PIC Simulations of the Anode Sheath in Low-Pressure DC Discharges

The behavior of plasma in the anode region of a DC discharge is complex due to its dependence on the geometry of the anode, gas type and pressure, and discharge current. Understanding this behavior is an ongoing effort due to its importance in developing a general theory for gas discharges and designs for charged particle sources. The anode plasma sheath displays interesting phenomena such as self-organization into complicated stationary or moving patterns and sign reversal of the potential drop across the sheath. This poster will describe recent efforts to better understand the physical mechanisms and characteristic length scales that govern the change in electric potential and its influence on plasma properties within the sheath in the electron-diffusion-dominated regime. A high-fidelity modeling approach using Sandia’s massively parallel plasma code, Aleph, is used to simulate the positive column and anode region plasma. Simulation results will be compared to recent theoretical work that has identified a similarity criterion that characterizes the transition between two unique modes of transport: the free-flight mode, where electrons are highly kinetic and the potential always decreases, and the drift-diffusion mode, where the potential can increase or decrease depending on the relative strength of diffusive forces [1].

References

[1] V. Martens, Elsevier 218, 112675 (2023).