Electron Sheaths and Fireballs

Probes and electrodes are the most common method of manipulation and diagnosis of low temperature low pressure laboratory plasmas. The variety of behavior that a probe can induce locally and globally in the plasma is in part determined by the electrode size, geometry, and bias relative to the plasma potential. When biased above the plasma potential electrodes and probes have been observed to modify electron and ion velocity distribution functions, induce electron flows, generate ion flows that are determined by probe geometry and proximity to insulating surfaces, and induce secondary discharges called fireballs that are driven by electron-impact ionization. Until recently, the understanding of the basic positive electron sheath and presheath properties that lead to many of these phenomena went unrecognized and was not well understood [1]. In this talk, recent advances in the understanding of the behavior of positive electrodes are presented and our current line of research on positive probes is discussed.

[1] Interaction of biased electrodes and plasmas: sheaths, double layers, and fireballs, Scott D Baalrud, Brett Scheiner, Benjamin T Yee, Matthew M Hopkins and Edward Barnat, 2020 Plasma Sources Sci. Technol. 29 053001