de Mj Mark Graaf

Axial temperatures and electron densities in a flowing cascaded arc: model versus experiment

A Fabry-PCot interferometer is used to measure argon ion line profiles in a strongly flowing cascaded arc plasma. Heavy-particle temperatures, electron densities, and electron temperatures are derived from the Doppler width, the Stark width and the lindcontinuum ratio respectively. The electron temperatures are also obtained from the electrical conductivity of the plasma. The plasma parameters along the arc channel are values averaged over the arc cross section and are determined with an accuracy of 2-5%. Comparison of the measurements with model calculations is also made, to improve understanding of the plasma Drocesses in the arc channel.

Hydrogen atom cleaning of archeological artefacts

For the development of H+ and H0 beams a new method has been developed based on the expansion of a cascade arc plasma. A partial aim was to develop an intense beam of atomic hydrogen. The result was a 100 A equivalent hydrogen atom beam with an energy conversion efficiency of typically 30–40%. The resulting hydrogen plasma has also been used to do preliminary experiments on restoration treatment of archeological artefacts according to the method of Vepřek et al. The present high density atom rich plasma beam with < 0.4 eV energies and temperatures proved to be effective in the treatment of these artefacts. The treated artefacts showed good erosion resistance compared to untreated as well as conventionally treated samples, notwithstanding the short treatment time of 20 minutes at a temperature of 400°C and the provisional character of the trial experiment.

The role of hydrogen during plasma beam deposition of amorphous thin films

Abstract The influence of wall-associated H 2 molecules and other hydrogen-containing monomers on the degree of ionization in the expanding thermal plasma used for the fast plasma beam deposition of amorphous hydrogenated carbon (a-C:H) and amorphous hydrogenated silicon (a-Si:H) was determined. Deposition models are discussed with emphasis on the specific role of the ion during deposition. The connection between the role of atomic hydrogen and the degree of ionization in the plasma beam deposition of a-C:H and a-Si:H is addressed.

Experimental characterization of a hydrogen/argon cascaded arc plasma source

A H2 /Ar cascaded arc plasma source has been experimentally characterized by determination of the efficiency, the electric field, and the pressure gradient of the arc. The results show that the efficiency of a H2/Ar cascaded arc drops when the hydrogen flow rate is increased. The electron temperature in the argon cascaded arc has been derived to be in the range 9000–12 500 K. For a hydrogen arc, the mass dissociation degree of hydrogen molecules has been derived to be above 60%.

Axial Temperatures and Electron Densities in a Flowing Cascaded arc

Since about 1985 a cascaded arc is used as a particle source in the deposition machine described by Kroesen [1a,1b]. This method of deposition showed to be very fast and efficient to grow amorphous carbon films (a–C:H), varying from graphite and diamond to polymers [1,2]. The most important difference of this method, with respect to R.F. techniques, is that the three most important functions of a deposition process, as there are dissociation/ionization, transport and deposition are spatially separated. The dissociation takes place in a cascaded arc burning on argon. The temperatures in the arc are about 10000–12000 K. At the end of this arc hydrocarbons are injected which are then dissociated and ionized effectively. At the end of the arc the plasma expands supersonically into a vacuum vessel. That means that the plasma cools down and the formed hydrocarbon fractions are transported towards the substrate, where an amorphous carbon film can grow. The quality of the films depend mainly on the amount of energy available for each injected carbon atom. The behavior of the refractive index as a function of this energy could be a confirmation that in our deposition method the carbon ions rather than radicals govern the deposition process [1,3,4]. Therefore the cascaded arc is investigated numerically and experimentally in order to improve the ionization efficiency. The conservation laws for mass, momentum and energy for both the electrons and the heavy particles are solved 2 dimensionally by a control volume numerical method with a non, staggered grid. By Fabry Perot interferometry heavy particle temperatures, electron temperatures and electron densities as a function of the axial position in the cascaded arc are measured. The obtained numerical results are compared to the experimental data, obtained by the optical Fabry Perot diagnostics.

Rotational and gas temperatures in a surface conversion negative ion source

The Fulcher band emission spectrum is used to determine rotational temperatures in the FOMSCE plasma setup. The measured temperatures are found to vary from 500 to 700 K, whereas usually in this kind of plasmas they are very close to room temperature. In this paper the interpretation of the spectra will be discussed. The influence of some plasma settings on the measured temperature will be presented.

Optical Diagnostics for High Electron Density Plasmas

Nowadays high electron density plasmas are, beside their fundamental interest, widely used for many applications, e.g., light sources and plasma processing. The well known examples of high electron density plasmas can be found among the class of thermal plasmas as, e.g., the Inductively Coupled Plasma (ICP) and the Wall Stabilized Cascaded Arc (WSCA). Usually the pressure of the plasma is high, i.e., sub atmospheric to atmospheric. Other examples are the plasmas generated in tokamaks for fusion purposes and the recently exploited plasmas for etching and deposition devices such as the Electron Cyclotron Resonance plasmas. For the plasmas mentioned, the electron density is typical in the range of 1018 to 1023 m−3, and the electron velocity distribution is close to a Maxwellian velocity distribution.

Active actinometry on a cold hydrogen afterglow

Summary form only given. A new method of actinometry has developed to characterize the cold afterglow of an expanding thermal plasma source in hydrogen. A small electrode is placed in the afterglow to generate a local low-frequency (100-500 kHz) plasma. In this plasma fast electrons are created that can excite particles from the ground state to visible light emitting levels. The atomic Balmer /spl alpha/ line and the molecular Fulcher band are used to determine the atomic and molecular abundances of the plasma. The power input from the low frequency discharge is kept low enough to assure that the plasma composition and the gas temperature are not significantly influenced. Active actinometry thus offers a method to sample the composition and the ground state molecular populations of the flowing afterglow plasma. The method has been successfully applied under plasma conditions with a low electron temperature (< 0.2 eV) and a low electron density (< 10/sup 17/ m/sup -3/).