1 sends normal waves from the low magnetic field side to the plasma 2 in a direction perpendicular to the magnetic field.
It is becoming more and more incidental.

By the way, the plasma heating efficiency by high-frequency electromagnetic waves is expressed by the attenuation rate K _i of the high-frequency electromagnetic waves, and as shown in FIG. 2, it largely depends on the angle of incidence of the high-frequency electromagnetic waves into the plasma. In FIG. 2, curves X, Y, and Z indicate the attenuation rate K _i when high-frequency electromagnetic waves are incident at angles α with the toroidal magnetic field of α=65°, 75°, and 85°, respectively.

Therefore, in the conventional nuclear fusion device, the waveguide 3 is installed so that the propagation direction of the high-frequency electromagnetic waves is directed to the incident angle α that provides the best plasma heating efficiency. However, the radiation directivity of high-frequency electromagnetic waves is not unidirectional as shown in FIG.

In Figure 3, curves P ₁ , P ₂ , P ₃ etc. are the radiation directivity curves of the waveguide with a rectangular opening shape.
Q ₁ , Q ₂ , Q ₃ , etc. indicate the radiation directivity of the same apertures with circular shapes. D is the length of each side in the case of a square, the diameter in the case of a circle, and λ is the wavelength of the high frequency electromagnetic wave. In addition, θ and φ are the axis perpendicular to the aperture surface of the waveguide,
In this opening plane, if the axis parallel to one side of the rectangle is the Y-axis, and the axis parallel to the other side is the Z-axis, then the propagation direction of the high-frequency electromagnetic wave and the X-axis in the X-axis-Y-axis plane and the angle formed by the X-axis - Z
This is the angle between the propagation direction of high-frequency electromagnetic waves and the X-axis in the axial plane. As you can see from this figure 3,
The radiation directivity of high-frequency electromagnetic waves is not only in the direction of θ and φ = 0 as shown by curves P ₁ and Q ₁ , but also in the direction of curves P ₂ and P ₃
etc., curves Q ₂ , Q ₃ etc. in each direction,
These high-frequency electromagnetic waves having radiation directivity in each direction are incident on the plasma, but as can be seen from Figure 2 above, even if the incident angle α is well selected, the waves propagate to a position away from the center of the plasma. in case of,
Since the attenuation rate K _i of high-frequency electromagnetic waves, that is, the plasma heating efficiency, decreases significantly, only a portion of the incident high-frequency electromagnetic waves reaches the region with high heating efficiency near the center of the plasma (hereinafter referred to as the absorption region). It contributes to plasma heating, and the rest is absorbed by the inner wall of the vacuum vessel without being absorbed by the plasma. Therefore, conventional nuclear fusion devices have the disadvantage that only a portion of the incident high-frequency energy is used for plasma heating, resulting in low heating efficiency.

An object of the present invention is to provide a nuclear fusion device that can effectively utilize incident high-frequency energy for plasma heating to improve its heating efficiency.

In order to achieve this object, the present invention is directed to a wall surface that is located close to the plasma and reflects the incident high-frequency electromagnetic waves, such as an inner wall surface of a vacuum container, or an inner wall surface of the first wall in the case of a device equipped with a first wall. The curvature of is set so that the high-frequency electromagnetic waves reflected by this wall reach the absorption region near the center of the plasma, and the part of the incident high-frequency electromagnetic waves that reaches the wall without being absorbed by the plasma is the absorption region of the plasma. It is characterized in that it converges on and is effectively used for plasma heating.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with respect to each of the illustrated embodiments.

FIG. 4 is a longitudinal sectional view of a tokamak-type nuclear fusion device according to an embodiment of the present invention. This embodiment differs from the conventional example shown in FIG. 1 in the curvature of the inner wall surface of the vacuum vessel 5. As mentioned above, the propagation direction of high-frequency electromagnetic waves is not unidirectional due to its radiation directivity, but has a spread of 40° to 80°. Of these, only a part of the high-frequency electromagnetic waves 6a reaches the absorption region 2a of the plasma 2 in series, and the remaining high-frequency electromagnetic waves 6b reach the inner wall surface 5a of the vacuum container 5, where a portion (in the case of stainless steel, approximately 10%) is absorbed and then reflected. Therefore, in this embodiment, the curvature of the inner wall surface 5a is set so that the high frequency electromagnetic wave 6b reflected by the inner wall surface 5a of the vacuum vessel 5 reaches the absorption region 2a of the plasma 2. Therefore, almost all of the incident high-frequency electromagnetic waves are focused on the absorption region 2a of the plasma 2, and the energy is effectively absorbed by the plasma 2, so that the plasma heating efficiency can be significantly improved. .

FIG. 5 is a longitudinal sectional view of a tokamak-type nuclear fusion device according to another embodiment of the present invention. In this example,
The inner wall surface 7a of the vacuum container 7 is divided into a plurality of regions, and the curvature of each divided region is adjusted so that the high frequency electromagnetic waves 6b reflected at each region of the inner wall surface 7a reach the absorption region 2a of the plasma 2. Each is set. Therefore, the torus central axis of the vacuum vessel 7
The plasma heating efficiency can be improved in the same manner as in the embodiments described above without increasing the dimension in the TC direction.

