Experimental Verification of the Two-Fluid Equilibrium Equation in a Torus Plasma Considered to be in a Two-Fluid Equilibrium State

Since the density in the peripheral region of a torus plasma is relatively low, the ion skin depth in that region is extended. In this situation, the equilibrium of the torus plasma is expected to follow a two-fluid equilibrium rather than magnetohydrodynamics (MHD). The difference between MHD and the two-fluid model can be understood by looking at the generalized Ohm's law, which represents the electron fluid equilibrium. In addition to terms commonly seen in ideal and resistive MHD, the degenerate terms, such as the Hall term and electron pressure gradient term, explicitly appear. To test the hypothesis that the low-density region around the torus plasma obeys a two-fluid equation set, we are conducting experiments using an all-in-one probe that can simultaneously measure each term of the generalized Ohm's law in three dimensions [1]. The feature of the all-in-one probe is that it can, in principle, measure all terms of the generalized Ohm's law in one shot in a region where the ion skin depth is a few centimeters. In this presentation, after explaining the academic background of this research, we describe the all-in-one probe and present experimental results aimed at investigating the validity of the generalized Ohm's law under plasma equilibrium.