Measurements of neutral particles and simulations of plasma-neutral dynamics in the HIT-SI3 experiment
Sutherland, Derek Aiden
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Clean, safe, and reliable energy sources are needed to displace those harmful to people and the environment. Fusion energy is such an energy source, provided it is both technically and economically viable. The HIT-SI3 experiment at the University of Washington seeks to develop a pathway towards commercially viable, economical fusion energy based on compact, toroidal (CT) magnetic confinement of fusion plasmas. This experiment makes use of a novel inductive helicity injection scheme that both forms and sustains CT plasma configurations known as spheromaks for confinement of high temperature fusion plasmas. This work details measurements of neutral particles and simulations of plasma-neutral dynamics in the HIT-SI3 experiment that is of interest for optimizing sustained spheromak performance for fusion energy applications. In particular, a two-photon absorption laser induced fluorescence (TALIF) diagnostic system measured monatomic, ground state deuterium neutral densities and temperatures in HIT-SI3 spheromak plasmas. These data were compared to dynamic plasma-neutral simulations performed with the PSI-Tet code. The plasma-neutral fluid model implemented in PSI-Tet includes an magnetohydrodynamic (MHD) plasma fluid and a monatomic, deuterium neutral fluid with electron impact ionization, radiative recombination, and resonant charge exchange plasma-neutral reactions. Plasma-neutral PSI-Tet simulations of decaying spheromaks in the HIT-SI3 flux conserver geometry are used to compare to experimental TALIF neutral density and temperature measurements. Validation results are presented that exhibit varying degrees of agreement that are strongly dependent on the choice of boundary conditions and limiting the usage of stabilizing artificial diffusivity. The observed levels of agreement between experimental TALIF measurements and plasma-neutral simulations, though promising, motivate the collection of additional data concerning the neutral particle composition and parameters in HIT-SI3 spheromak plasmas and an expansion of the currently implemented plasma-neutral model to include a diatomic, molecular fluid to more accurately capture the physical system under consideration.