Publications de Alan Howling | EPFL Graph Search

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Negative hydrogen or deuterium ions are the precursor particles used to generate a high power beam of neutrals in order to heat the tokamak plasma core of magnetic fusion devices, inject current, and to some extent control instabilities. In the case of ITE ...

Plasma conditions for microcrystalline silicon deposition generally require a high flux of atomic hydrogen, relative to SiH alpha=0 -> 3 radicals, on the growing film. The necessary dominant partial pressure of hydrogen in the plasma is conventionally obta ...

This paper describes a helicon-wave-sustained plasma generated by a novel birdcage antenna with cosine azimuthal current distribution. The resonant birdcage source maintains a stable intense plasma column from low (300 W) to high (10 kW) steady-state RF po ...

Not all agricultural practices are sustainable; however, non-thermal plasma treatment of seeds may be an eco-friendly alternative to improve macroscopic plant growth parameters. Despite the numerous successful results of plasma-seed treatments reported in ...

Negative ions are characterized in the helicon plasma source resonant antenna ion device (RAID) at the Swiss plasma center by means of cavity ring-down spectroscopy (CRDS) and Langmuir probe (LP)-assisted laser photodetachment. A high density and axially h ...

Neutral Beam Injectors (NBI) for post-DEMO-like reactors must achieve a neutralization efficiency (fraction neutrals/ions) above 70%. To reach this, NBIs based on negative ions are necessary and an innovative concept of this type of injector is based on ph ...

The time-resolved fluxes of negative polysilicon hydride ions from a power-modulated rf silane plasma have been measured by quadrupole mass spectrometry and modeled using a simple polymerization scheme. Experiments were performed with plasma parameters suitable for high-quality amorphous silicon deposition. Polysilicon hydride anions diffuse from the plasma with low energy (approximately 0.5 eV) during the afterglow after the electron density has decayed and the sheath fields have collapsed. The mass depend

The possibility of performing electron density and temperature measurements in a high power helicon plasma is a crucial issue in the framework of the AWAKE (Advanced WAKefield Experiment) project, which demonstrates acceleration of particles using GeV m(-1 ...

This paper presents solutions for the classical one-dimensional (1D radial and Cartesian) problem of Langmuir probes in a collisionless, isothermal plasma. The method is based on two-fluid equations derived from the first two moments of Vlasov's equation. ...

In small area capacitive reactors, the rf and dc components of the plasma potential can be assumed to be uniform over all the plasma bulk because of the low plasma resistivity. In large area reactors, however, the rf plasma potential can vary over a long range across the reactor due to rf current flow and the nonzero plasma impedance. A perturbation in rf plasma potential, due to electrode edge asymmetry or the boundary of a dielectric substrate, propagates along the resistive plasma between capacitive shea

In this article, a setup including a passive gas breakdown mitigation technique for satellite slip ring assemblies (SRAs) is introduced and tested. The setup features a central conducting ring, separated from two external conducting limiting discs (LDs) by ...

This topical review gathers the last updates concerning caesium-free negative ion sources presented during the 63rd Course of the International school of Quantum Electronics of the Ettore Majorana Foundation and European collaborative works related to thes ...

This paper presents an investigation into radio frequency (rf) breakdown for electrodes with holes or protrusions, approximating the situation in real reactors and providing a benchmark for fluid simulations. rf breakdown curves (voltage versus pressure) g ...

To determine self-consistently the time evolution of particle size and their number density in situ multi-angle polarization-sensitive laser light scattering was used. Cross-polarization intensities (incident and scattered light intensities with opposite polarization) measured at 135 degrees and ex situ transmission electronic microscopy analysis demonstrate the existence of nonspherical agglomerates during the early phase of agglomeration. Later in the particle time development both techniques reveal spher

Hydrogenated amorphous silicon has been prepared at a plasma excitation frequency in the very-high-frequency band at 70 MHz with the glow discharge technique at substrate temperatures between 280 and 50-degrees-C. The structural properties have been studied using hydrogen evolution, elastic recoil detection analysis, and infrared spectroscopy. The films were further characterized by dark and photoconductivity and by photothermal deflection spectroscopy. With respect to films prepared at the conventional fre

Micro-particle formation in low pressure silane (SiH4) plasmas has been of technical interest and concern for at least 40 years. Negative ion plasma chemistry is a candidate for the initial nucleation, which has been extensively studied both experimentally ...

