Irina Schweigert

Transition between different modes of a capacitively coupled radio frequency discharge in CH/sub 4/ in one- and two-dimensional PIC-MCC Simulations

Two regimes of a capacitevely coupled radio frequency (CCRF) gas discharge operating in methane are studied with a combined particle-in-cell Monte Carlo collisions (PIC-MCC) algorithm (one-dimensional model) and with accelerated PIC-MCC algorithm (two-dimensional model) for gas pressure P=(0.01--1) torr and discharge current j=(0.45--2.2) mA/cm/sup 2/. The areas of existence of different discharge regimes are shown on a P-j phase diagram and compared with known numerical results. The role secondary electrons from electrodes during transition is discussed. The phenomena of hysteresis is observed in discharge behavior with current change over growing and falling current branches.

Picosecond Breakdown in High-Voltage Open Pulse Discharge With Enhanced Secondary Electron Emission

A 300-ps breakdown was registered in the experiments in the high-voltage open discharge with counter-propagating electron-beams with applying voltage pulses with rise times in 10–20 ns range. Discharge operates between two cathodes and grid-anode in the midplane at 10–35 Torr in helium at voltage 5–13 kV. It is shown in Particle-in-cell Monte Carlo collision (PIC MCC) simulations that the contributions of electrons, ions and energetic atoms in ionization and excitation processes are important for current development. The influence of different emissive cathode materials (titanium, silicon carbide, and CuAlMg-alloy) on evolution of discharge current is studied in the experiment and in kinetic PIC MCC simulations. The secondary electron emission from the cathodes is found to be a dominant process at the final stage of the breakdown. The current growth rate is larger (up to 700 A/cm2ns) for the cathode with a higher secondary electron emission yield. By choosing the cathode material, applied voltage amplitude and gas pressure, the characteristic time of the gas breakdown can be reduced.

Nonlocal kinetic theory of plasma discharges

Summary form only given. The purpose of the talk is to describe recent advances in nonlocal electron kinetics in low-pressure plasmas. Low-pressure discharges are widely used in industry as the main plasma sources for many applications including plasma processing, discharge lighting, plasma propulsion, particle beam sources and nanotechnology. Being partially-ionized, bounded, and weakly-collisional, the plasmas in these discharges demonstrate nonlocal electron kinetic effects, nonlinear processes in the sheaths, beam-plasma interaction, collisionless electron heating, etc. Such plasmas often have a non-Maxwellian electron velocity distribution function. The plethora of kinetic processes supporting the non-equilibrium plasma state is an invaluable tool, which can be used to adjust plasma parameters to the specific needs of a particular plasma application. We report on recent advances in nonlocal electron kinetics in low-pressure plasmas where a non-Maxwellian electron velocity distribution function was “designed” for a specific purpose: in dc discharges with auxiliary biased electrodes for plasma control, hybrid DC/RF magnetized and unmagnetized plasma sources, and Hall thruster discharges. We show using specific examples that this progress was made possible by synergy between full-scale particle-in-cell simulations, analytical models, and experiments. Examples of recent progress are described in Special Section of Physics of Plasmas “Electron kinetic effects in low temperature plasmas” [1] and Special Issue of Plasma Sources Science and Technology “Transport in B-fields in low-temperature plasmas” [2].

Effect of gas discharge and magnetic field on plasma layer at the surface in gas flow

Summary form only given. When returning to the Earth, the spacecrafts enter the upper atmospheric layers with a hypersonic speed. In this case, the shock heated air around them becomes weakly ionized. The gas ionization behind the shock front is associative in nature and occurs through chemical reactions between fragments of molecules. The formation of a plasma layer near the surfaces of spacecraft causes serious problems related to the blocking of communication channels with the Earth and other spacecraft. A promising way of restoring the radio communications is the application of electrical and magnetic fields for controlling the plasma layer parameters. Sheaths with an almost zero electron density and a high ion density are known to be formed near a surface when an ac or dc gas discharge is ignited in a plasma. Since the electromagnetic waves interact mainly with the plasma electron component, a decrease in electron density ensures the passage of the electromagnetic waves through the plasma sheath. In this work, we consider the combined action of a direct current (DC) discharge and a magnetic field on the plasma flow near a flat surface at a low gas pressure. Our simulations ar e performed using a two dimensional Particle in cell method (PIC MCC). The kinetics of electrons in nitrogen includes elastic collisions, the excitation of rotational, vibrational, and meta stable levels, and ionization. Based on two dimensional kinetic PIC MCC simulations, we considered the possibility of locally controlling the plasma sheath parameters near a flat surface i n a hypersonic flow. We showed that the combined action of D C discharge, a constant voltage, and a magnetic field on the plasma sheath allows the local electron density to be reduced manyfold. We did not consider the effect of gas flow acceleration during the momentum transfer from ions to gas molecules under resonant charge exchange. The gas flow velocity distribution is specified by a model function.

Nonlocal effects in beam generated plasmas for plasma electronics

Summary form only given. Given that the development of future plasma energetics depends on the application and control of nonequlibrium, anisotropic electron energy distribution functions (EEDF) in plasmas, the development of methods to measure and control EEDF is of great importance.

Hydrocarbon nanoparticle formation in C2H2/AR discharge plasma

The formation and growth of hydrocarbon nanoparticles in a reactive plasma is the result of a complex chemistry, a chemistry that itself strongly depends on the plasma parameters. Recently this phenomenon is not clear yet. In this work, first we developed a hybrid model for simulations of the 13.56 MHz discharge in a C2H2/Ar mixture.