Boundary-induced effect on electron and ion kinetics in a low-pressure electron beam generated plasma*

Electron beam (e-beam) generated plasmas are promising for low-damage material processing applications [1]. The production of reactive species generated by electron impact is controlled by the electron energy distribution function (EEDF), and ion-induced damage on material substrates is determined by the ion velocity distribution function (IVDF). In this work, we investigate the EEDF and IVDF of a partially magnetized e-beam generated plasma in low pressure (0.1-0.5 mTorr) argon.  The e-beam (energy <100 eV) is extracted from a thermionic cathode and injected into a cylindrical vacuum chamber with applied axial magnetic field. The EEDF is measured using a Langmuir probe, and the plasma potential is measured using an emissive probe. The argon IVDF is determined with a laser induced fluorescence (LIF) diagnostic. Results of probe diagnostics indicate the presence of beam electrons with energy at roughly the applied cathode potential, as well as a group of warm electrons (10-30 eV). Additionally, the LIF diagnostic indicates ions are energized to nearly 1 eV at the center of the plasma [2]. Analysis of these measurements within the context of relevant plasma instabilities will be presented.

[1]       Zhao F et al 2021 Carbon 177 244–51

[2]       Chopra N S et al 2024 Appl. Phys. Lett. 124