In DEMO reactor to produce electricity, a total installed power up to 150 MW is considered. In the heating mix, neutral beam (NB) injectors of high neutral particle energy (0.8-1 MeV) with high wall-plug efficiency (η in the range of 50% to 60%) will be required. Present design considered a NB system delivering in total 50 MW. In the Siphore NB concept [1], one of the promising candidates to meet these challenging requirements, negative ions will be extracted from a long, thin ion source 3 m high and 15 cm

In situ Fourier transform infrared absorption spectroscopy has been used to study the composition of particles formed and suspended in radio-frequency discharges of silane-oxygen-argon gas mixtures. The silane gas constumption was observed by infrared absorption. The stoichiometry of the produced particles depends on the silane flow rate and was compared with commercial colloidal silica. A small proportion of silane gas produces nanometric stoichiometric particles whereas a large proportion produces larger

Helicon plasma sources operating with hydrogen or deuterium might be attractive for fusion applications due to their higher power efficiency compared to inductive radiofrequency plasma sources. In recent years, the resonant antenna ion device (RAID) has be ...

Following the analytical description of the collisionless high-voltage capacitive RF sheath in Lieberman (1988) and of the collisional high-voltage capacitive RF sheath in Lieberman (1989), electrical sheath parameters are calculated for a square-wave ie RF discharge current. The interest in the square-wave current lies in the analytical simplicity of the solutions, The spatial dependences of the time-averaged electrostatic potential electric field (E) over bar, net-charge carrier density

Alan Howling

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Negative hydrogen ion dynamics inside the plasma volume of a linear device: Estimates from particle-in-cell calculations

Hydrogen-dominated plasma, due to silane depletion, for microcrystalline silicon deposition

Helicon wave plasma generated by a resonant birdcage antenna: magnetic field measurements and analysis in the RAID linear device

RNA Sequencing of Arabidopsis thaliana Seedlings after Non-Thermal Plasma-Seed Treatment Reveals Upregulation in Plant Stress and Defense Pathways

Negative ion characterization in a helicon plasma source for fusion neutral beams by cavity ring-down spectroscopy and Langmuir probe laser photodetachment

A double-ended helicon source to symmetrize RAID plasma

Time-Resolved Measurements of Highly Polymerized Negative-Ions in Radio-Frequency Silane Plasma Deposition Experiments

Application of Thomson scattering to helicon plasma sources

Two-fluid solutions for Langmuir probes in collisionless and isothermal plasma, over all space and bias potential

Nonuniform radio-frequency plasma potential due to edge asymmetry in large-area radio-frequency reactors

Slip Ring Test Assembly With Increased Breakdown Voltage Limit for High-Voltage Bus Satellites

Latest experimental and theoretical advances in the production of negative ions in caesium-free plasmas

Radio frequency breakdown between structured parallel plate electrodes with a millimetric gap in low pressure gases

Particle agglomeration study in rf silane plasmas: In situ study by polarization-sensitive laser light scattering

Influences of a High-Excitation Frequency (70 Mhz) in the Glow-Discharge Technique on the Process Plasma and the Properties of Hydrogenated Amorphous-Silicon

Multiple dehydrogenation reactions of negative ions in low pressure silane plasma chemistry

A novel helicon plasma source for negative ion beams for fusion

Silicon oxide particle formation in RF plasmas investigated by infrared absorption spectroscopy and mass spectrometry

A 1.5D fluid-Monte Carlo model of a hydrogen helicon plasma

Power laws for the spatial dependence of electrical parameters in the high-voltage capacitive RF sheath