Observation of nonlinear sheath oscillations in symmetric capacitive discharges at low pressures

• Published in: Physics of plasmas 2021-01, Vol.28 (1)
• Main Authors: Sun, Jing-Yu, Zhang, Quan-Zhi, Wang, You-Nian
• Format: Article
• Language: English
• Subjects: Electric fields; Electron beams; Filaments; High energy electrons; Nonlinear phenomena; Nonlinearity; Oscillations; Particle in cell technique; Plasma density; Plasma physics; Plasmas (physics); Sheaths; Thickness
• ISSN: 1070-664X; 1089-7674
• DOI: 10.1063/5.0022457

The mechanism of nonlinear oscillations in symmetric capacitively coupled plasmas is studied by the particle-in-cell/Monte Carlo collisions approach. A physical origin of this nonlinear phenomenon is identified by spatiotemporal kinetic analysis of electron dynamics. It is found that multi-beams of high-energy electrons are stimulated at the sheath expansion phase, following with reversed electric field filaments. The instantaneous absence of the quasi-neutrality in the vicinity of the sheaths is responsible for the observed phenomenon. In addition, a simple theoretical model is introduced to qualitatively illustrate the numerical findings. Our simulations demonstrate that the frequency and intensity of this nonlinearity are very sensitive to the plasma density, sheath velocity, and sheath thickness. More nonlinear oscillations could be stimulated at the condition of high density and high sheath velocity, while a large sheath thickness normally induces large-amplitude oscillations. A simple relation of pressure and gap distance for nonlinear sheath oscillations has been built.