JPH0770881B2 - Polarization conversion antenna for whispering gallery mode - Google Patents

Description

The present invention relates to a whispering gallery mode polarization conversion antenna.

[Conventional technology]

One of the methods of fusion plasma heating is called ERCH (electron cyclotron heating), which generally uses high power millimeter waves generated by a gyrotron. Here, a simplified structure of the gyrotron (1) is shown in FIG. 6. (2) is a cavity that oscillates millimeter waves, (3) is a collector for collecting high-speed electrons, and (4) is high power. Cylindrical waveguide that outputs millimeter waves,
(5) is a circular waveguide that guides the output millimeter wave to the heated side.

Until recently, the oscillation mode of this gyrotron was an axially symmetrical annular mode called TEon, and its power was 200 kw or less per oscillator tube. However, in order to obtain higher temperature and higher density plasma, when higher frequency and higher power millimeter waves are required, higher order modes are required as operation modes. As a result, the radius of the cavity of the cavity (2) becomes large, and the separation between the operation mode and other modes becomes poor, causing a problem of so-called mode competition. Therefore, in recent years, a mode called whispering gallery mode has attracted attention. This mode is a mode in which a strong electric field exists only near the tube wall, as shown in Figs. 7 (a) and 7 (b), and mode competition is relatively small, and it is possible to output as much as 1 MW per oscillation tube at a high frequency of 100 GHz or more. It is said that there is. This mode is considered to be a collection of beams (local plane waves) that spirally follow the control as shown in FIG.
When the beam trajectory is projected on the cross section perpendicular to the waveguide axis,
As shown in FIG. 8B, the beam is repeatedly reflected in the circumferential direction.

A linearly polarized beam is suitable for the ECRH of plasma.
In addition, the efficiency of the conventional waveguide transmission is greatly reduced in the transmission of high-frequency and high-power millimeter-wave beams. So VLAS
OV et al. Proposed a simple quasi-optical polarization conversion antenna as shown in FIGS. 9 (a) and 9 (b) that converts a whispering gallery mode into a linearly polarized wave using a parabolic reflector. ing.

This is a straight line S in the tube axis direction (Z axis) at the tip of the circumferential waveguide (4), and a straight line S extending from the base end Z ₁ of this straight line S along the beam transmission direction in a spiral shape. A beam emission hole (4a) is formed by a cut end composed of a curve C reaching the other end Z ₂ .
Further, a reflection plate (6) having a parabolic cylindrical surface is arranged opposite to the beam emission hole (4a) in parallel. As described above, the whispering gallery mode is considered to be a collection of beams that make an angle of θB with respect to the tube axis (Z axis) and travel while reflecting at an angle of θw with the tube wall in the waveguide cross section. Therefore, if such a cut is given to the cylindrical waveguide (4), each beam is evenly radiated at an angle of 2θw like a cylindrical wave having a straight line S (Z _{1 to} Z ₂ ) as a wave source. . Therefore, as shown in FIGS. 9 (a) and 9 (b), the straight line S (Z ₁ -Z ₂ )
By arranging the reflector (6) of the radiation cylinder surface with the focal line on the top,
This cylindrical wave is converted into a linearly polarized beam suitable for plasma heating.

[Problems to be Solved by the Invention]

When the electric field of the beam radiated from the cylindrical waveguide (4) with the above conventional polarization conversion antenna is measured and observed in a cross section perpendicular to the propagation direction, it converges on one main rope as shown in FIG. Instead, it includes many side ropes, and even if you look at the energy distribution after it is reflected by the curved reflector (6),
It has a large spread as shown in Fig. 11. For this reason, it is easy to diffuse before reaching the heated side, and the energy ratio that reaches the heated side and can be used for heating is as low as about 70% of the total radiant energy. In addition, as an invention that improves the research of VLASOV described above, as a technical report of the Institute of Electronics, Information and Communication Engineers, vol.88, No.67, MW88-8, "Whisperin
There is a quasi-optical antenna for g Gallery Mode, design and calculation of reflection characteristics.

This is because the polarization conversion antenna using a parabolic reflector such as VLASOV improves the accuracy of analysis to convert it into a beam of strictly linear polarization, corrects the shape of the reflector, and changes the phase of the beam. The surface is close to the plane.

