Estimation of the electrical resistivity in field-reversed configuration plasmas from detailed interferometric measurements

Electrical resistivity at the magnetic axis η(R) and at the separatrix η(rs) of a field-reversed configuration (FRC) plasma produced by theta pinch machines are estimated from detailed interferometric measurements, assuming that the temperature is uniform within the separatrix. The ratio f0[=η(R)/η(rs)] increases with the beta value at the separatrix βs, which is consistent with the fact that f0 decreases when xs (separatrix radius normalized by the inner radius of a theta pinch coil) increases [Phys. Fluids 28, 888 (1985)]. This tendency is a natural consequence of the transport properties of the FRC plasma when the particle confinement time is nearly equal to the decay time of the trapped reversed magnetic flux, as is normally the case. Theoretical expectations of the anomaly of η(rs) over the classical resistivity η0 increases and decreases slightly with βs for the case of the lower hybrid drift and the low-frequency drift instability, respectively. On the other hand, the observed η(rs)/η0 decreases substantially with βs. [The value of η(rs)/η0 changes from about 15 to 5 as βs changes from 0.45 to 0.6.]