Observations of Anisotropic Ion Temperature during RF Heating in the NSTX Edge
Authors: T.M. Biewer, R.E. Bell, D.S. Darrow, C.K. Phillips, and J.R. Wilson
Date of PPPL Report: May 2003
Presented at: the 15th Topical Conference on Radio Frequency Power in Plasmas, Grand Teton National Park, Moran, Wyoming, May 19 through 21, 2003
A new spectroscopic diagnostic on the National Spherical Torus Experiment (NSTX) measures the velocity distribution of ions in the plasma edge with both poloidal and toroidal views. An anisotropic ion temperature is measured during the presence of high power HHFW RF heating in He plasmas, with the poloidal Ti roughly twice the toroidal Ti. Moreover, the measured spectral distribution suggests that two populations have temperatures of 500 eV and 50 eV with rotation velocities of -50 km/s and -10 km/s, respectively. This bi-modal distribution is observed in both the toroidal and poloidal views (in both He II and C III ions), and is well correlated with the period of RF power application to the plasma. The temperature of the edge ions is observed to increase with the applied RF power, which was scanned between 0 and 4.3MW. The ion heating mechanism from HHFW RF power has not yet been identified.