Table of contents

We measured the parameters of the electron beam produced in a hollow-cathode transient discharge with an open-ended cathode but using a proper pre-ionization. The mean energy of the energetic electron spectrum is 0.6 - 0.76 of the breakdown voltage (18 - 23 kV) and the energetic beam duration is less than 10 ns. The electron beam current is approximately 0.1 of the maximum discharge current (600 - 700 A). The integrated diameter of the x-ray emission spot at beam interaction with Al foils for several tens of thousands of shots was estimated to . The beam parameters are similar to those obtained in a pseudo-spark configuration; however, the FWHM of the beam energy distribution seems smaller for the same breakdown voltages.

Films of poly(ethylene terephthalate) (PET) have been subjected to a low frequency (70 kHz) helium discharge, with a non-symmetrical configuration of electrodes, in order to study the treatment conditions for which the `ageing' effect is slowed down. Treatments were made for different gas flow rates (40, 70 and 100 sccm) and different exposure times (1, 10 and 30 s). Emission spectroscopy and mass spectrometry were used to characterize the discharge plasma. The resulting modifications to the polymer surface were analysed via contact angle measurements and the XPS technique. It is pointed out that treatments on an He discharge induce both a functionalization and a cross linking of the uppermost layers of the polymer film. The residual oxygen, which partially originates within the polymer, induces surface oxidation. The cross-linked content critically depends on the residence time and concentration of implicated species. It seems that a change in the surface work function takes place as a result of a surface restructuring in the earliest stages of the reactions. This could involve an increase in the rate constant for the surface de-excitation of the helium metastables in the presence of the polymer. A contribution to the understanding of the competitive processes of cross linking and functionalization, as a function of the helium flow rate, is accomplished.

Spectroscopic measurements have been made on a transferred arc burning in pure argon at atmospheric pressure seeded with iron vapours arising from the anode erosion. The transferred arc was operated with a current intensity of 90 A, an arc length of 18 mm, and a gas flow rate of . Temperature and relative iron concentration profiles determined experimentally were compared to theoretical values obtained from a two-dimensional model based on mass, momentum, and energy conservation equations and taking into account anode erosion. This comparison partially validated the model and showed that the presence of iron vapours, with a relative concentration of about 0.1%, led to a temperature decrease of about 1000 K. Differences between experimental and calculated temperature fields may be due to departures from equilibrium and to uncertainties about the iron vapour concentration and the radiative losses.

We present a self-contained theoretical description of azimuthally symmetric surface wave (SW) sustained discharges in argon at low pressure in a coaxial setup with a central cylinder. The model is based on a complete set of equations, including the homogeneous Boltzmann equation, Maxwell's equations, and the continuity and the momentum transfer equations for electrons and ions. The radially inhomogeneous plasma is described as a lossy dielectric medium with a complex permittivity. The above formulation provides a complete, self-contained description of the spatial distributions of the SW sustaining field and the plasma density, of the wave dispersion relation, and of the power transfer from the wave to the plasma. The theoretical results are compared to experimental data from absolute electric and magnetic field measurements and Langmuir probe and spectroscopic diagnostics, in an accompanying experimental paper.

The effects of nozzle design on the plasma characteristics of supersonic flow conditions are investigated using a D.C. plasma jet under low-pressure plasma spraying conditions. Comparison is made between a 5 mm I.D. standard nozzle and a 13 mm E.D. (exit diameter) Mach 3 Laval nozzle. Emission spectroscopy is used to study the temperature and electron density distributions in the plasma jets produced by the different nozzle configurations. The effects of the observed modifications of the temperature and electron density fields on the properties of the plasma sprayed deposits are studied using Rene 80 powders which are sprayed using both types of nozzle under similar operating conditions. The results show that the M3 Laval nozzle provides a better spraying efficiency and spraying density than a standard anode nozzle under similar conditions.

This paper deals with Langmuir probe measurements in a planar magnetron sputtering system in which the plasma confinement near a target can be improved by means of an assembly of permanent magnets placed above the target. The electron density, electron temperature, plasma and floating potentials and electron distribution function are measured in various positions between the target and a substrate under various conditions in the discharge. Our experiments proved that the additional magnetic confinement leads to approximately two times higher electron density and strong enhancement (by about an order of magnitude) of the electron temperature in almost all positions of the deposition system investigated.

In distributed electron cyclotron resonance plasma sources, the acceleration of electrons is produced by microwave electric fields, applied and distributed close to a multipolar magnetic field structure, providing along the magnets the condition for electron cyclotron resonance. The ensuing fast electrons are trapped in the multipolar magnetic field and drift along the magnets, hence the interest of a closed magnetic configuration to avoid losses at the boundaries of the confinement structure. The performances of two cylindrical reactors fed with microwave power through eight linear applicators and surrounded by either eight magnet bars or eight racetracks (magnetron-like magnetic structures) are measured and compared. In both cases plasma density saturates at the critical density, but in the case of the closed magnetic configuration the saturation is reached for a microwave input power a factor of ten lower than with the open magnetic configuration. This result confirms that the confinement effect of the multipolar magnetic field mainly applies to the fast electrons which generate the plasma.

We have modelled dust dynamics in capacitively coupled, self-cleaning reactors with grooved electrodes. Our model includes plasma dynamics, gas drag, complex geometry, and dust motion. Our calculations show that dust is trapped in grooves as observed in experiments. We also have investigated the effect of groove shape on dust trapping and find that circular-cross-section grooves are more effective traps than the square-cross-section grooves considered previously. Finally, we include the results of calculations of particle trapping in the complex geometry of a realistic device.

