Rapid global response of the electron temperature during pellet injection on TORE SUPRA

During pellet injection in the TORE SUPRA tokamak, two distinct phases of electron temperature response, a gradual decrease phase followed by a sudden drop phase, have been observed by means of a fast acquisition ECE Fabry-Perot interferometer system. The time delay of the temperature drop between the plasma edge and centre is less than 20 mu s, corresponding to a propagation velocity of the order of 25 km/s, much larger than both the pellet velocity and the ordinary diffusion velocity. A neutral atom diffusion model, together with a modified plasmoid ablatant description, is proposed to explain such phenomena