title: Predicting high harmonic ion cyclotron heating efficiency in Tokamak plasmas.
abstract: Observations of improved radio frequency (rf) heating efficiency in ITER relevant high-confinement (H-)mode plasmas on the National Spherical Tokamak Experiment are investigated by whole-device linear simulation. The steady-state rf electric field is calculated for various antenna spectra and the results examined for characteristics that correlate with observations of improved or reduced rf heating efficiency. We find that launching toroidal wave numbers that give fast-wave propagation in the scrape-off plasma excites large amplitude (∼kV m(-1)) coaxial standing modes between the confined plasma density pedestal and conducting vessel wall. Qualitative comparison with measurements of the stored plasma energy suggests that these modes are a probable cause of degraded heating efficiency.
authors: Oak Ridge National Laboratory, Post Office Box 2008, Oak Ridge, Tennessee 37831-6169, USA. greendl1@ornl.gov
authors: D L
authors: DL
authors: Green
authors: L A
authors: LA
authors: Berry
authors: G
authors: G
authors: Chen
authors: P M
authors: PM
authors: Ryan
authors: J M
authors: JM
authors: Canik
authors: E F
authors: EF
authors: Jaeger