Electron Bernstein Wave Research on the National Spherical Torus Experiment
Authors: G. Taylor, A. Bers, T.S. Bigelow, M.D. Carter, J.B. Caughman, J. Decker, S. Diem, P.C. Efthimion, N.M. Ershov, E. Fredd, R.W. Harvey, J. Hosea, F. Jaeger, J. Preinhaelter, A.K. Ram, D.A. Rasmussen, A.P. Smirnov, J.B. Wilgen, 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
Off-axis electron Bernstein wave current drive (EBWCD) may be critical for sustaining noninductive high-β National Spherical Torus Experiment (NSTX) plasmas. Numerical modeling results predict that the ~100 kA of off-axis current needed to stabilize a solenoid-free high-β NSTX plasma could be generated via Ohkawa current drive with 3 MW of 28 GHz EBW power. In addition, synergy between EBWCD and bootstrap current may result in a 10% enhancement in current-drive efficiency with 4 MW of EBW power. Recent dual-polarization EBW radiometry measurements on NSTX confirm that efficient coupling to EBWs can be readily accomplished by launching elliptically polarized electromagnetic waves oblique to the confining magnetic field, in agreement with numerical modeling. Plans are being developed for implementing a 1 MW, 28 GHz proof-of-principle EBWCD system on NSTX to test the EBW coupling, heating and current-drive physics at high radio-frequency power densities.