Sawtooth Activity And Heat Pulse-Propagation In Ohmically Heated And Center And Edge Beam Heated Tftr Plasmas

Propagation of the heat pulse arising from a sawtooth crash was studied in ohmically heated plasmas as a function of density, and in neutral beam heated plasmas with centrally peaked and hollow power deposition profiles at two densities- The sawtooth period became longer with centre heating than with edge heating and with co-injection than with counter-injection. The lengthening of the sawtooth period was consistent with the reduction of the core loop voltage due to heating and non-inductive current drive. In Ohmic plasmas, the electron thermal diffusivity chi(e)HPP determined from a time-to-peak analysis decreased inversely.proportionally to density for n(e)BAR less-than-or-similar-to 2 x 10(19) m-3 where the energy confinement time tau(E) increases linearly with density, but chi(e)HPP became independent of density for n(e)BAR greater-than-or-similar-to 2 x 10(19) m-3 where tau(E) becomes independent of density. The values of chi(e)HPP for both beam heating profiles were nearly the same as for Ohmic plasmas, in contrast to the heat conduction coefficient chi(e)PB determined from power balance analysis which was enhanced for centre heated plasmas. Chi(e)HPP was always larger than chi(e)PB, typically by a factor of five.