Investigation of HHFW and NBI Combined Heating in NSTX
Authors: B.P. LeBlanc, R.E. Bell, S. Bernabei, T.M. Biewer, J.C. Hosea, and J.R. Wilson
Date of PPPL Report: April 2005
Presented at: the 16th Topical Conference on Radio Frequency Power in Plasmas, Park City, Utah, April 11-13, 2005
A series of experiments was conducted to investigate the combined utilization of high-harmonics fast-wave (HHFW) and neutral-beam injection (NBI) auxiliary heating in National Spherical Torus Experiment (NSTX) plasmas. A modest increase of the total stored energy coincident with a near doubling of the neutron production rate is observed when NBI heating is added to HHFW in L-mode plasmas. An increase in the core electron temperature is also observed. On the other hand, essentially no stored energy augmentation nor neutron production rate enhancement is observed when applying HHFW during the "H" phase of NBI-driven H-mode plasmas. Spectroscopic measurements of the edge carbon line radiation indicate an unpredicted ion temperature increase, suggesting that edge effects are reducing the amount of HHFW power reaching the plasma core.