Measurement of atomic hydrogen densities and velocities by laser-induced fluorescence at Lsub(α)

The possibilities are discussed to measure densities and velocities of atomic hydrogen near the wall of a tokamak by laser-induced Lsub(α)-fluorescence, and preparatory experiments are described. Up to 80 Watt Lsub(α)-radiation in 2 ns (1011 photons) have been produced by frequency tripling of a 2 MWatt dye laser in a phase matched Kr-A mixture. First fluorescence experiments have been performed on the ASDEX cleaning discharges (2 A glow discharge and 600 A, 50 Hz discharge) having H-densities around 1010 atoms/cm3. The laser enters the tokamak radially, and the fluorescence is also observed radially at an angle of 50 with respect to the laser beam and at a distance of 2.5 m by a cassegrain mirror system. Profiles of Lsub(α) have been measured by scanning the absorption line with the laser. From its half-width, room temperature was found for the glow-discharge and about 6000 K for the 50 Hz discharge. (orig.)