Thermal instability in current-carrying plasmas

Summary Form only given, as follows. Plasmas, especially when they are carrying electric currents, are prone to spatial nonuniformities in the form of filaments and striations that result from a variety of instabilities. Among them, thermal instability plays a leading role, especially when electrodes are present. A modal analysis of the thermal instability has shown that a constriction always starts near the electrodes. It is localized there, where the temperature dependences of the thermal and electrical conductivities are characteristic of plasma in MHD channels. In the case of practically full ionization and very large pressures that prevail in arc-driven railguns, the constriction expands axially over the entire length of the discharge. In this work, a single equilibrium temperature among the species of the medium is assumed. However, such an assumption becomes invalid as the pressure is reduced. For a low-pressure fully ionized plasma, it has been shown that ion temperature becomes much lower than that of electrons due to low collisionality. A modal analysis of the thermal instability of this situation has shown that the current constriction caused by the perturbations of thermal instability starts near the electrodes and gradually expands over the entire length of the discharge. The presence of nonequilibrium electron and ion temperatures introduces a stabilizing effect.<>