However, the theoretically available energy efficiency is 80
%, The measured value was 70%, showing almost no improvement compared with that of the study by VLASOV et al.

Therefore, an object of the present invention is to provide a polarization conversion antenna capable of improving the efficiency of energy transmission by reducing the side rope component and increasing the energy comparison of the main rope that directly contributes to heating.

[Means for Solving the Problems]

In order to achieve the above object, the present invention transmits a beam of a whispering gallery mode oscillated and generated in a cavity of a large gyrotron spirally along an inner wall while repeatedly reflecting it at a predetermined angle, and outputs it to the output side. A cylindrical waveguide that radiates for heating with high power from the beam radiation hole provided, and a curved reflector that faces the beam radiation hole and has a curvature that converts the incident beam into a parallel beam, In the inner peripheral surface of the cylindrical waveguide, a portion that directly reflects the beam toward the curved reflection plate through the beam radiation hole (for example, a portion E hatched in FIG. (Refer to "Reflecting surface") The circumferential shape is seen in order along the spiral beam traveling direction, and with respect to the basic shape that evenly radiates the beam to the curved reflector, the first is tilted inward and finally outward. Provided is a polarization conversion antenna for a whispering gallery mode in which a beam emitted from a beam emission hole has an energy distribution similar to a Gaussian distribution at a position of a curved reflector, which is continuously changed so as to be inclined.

[Action]

In the present invention, the basic shape for radiating a beam evenly to the curved reflector is a perfect circular arc in the conventional polarization conversion antenna described in FIGS. 9 (a) and 9 (b), for example. This shape changes depending on the installation location and size of the curved reflector.
For example, when it is placed laterally instead of below the cylindrical waveguide (4), it has a shape that projects laterally or a shape that tilts laterally. In other words, after deciding the size and installation location of the curved reflector, the geometrical optics is used so that the beam incident on the final reflection surface of the cylindrical waveguide at a predetermined angle is reflected toward the curved reflector with an even distribution. The basic shape in the circumferential direction can be determined by using approximation. Here, the case where the basic shape is a perfect circular arc as shown by the dotted line in FIG. 1 (b) and the circumferential shape is changed as shown by the solid line will be described. In FIG. 2 (a), which is an enlarged view of FIG. 1 (b), the normal line of reflection, which is set on a plane orthogonal to the tube axis with respect to the final reflection surface portion whose inclination is changed, is the spiral beam transmission direction. As seen in order toward the beam emission hole, the beam supply side is inclined toward the tube axis in the direction opposite to the transmission direction. This inclination gradually becomes smaller, and after overlapping with the diameter passing through the tube axis, it begins to tilt in the same direction as the transmission direction. The maximum inclination is obtained in the vicinity of the linear cut of the beam emission hole.

This is because the beam reaching the curved reflector through the beam emission hole as shown in FIG. 2 (b), when viewed in a plane orthogonal to the tube axis, has a small beam distribution at both end portions and a large beam distribution at the central portion. That is, it means that the energy distribution of the radiation beam becomes close to a Gaussian distribution near the surface of the curved reflector.

Further, since this beam bundle gradually decreases from the center to the periphery and becomes zero, it reaches the curved reflecting plate with almost no diffraction loss, thus improving the energy conversion efficiency.

In this way, the beam incident on the curved reflecting plate with the Gaussian distribution is converted into a parallel beam, that is, a linear braided beam, with a distribution similar to the Gaussian distribution.

Further, although it has not been clarified theoretically at this time, if the tilt near the cut end of the waveguide is changed to apply the geometrical optics as described above to make the energy distribution in the circumferential direction a Gaussian distribution, It was measured that the energy distribution in the axial direction of the beam also has a Gaussian distribution. As a result, according to the configuration of the present invention, the beam is emitted from the beam emission hole with an energy distribution similar to a Gaussian distribution in both the tube axis direction and the circumferential direction, and this causes the curved reflector to form a two-dimensional Gaussian distribution. It is converted to a linear braided beam.

〔Example〕

An embodiment of the wave conversion antenna for whispering gallery mode of the present invention is shown in FIGS. 1 (a) and (b), and will be described below.

