Speaker
Roman Samulyak
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1073.pdf
Simulation studies of neon pellet ablation clouds for plasma disruption
mitigation in tokamaks.
N. Bosviel1 , R. Samulyak1 , P. B. Parks3
1 Stony Brook University, Stony Brook, USA
2 General Atomics, San Diego, USA
A leading candidate for the ITER plasma disruption mitigation system is the Shattered Pellet
Injection (SPI) [1] that performs fragmentation of a large, frozen, neon-deuterium pellet before
its injection into a tokamak, and forms a stream of small fragments into plasma, causing a ther-
mal quench. In this work, we report numerical studies of properties of ablation clouds formed
by the injection of a single neon pellet into a tokamak. Simulations of a large number of pellet
fragments are in progress.
Simulations use the numerical pellet ablation model [2] based on the FronTier code. The
main features of the model include an explicit tracking of the solid pellet - ablated gas inter-
face, kinetic models for the energy deposition of hot electrons into the ablation cloud, a pellet
surface ablation model, atomic processes in the cloud, radiation losses, an improved electrical
conductivity model, and MHD in the electrostatic approximation.
Verification studies have been performed by comparing spherically-symmetric simulations
with a semi-analytic model that improves the Neutral Gas Shielding model [3]. Good agreement
of pellet ablation rates and properties of the ablation flow at the sonic radius have been achieved.
Simulations are also in agreement with theory on the scaling laws for the pellet ablation rate G,
5/3 4/3 1/3
namely G ∼ Te r p ne , where r p is the pellet radius, and Te and ne are the temperature and
density of the background tokamak plasma.
In the presence of MHD forces and atomic processes, the dense, cold ablated material gradu-
ally ionizes and streams along magnetic lines, forming a narrow ablation channel. Simulations
study the dependence of ablation channel properties and the pellet ablation rate on the magnetic
field strength, and parameters of the background plasma, including the pedestal.
References
[1] L.R. Baylor, et al, Disruption mitigation system developments and design for ITER, Fusion Sci. Technol. 68,
211 (2015)
[2] R. Samulyak, T. Lu, P. Parks, A magnetohydrodynamic simulation of pellet ablation in the electrostatic
approximation, Nucl. Fusion 47, 103 (2007)
[3] P. B. Parks, R. J. Turnbull, Effect of transonic flow in the ablation cloud on the lifetime of a solid hydrogen
pellet in a plasma, Phys. Fluids 21, 1735 (1978)
