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 Г₀ which also precedes it but trails non-concentrically behind Г. Plasma response continues after switch-off. Response properties between Г and Г₀ differ strikingly from those inside Г₀. Applications are next considered, first in three dimensions, for a subthermal pulsating electron with a generally complex frequency ω. The prepermanent state response inside Г comprises an axisymmetric dominant component ø_∞ plus a spherically symmetric transient component ø_tr. ø_∞ acquires the frequency ω. ø_tr has amplitudes dependent on and wave crests independent of both frequency ω and drift; it suffers a fast (slow) ω–independent temporal attenuation in a collisional (collisionless) plasma. The geometrical drift wave structure of ø_∞ is closely examined for real ω and a collisionless plasma. Every energy surface associated with ø_∞ 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 sustaining ø_∞ since switch-on. Finally, the two-dimensional evolving drift field of an activated antenna line is computed.