Enhancement of energy and particle confinement after pellet injection

In this work, the influence of pellet injection on the energy confinement time in different types of discharges has been investigated. During the ablation of a pellet, the electron density is increased. At the same time the electron temperature is decreased because the energy of the plasma is used to ionize and heat the ablated particles of the pellet. After the pellet injection the plasma is reheated. In ohmic plasmas with high density particles are transported into the core during this phase. In this way the density and the temperature in the core are increased leading to a pressure increase and an increase in the energy content of the plasma and to an increase in the energy confinement time. The inward transport of particles can be stopped by reappearing of sawtooth activity which was stopped by the pellet injection; the plasma relaxes to the initial state. In strongly heated plasmas with low confinement (L-mode) and ohmic discharges with low density, the increased transport causes a rapid loss of the additional density coming from the pellet. Because of this the energy increase is much smaller or vanishes. (orig.)