Non-Maxwellian electron velocity distributions observed with Thomson scattering in the TORTUR tokamak

The Thomson scattering spectrum represents the projection of the three-dimensional electron velocity distribution on the scattering vector. From this the local electron temperature and density can be derived. To determine the three-dimensional electron velocity distribution it is necessary to have several viewing directions, assuming axial symmetry in velocity space perpendicular to the magnetic field. Thomson scattering experiments in the TORTUR tokamak demonstrated the first experimental determination of f(v⊥, v||) from radially and tangentially observed spectra. The latter made it possible to determine the toroidal current density. The scattering spectra, averaged over 30 laser pulses observed in both the radial and the tangential direction, show clearly two symmetrical dips near the top of the Gaussian spectrum