JPH0158840B2 - - Google Patents

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a millimeter-wave convergence antenna that converges high-power millimeter waves for electron cyclotron resonance heating of nuclear fusion plasma. This allows the millimeter waves guided by the method to converge almost to any single point.

(Prior technology) Since the development of the Gyrrotron, which generates millimeter waves with 100KW class high power, the use of electromagnetic waves to heat plasma to cause nuclear fusion has become popular.
As one of these, electron cyclotron resonance (ECR) heating using the cyclotron resonance frequency in the millimeter wave band of electrons is being studied.

Therefore, the oscillation of the Gyrrotron is circular TE _po
mode, and the output electromagnetic wave is a circular mode,
In this mode, when guided through a circular waveguide, the electric field component on the tube wall becomes zero, so the transmission loss is small and it is optimal for transmission. However, if the electromagnetic wave is emitted with a circular aperture, the electromagnetic wave will be shaped like a cone. spread to Therefore, in order to use this electromagnetic wave for plasma heating, mode conversion is performed to convert the circumferentially polarized wave to linearly polarized wave, aligning the plane of polarization in one direction, and radiating the electromagnetic wave in the form of a narrow beam. Mode converters have been developed in the past, and the following two modes of mode conversion have been mainly performed.

A. Three types of waveguides are continuously coupled: a circular waveguide whose diameter is changed periodically, a circular waveguide whose propagation direction is changed in a wavy manner, and a spiral circular waveguide. Mode conversion B converts the circular TE _po mode of the output electromagnetic wave into the HE ₁₁ mode A parabolic reflector is placed in front of the opening of the circular waveguide that guides the output electromagnetic wave of the Gyrrotron, cut stepwise or diagonally with respect to the tube axis. by placing it in a circular shape
Mode conversion to convert to TE _po mode electromagnetic field (problem to be solved by the invention) However, the above-mentioned conventional mode conversion
The purpose of this method is to obtain an electromagnetic wave beam whose thickness does not change and the energy of the electromagnetic waves radiated from the circular waveguide that guided the output electromagnetic waves of the Gyrrotron is not dispersed in a conical shape, and the energy of the radiated electromagnetic waves The problem was that it was not specifically aimed at concentrating on people.

On the other hand, in nuclear fusion research, it is necessary to locally heat a part of the plasma during electron cyclotron heating of the plasma.

The purpose of the present invention is to develop a mode conversion that can converge the energy of circular TE _po mode electromagnetic waves radiated from a circular waveguide, in order to use the concentrated radiation of high-power electromagnetic waves from a gyrotron for electron cyclotron heating of a nuclear fusion plasma. The object of the present invention is to provide a millimeter wave convergence antenna that achieves the above-mentioned results.

(Means for Solving the Problems) The millimeter-wave convergent antenna of the present invention combines an elliptical cylindrical reflector and a parabolic reflector to locally collect the energy of electromagnetic waves radiated from a circular waveguide. A circular waveguide having an aperture shaped like a stepwise or oblique cut with respect to the tube axis, and a circular waveguide arranged in front of the aperture so that the focal axis coincides with the tube axis. an elliptical cylindrical reflector with a reflective surface close to its focal axis facing the aperture; It is characterized by comprising a parabolic reflecting mirror whose axes are arranged parallel to each other, so that the energy of the electromagnetic waves is substantially converged on a desired point.

(Function) By using the millimeter-wave convergent antenna of the present invention, a gyroscope that generates high-power millimeter waves can be applied to plasma heating in a magnetic confinement fusion device, and the gyroscope can be efficiently transferred from the gyroscope to a low-loss circular waveguide. By radiating guided circular TE _po mode electromagnetic waves and focusing the energy on a part of the plasma, extremely efficient local heating can be achieved.

(Example) The present invention will be described in detail below with reference to the drawings.

The electromagnetic field of the circular TE _po mode propagating in the circular waveguide has a cutoff frequency in the waveguide of K _c ,
When the wave number in free space is K, α=sin ^-1 K _c /K (1) With respect to the tube axis, let ρ′ _po be the nth root of J _p(x) = 0, and form a circular waveguide. It can be treated as a set of countless plane waves propagating at an angle α of α=sin ⁻¹ (ρ′ _po・λ/2πa) (1)′ where the radius of is a. i.e. circular
As shown in Figure 1 a and b, the electromagnetic waves in the TE _po mode form a constant angle α with respect to the tube axis z of the circular waveguide, and while repeatedly reflecting on the tube wall, the electromagnetic waves move near the tube axis z. It can be regarded as a set of elementary plane waves having a wave source on the tube axis z, which travels in the z direction.

