Modelling of pellet ablation in additionally heated plasmas

Abstract

A neutral gas and plasma shielding model is presented that describes the interaction of a pellet with the high energy ions and electrons generated during heating or current drive experiments. The main improvements are the self-consistent calculations of the electrostatic sheath at the cloud–plasma interface and of the extra ablation due to the fast tail of the electron and ion distributions, including heating in the volume of the pellet. With regard to the comparison between the code predictions and the experimental results, realistic three-dimensional (space, energy, pitch angle) distributions have been used for both the ions and electrons. For ohmic discharges, the code has been tested on more than 40 well-documented pellets selected in the International Pellet Ablation DataBASE. For additionally heated plasmas (ion cyclotron resonance heating—minority regime—and lower hybrid current drive, 2–4 MW of injected power), Tore Supra data have been used. In these different cases, the calculations are in good agreement with the experimental penetrations and ablation profiles. A parametric study is also presented, which enlightens the control parameter that governs the pellet penetration. In what concerns the capability of pellet injection to fuel reactor grade plasmas, it is shown that no strong extra ablation due to the α-particles is expected.