Pierre Descamps

One-dimensional modelling of a capacitively coupled rf plasma in silane/helium, including small concentrations of O2 and N2

Functional coating deposition using plasma is broadly used in industrial application working at a pressure ranging from low pressure discharges (a few Pascals) to atmospheric plasmas. The active gas (silane is selected for this study) is often diluted in a gas that helps in stabilizing the discharge like helium or argon. In addition, the discharge can be polluted by uncontrolled external gas source like air or oxygen coming from water adsorbed in reactor walls. In this paper, we study the interactions taking place within the bulk of a capacitively coupled plasma and study the impact of these reactions on the flux of species moving towards the substrate and so the impact on the composition of deposited film. A one-dimensional fluid model is presented for the modelling of radio frequency capacitively coupled plasmas in a mixture of silane/helium, including small concentrations of O2 and N2. In total, 48 different species (electrons, ions, neutrals, radicals and excited species) are considered in the model. After a sensitivity study, 27 electron–neutral and 76 chemical reactions (i.e. ion–neutral and neutral–neutral reactions) were maintained in the fluid model. The fluid model itself consists of a set of mass balance equations (i.e. one for every species), the electron energy equation and the Poisson equation. The reaction rate coefficients of the electron–neutral reactions, as a function of average electron energy, are obtained from a Boltzmann model. The reaction rate coefficients of the ion–neutral and neutral–neutral reactions are assumed to be constant. It is found that helium does not affect the silane plasma chemistry drastically. The incorporation of small amounts of air (containing about 82% N2 and 18% O2) in a silane/helium plasma, however, influences the plasma chemistry to a large extent. A large number of nitrogen species (i.e. N2, N, N2+), and species containing oxygen (i.e. SiH3O SiO, OH and others), are present in the discharge at relatively high densities (i.e. of the order of 1014–1017 m−3).

The high-power (3-MW) long-pulse (3-s) radio-frequency system for ion cyclotron resonance heating experiments on TEXTOR

A multimegajoule ion cyclotron resonance heating (ICRH) experiment was installed on the Torus Experiment for Technology-Oriented Research (TEXTOR) tokamak. The system consists of two independent power lines each designed to generate and launch 1.5 MW of radio-frequency (rf) power into the machine during a 3-s period in the 25- to 29-MHz frequency range. Each power line consists of the following items: a 1.5-MW transmitter, a transmission line system, and an interface linking the transmission line to the antenna of the shielded strip-line type placed along the tokamaks hot liner. Details of the line and antenna diagnostics and data acquisition system together with the subsequent impedance characteristic calculations are given. The rf radiation shielding for the ICRH experiment is explained. The control of the rf setup as a TEXTOR sub-system and the generator pulse control and operation modes are outlined. The antenna loading and power limitation in the presence of plasma and the conditioning procedure are discussed. Finally, the new rf system compatible with the toroidal pump limiter Advanced Limiter Test-II is presented.

Determination of central q and effective mass on textor based on discrete Alfvén wave (DAW) spectrum measurements

The use of the discrete Alfven wave spectrum to determine the current dessity profile and the effective mass density of the plasma in the TEXTOR tokamak is studied; the measurement, the validity of which is discussed, confirms independently the central qr = 0< 1 already obtained by polarimetry.

Atmospheric-pressure plasma enhanced chemical deposition: role of the reactor flow dynamics

An atmospheric- instead of low-pressure plasma deposition reactor for the inline production and processing of thin films is investigated. Process optimization and scale-up require a fundamental understanding of the reactor behaviour. The influence of the reactor design and the operating conditions on the reactor hydrodynamics and the film deposition rate are studied experimentally and by means of detailed computational fluid dynamics simulations. The influence of the process gas and its flow rate to the inlet channels, the precursor injection velocity and different geometric reactor design parameters is focused on.

Effects of anodized aluminium surface parameters on the long-term adhesion of silicone structural glazing sealants

Abstract The quality of silicone sealant adhesion to anodized aluminium varies widely. Key parameters that affect adhesion are the degree of surface sealing, the pigmentation of the anodization layer, the nature of the cleaner, and the time period allowed between cleaning the substrate and sealant application. While the cleaners display different effectiveness in removing organic contamination from the anodized aluminium surface, this effectiveness does not correlate with adhesion quality. It is hypothesized that by absorbing on the anodized aluminium substrate the cleaning solvents ‘condition’ the surface for improved silicone sealant adhesion. This conditioning effect diminishes, as the cleaning solvents desorb over time. For a given cleaning solvent, optimum adhesion is observed for a certain degree of surface sealing. Adhesion to unpigmented anodized aluminium substrates can be predicted by measuring the degree of surface sealing according to the ISO 2143 acid etch method. For pigmented anodized aluminium substrates, electrical phase shift measurements, made in accordance with the ISO 2931 test standard, can be used to predict adhesion quality. A quality control method for anodized aluminium surfaces is proposed that allows successful correlation of the electrical impedance measured at various frequencies with the long-term adhesion of silicone sealants to this surface.

Influence of discharge and jet flow coupling on atmospheric pressure plasma homogeneity

The effect of flow dynamics on the discharge mode is studied in order to design a technical solution for thin film coating on large surfaces. The configuration consists in two atmospheric pressure helium plasma jets impacting a surface and confined in a tube. This system operates in open air. It has been studied by short exposure time pictures, current and voltage measurements, optical emission spectroscopy, schlieren flow visualization and computational fluid dynamics. Two discharge regimes directly connected to the gas flow dynamic have been pointed out. One is localized from the point electrodes to the surface; the other one entirely fills the confinement tube. A correlation between air intake inside the confinement tube and the discharge mode has been highlighted. Indeed, the discharge only develops in helium and the air intake confines the helium jets in volumes smaller than the confinement tube. The air intake is determined by the gas flow rate and the distance from the tube bottom to the substrate surface, parameters which have been linked to the change from laminar to turbulent flow. Finally, the understanding of flow dynamics and discharge plasma coupling allowed the design of a technical solution favoring plasma homogeneity for large surface treatment.

Using a Monte-Carlo model to identify best filler arrangement in thermally conductive materials

A 2D Monte-Carlo model was built to calculate the probability of paths creation between the two interfaces of a TC material via direct contact between filler particles. This model allowed studying the impact of the filler size with respect to the distance between the two interfaces on the probability of direct TC paths creation. Calculation is carried-out considering one single filler size and the mixture of two fillers of different dimensions. We demonstrate that at low degree of filler loading, it is preferable to use large size filler compared to the volume to fill; when increasing filler loading, the trend reverses and it becomes beneficial to use smaller size filler for increasing probability of path creation. In case of two fillers of different dimensions, an optimum fraction of large size filler exists that depends on the filler loading level: at low filling level, the optimum corresponds to a high fraction of large size particles, this optimum displacing towards a lower fraction of large size filler when the filling level increases.