Experimental validation and simulation of collisionless bounce-resonance heating in capacitively coupled radio-frequency discharges

In low-pressure capacitively coupled radio-frequency discharges, when the driving frequency and discharge gap satisfy certain resonant conditions, the high-energy beam-like electrons generated by fast sheath expansion are bounced back and forth between two sheath edges, during which they can gain energy in each of the collisions with either of the expanding sheaths, and can consequently be heated by the two sheaths coherently. This is the so-called collisionless electron bounce-resonance heating (BRH). The first experimental evidence of BRH was reported by Liu et al (2011 Phys. Rev. Lett. 107 055002). Using a combined measurement of floating double probe and optical-emission spectroscopy, we further demonstrate the effect of BRH on plasma properties, such as plasma density and light emission. It is found that plasma density and excitation are enhanced due to BRH and have a significant dependence on the gap length, pressure, low frequency, high-frequency power and driving frequency, which are presented and discussed in detail. These observations can be explained satisfactorily by a self-consistent 1D3v particle-in-cell/Monte Carlo collision simulation in more detail.