Electron Energy Confinement for HHFW Heating and Current Drive Phasing on NSTX
Authors: J.C. Hosea, S. Bernabei, T. Biewer, B. LeBlanc, C.K. Phillips, J.R. Wilson, D. Stutman, P. Ryan, and D.W. Swain
Date of PPPL Report: May 2005
Presented at: the 16th Topical Conference on Radio Frequency Power in Plasmas, Park City, Utah, April 11-13, 2005. Conference proceedings will be published by the American Institute of Physics.
Thomson scattering laser pulses are synchronized relative to modulated HHFW power to permit evaluation of the electron energy confinement time during and following HHFW pulses for both heating and current drive antenna phasing. Profile changes resulting from instabilities require that the total electron stored energy, evaluated by integrating the midplane electron pressure Pe(R) over the magnetic surfaces prescribed by EFIT analysis, be used to derive the electron energy confinement time. Core confinement is reduced during a sawtooth instability but, although the electron energy is distributed outward by the sawtooth, the bulk electron energy confinement time is essentially unaffected. The radial deposition of energy into the electrons is noticeably more peaked for current drive phasing (longer wavelength excitation) relative to that for heating phasing (shorter wavelength excitation) as is expected theoretically. However, the power delivered to the core plasma is reduced considerably for the current drive phasing, indicating that surface/peripheral damping processes play a more important role for this case.