During the initiation of a gas discharge under radio-frequency excitation we find that the system undergoes a sequence of distinct electron power absorption modes, while its impedance changes on the nanosecond timescale within the pre-breakdown, breakdown and post-breakdown phases. The experimental results for the spatiotemporal distribution of the excitation rate as well as other plasma parameters during the breakdown process are confirmed by particle-based kinetic simulations. The phenomenon is followed by an analytical model that sheds light on the temporal variation of the current and voltage waveforms as well as their phase difference leading to the rapid variation of the impedance during the build-up of the plasma.

The effect of the pulse-off duration on the time evolution of the plasma and electrical parameters during the ignition phase in a pulsed capacitively coupled radio frequency argon discharge operated at 450 mTorr and 12.5 MHz is investigated synergistically by multifold experimental diagnostics, particle-in-cell/Monte Carlo collision simulations and an analytical model. In the experiment, the electron density is measured time-resolved by a hairpin probe, the spatio-temporal distribution of the electron impact excitation dynamics is studied by phase resolved optical emission spectroscopy, and the amplitudes and the relative phase, φ vi, of the discharge voltage and current are determined based on the waveforms measured by a voltage and a current probe. The experimental results show that the plasma and electrical parameters during the ignition process depend strongly on the duration of the afterglow period, T off, primarily because of the dependence of the remaining charge density on this parameter. Computed values of φ vi show a similar time-dependence compared to the experiment, if the simulations are initialized with specific initial charged particle densities, n ini. This allows us to further understand the time evolution of φ vi for different values of T off based on the simulation results together with an analytical model. In particular, the optical emission intensity is found to change with time in the same fashion as the power deposition into the system at T off ⩾ 100 μs, suggesting that the power is primarily absorbed by the electrons, which dissipate their energy via inelastic collisions. The system goes through different mode transitions of electron power absorption during the ignition phase depending on T off. Specifically, for short T off (high n ini), the α mode dominates during the entire ignition process, as the electric field is largely shielded by the abundant charge located in the interelectrode space. For intermediate values of T off (moderate n ini), another excitation pattern caused by an enhanced drift electric field at the center of the gap is observed, since a large fraction of the externally applied potential can penetrate into the central region in the absence of high charged particle densities. For longer T off (very low n ini), the ignition of the pulsed plasma behaves like a gas breakdown.

In electronegative radio frequency plasmas, striations can appear if the bulk plasma is dominated by positive and negative ions, that can react to the driving frequency. Here, we investigate such self-organized structures in dual-frequency (DF, 2/10 MHz) capacitively coupled CF4 plasmas by PROES and PIC/MCC simulations. This choice of the frequencies is made to ensure that the ions can react to both the lower (2 MHz, "low frequency", LF) and the higher (10 MHz, "high frequency", HF) components of the excitation waveform. A strong interplay of the two excitation components is revealed. As the striations appear in the plasma bulk, their number depends on the length of this region. By increasing the LF voltage, ΦLF, the sheath widths at both electrodes increase, the bulk is compressed, and the number of striations decreases. The maximum ion density decreases slightly as a function of ΦLF, too, due to the compressed plasma bulk, while the minimum of the ion density remains almost constant. The spatio-temporal distribution of the excitation and ionization rates are modulated both by the LF and HF with maxima that occur at the first HF period that follows the complete sheath collapse at a given electrode. These maxima are caused by a high local ambipolar electric field. At a given phase within a HF period, the current density is different at different phases within the LF period because of frequency coupling. The LF components of the F- ion velocity and of the electric field are much lower than the respective HF components due to the lower LF component of the displacement current in the sheaths. The LF component of the total current is dominated by the ion current at low values, but by the electron current at high values of ΦLF.

The effects of gas pressure and voltage amplitude on the ignition process of a pulse capacitively coupled RF argon discharge are experimentally investigated. The electron density is measured by a hairpin probe, the spatiotemporal distribution of the electron impact excitation dynamics is determined by phase resolved optical emission spectroscopy, and the electrical parameters are obtained by analyzing the measured current and voltage waveforms. In this work, the pulse plasma is ignited with few initial electrons, so the ignition process behaves like gas breakdown. Based on the measured RF breakdown curve, the gas pressures and voltage amplitudes are selected, and then different characteristics of ignition processes are compared and discussed in detail. Particularly, the spatiotemporal pattern of the electron impact excitation rate obtained within the selected pressure range, as well as other results, aid the intuitive understanding of a typical “V-shaped” RF breakdown curve. At lower pressures, the excitation pattern exhibit shorter and tilted regions, ending at electrodes during the early ignition stage, implying a substantial electron energy loss, while at relatively high pressures, the excitation pattern becomes wider and less tilted, and the proportion of electron energy consumed by excitation processes increases. In addition, by increasing the voltage amplitude, the ignition is advanced and becomes more significant, manifesting a faster increase in discharge current and a stronger overshoot of RF power deposition. Meanwhile, at high voltage amplitude, the excitation pattern exhibits complex spatiotemporal distribution due to enhanced local electric field when the plasma emission intensity overshoots.