Electron Bernstein Wave Research on the National Spherical Torus Experiment

Off‐axis electron Bernstein wave current drive (EBWCD) may be critical for sustaining non‐inductive high β NSTX plasmas. Modeling results predict that the ∼ 100 kA of off‐axis current needed to stabilize a solenoid‐free high β NSTX plasma could be generated by by 3 MW of 28 GHz EBW power. Synergy with the bootstrap current may enhance CD efficiency by ∼ 10%. EBW radiometry measurements on NSTX support coupling to EBWs by launching elliptically polarized electromagnetic waves oblique to the confining magnetic field. Plans are being developed to implement a 1 MW, 28 GHz proof‐of‐principle EBWCD system to test the EBW coupling, heating and CD physics at high rf power densities on NSTX.