AN ECH BEAM MONITOR FOR THE TEXAS EXPERIMENTAL TOKAMAK

A compact poloidal array of ten receiving antennae has been installed on the high-field wall (x = +30 cm) of the Texas Experimental Tokamak (TEXT) opposite the electron cyclotron heating (ECH) microwave launch port (x = -45 cm, 60 GHz, 200 kW). Both these antennae and the launching structure are oriented to couple to the ordinary mode in plasma. The array serves as a diagnostic of the unabsorbed, first-pass ECH microwave power, which includes both power refracted by the equilibrium plasma density gradients and power scattered by density fluctuations. Each antenna has a DELTAtheta(y) = 13-degrees poloidal and DELTAtheta(z) = 32-degrees toroidal half-power beam width, corresponding to 12-dB gain. For refraction studies, interchannel and intrachannel poloidal resolutions are DELTAy = 3.5 and 2.5 cm, respectively, at the array aperture surface. For scattering studies, the wave number selectivity extends from k perpendicular-to = 0+/-2.5 cm-1 to k perpendicular-to = 7+/-2.5 cm-1.