Ablation of High-Z Pellets in Hot Plasma

How pellet material is ablated and assimilated into plasma is relevant to disruption mitigation via impurity injection. The pellet ablation rate is determined by the power deposited by the incident fast electrons. The present work describes fast electrons within the pellet material self-consistently from the kinetic equation that includes electron scattering. Prior efforts to calculate the power deposition kinetically have been reported in Ref. [1] (for C pellets) and Ref.[2]-[3] (for H). Our work focuses on high-Z pellet material in which case Z is an ordering parameter. To lowest order in Z, the distribution function of the incident electrons is nearly isotropic, and the electrons diffuse spatially in the ablation cloud until they lose energy due to collisional friction. We consider two limits: one in which the cloud geometry is 1-d and another in which the geometry is 3-d but the cloud is nearly transparent. A perturbative procedure is then presented that relaxes the transparent constraint.

[1] B.V. Kuteev, et al, Sov. J. Plasma Phys. 10, 6 (1984)

[2] A.K. MacAulay, NF 34, 43 (1994)

[3] R. Ishizaki, et al, PoP 11, 8 (2004)