However, since the TE _po mode of a circular waveguide is an annular mode with an electric field vector directed in the circumferential direction, the electromagnetic wave of the circular TE _po mode as described above moves through the circular waveguide in a plane perpendicular to the z-axis. When radiated into free space from the cut open aperture, the electromagnetic waves are directed along the tube axis z
It advances in all directions forming the above-mentioned constant angle α, and spreads out in a conical shape. Therefore, we installed a circular waveguide as a second waveguide.
When cut in a step-like manner as shown in Figure a, or diagonally at an almost complementary angle to the angle α as shown in Figure b, the electromagnetic waves described above extend 180° downward with respect to the opening. The wave propagates equally in all angles using the tube axis as the wave source.

The millimeter-wave convergent antenna of the present invention first has a circular shape.
The opening of the circular waveguide that guides the TE _po mode electromagnetic wave is shaped as described above, and as shown in Figure 3 a and b,
An elliptical cylindrical reflecting mirror 2 and a parabolic reflecting mirror 3 are sequentially combined with the circular waveguide 1 to locally converge the energy of electromagnetic waves radiated from its opening. That is, the elliptical cylindrical reflector 2 is placed in front of the opening of the circular waveguide 1 so that the tube axis and the focal axis coincide, and further in front of the mirror 2, the elliptical cylindrical surface is emitted from the circular waveguide 1. A parabolic reflector 3 is placed so that its axis is parallel to the traveling direction of electromagnetic waves reflected by the reflector 2.

First, as shown in FIGS. 4a and 4b, an elliptical cylindrical reflector 2 is placed in front of the circular waveguide 1, and the bottom of the elliptical cylindrical surface among the two focal points existing on the long axis of the elliptical cross section is placed in front of the circular waveguide 1. When the focal axis passing through the focal point closer to The polarization plane of each elementary wave is perpendicular to the plane containing the focal axis and the traveling direction, and the polarization direction is approximately aligned with the y direction. converted into waves. However, it is not focused in the direction of the waveguide axis z.

Next, as shown in Fig. 5, a parabolic reflector 3 is placed in front of each elemental plane wave reflected by the elliptical cylindrical reflector 2 converging on a distant focal axis, and the axis of the paraboloid is adjusted to that point. The parabolic reflector 3 is arranged to be parallel to the traveling direction of the reflected electromagnetic wave and to form the above-mentioned angle α with respect to the circular waveguide tube axis z, and convergence in the tube axis z direction is performed by this parabolic reflector 3. That is, in FIG. 5, the elementary plane wave reflected by the elliptical cylindrical reflecting mirror 2 has focal axes S ₁ ,
When converging onto S ₂ , the equiphase surface S ₁ ′ of each elementary plane wave,
S ₂ ′ is perpendicular to the traveling direction z′ of the elementary plane wave.
In order to converge these elementary plane waves in the direction of the tube axis z, it is necessary to converge the equal phase planes S ₁ ′ and S ₂ ′ in the direction of the tube axis z. Therefore, if we take the x' axis passing through the midpoint O' of the focal axis S ₁ S ₂ and perpendicular to the traveling direction z' of the reflected elementary plane wave, we can converge the equiphase lines S ₁ ' and S ₂ ' to one point. is a parabolic reflector whose directrix is the x′ axis, and its axis is parallel to the traveling direction z′ of the reflected elementary plane wave. Figure 5 shows an example in which the convergence point is located on the tube axis z, but the shape and dimensions of the elliptical cylindrical reflector 2 and the focal length and position of the parabolic reflector 3 are appropriately selected. By doing so, the convergence point can be set at any position in front of the opening of the circular waveguide 1.

Next, the dimensions of each part of the antenna of the present invention shown in FIG. 5 will be explained assuming that an elementary plane wave behaves like a light wave. However, in reality, the wavelength of electromagnetic waves is not as short as a light wave, so it is assumed that the antenna spreads somewhat as it propagates. Please take this into consideration and allow some space in the dimensions.

