Pellet Ablation in Large Helical Device

"In the program of physical studies on the Large Helical Device (LHD) injection of several hydrogen and deuterium pellets is foreseen. Injection of impurity pellets also may be useful for the plasma diagnostics. The pellet penetration into the LHD plasma is analyzed. In part 1, the present status of the ablation theory and experiment is discussed and an ablation model is formulated It takes into account energy distribution of the particles (both electrons and ions) participating in the ablation process, electrostatic effects of the cloud charging and changes of the pellet form during ablation. Plasma shielding effects are not significant in the ablation. The ablation model is compared with the experiments on T-10, JET, TFTR, Heliotron-E and Tore Supra in part 2. Finally, in part 3, several regimes of the pellet infection into the LHD plasma are simulated including multiple-pellet sequence injection. Optimization of the injection regime is discussed.