Two dimensional Particle-in-Cell Modeling of Electron-Beam Generated Low Electron Temperature Plasma

Plasmas generated using energetic electron beams can be important for plasma processing applications requiring atomic precision due to their low electron temperature. Electron beam plasmas are typically confined using a static magnetic field and operated at low gas pressures. In previous experimental studies at the Naval Research Lab, Langmuir probes measurements suggested that the plasma transport across the magnetic field lines is non-classical in this operating regime. Consequently, fluid or hybrid modeling must adjust their implemented transport coefficients to empirically fit experimental data. For more predictive results, we propose in this paper a self-consistent fully kinetic 2D axisymmetric Particle-In-Cell study using the open-source code EDIPIC-2D. The model examines the creation and evolution of plasma in low pressure (10 – 40 mTorr) Ar gas on injection of an energetic electron beam (2 keV). A steady-state is reached after a few hundreds of microseconds and the plasma is mostly confined by the imposed magnetic field, near the symmetry axis. Charged particles are able to travel across the magnetic field lines in the x direction and the subsequent transport is being compared with analytical theory. To study the scaling of the electron transport, we also performed a large parametric study with different values of the neutral gas density, beam current, and magnetic field strength. The impact of these parameters on electron density, plasma potential, and electron temperature are found consistent with probe-based experimental measurements.