0883-6272/86 $3.00 + .00 Copyright ® 1986 SUNSAT Energy Council REFLECTOR ANTENNAS FOR ELECTRON CYCLOTRON RESONANCE HEATING OF FUSION PLASMA OSAMI WADA and MASAMITSU NAKAJIMA Department of Electronics Kyoto University Kyoto 606, Japan Abstract — For electron cyclotron resonance heating (ECH) of fusion plasma, transformation is required of the millimeter wave output from a gyrotron, circular TE„„ mode, into a linearly polarized wave beam. It is easily realized by use of a parabolic cylinder reflector. Vlasov el al. proposed this type of reflector antenna which has a stair-cut aperture at an end of a circular waveguide (1). On the other hand, we proposed another type of antenna which also uses a parabolic cylinder and has an obliquely cut aperture (2). In this paper, the transformation efficiencies of polarization and radiation fields of the two types of antennas are calculated by means of geometrical optics and the Kirchhoff-Huygens principle. Then we propose a mode converter, in which the output of this type of parabolic reflector is led to a rectangular waveguide and transformed into TEW mode. In addition, another reflector antenna is proposed which focuses the wave beam using an elliptic cylinder reflector and a parabolic one. GEOMETRICAL-OPTICS TREATMENT The longitudinal magnetic field of TE()n mode from a gyrotron is given by where kcn = p' onla, p'on is the root of J (p) =0, and a is the radius of the circular waveguide. By virtue of Hansen’s Integral, Eq. (1) is written as where IJUn is a transverse wave vector and A is the angle between \kcn andlr. According to Eq. (2), TE()n mode is represented by a superposition of plane waves which propagate at an angle a with the waveguide axis, where The electric field vectors are perpendicular to the waveguide axis. Radiation from a highly oversized waveguide can be approximately treated by means of geometrical optics. From the aperture of the waveguide, each plane wave above-mentioned is radiated in free space at the same angle a. If the aperture is perpendicular to the waveguide axis, the radiation is axi-symmetric. But when the
RkJQdWJsaXNoZXIy MTU5NjU0Mg==