Measurement of the Time Constants of Fast Electron Distributions in the Tore Supra Tokamak

The fundamental phenomena governing the dynamics of anisotropic electron distributions in a tokamak plasma are investigated. A fast electron tail driven by modulated pulses of lower-hybrid waves is analyzed by a combination of three diagnostics, i.e., hard x rays, electron-cyclotron emission, and transmission. Three different time constants, characterizing radial diffusion, collisional friction, and pitch-angle scattering, respectively, are identified. Two distinct relaxation regimes are observed, related to the degree of anisotropy of the electron distribution.