Measurement of the parallel distribution function during lower-hybrid current drive in Tore Supra

A transmission diagnostic system working in the frequency range 77–109 GHz has been implemented in the Tore Supra tokamak. It makes use of an ordinary mode launched along a vertical diameter, i.e., propagating along a nearly constant magnetic field. The purpose of the diagnostic is to measure electron cyclotron absorption (ECA) below the electron cyclotron frequency fc in the presence of the fast electron tails created during lower‐hybrid current drive. Transmission spectra measured by this method are compared with spectra obtained by Fokker‐Planck simulations and the relaxation properties of the tail are discussed.