First, regarding the size of the elliptical cylindrical reflector 2,
The elliptical cross section of the elliptical cylindrical surface cut perpendicular to the waveguide axis z is expressed by the following equation (2): Y ² /A ² + (x-f) ² /B=1 (2) Here , f = B ² - ^{A 2The} z-coordinate value of the reflection point Q of the elementary plane wave P that is closest to the circular waveguide 1 and hits the elliptical cylindrical reflector 2 is as follows with respect to the radius a of the circular waveguide 1. Equation (3) is obtained.

z=(B-f-2a) cot α (3) On the other hand, as shown in FIG. The value is given by the following equation (4).

z=(2a+A ² /B) cot α (4) Therefore, the dimension of the elliptical cylindrical reflecting mirror 2 in the direction of the tube axis z is the minimum length of QS. Furthermore, since the elementary plane wave is radiated only downward in FIG. 5 from the opening shown in FIG. 2a of the circular waveguide 1,
The height h of the elliptical cylindrical reflecting mirror 2 is expressed by the following equation (5).

h=B−f (5) Next, the position of the parabolic reflector 3 is as described above.
The x' axis is set as the directrix, but as an example, the 5th
As shown in the figure, in order to set the focal point E of the paraboloid on the z-axis, the parabolic reflector 3 is placed at x' The focal length of the parabola in the cross section cut along the z′ plane is FG, and the axis of symmetry is FH.
shall be. That is, by setting O'H=l and HG=FG=fp, a parabola on the x'z' plane becomes the following equation (6).

x′=−1/4fp(x′+l) ² −fp (6) Therefore, the dimension of the parabolic reflector 3 in the z-axis direction
Among the values of the above equation (6), a value within the range of the following equation (7) is adopted as x′.

-2acosα≦x′≦2acosα (7) Next, regarding the dimension y of the parabolic reflector 3 in the y-axis direction, as shown in FIG.
In a cross section cut along the xy plane, the range in the y-axis direction where an elementary plane wave exists at a height of x= _x1 is expressed by the following equation (8).

−A ² /B(2f−x ₁ )/2f≦y≦A ² /B(2f−x ₁ )/2f (8) In other words, the parabola and z in the cross section shown in Figure 7
Find the height of the point where the distance from the axis is the shortest and use the above method.
By applying equation (7), the dimension in the y-axis direction can be determined.

Next, the results of prototyping the antenna of the present invention constructed as described above and measuring its performance will be described. frequency by a circular waveguide with an inner diameter of 16 mm.
The following is an example of the configuration of the waveguide system of the antenna of the present invention when a circular TE ₀₁ mode electromagnetic wave of 35.56 Hz, wavelength λ = 8.445 mm, and ρ′ ₀₁ = 3.831706 is radiated using a 200 mW Gunn oscillator at an angle α = 40.1°. 8, and the dimensions of each reflecting mirror 2, 3 are shown in FIGS. 9a and 9b. In the waveguide system shown in FIG. 8, the oscillation output of the Gunn oscillator 4 is connected to a circulator 6 to which a matched load 5 is connected, an adjustable attenuator 7, a mode converter 8, and a mode filter 9.
are sequentially supplied to the circular waveguide 10 described above. Further, in the dimension example shown in FIG. 9, the parameters of equation (2) representing the elliptical cross-section of the elliptical cylindrical reflecting mirror 2 are set to A=6.24 cm and B=8.0 cm.

Further, FIG. 10a shows a schematic configuration of a power detector that can be used to measure the performance of a prototype antenna to measure local electromagnetic wave power values. The part that actually detects the electric field is constructed by exposing the center conductor of a high-frequency coaxial line by 1/4 wavelength, as shown in Figure b, and detects the electric field component in the direction parallel to the exposed center conductor at the measurement point. To detect. The detector was moved to measurement points selected in a grid pattern at 3 mm intervals vertically and horizontally on the plane to be measured, and the electromagnetic waves detected by the detector 11 shown in FIG.
3, and the position coordinates of the detector 11 are measured by potentiometers 13 and 14.

