Two-Fluid Hall Effect on Plasma Relaxation in a High-Temperature Plasma

We report on experimental observations that the two-fluid Hall dynamo plays an important role in plasma relaxation. Measurements of the Hall effect during relaxation are made in the plasma core and edge. The Hall dynamo is found to be small at the edge ( ! r /a " 0.85) but increases substantially towards the interior (r/a=0.82) as measured by probes. In the high-temperature plasma core (r/a=0.35), using a fast laser Faraday rotation diagnostic, the Hall electromotive force is found to be significant (~40 V/m ), suppressing (flattening) the equilibrium core current near the resonant surface. Quasilinear two-fluid dynamo theory based on tearing modes predicts that the Hall dynamo can exceed the MHD dynamo under certain conditions. A one dimensional temporal model is used to determine how the effect of the Hall and MHD dynamos is divided between local current density production and local electric field production. Theoretical expectations are qualitatively consistent with experimental observations, implying that effects beyond single-fluid MHD are important.