The dynamic sheath: Objects coupling to plasmas on electron-plasma-frequency time scales

Publisher Website
Google Scholar
Abstract
The time‐dependent interaction between solid objects and the unmagnetized plasmas in which they are immersed is investigated. To this end over 1900 high‐resolution, one‐dimensional particle‐in‐cell simulations of the plasmas surrounding cylindrical and planar objects are statistically analyzed. Numerical shot noise produces an electron‐plasma‐frequency ringing in the simulations, the amplitude of which is related to the plasma temperature and to the numerical system temperature. Whenever the potential of an object is rapidly biased, the surrounding plasma rings with a large amplitude at the electron‐plasma frequency. During this ringing, a depletion layer forms around the object on ion‐acoustic time scales. Positively charged objects discharge via plasma currents in about τpe /4 and negatively charged objects discharge in about τpi . Owing to charge separations in the plasmas, for the first few ion‐plasma periods after a perturbation, the potential of an object is not directly related to the charge on it. The electron‐plasma‐frequency ringing drives large‐amplitude Langmuir waves, which energize electrons and drive cavitation in the plasma. The fluxes of electrons reaching the objects are bursty at ωpe, and the energies of the ions striking the object slowly and systematically vary with time.