Voids in dust clouds suspended in the plasma sheath

Voids in dusty plasma are a new phenomenon, which is still not understood. In this work we have studied experimentally for first time voids in the sheath of a radio-frequency (RF) dusty plasma. Injecting big dust particles into the plasma, we form a dust cloud in the sheath. The behaviour of the cloud as a function of RF power and gas pressure is investigated using video imaging. Both dependencies show a threshold for the void formation. This threshold is characterised by a sudden decrease in the inter-particle distance, while in the non-void mode the distance increases with power and pressure. We have performed Langmuir probe measurements of the floating potential in the bulk plasma close to the sheath in order to estimate the form of the potential well trapping the dust grains

The chemistry of a CCl2F2 radio frequency discharge

A systematic study of the chemistry of stable molecules and radicals in a low pressure CCl2F2 radio frequency discharge for dry Si etching has been performed. Various particle densities have been measured and modeled. The electron density, needed as an input parameter to model the CCl2F2 dissociation, is measured by a microwave cavity method. The densities of stable molecules, like CClF3, CF4, 1,2-C2Cl2F4 and the etch product SiF4, are measured by Fourier transform absorption spectroscopy. The density of the CF2 radical is measured by means of absorption spectroscopy with a tunable diode laser. Its density is in the order of 1019 m-3. All density measurements are presented as a function of various plasma parameters. Moreover, optical emission intensities of Cl and F have been recorded as a function of plasma parameters. It appears that the feed gas (CCl2F2) is substantially dissociated (about 70%–90%) in the discharge. Based on the obtained data the dissociation rates of several molecules have been estimated. The measured total dissociation rate of CCl2F2 is 8×10-15 m3¿s-1. For this molecule the dissociation rate is substantially higher than the dissociative attachment rate (10-15 m3¿s-1). The dissociation rate for CClF3 is 2×10-15 m3¿s-1 and for CF4 about 3×10-16 m3¿s-1. The total dissociation rate of C2Cl2F4 is higher than 5 ×10-15 m3¿s-1, of which 2.5±0.5 × 10-15 m3¿s-1 is due to dissociative attachment. Furthermore it has been found that the presence of a silicon wafer strongly affects the plasma chemistry. Optical emission measurements show that the densities of halogen radicals are significantly depleted in presence of Si. Moreover, the densities of several halocarbon molecules display a negative correlation with the density of the etch product SiF4. © 1995 American Vacuum Societ

Departures from local thermodynamic equilibrium in HID lamps

No abstract

Rotational kinetics of absorbing dust grains in neutral gas

We study the rotational and translational kinetics of massive particulates (dust grains) absorbing the ambient gas. Equations for microscopic phase densities are deduced resulting in the Fokker-Planck equation for the dust component. It is shown that although there is no stationary distribution, the translational and rotational temperatures of dust tend to certain values, which differ from the temperature of the ambient gas. The influence of the inner structure of grains on rotational kinetics is also discussed.Comment: REVTEX4, 20 pages, 2 figure

Hypergravity effects on glide arc plasma

The behaviour of a special type of electric discharge – the gliding arc plasma – has been investigated in hypergravity (1g –18g) using the Large Diameter Centrifuge (LDC) at ESA/ESTEC. The discharge voltage and current together with the videosignal from a fast camera have been recorded during the experiment. The gliding of the arc is governed by hot gas buoyancy and by consequence, gravity. Increasing the centrifugal acceleration makes the glide arc movement substantially faster. Whereas at 1g the discharge was stationary, at 6g it glided with 7 Hz frequency and at 18g the gliding frequency was 11 Hz. We describe a simple model for the glide arc movement assuming low gas flow velocities, which is compared to our experimental results