NEUTRAL GAS AND PLASMA SHIELDING SCALING LAW FOR PELLET ABLATION IN MAXWELLIAN PLASMAS

Pellet penetrations are generally well reproduced by the neutral gas s hielding (NGS) scaling law when neutral gas and plasma shielding (NGPS ) models are less successful, although their description of the ablati on physics is much more realistic. The solution of this apparent contr adiction is to be found in the structure of the NGPS models. Indeed, s ince they are generally not fully self-consistent, several choices are possible in the description of the elementary shielding processes. Th e problem thus reduces to finding a set of compatible assumptions defi ning an NGPS model that can fit the experimental measurements on a dat abase as large as possible. The model presented here reproduces the pe netrations of approximate to 120 pellets from 5 different machines: To re Supra, JET, FTU, T-10 and RTP. An NGPS scaling law has been constru cted for the ablation rate that exhibits dependences on n(e), T-e and r(p) close to those of the NGS model, in addition to weak dependences on the magnetic field and tokamak major radius. For reactor grade plas mas, the penetrations calculated by the NGPS model are approximate to 15% smaller than the NGS predictions.