Exploration of High Harmonic Fast Wave Heating on the National Spherical Torus Experiment
Authors: J.R. Wilson, R.E. Bell, S. Bernabei, M. Bitter, P. Bonoli, D. Gates, J. Hosea, B. LeBlanc, T.K. Mau, S. Medley, J. Menard, D. Mueller, M. Ono, C.K. Phillips, R.I. Pinsker, R. Raman, A. Rosenberg, P. Ryan, S. Sabbagh, D. Stutman, D. Swain, Y. Takase, J. Wilgen, and the NSTX Team
Date of PPPL Report: February 2003
Presented as: an invited paper at the 44th Annual Meeting of APS/DPP, in Orlando, Fla., November 11-15, 2002. Published in Physics of Plasmas 10 No. 5 (May 2003) 1733-1738.
High Harmonic Fast Wave (HHFW) heating has been proposed as a particularly attractive means for plasma heating and current drive in the high-beta plasmas that are achievable in spherical torus (ST) devices. The National Spherical Torus Experiment (NSTX) [Ono, M., Kaye, S.M., Neumeyer, S., et al., Proceedings, 18th IEEE/NPSS Symposium on Fusion Engineering, Albuquerque, 1999, (IEEE, Piscataway, NJ (1999), p. 53.] is such a device. An radio-frequency (rf) heating system has been installed on NSTX to explore the physics of HHFW heating, current drive via rf waves and for use as a tool to demonstrate the attractiveness of the ST concept as a fusion device.
To date, experiments have demonstrated many of the theoretical predictions for HHFW. In particular, strong wave absorption on electrons over a wide range of plasma parameters and wave parallel phase velocities, wave acceleration of energetic ions, and indications of current drive for directed wave spectra have been observed. In addition HHFW heating has been used to explore the energy transport properties of NSTX plasmas, to create H-mode (high-confinement mode) discharges with a large fraction of bootstrap current and to control the plasma current profile during the early stages of the discharge.