Sawtooth activity and heat pulse propagation in Ohmically heated and centre 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 noninductive current drive. In Ohmic plasmas, the electron thermal diffusivity χ_e^HPP determined from a time-to-peak analysis decreased inversely proportionally to density for n _e ≤ 2 × 10¹⁹ m^-3.