Volume 86, Issue 5, 01 September 1999
Index of content:
- PLASMAS AND ELECTRICAL DISCHARGES (PACS 51-52)
Electrohydrodynamic flow associated with unipolar charge current due to corona discharge from a wire enclosed in a rectangular shield86(1999); http://dx.doi.org/10.1063/1.371069View Description Hide Description
Unipolar chargecurrent can be generated through corona discharge from a thin wire enclosed in a shield electrode. Except for an ionization sheath adjacent to the coronating wire surface, most parts of the region in the enclosing shield contain drifting ions of a single polarity in response to the electric field. Momentum transfer as a consequence of collisions between drifting ions and electrically neutral air molecules gives rise to the electrohydrodynamic flow known as “corona wind.” Although primarily driven by the Coulomb force due to unipolar charge in the electric field, the electrohydrodynamic flow cannot simply follow the direction of electric field lines because of the confinement of the solid walls of the shield. Therefore, the structure of the electrohydrodynamic flow can vary significantly depending on the system configuration. In the present work, the electrohydrodynamic flow in a rectangular shield is studied by solving the nonlinearly coupled governing equations via the Galerkin finite-element method. A highly symmetric system with the wire positioned at the center of a square shield is shown to contain eight equal-sized, two-dimensional recirculation vortices. The number of recirculation vortices tends to be reduced by a slight asymmetry in the system. The flow structure of two major counter-rotating recirculation vortices is found to be most common in systems where the wire is positioned off the center of the rectangular shield in a two-dimensional domain. The results reported here may be brought to bear upon the “corona wind” effect in charging devices such as corotrons and scorotrons used in electrophotographic printing processes.
86(1999); http://dx.doi.org/10.1063/1.371070View Description Hide Description
Experimental studies of a broad-area hyperthermal neutral stream source for photoresistcleaning are reported. Low energy neutrals are generated from a high-density inductively coupled plasma by the surface reflection neutralization method. Rates of removal of photoresistpolymers such as polymethyl methacrylate as functions of the hyperthermal translational energy and background neutral pressure are reported. The results demonstrate this low energy neutral source provides controllable fast neutrals for cleaning applications. Ex situ and in situ measurements yield typical removal rates of about 10 Å/s without stream collimation. The removal rates at increasing pressures show a trade-off between creating higher density plasma, leading to a greater initial neutral flux and attenuation of neutrals due to collisions. These observations are in good agreement with previous Monte Carlo simulations. The removal rate increases linearly with rf power and is nearly constant as the neutral energy is varied by varying the reflector bias. One consequence of neutral directionality in collimated stream applications is the presence of unremoved carbon compounds on the sidewalls as indicated by angle-resolved x-ray photoelectron spectroscopy.
86(1999); http://dx.doi.org/10.1063/1.371071View Description Hide Description
The effect of charged particulates or dusts on surface wave produced microwavedischarges is studied. The frequencies of the standing electromagnetic eigenmodes of large-area flat plasmas are calculated. The dusts absorb a significant amount of the plasma electrons and can lead to a modification of the electromagnetic field structure in the discharge by shifting the originally excited operating mode out of resonance. For certain given proportions of dusts, mode conversion is found to be possible. The power loss in the discharge is also increased because of dust-specific dissipations, leading to a decrease of the operating mode quality factor.
Global modeling of a dielectric barrier discharge in Ne–Xe mixtures for an alternating current plasma display panel86(1999); http://dx.doi.org/10.1063/1.371072View Description Hide Description
A global model of a dielectric barrier discharge in Ne–Xe mixtures for an alternating currentplasma display panel was developed. This model was used to evaluate electron temperature,plasma density, densities of excited state atoms, wall charge density, current density, excimer density, and vacuum ultraviolet (VUV) intensity, and their gas composition-pressure dependencies, in order to analyze the mechanism of VUVradiation and discharge efficiency. The results show that the intensity ratio of 173 to 147 nm VUV is about a few percent. This means that the contribution of excimers is small in terms of VUVradiation. The maximum discharge efficiency was about 9% for Xe fraction in the range of 2%–12% and gas pressure in the range of 100–600 Torr. Discharge efficiency increases in the high Xe fraction and gas pressure region. The increase of the discharge efficiency is attributed to a decrease of discharge current and an increase of excited state atom, due to the low electron temperature in the high Xe fraction and gas pressure region.