High harmonic fast wave heating and current drive on NSTX-system and experimental plan

For the National Spherical Torus Experiment (NSTX) device, High Harmonic Fast Wave (HHFW) heating has been selected for its strong single pass absorption on electrons as the initial heating and current drive scenario. A frequency of 30 MHz has been selected (f∼16 fcd). The waves will be launched into the plasma from a twelve element phased antenna array. Six transmitters will feed the elements in pairs of six independently phasable subsections. Modeling predicts strong single pass damping (>40%) for temperatures as low as 250 eV. As the ion temperature is increased ion damping may compete with the electron absorption for ion temperatures >1.5 keV. Experiments will be aimed at demonstrating HHFW heating of a small aspect ratio device leading towards the goal of fully non-inductive operation. In the first year of operation the HHFW system will be brought into operation and plasma heating under a variety of plasma conditions will be explored. In the second year, when current drive diagnostics are expected to...