Electrothermal instabilities in MHD boundary layers

Abstract

Electrothermal instabilities occurring in the boundary layers of MHD generator channels can cause the breakdown of the electrostatic sheath and lead to the transition from the diffuse to an arc mode current transport. This instability may occur at the electrostatic sheath edge and the arc can punch through the sheath from the plasma side. A stability analysis, carried out for the occurrence of the instability, however, shows that the values of the critical parameter for the onset of instability at the sheath edge were much less than the critical values for breakdown from the electrode plasma interface. Since the perturbations occurring at the sheath edge were found to get damped at higher applied potentials, it is predicted that the instability occurring at the sheath edge at low potential differences cannot lead to the arc transition, but may lead to fluctuations in the values of observable parameters.