Effect of the Parallel Flow on the Ion Resonance in HSX

Experimental data to date have shown no evidence of the ion resonance in poloidal viscosity with respect to the radial electric field in HSX.  To explain this, we use a coupled set of momentum balance equations and Shaing's [1] model of nonlinear viscosity to examine the influence of the parallel flow on the ion resonance in HSX. Due to quasihelical symmetry (QHS), the damping of the parallel flow from viscosity is very low. The parallel flow can become large compared to the ion thermal velocity. Including the neutral damping, the calculations show that the resonant electric field (E_res) can be a factor of 2.5 higher compared to the solution assuming that Vpar = 0.  By increasing the neutral damping in these calculations by a factor of 5, E_res decreased by a factor of 2. Calculating the E_res in a Mirror configuration, where the parallel viscous damping is increased, resulted in a factor of 2 decrease from the QHS solution with standard neutral profiles.  A charge exchange recombination spectroscopy (CHERS) system has been used in HSX to determine E_r and the mean ion parallel flow from measurements of the inboard/outboard asymmetry of the C+6 parallel flow [2]. An experimental program using the CHERS system and physical probes is detailed that will enable comparisons to the model.