Electric fields and currents in front of a biased electrode (flush mounted probe) and the I - V characteristics of the electrode for various mechanisms of transverse conductivity

The current-voltage characteristics of a biased electrode (flush mounted probe) and the potential and current distributions are analysed for three basic mechanisms of conductivity across the magnetic field (viscosity, inertia, ion-neutral collisions) in a fully ionized plasma for probe sizes larger than the ion gyro-radius. The analysis was performed both analytically (for small probe potentials) and numerically. It is shown that the slope of the transitional part of the I-V characteristics is approximately the same for all types of conductivity, provided the probe current is normalized to the ion sonic flow to the return current collecting area, while the probe voltage is measured in electron temperature units. The characteristic scale of the plasma perturbed region along the magnetic field is of the order of λmfp(mi/me)1/2 for all three mechanisms considered. The transverse scale is essentially determined by the type of transverse conductivity.