Reconstruction of superthermal electron velocity distribution function from electron cyclotron spectra at down-shifted frequencies in tokamak T-10

Abstract

A model is developed to quantitatively interpret the electron cyclotron (EC) spectra in tokamak T-10 at frequencies lower than the first EC harmonic at the plasma edge. The model is based on the almost free propagation and isotropy of EC radiation in between the vacuum chamber wall and the cut-off zone in plasma. The inverse problem for the reconstruction of the velocity distribution function of superthermal electrons (in parallel and perpendicular momenta, and magnetic flux surfaces at the plasma edge) is formulated and solved. It is shown that in the Ohmic discharges in the tokamak T-10 the superthermal electrons are the trapped particles at the low magnetic field side of toroid. Their mean kinetic energy lies in the range ∼ 150-200 keV, and the density fraction is about ∼ 10-4 relative to the main plasma. © Owned by the authors, published by EDP Sciences, 2012.