Electron Bernstein Wave Research on NSTX and PEGASUS

Abstract

Spherical tokamaks (STs) routinely operate in the overdense regime (ωpe≫ωce), prohibiting the use of standard ECCD and ECRH. However, the electrostatic electron Bernstein wave (EBW) can propagate in the overdense regime and is strongly absorbed and emitted at the electron cyclotron resonances. As such, EBWs offer the potential for local electron temperature measurements and local electron heating and current drive. A critical challenge for these applications is to establish efficient coupling between the EBWs and electromagnetic waves outside the cutoff layer. Two STs in the U.S., the National Spherical Tokamak Experiment (NSTX, at Princeton Plasma Physics Laboratory) and PEGASUS Toroidal Experiment (University of Wisconsin‐Madison) are focused on studying EBWs for heating and current drive. On NSTX, two remotely steered, quad‐ridged antennas have been installed to measure 8‐40 GHz (fundamental, second and third harmonics) thermal EBW emission (EBE) via the oblique B‐X‐O mode conversion process. This diag...