Electromagnetic particle-in-cell simulations of surface wave effects in various plasmas

Surface waves emerge in bounded plasmas due to a layered structure of the discharge,

where central plasma is separated from electrodes by electron-depleted plasma sheaths and/or

dielectrics. The name comes from the fact that the electric field in such modes is concentrated close

to the corresponding interface, provided that the skin depth is smaller than the plasma

size. It is the case in typical microwave-driven surface wave discharges, allowing

for stable sustainment of plasmas over large areas and with large densities by far exceeding

the critical density where the plasma frequency matches the driving frequence, which is advantageous.

In contrast, in rf-driven capacitively coupled discharges, the skin depth is larger than the electrode gap

and the modes can have an electric field comparable to the driving electric field. Due to

the fact that phase velocity of the surface modes is much smaller than the speed of light in vacuum,

they can be excited at relatively low frequencies above 50 MHz. Since the corresponding

wavelength in such discharges can be comparable to the system size, the excitation of surface waves may

lead to substantial plasma nonuniformities because of their efficient interaction with electrons

at the plasma-sheath boundary, which is detrimental. In this work we study both the rf- and microwave-driven

discharges numerically using the recently constructed EM PIC code [1] and show that

these discharges have much in common, but also have certain differences.

[1] D. Eremin et al., Plasma Sources Sci. Technol. 32 044007 (2023)