Fluid dynamics simulations of gas retention systems for shattered pellet injectors

The HUN-REN Centre for Energy Research’s Fusion Plasma Physics Laboratory team is developing a shattered-pellet injector (SPI) system for plasma disruption mitigation of the ITER experiment. A high-pressure valve accelerates the cryogenic protium and neon pellets to speeds of a few hundred metres per second before they hit the shattering head. For effective disruption mitigation, it is necessary that the propellant gas does not reach the plasma before the solid particles. The propellant retention system, or gas suppressor, requires numerical analysis to determine its efficiency. This paper discusses the modelling constraints and difficulties of Computational Fluid Dynamics (CFD) simulations of such systems. It addresses the difficulty of continuum modelling, shock capturing, and the selection of numerical methods using commercially available ANSYS Fluent software. The simulations take advantage of overset mesh approaches, as well as adaptive meshing, to accurately model the expansion of high-pressure gas into vacuum and high-vacuum environments. The study presents different modelling approaches and analyses the effect of different simulation parameters. It also offers a brief comparison of measurement data with the simulation results for different configurations of the SPI suppressor system. The results serve as a basis for the development of an effective gas retention system to be used at the ITER experiment and potentially in other more exotic uses.