Overview of neoclassical flows and electric field studies in HSX*

The reduced parallel viscous damping in the direction of symmetry for a quasi-helically symmetric stellarator allows for large helical plasma rotation. Previous experiments in HSX have demonstrated good agreement with neoclassical modeling in terms of direction, and to some extent the magnitude, of plasma flows and neoclassical currents. Experiments and modeling are underway to further improve our understanding of flows and radial electric field in HSX. The effect of neutrals on the flow damping is being studied using multiple puffing locations, in conjunction with the neutral simulation code DEGAS. The neoclassical code PENTA has been modified to include collisions with background neutrals. New viewing port locations have been identified for Charge Exchange Spectroscopy to improve measurements of Pfirsch-Schlüter flows. Feasibility of using an alkali neutral beam for measuring time evolution of flows is being studied. To validate GNET code simulations on the ECH driven parallel flows, measurements with X-mode ECH is planned. A biased electrode experiment is being carried out to understand the effect of parallel flow on the ion resonant electric field. Time dependent neoclassical models are being extended for low collisionality ions that are expected in the HSX upgrade.