0883-6272/86 $3.00 + .00 Copyright ® 1986 SUNSAT Energy Council ANALYSIS OF APERTURE ANTENNA ATTACHED TO CUTOFF CAVITY FOR ICRF PLASMA HEATING KUNIO SAWAYA and SABURO ADACHI Department of Electrical Engineering Faculty of Engineering Tohoku University Sendai 980, Japan Abstract — Basic characteristics of an aperture antenna attached to a cutoff cavity for ICRF plasma heating are investigated. The analysis is performed for antennas radiating into semiinfinite free space rather than a magnetoplasma. Good agreement between theory and experiment is observed, indicating the validity of the analysis. INTRODUCTION RF plasma heating in the Ion Cyclotron Range of Frequency (ICRF) has proven to be very efficient in plasma experiments (1). In these experiments, antennas to heat plasmas have been half-turn loop antennas located inside tokamaks. Such antennas, however, have some disadvantages in a fusion reactor, where high power will be applied and impurity ions are produced from metallic materials of antennas and surrounding Faraday shields (1). Under this circumstance, aperture antennas located on a tokamak wall and attached to cavity outside of vacuum vessel are proposed (2—4). Since available dimensions of a port area of tokamak is limited and the frequency used to heat plasma is the order of 100 MHz, the attached cavity would be cut off even if a large tokamak is used. The purpose of this report is to show the basic properties of such an aperture antenna attached to a cutoff cavity. THEORY The geometry of the aperture antenna attached to a rectangular cutoff cavity is illustrated in Fig. 1, where the width of the aperture h is less than X/5 even for large tokamaks. The surface current of the antenna conductor J(x,y) and the tangential electric field E,,(x,y) on the aperture are expressed respectively as follows:
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