Rotating spokes, potential hump and modulated ionization in radio frequency magnetron discharges

Abstract

In this work, the transition from the gradient drift instability (GDI) into an m = 1 rotating spoke in the radio frequency magnetron discharge was studied by means of the two-dimensional axial-azimuthal (z − y) particle-in-cell/Monte Carlo collision method. The kinetic model combined with the linear analysis of the perturbation revealed that the cathode sheath (axial) electric field E z triggers the GDI, deforming the local potential until the instability condition is not fulfilled and the fluctuation growth stops in which moment the instability becomes saturated. The potential deformation consequently leads to the formation of the potential hump, surrounding which the azimuthal electric field E y is present. The saturation level of E y was found to be synchronized with and proportional to the time-changing voltage applied at the cathode, resulting in the RF-modulation of the electron heating in the E y due to ∇ B drift. In the saturated stage of the instability, it was shown that the rotation velocity and direction of the spoke present in the simulations agree well with the experimental observation (Panjan 2019 J. Appl. Phys. 125 203303). In the instability linear stage, the instability mode wavelength and the growth rate were also found to be in good agreement with the prediction of the GDI linear fluid theory.

Plasma dynamics of individual HiPIMS pulses: imaging study using high-frame-rate camera

“…Such a timeframe is in qualitative agreement with recent simulations of spokes in RFMS discharges, which demonstrate a comparable time period (i.e. several µs) for small density fluctuations to evolve into spokes [56]. If plasma dynamics is carefully inspected, the spoke patterns initially rotate in the −E z × B direction and change the direction of the rotation when the discharge current increases above ∼30-75 A.…”

Oblique streaming waves observed in multipactor-induced plasma discharge above a dielectric surface

“…Cross sections for these reactions are sourced from [6,7,67,68]. All the physical processes described above have been implemented in a well-benchmarked 2D Electrostatic Direct Implicit Particle-In-Cell (EDIPIC) code [66,[68][69][70][71], which has been used widely in low-temperature plasma studies such as radio-frequency plasma discharge [72,73], gas breakdown [67,74] and electron beam-generated plasma [68,70,75,76]. And such model is well validated against experimental measurements [77,78] and theoretical calculation [1] in terms of the threshold electric fields for the onset of multipactor phenomenon, and saturated surface charge densities from other PIC simulation [79].…”