Complex Electron Heating in Capacitive Multi-Frequency Plasmas

Complex spatio-temporal electron heating dynamics are observed in kinetic simulations of geometrically symmetric low-pressure capacitive argon plasmas driven by multiple consecutive harmonics of 13.56 MHz. These dynamics are caused by an electrically induced asymmetry that leads to the self-excitation of plasma series resonance oscillations of the current. Such oscillations cause a nonsinusoidal movement of the boundary sheath edges and multiple phases of fast sheath expansions. These expansion phases lead to the generation of negative space charges that propagate into the bulk, where they affect the heating rate significantly and relax quickly.