Measurements of Linear and Nonlinear Hall Reconnection

Previous measurements in MST have established that two-fluid Hall effects produce a dynamo during sawtooth relaxation events, and therefore two-fluid dynamics are important when evaluating the macroscopic effects of reconnection. This was established by measuring the nonlinear Hall term $(J_1 \times B_1)$ in the axisymmetric (flux-surface averaged) Ohm's Law. Here, we report measurements of terms in the non-axisymmetric Ohm's Law, including the \em linear \em Hall term, $(J_1 \times B_0 + J_0 \times B_1)$, and other spatially varying quantities. These measurements are a more direct indicator of the role of two-fluid effects on reconnection. Measurements are performed by probes in the vicinity of the reversal surface to measure reconnection associated with modes of poloidal mode number m=0. Results show that the linear Hall term is large compared to $\eta \widetilde{J}_{||}$, indicating the possibility of fast collisionless reconnection. Results are compared to a theoretical interpretation based on two-fluid MHD.