Switched-on evolution due to a temporal electron charge drifting subthermally through a warm collisional plasma

Abstract

An electron charge is suddenly switched on while drifting through a warm collisional plasma. It acts thereafter with an arbitrary time-dependence. The evolution of the plasma, initially at rest, is considered in two and three dimensions. A general solution is first established for drift-modified slow plasma modes and then employed in subthermal drift analysis. Its abrupt switch-on causes the electron charge to release, during subthermal drift, a fully symmetric thermal front Г which subsequently expands ahead of it into an undisturbed receding expanse. A transversely symmetric response develops inside Г. On switch-off, the drifting charge releases another thermal front Г0which also precedes it but trails non-concentrically behind Г. Plasma response continues after switch-off. Response properties between Г and Г0differ strikingly from those inside Г0. Applications are next considered, first in three dimensions, for a subthermal pulsating electron with a generally complex frequencyω. The prepermanent state response inside Г comprises an axisymmetric dominant componentø∞plus a spherically symmetric transient componentøtr.ø∞acquires the frequencyω.øtrhas amplitudes dependent on and wave crests independent of both frequencyωand drift; it suffers a fast (slow)ω–independent temporal attenuation in a collisional (collisionless) plasma. The geometrical drift wave structure ofø∞is closely examined for realωand a collisionless plasma. Every energy surface associated withø∞nucleates at the electron; from there, it evolves slower than a phase surface, which eventually ‘disappears’ past Г. The leading energy surface, which nucleated at switch-on, develops permanently inside Г; it serves as an energy front that seals off the energy sustainingø∞since switch-on. Finally, the two-dimensional evolving drift field of an activated antenna line is computed.