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 \em non\em -axisymmetric Ohm's Law, including the reconnection electric field and terms that may balance this field. In particular, the linear Hall term, $(J_1 \times B_0 + J_0 \times B_1)$, and nonlinear three wave interaction Hall terms are considered. These fluctuation 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 of these measurements lead to an estimation of the extent to which classical resistivity can balance Ohm's Law at the reconnection x-point.