Current driven weak double layers under linearly stable conditions

Abstract

Extensive one-dimensional Vlasov simulations have been performed in order to study the dynamics of double-layer generation in a stable current carrying plasma. An initial density perturbation, which shortly builds a potential well, leads to a weak double layer and to a recurrent formation of electron vortices for a large range of temperature ratios and electron drift velocities. The electron–vortex formation is inhibited for very small velocity drifts. While the electrostatic energy is generally almost constant, a weak growth develops for an electron drift velocity that is sufficiently high, but less than the critical drift velocity for marginal stability. The amplitude of individual double layers is rather weak, but the collision of two double layers drives a nonlinear instability related to the fusion of electron vortices, amplifying the double-layer potential to several times the electron thermal energy.