Search

Breakdown in oxygen, in external radio-frequency (RF) electric field is analyzed by employing a Monte Carlo simulation (MCS). Results were obtained for 13.56 MHz and distance between electrodes of 15 mm. Physical background of an oxygen RF breakdown is explained by observing time-resolved spatial distributions of electron concentration, mean energy, elastic scattering rate, ionization rate and attachment. The role of attachment is investigated in cases when these processes are included and when they are not. Especially influence of the attachment is highlighted by comparing oxygen and argon breakdown-voltage curves and spatial profiles. The electron losses induced by attachment extend the motion of the electron prebreakdown swarm much closer to electrodes to achieve a greater production; hence, spatial profiles at high values of the product pd where p is the pressure and d is the gap between electrodes, become more similar to those at the minimum of the breakdown curve. The most striking difference between the breakdown curves in argon and in oxygen is in the high increase of the breakdown voltage for high pd in oxygen. [ABSTRACT FROM AUTHOR]

We have developed a large-volume low-pressure cylindrical plasma reactor with a size that matches industrial reactors for treatment of textiles. It was shown that it efficiently produces plasmas with only a small increase in power as compared with a similar reactor with 50 times smaller volume. Plasma generated at 13.56 MHz was stable from transition to streamers and capable of long-term continuous operation. An industrial-scale asymmetric cylindrical reactor of simple design and construction enabled good control over a wide range of active plasma species and ion concentrations. Detailed characterization of the discharge was performed using derivative, Langmuir and catalytic probes which enabled determination of the optimal sets of plasma parameters necessary for successful industry implementation and process control. Since neutral atomic oxygen plays a major role in many of the material processing applications, its spatial profile was measured using nickel catalytic probe over a wide range of plasma parameters. The spatial profiles show diffusion profiles with particle production close to the powered electrode and significant wall losses due to surface recombination. Oxygen atom densities range from 1019 m-3 near the powered electrode to 1017 m-3 near the wall. The concentrations of ions at the same time are changing from 1016 to the 1015 m-3 at the grounded chamber wall. [ABSTRACT FROM AUTHOR]

Abstract: In this work we present the spatial distributions and excitation coefficients for the level O I 2p33s–2p3(4S0)3p (leading to λ =777.4 nm transition), produced by dissociative excitation by electron swarms in oxygen. We used a simple parallel plate drift tube and obtained absolute emission intensities in a low-current self-sustained Townsend type discharge. The data were obtained between moderate E/N (E—electric field, N—gas density) where electrons are in equilibrium and very high E/N where electrons may not be in equilibrium with the field and where heavy particles may be the dominant contributor to the excitation. Even at moderate E/N heavy particle effects become considerable. [Copyright &y& Elsevier]

We have presented measurements of spatial profiles of electron induced emission coefficients for the 777.4 nm radiation of oxygen in low current discharges. Measurements were performed by the drift tube technique in low-current self-sustained Townsend type discharges. We have also compared results for the delay distance for electrons in oxygen calculated using Monte Carlo simulation code and results from a semi-empirical formula adjusted to fit the oxygen data. Finally, from the spatial profiles we have determined ionization coefficients. The spatial profiles of emission provide us also with information on heavy particle excitation and on the reflection of electrons from the anode. The absolutely calibrated spatial profiles of emission may be used to separate the effects of electrons and heavy particles in excitation at high E/N values and obtain the cross sections for fast neutral excitation. [ABSTRACT FROM AUTHOR]