Evolution of plasma flow and radial electric field in HSX

The fluid equation approach is used to model the evolution of the plasma flow and ambipolar radial electric field in HSX subject to a steady-state radial current, such as that induced by a biased electrode. Previous work [1] on this problem assumed that the drag due to the parallel viscosity increases linearly with the velocity. Here we extend the approach to include regimes where the viscosity is nonlinear using the approach of Sugama and Nishimura [2]. Included in the model is momentum damping due to neutrals, which is significant for the low density, ECRH heated plasmas of HSX. We also examine the role of electron viscosity which was previously neglected in the momentum balance equation when summed over species. Results are presented for the evolution and steady-state plasma flow and radial electric field and compared to the previous formulation which assumed that the viscosity was linear.

[1] M. Coronado and J.N. Talmadge, Phys. Fluids B 5 1200 (1993).

[2] H. Sugama and S. Nishimura, Phys. Plasmas 9 4637 (2002).