Formation Mechanism and Velocity Distribution of Electron Beam Driven by Sheath Expansion in RF Capacitively Coupled Plasmas

Electron heating in capacitively coupled plasma (CCP) discharges plays a crucial role in generating and sustaining the plasma. At low pressures, stochastic heating becomes particularly significant to generate high-energy electrons. In this study, we analyzed the condition for the formation of high-energy electron beams generated by sheath oscillations in low-pressure argon CCP using a two-dimensional Particle-in-Cell/Monte Carlo Collision (2D PIC/MCC) simulation. As the sheath expands under high-frequency driving conditions (above 30 MHz), electrons are accelerated, resulting in the formation of energetic electron beams [1]. The velocity of these beams increases in proportion to the sheath expansion distance and duration. Furthermore, by adjusting plasma parameters, such as driving frequency, voltage, and secondary electron emission, we observe that the sheath characteristics can be controlled, which in turn enables modulation of the temperature and velocity of the emitted electron beams. These findings suggest that the ability to control the characteristics of electron beams provides fundamental insight into the mechanisms of electron heating.



[1] D.-Q. Wen et al., Applied Physics Letters 123, 264102 (2023).