In the knitting wave conversion antenna (10) for whispering gallery mode shown in the figure, (11) is a cylindrical waveguide, and a cavity oscillating in the whispering gallery mode as shown in FIGS. 7 (a) and 7 (b). The beam emission hole (12) is formed at the output end, which is connected directly or through another waveguide. The shape of the beam emission hole (12) in the illustrated example is composed of a straight line S along the tube axis direction, and a curve C spirally extending 360 ° from the base end Z ₁ to the tip Z ₂ . Reference numeral (13) is a curved reflector which is arranged in parallel with the tube axis of the cylindrical waveguide (11) so as to face the beam emission hole (12).

Of the circumferential surface of this cylindrical waveguide, the circumferential direction shape of the final reflecting surface E (the plane orthogonal to the tube axis) that directly reflects the beam toward the curved reflecting plate (13) through the beam radiating hole (12) The cut) is as shown in FIG. 1 (b). This is because the curved reflector (13) represented by the dotted line has a shape in which the beam is uniformly radiated, and as shown by the solid line, it is first tilted inward when viewed along the spiral beam traveling direction. Finally, it is continuously deformed so that it tilts outward. Therefore, as shown in Fig. 2 (a), the normal line of reflection standing on the XY plane orthogonal to the tube axis is different from the normal line of the other inner peripheral surface, which is the same as the diameter, Looking at each of these along the direction of travel, the first thing that is inclined in the direction opposite to this direction with respect to the diameter gradually approaches the diameter so that it gradually overlaps with the diameter, and then the beam emission hole. As it approaches the straight cut S of (12), the inclination becomes larger in the traveling direction and the forward direction.

Therefore, when viewed in the spiral traveling direction of the beam, the beam radiated from the portion where the inclination first changes is shown in FIG.
As shown in (3), with respect to the radial radiation range X ₁ -X _{2 of the} beam radiation hole (12), the beam comes closer to the center from the original reflection direction X ₁ . Then, the beam incident on the portion following this is radiated to the center of the radiation range X ₁ -X ₂ , and as it further approaches the cut S of the beam radiation hole, the beam reflection direction changes from the original reflection direction X ₂ to the radiation range X _2. It approaches the center of _1- X ₂ . Therefore, the energy distribution in the radiation range X ₁ –X ₂ in the circumferential direction of the beam is also close to the Gaussian distribution.

Next, the shape of the curved reflector (13) will be described.

The curved reflector (13) has a parabolic cylindrical surface as a basic shape, but in the present invention, the shape of the final reflective surface of the inner peripheral surface of the cylindrical waveguide (11) that reflects the beam toward the reflector. Is transformed. For this reason, in order to correspond to this, the transformation is added so that the conversion into the parallel beam is completely performed. This can be determined by geometrical optics calculations.

As described above, in the present invention, the deformation of the cylindrical waveguide (11) and the curved reflecting plate (13) is performed only in the plane orthogonal to the tube axis of the cylindrical waveguide (11), and in the tube axis direction. The shape has not been changed. According to such a method using geometrical optics, it is considered that the Gaussian distribution is only in the circumferential direction, and the tube axis direction has a uniform beam distribution as in the conventional case.

However, when the polarization conversion antenna (10) of the present invention was actually manufactured and the distribution of the beam was measured, it was found that a beam having a Gaussian distribution was obtained not only in the circumferential direction but also in the tube axis direction. An example of this measurement result is shown in FIG. 3 and FIG. FIG. 3 is a diagram in which the electric field of the beam radiated from the circumferential waveguide (11) is measured on a plane orthogonal to the propagation direction. The main beam M contains 93% of the total energy, and the side beam S ₁ , The energy contained in S ₂ was as small as 7%, and the energy loss could be considerably reduced compared to the conventional polarization conversion antenna. Further, FIG. 4 is an energy distribution diagram immediately after the beam converged to the Gaussian distribution as shown in FIG. 3 is reflected by the curved reflecting plate (13) and converted into a parallel beam. Compared with the energy distribution of the wave conversion antenna, it can be seen that it is in a state in which it is difficult to diffuse.

