Two-dimensional simulation of pellet ablation with atomic processes

Abstract

A two-dimensional hydrodynamic simulation code CAP has been developed in order to investigate the dynamics of hydrogenic pellet ablation in magnetized plasmas throughout their temporal evolution. One of the properties of the code is that it treats the solid-to-gas phase change at the pellet surface without imposing artificial boundary conditions there, as done in previous ablation models. The simulation includes multispecies atomic processes, mainly molecular dissociation and thermal ionization in the ablation flow beyond the pellet, with a kinetic heat flux model. It was found that ionization causes the formation of a quasistationary shock front in the supersonic region of the ablation flow, followed by a ''second'' sonic surface farther out. Anisotropic heating, due to the directionality of the magnetic field, contributes to a nonuniform ablation ͑recoil͒ pressure distribution over the pellet surface. Since the shear stress can exceed the yield strength of the solid for a sufficiently high heat flux, the solid pellet can be fluidized and flattened into a ''pancake'' shape while the pellet is ablating and losing mass. The effect of pellet deformation can shorten the pellet lifetime almost 3ϫ from that assuming the pellet remains rigid and stationary during ablation.

Role of shielding in modelling cryogenic deuterium pellet ablation

“…A kinetic heat flux model taking into account the influence of magnetic field on the cloud heating and on the ablation process itself was developed [14]. The possibility of a shock wave formation due to ionization in connection to the strong pressure anisotropies in the pellet cloud and the melting of the pellet was studied as well [14,15].…”

Terascale Simulation Tools and Technologies

“…In an operator splitting approach, we solve the hyperbolic subsystem (5) - (7) using the hydrodynamic package of the FronTier code. The elliptic problem (8) is solved using either a mixed finite element discretization on a triangular (tetrahedral) mesh dynamically conforming to the moving interface, or the embedded boundary discretization MacAulay [35], and Ishizaki et al [29]. Our work goes beyond these studies and calculates properties of the ablation channel in magnetic fields.…”

Recent Fusion Research in the National Institute for Fusion Science

“…The magnetic reconnection, which is known as a multi scale phenomenon, has been investigated by using a multi-hierarchy simulation model [33,34]. The simulation works with regard to pellet injection [35], plasma-wall interaction including blob dynamics [36] and molecular dynamics [37] have been successfully developed. These works are expected to contribute the development of the LHD-NTR.…”