Radial electric field and ion parallel flow in the quasi-symmetric and Mirror configurations of HSX

In this paper, the radial electric field and the ion mean parallel flow are obtained in the helically symmetric experiment stellarator from toroidal flow measurements of C⁺⁶ ion at two locations on a flux surface, using the Pfirsch–Schlüter effect. Results from the standard quasi-helically symmetric magnetic configuration are compared with those from the Mirror configuration where the quasi-symmetry is deliberately degraded using auxiliary coils. For similar injected power, the quasi-symmetric configuration is observed to have significantly lower flows while the experimental observations from the Mirror geometry are in better agreement with neoclassical calculations. Finally, indications are that the radial electric field near the core of the quasi-symmetric configuration may be governed by non-neoclassical processes.