NIFS-717

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Author(s):

Boris V. Kuteev and Lev D. Tsendin

Title:

Analytical Model of Neutral Gas Shielding for Hydrogen Pellet Ablation

Date of publication:

Nov. 2001

Key words:

pellet, ablation, model, neutral gas shielding, gas dynamics, scaling

Abstract:

A kinetic gasdynamic scaling for hydrogen pellet ablation is obtained in terms of a neutral gas shielding model using both numerical and analytical approaches. The scaling on plasma and pellet parameters proposed in the monoenergy approximation by Milora and Foster dR_pe/dt~S_n^2/3R_p^-2/3q_eo^1/3m_i^-1/3 is confirmed. Here R_p is the pellet rsdius, S_n is the optical thickness of a cloud, q_eo is the electron energy flux density and m_i is the molecular mass. Only the numeral factor is approximately two times less than that for the monoenergy approach. Due to this effect, the pellet ablation rates, which were obtained by Kuteev on the basis of the Milora scaling, should be reduced by a factor of 1.7. Such a modification provides a reasonable agreement (even at high plasma parameters) between the two-dimensional kinetic model and the one-dimensional monoenergy approximation validated in contemporary tokamak experiments. As the cloud (in the kinetic approximation) is significantly thicker than that for the monoenergy case as well as the velocities of the gas flow are much slower, the relative effect of plasma and magnetic shielding on the ablation rate is strongly reduced.

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