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A one-dimensional (1D) fluid model is developed to investigate the effect of multi-frequency excitation consisting of consecutive harmonics on the charge of a single dust grain in a weakly collisional capacitively coupled plasma discharge. The spatial distributions of the electron density, the electrons temperature, and the charged particle flux are obtained and analyzed under the effects of the number of harmonics. It is shown that the number of harmonics considerably affects the discharge properties and the sheath thickness. In order to analyze the charge of an injected dust particle under the effect of different operating parameters, the model takes into account the electron and ion currents, as well as the effect of collisions between ions and neutral atoms. The results showed that as the number of harmonics increases, the particle charge increases in the powered sheath region while it decreases in the grounded sheath due to the electrical asymmetry effect. However, the charge remains constant in the central region where the electron temperature is constant. The present study further shows that the gas pressure and the driving frequency affect the dust charge oppositely, where an increase in pressure leads to a decrease in the dust charge, especially in the sheath regions, while the particle charge negatively increases as the driving frequency increases for all excitation waveforms. [ABSTRACT FROM AUTHOR]

The results of an experimental study of the initiation, development and maintenance of a plasma surface discharge initiated by microwave (microwave) radiation of a gyrotron (75 GHz, 300 kW, 6 ms) in air under normal conditions on the surface of a quartz substrate with metal inclusions are presented. It is shown that the velocity of the propagation of the discharge ionization front reaches 40 m/s, which corresponds to the thermal conduction propagation mechanism. In this case, the maximum calculated gas temperature of the plasma reaches 5500 K, which leads to the sublimation of metal inclusions. For the first time, the plasma parameters of a surface microwave discharge on metal-dielectric targets, which have been used in various aeroplasma and plasma-chemical applications, are presented. [ABSTRACT FROM AUTHOR]

An analysis of the formation of a void in the PK3 setup in dusty plasma with 3.4-μm-diameter melamine–formaldehyde particles—in an RF discharge in argon at a pressure of 12–50 Pa under microgravity conditions at the ISS is presented. The uniform state of the plasma can only be obtained at a voltage close to the discharge extinction voltage. The application of a low-frequency voltage of 20–50 Hz stabilizes the state of the dusty plasma and shifts the void formation threshold towards higher RF voltages. It is shown that the formation of a void is associated with non-local ionization of the plasma at the center of the discharge by fast electrons, which are heated in the near-electrode layers. [ABSTRACT FROM AUTHOR]

Some types of the slot input of high energy into cylindrical and rectangular cavities are considered. The energy input through slot waveguiding apertures located at the central circle of the cavity is selected and optimized. The standing wave ratio of the system is determined. The change in the electrical field energy in the cavity, when the position of the slot waveguide is shifted, is simulated. The optimum (best for processing with microwave discharge plasma) positions of the objects and waveguide slots as well as critical positions (choosing which can put the oscillator out of action) are shown. The increase in the field density between two metallic objects is calculated. The results demonstrating the inacceptable way of the slot input of energy for solving some types of problems related to processing of complex surfaces with the microwave discharge are obtained. [ABSTRACT FROM AUTHOR]

A microwave beam (wavelength 4 mm, power 150–300 kW) generates an ionization wave in air in the subthreshold field in the shape of a conglomerate of thread-like channels that moves toward the beam. The periphery of the beam refracts in the plasma of the non-self-sustained discharge in the UV halo of the thread-like discharges and self-focuses in the recombining plasma behind the front of the plasmoid that consists of thread-like channels. The self-focusing of the peripheral regions of the wave beam causes local bursts of ionization behind the front of the leading plasmoid. [ABSTRACT FROM AUTHOR]

The formation dynamics of the parameters of a microwave discharge in air localized at electric field maxima created by a specially developed focusing system is investigated using numerical simulations within an extended hydrodynamic model. All main parameters of the microwave discharge plasma are determined. The results on neutral gas heating demonstrate good agreement with the earlier experimental results. [ABSTRACT FROM AUTHOR]