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Author: Adrian K Fontanilla
Requested Type: Pre-Selected Invited
Submitted: 2018-02-28 19:18:11

Co-authors: B.N. Breizman

Contact Info:
University of Texas at Austin
2515 Speedway C1600
Austin, TX   78712
United States

Abstract Text:
How pellet material is ablated and assimilated into plasma is relevant to the two problems of re-fueling and disruption mitigation via impurity injection. Contact of the pellet surface with the plasma causes material to be ablated from which a gas cloud is formed. The cloud shields the pellet from the surrounding plasma. In this case, a stationary solution of the fluid equations describing the cloud can be considered as was done in Ref. [1]-[3]. We expand upon the prior efforts by determining the stopping power for incident electrons self-consistently from the kinetic equation. The distribution function of the incident electrons is nearly isotropic due to the high Z of the pellet. These electrons diffuse spatially into the ablation cloud until they lose energy due to collisional friction. The periphery of the ablation cloud is transparent to the incident electrons due to the spherical nature of the cloud expansion. In this region of the cloud, a self-similar solution tells us that the temperature goes as the two-thirds power of the radial coordinate, while the velocity goes as the one-third power. Integration of the fluid equations is initiated in the supersonic region where the self-similar descriptions provide a reasonable boundary condition. The location of the sonic transition point and the size of the pellet is determined as a function of the incident flux. As the pellet traverses the hot plasma, it leaves behind a dense wake of colder particles that expand in a self-similar manner. The initial 3-d expansion changes to 1-d as the wake becomes magnetized.

[1] P.B. Parks and R.J. Turnbull, Phys. Fluids 21, 1735 (1978)
[2] B.V. Kuteev and L.D. Tsendin, Res. Report No. NIFS-717, National Inst. for Fusion Science, Nagoya (2001)
[3] V.Yu. Sergeev, O.A. Bakhareva, B.V. Kuteev, M. Tender, Plasma Phys. Reports 32, 5 (2006)