IMPROVED HHFW HEATING AND CURRENT DRIVE AT L ONG WAVELENGTHS ON NSTX

INTRODUCTION The High Harmonic Fast Wave (HHFW) system on NSTX is used for plasma (electron) heating and current drive. It consists of twelve current straps powered by six 1-MW transmitters operating at 30 MHz, with straps 1&7, 2&8, ... connected by 2! of transmission line and oriented to have opposite currents [1]. Thus, straps 1-6 and 7-12 form two phased arrays which are permanently 180o out of phase with each other; the phase shift between transmitters can be rapidly and arbitrarily varied during a pulse. For relative phase shifts of ±30o, ±90o, and ±150o, the launcher operates as a highly directional, 12-element array with spectral peaks at k|| ~ ±3, ±8, ±14 m -1 respectively, where k|| is equivalent to n"/(R+a).