Volume 96, Issue 12, 15 December 2004
Index of content:
- PLASMAS AND ELECTRICAL DISCHARGES (PACS 51-52)
96(2004); http://dx.doi.org/10.1063/1.1808481View Description Hide Description
Langmuir probes are important means for the characterization of plasma discharges. For measurements in plasmas used for the deposition of thin films, the Langmuir double probe is especially suited. With the increasing popularity of pulsed deposition discharges, there is also an increasing need for time-resolved characterization methods. For Langmuir probes, several single-probe approaches to time-resolved measurements are reported but very few for the double probe. We present a time-resolved Langmuir double-probe technique, which is applied to a pulsed magnetron discharge at several 100 kHz used for MgO deposition. The investigations show that a proper treatment of the current measurement is necessary to obtain reliable results. In doing so, a characteristic time dependence of the charge-carrier density during the “pulse on” time containing maximum values of almost was found. This characteristic time dependence varies with the pulse frequency and the duty cycle. A similar time dependence of the electron temperature is only observed when the probe is placed near the magnesium target.
96(2004); http://dx.doi.org/10.1063/1.1810201View Description Hide Description
In this study the variations of the velocity and electric fields in electrohydrodynamic (EHD) flows in a positive single-wire electrostatic precipitator are studied. The fully coupled systems of electrical and hydrodynamical governing equations are solved for both laminar and turbulent flow conditions. Particular attention is given to the flow-electric field coupling effects and the variation of the electrical potential and charge distribution induced by the gas flow field. The presented results show that the effects of airflow on electrical potential and charge density become noticeable at high cross-flow velocities. The electrical conditions in an electrostatic precipitator that was used in an earlier experimental study are also simulated. It is shown that the computational model predictions are in good agreement with the experimental data. A series of parametric studies for a range of parameters for the EHD flows in the single-wire precipitator are performed and the corresponding flow and electric fields are presented. An example of extension of the model to multiwire precipitator is also presented.
96(2004); http://dx.doi.org/10.1063/1.1815047View Description Hide Description
The physics of helium and argon rf discharges have been investigated in the pressure range from 50 to . The plasma source consists of metal electrodes that are perforated to allow the gas to flow through them. Current and voltage plots were obtained at different purity levels and it was found that trace impurities do not affect the shape of the curves. The electron temperature was calculated using an energy balance on the unbound electrons. It increased with decreasing pressure from 1.1 to for helium and from 1.1 to 2.0 for argon. The plasma density calculated at a constant current density of ranged from to for helium and from to for argon, increasing with the pressure. At atmospheric pressure, the electron density of the argon plasma is 2.5 times that of the helium plasma.