In the embodiment of the present invention described with reference to FIGS. 1 to 4, as shown in FIGS. 1 (a) and 1 (b), the curved reflecting plate (13) is provided on the lower front side of the cylindrical waveguide (11). It was arranged. By the way, in the actual fabrication, the curved reflector (13) is attached to the cylindrical waveguide (11).
Placing it to the side of increases the design freedom. In this case, the final reflecting surface E facing the curved reflecting plate (13) of the cylindrical waveguide may be formed in the shape of a canopy protruding laterally as shown in FIG. 5, for example. Then, the inclination is based on the shape of radiating the beam evenly to the curved reflecting plate (13) as in the above-mentioned way of thinking, and if it is inclined inward or outward as it approaches the both ends when viewed in the circumferential direction. Good.

〔The invention's effect〕

The present invention shows the property of the beam reflected by this portion as a radiation source by changing the shape of the inner peripheral surface of the output end of the radiator (waveguide), research by VLASOV et al. Different from the invention of the above-mentioned research report which is, the millimeter wave beam transmitted through the cylindrical waveguide in the whispering gallery mode is changed to a Gaussian distribution in the horizontal and vertical directions by changing it to one that does not cause diffraction loss. It can be converted into a linear wave having an approximate energy distribution. Further, since the energy diffusion can be reduced and the radiation can be propagated to the heated side, the energy transmission efficiency can be improved.

[Brief description of drawings]

1 (a) and 1 (b) show the structure of one embodiment of the polarization conversion antenna of the present invention, in which (a) is a perspective view and (b) is a cross-sectional view in a direction orthogonal to the tube axis. . Fig. 2 (a)
(B) is FIG. 1 (a) (b) calculated using geometrical optics.
It is a figure which shows the beam reflection state in the Example of. FIG. 3 is a diagram showing an example of an electric field distribution of a beam emitted from a cylindrical waveguide in the polarization conversion antenna of the present invention, and FIG. 4 is a diagram showing a beam having the electric field distribution shown in FIG. It is an energy distribution map in the plane orthogonal to the propagation direction immediately after converting into a beam. FIG. 5 is a diagram showing the overall configuration of the polarization conversion antenna when the curved reflecting plate is arranged laterally of the cylindrical waveguide. FIG. 6 is a schematic diagram of the structure of a gyrotron using a circular waveguide for millimeter wave beam transmission, and FIGS. 7 (a) and 7 (b) are electric field distributions of the gyrotron oscillating in the whispering gallery mode, respectively. Sectional view of the cylindrical waveguide showing the
Figures (a) and (b) show the states where the whispering-gallery mode beam propagates through the cylindrical waveguide, respectively, in the XZ plane and
9A and 9B are schematic views showing the XY plane, and FIG. 9A and FIG. 9B show a conventional polarization conversion antenna for converting a whipering gallery mode beam into a linearly polarized beam, and FIG. b) shows a sectional view. Fig. 10 is an electric field distribution diagram of the beam radiated from the cylindrical waveguide of the conventional polarization conversion antenna, and Fig. 11 is a diagram after the beam having the distribution shown in Fig. 10 is converted into a parallel beam by the curved reflector. It is an energy distribution map. (10) …… Polarization conversion antenna for whispering gallery mode, (12) …… Beam emission hole, (13) …… Curved reflector.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A 64-49405 (JP, A) Technical Report of IEICE, Vol. 88, No. 67, MW88-8, "Quasi-optical reflective antenna for Whispering Gallery Mode, design and calculation of reflection characteristics" Technical Report of IEICE, Vol. 89, No. 39, MW89-23, "Analysis of radiation characteristics of primary feed waveguide of polarization conversion antenna for whispering-gallery-mode"

Claims (1)

[Claims] 1. A whispering gallery mode beam oscillated and generated in a cavity of a large gyrotron is spirally transmitted along an inner wall while being repeatedly reflected at a predetermined angle, and a beam emission hole is provided on an output side. A cylindrical waveguide that radiates for heating with high power, and a curved reflecting plate that faces the beam radiation hole and has a curvature that converts an incident beam into a parallel beam. Of the inner peripheral surface, the circumferential shape of the part that reflects the beam toward the curved reflector is viewed in order along the spiral beam traveling direction, and a basic shape that uniformly radiates the beam to the curved reflector is formed. On the other hand, the beam emitted from the beam emission hole has a Gaussian distribution-like energy distribution at the curved reflector position by continuously changing it so that it first tilts inward and finally tilts outward. Polarization conversion antenna for whispering gallery mode.