A microwave source of nitrogen atoms is described. Atom production in the discharge bulk ( mixtures) and atom losses in the flowing afterglow are analysed. The rotational temperature is measured by emission spectroscopy along the discharge (0 - 0 band of the second positive system) and the afterglow (first positive or first negative system depending on the afterglow type). Depending on the experimental conditions ( concentration), two types of flowing afterglow can exist. At high percentage, a `pink' afterglow occurs upstream of the classical `Lewis - Rayleigh' afterglow. An NO titration method provides the atom concentration downstream of the discharge. Then, the N atom transport is explained from a simple model accounting for the energy characteristics of the plasma (obtained by the microwave interferometry methods) and the kinetics.

Using composite anodes in a 3 kJ plasma focus device operated in deuterium, peak axial sheath velocities up to are achieved. The temporal characteristics of the soft x-ray emission are investigated by means of filtered PIN diodes. Correlations with hard-x-ray and neutron emission as well as with electrical parameters of the discharge are performed. Two distinct operation regimes are identified regardless of the shape of the anode. Various scaling laws of the soft x-ray production are investigated. We propose a new scaling law for the soft x-ray yield.

A scintillation technique was applied to directly monitor high-energy secondary electrons during the process of plasma immersion ion implantation (PIII). The spectral peak of the scintillation appeared at the wavelength of nm, and the temporal behaviour of the secondary electrons was measured with a response time as short as several microseconds. A maximum absolute secondary-electron flux for a target peak voltage of 25 kV reached at a measuring point, which showed good agreement with a calculated value. The kinetic energy of the secondary electrons was also measured by penetration depth into an aluminium layer coated on the scintillator surface, revealing acceleration of the secondary electrons up to an energy corresponding to the sheath voltage.

A theory describing the temporal evolution of the ion energy distribution function at a planar electrode for an expanding plasma sheath with charge-exchange collisions is presented. The theory spans the entire range of ion collisionality, from collisionless to fully collisional. Good agreement is found with fluid theory in the collisionless and collisionally dominated regimes.

The axial profile of the axial component of the wave magnetic field has been measured for m = 0 helicon waves. A dip in is observed at cm from the antenna, and is explained as a result of the beat between the fundamental and the second-order radial modes of the m = 0 helicon wave. The measured imaginary part of , which consists only of the wave field, is compared with that of the calculated wave field using the theory of the uniform plasma case. It is found that % of the amplitude arises from the second-order mode and the axial damping length of the fundamental mode .

We present an experimental study of azimuthally symmetric surface wave (SW) sustained discharges in argon at reduced pressure in an annular tube with a conducting inner. The presence of this conducting cylinder makes it possible to calibrate the field measuring antennas and perform absolute measurements of the SW field. The experimental data from these absolute measurements, and from Langmuir probe and spectroscopic diagnostics, are compared with the theoretical predictions of an accompanying paper.

In previous volumes of Plasma Sources Science and Technology articles have been ordered from low pressure to high pressure for ease of use.

However, the electronic version of this journal now has a new feature of Accelerated Publication whereby an article is published electronically as soon as it is ready for publication. Articles in the printed journal are now ordered in this manner and the contents on the back cover lists the articles as they appear in the issue.

For your convenience we will continue to list the contents in the low pressure to high pressure order. This is given below.

PAPERS

A comparison of internal plasma parameters in a conventional planar magnetron and a magnetron with additional plasma confinement (46-52) P Spatenka, I Leipner, J Vlcek and J Musil

Development of a new technique for high-energy secondary-electron measurements in plasma immersion ion implantation (86-90) K Nakamura, S Mändl, J Brutscher, R Günzel and W Möller

Influence of the multipolar magnetic field configuration on the density of distributed electron cyclotron resonance plasmas (53-60) T Lagarde, J Pelletier and Y Arnal

A higher-order radial mode of helicon waves (96-100) Y Sakawa, N Koshikawa and T Shoji

The characterization of pre-ionization-controlled electron beams produced in open-ended hollow-cathode transient discharges(1-7) N B Mandache, A M Pointu, E Dewald, M Nistor, M Ganciu, G Musa and I I Popescu

Evolution of the ion distribution function for an expanding sheath with collisions (91-95) T E Sheridan

A self-contained modelling and experimental study of surface wave produced argon discharges in a coaxial setup with a central metallic cylinder: I. Modelling (29-38) X L Zhang, F M Dias and C M Ferreira

A self-contained modelling and experimental study of surface wave produced argon discharges in a coaxial setup with a central metallic cylinder: II. Experiment (101-110) X L Zhang, F M Dias and C M Ferreira

Simulation of dust particle dynamics for electrode design in plasma discharges (61-69) G Lapenta and J U Brackbill

Surface cross linking and functionalization of poly(ethylene terephthalate) in a helium discharge (8-19) M Gheorghiu, F Arefi, J Amouroux, G Placinta, G Popa and M Tatoulian

A microwave plasma source of neutral nitrogen atoms (70-77) C Boisse-Laporte, C Chave-Normand and J Marec

Soft x-ray emission from a small plasma focus operated in deuterium (78-85) A Serban and S Lee

A torch nozzle design to improve plasma spraying techniques (39-45) M Cao, F Gitzhofer, D V Gravelle, R Henne and M I Boulos

The influence of iron vapour on an argon transferred arc (20-28) J J Gonzalez, M Bouaziz, M Razafinimanana and A Gleizes