The embodiments shown in FIGS. 6 and 7 are modifications of the embodiments shown in FIGS. 4 and 5.
That is, in each of these embodiments, as described above, among the high-frequency electromagnetic waves 6b that are reflected from the inner wall surfaces 8a and 9a of the vacuum vessels 8 and 9 on the opposite side to the high-frequency electromagnetic wave incident ports and reach the absorption region 2a of the plasma 2, , the high-frequency electromagnetic wave incident port side so that the high-frequency electromagnetic wave 6b that is not absorbed by the plasma 2 and reaches the inner wall surfaces 8a and 9a on the high-frequency electromagnetic wave incident port side, and is reflected again here, reaches the absorption region 2a of the plasma 2 again. The inner wall surfaces 8a, 9a are formed in a circular shape. Therefore, the above-mentioned FIGS. 4 and 5
Plasma heating efficiency can be further improved than in each of the illustrated embodiments.

In each of the above embodiments, a case has been described in which the present invention is applied to a tokamak-type nuclear fusion device that does not have a first wall, but the present invention is not limited to this.
It can be widely applied to tokamak-type fusion devices and non-axisymmetric fusion devices, such as heliotron-type fusion devices, which each have a first wall as shown in the figure, as well as stellarator-type, mirror-type fusion devices, etc. be able to. That is, the inner first wall (11 in FIG. 8, 13 in FIG. 9) usually made of stainless steel is supported within the vacuum container 1 via a bracket 10.
and each inner wall surface 11a, 13a and 12a of the outer first wall (12 in FIG. 8, 14 in FIG. 9),
By setting the curvature of 14a so that the high-frequency electromagnetic waves reflected by these inner wall surfaces reach the absorption region 2a of plasma 2, plasma heating efficiency can be improved as in each of the embodiments described above. In addition, in FIG. 8 and FIG. 9, the inner first walls 11, 13 and the outer first walls 12, 14
Each inner wall surface 11a, 13a and 12a, 14a of
is divided into a plurality of regions as shown in FIG. 5, and the curvature of each divided region is set so that the high frequency electromagnetic waves reflected in each region reach the absorption region 2a of the plasma 2. Even in this case, the same effect as shown in FIG. 5 can be obtained. Further, the present invention provides the first
It can be similarly applied to those in which cooling pipes are provided on the blanket side of the wall.

Further, in each of the above embodiments, the inner wall surface of the vacuum vessel or the first wall, which is usually made of stainless steel, is used as a direct reflection surface for high-frequency electromagnetic waves, but a reflective film made of a material with a higher reflection coefficient than stainless steel is provided on these inner wall surfaces. For example, it is possible to reduce the amount of high-frequency electromagnetic waves absorbed here and further improve the plasma heating efficiency. The material for the reflective film is preferably a material that not only has a large reflection coefficient but also has high conductivity and does not emit impurities in a vacuum, such as silver, which can be applied to the inner wall surface as silver plating or the like. Bye.

Incoming high-frequency electromagnetic waves include ion cyclotron waves (10 MHz to 100 MHz), low-frequency hybrid waves (1 GHz to 2 GHz), and electron cyclotron waves (10 GHz to 100 GHz). It is preferable to use high frequency electromagnetic waves, such as electron cyclotron waves.

As explained above, according to the present invention, the curvature of the wall surface that is located close to the plasma and reflects the incident high-frequency electromagnetic waves, such as the inner wall surface of the vacuum container or the inner wall surface of the first wall, can be reflected by this wall surface. In order for the high-frequency electromagnetic waves to reach the absorption region of the plasma,
With this setting, it is possible to effectively utilize the incident high-frequency electromagnetic waves that reach the wall surface without being absorbed by the plasma by converging them in the plasma absorption region, and as a result, it is possible to improve the plasma heating efficiency. becomes.

[Brief explanation of the drawing]

Figure 1 is a vertical cross-sectional view of the right side of the torus center in a conventional fusion device, Figure 2 is a characteristic diagram showing the attenuation rate of high-frequency electromagnetic waves, Figure 3 is a characteristic diagram showing the radiation directivity of high-frequency electromagnetic waves, and Figure 4 is a characteristic diagram showing the radiation directivity of high-frequency electromagnetic waves. 9 to 9 are vertical cross-sectional views of the right side of the torus center of nuclear fusion devices according to different embodiments of the present invention. 2... Plasma, 2a... Absorption region, 3... Waveguide for high frequency oscillation, 5, 7, 8, 9... Vacuum container, 5a,
7a, 8a, 9a...inner wall surface, 6a, 6b...high frequency electromagnetic waves, 11-14...first wall, 11a-14a...
Inner wall surface.

Claims (1)

[Scope of Claims] 1. In a nuclear fusion device that injects high-frequency electromagnetic waves into plasma in a vacuum container and heats it to cause a nuclear fusion reaction, a wall surface that is located close to the plasma and reflects the high-frequency electromagnetic waves. A fusion device characterized in that the curvature of the wall surface is set such that the high frequency electromagnetic wave reflected by the wall surface reaches an absorption region near the center of the plasma. 2. The nuclear fusion device according to claim 1, wherein the wall surface is an inner wall surface of the vacuum vessel. 3. The nuclear fusion device according to claim 1, comprising a first wall in the vacuum container at a position close to the plasma, and the wall surface is an inner wall surface of the first wall. 4. The nuclear fusion device according to claim 1, characterized in that a reflective film with a large reflection coefficient is provided on the wall surface.