As described above, the power distribution obtained by reflecting the circular TE _po mode electromagnetic waves radiated from the opening of the circular waveguide 1 only by the elliptical cylindrical reflector 2 is calculated using the elliptical cylindrical shape of the antenna of the present invention having the dimensions shown in FIG. The results of measurement on four planes parallel to the yz coordinate plane that sandwich the upper and lower focal axes of the surface emitting mirror 2 at a distance of 10 cm are shown in FIGS. 11 to 14. Each figure consists of a, b, and c, respectively. Diagram a shows the power distribution on each plane, the "+" point is the measurement point of the maximum power, and diagrams b and c show the power distribution at the maximum power point "+" The power distributions in the y-axis and z-axis directions through , respectively, are shown. From these measurement results, the effect of electromagnetic wave convergence in the y-axis direction by only the elliptical cylindrical reflecting mirror 2 can be seen.

Next, we will calculate the predicted convergence by measuring the same power distribution when the parabolic reflector 3 is combined with the elliptical cylindrical reflector 2 described above by moving the detector described above on the xz coordinate plane. Three locations in the z-axis direction centered on the point are shown in FIGS. 15 to 17.
From these measurement results, it can be seen that, unlike the conventional method, the effect of electromagnetic wave convergence is significant also in the direction of the tube axis z of the circular waveguide.

In addition, X in the measurement results shown in each part mentioned above
The coordinates and Y coordinates are set as shown in FIG. 18, and Y=5 cm corresponds to the position of the tube axis of the circular waveguide.

(Effects of the Invention) As is clear from the above description, according to the present invention, the energy density of the radiated electromagnetic waves is increased by aligning and converging the polarization directions of the electromagnetic waves radiated from the circular waveguide, thereby increasing the energy density of the radiated electromagnetic waves. A remarkable effect is that the fused plasma can be heated locally and efficiently.

[Brief explanation of drawings]

Figures 1a and b are diagrams showing the mode of electromagnetic wave propagation within a circular waveguide, Figures 2a and b are diagrams each showing an example of the opening shape of the circular waveguide in the antenna of the present invention, and Figure 3 Figures a and b are diagrams showing configuration examples of the millimeter wave convergent antenna of the present invention, respectively;
Figures 4a and b are diagrams showing the effects of combining only the circular waveguide with the elliptical cylindrical reflector in the antenna of the present invention, and Figure 5 is a diagram showing the effects of the antenna of the present invention. , FIG. 6 is a diagram showing a part of the effect, FIG. 7 is a diagram showing another part of the effect, and FIG. 8 is a diagram of the waveguide system for measuring the performance of the antenna of the present invention. A block diagram showing the configuration, FIGS. 9a and 9b are diagrams each showing an example of the dimensions of the antenna of the present invention, and FIGS. 10a and b are diagrams showing the configuration of a power distribution measuring device for measuring the performance of the antenna of the present invention, respectively. Figures 11 a to 14 a to 14 a to c are characteristic curve diagrams showing the results of measuring the effects of only the elliptical cylindrical reflector in the antenna of the present invention, and Figures 15 to 17 are characteristic curve diagrams of the antenna of the present invention. Characteristic curve diagram showing the effect measurement results, 1st
Figures 8a and 8b are diagrams showing the coordinate axes of characteristic curves showing the effects of the antenna of the present invention. DESCRIPTION OF SYMBOLS 1... Circular waveguide, 2... Elliptical cylindrical reflector, 3... Parabolic reflector, 4... Gunn oscillator, 5... Matched load, 6
... Circulator, 7 ... Adjustable attenuator, 8 ... Mode converter, 9 ... Mode filter, 10 ... Circular waveguide, 11 ... Detector, 12 ... Rectangular waveguide, 13 ... Coaxial line, 14, 15 ... Port tensiometer.

Claims (1)

[Claims] 1. A circular waveguide having an aperture shaped like a step or cut obliquely to the tube axis, and a reflecting surface placed in front of the aperture so that its focal axis coincides with the tube axis and is close to the focal axis. an elliptical cylindrical reflector facing the aperture, and a paraboloid arranged in front of the aperture and the reflective surface with its axis parallel to the traveling direction of electromagnetic waves radiated from the aperture and reflected by the reflective surface. What is claimed is: 1. A millimeter-wave convergence type antenna, comprising: a surface reflecting mirror to substantially converge the energy of the electromagnetic waves at a desired point.