Abstract Details
Abstracts
Author: Adrian K Fontanilla
Requested Type: Poster
Submitted: 2019-02-21 11:31:31
Co-authors: B.N. Breizman
Contact Info:
University of Texas at Austin
2515 Speedway C1600
Austin, TX 78751
United States
Abstract Text:
High-Z pellet injection is currently under consideration as a disruption mitigation technique. Pellets have a deeper penetration depth than massive gas injection. In addition, impurity pellets can be doped with hydrogen to affect the plasma cooling rate. These two factors help to meet the time constraints on the thermal and current quench. Pellet ablation is governed by the power deposition from the hot plasma electrons. For high-Z, the velocity distribution of the hot electrons is nearly isotropic, and we use this feature to calculate the power deposition which is then used to find the ablation rate. In contrast to pre-existing models, we consider the effect of gyro-motion as well as elastic scattering of the hot electrons. When the gyro-frequency is much greater than the elastic collision frequency, the hot electrons will diffuse longitudinally along the field lines as they slow down. In the opposite limiting case of very high elastic collision frequency, the hot electrons diffuse radially with respect to the pellet center. In both limits, our solution of the kinetic equation determines the hot electron distribution as a function of line-integrated density of the ablated material. This gives a universal expression for the power deposition irrespective of the density profile. Our fluid simulations yield ablation rates that are much lower than those produced by the scaling law of Ref.[1].
[1] V.Yu. Sergeev, O.A. Bakhareva, B.V. Kuteev, M. Tender, Plasma Phys. Reports 32, 5 (2006)
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