Influence of molecular processes on the hydrogen atomic system in an expanding argon–hydrogen plasma (original) (raw)
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Journal of Applied Physics, 1994
Optical absorption spectroscopy has been applied to measure the absolute population densities of the first excited levels of atomic hydrogen H*(n = 2) and argon Ar"(4s) in an expanding cascaded arc plasma in hydrogen-argon mixture. It is demonstrated that the method allows us to determine both H*(n =2) and Ar"(4sj absolute density radial profiles for H, admixtures in Ar ranging from 0.7% to 10% with good accuracy. The measured H*(n =2) densities are in the 1014-1016 mm3 range, -and Ar*(4s) densities are in the range of 1015-1018 rnw3. It has been shown, that the density of hydrogen excited atoms H*(n =2) serves as an indicator of the presence of argon ions and hydrogen molecules in the expanding plasma. A kinetic model is used to understand evolution of H*(n=2) density in the expansion, and to estimate the total atomic hydrogen population density and hydrogen dissociation degree in sub-and supersonic regions of the plasma.
The argon-hydrogen expanding plasma: model and experiments
Plasma Sources Science and Technology, 1995
An argon expanding cascaded arc plasma, with small amounts (0-lOvol.%) of hydrogen added to the flow, is investigated by means of Thomson-Rayleigh scattering and optical emission spectroscopy. The results, especially the electron density behaviour as a function of the distance from the onset of the expansion, are interpreted by comparison with results of a quasi one-dimensional model. The associative charge exchange reaction between Ar* ions and H, molecules plays a dominant role in the model. Assuming that H, molecules from the wall enter the plasma in the shock region, the large ionization loss can be explained. Good agreement between model and experiment is found for the electron and neutral density and the electron temperature behaviour. This makes plausible the existence of a recirculation flow inside the vacuum vessel, which transports wall-associated hydrogen molecules towards the plasma
Thermal plasma source of hydrogen atoms and ions
Le Journal De Physique Colloques, 1990
A cascade arc is used as a source for a hydrogen/argon particle beam. The plasma is produced at thermal plasma conditions in the pressure range of 0.1 to 1 bar. It is expanded with a high velocity into a vacuum chamber. Measurements with a Langmuir double probe and with a mass spectrometer are performed. The resulting parameters of the plasma
Contributions to Plasma Physics, 1995
This work is devoted to the determination of the vibrational population of hydrogen molecules in the ground and excited electronic states from the analysis of visible spectra of the H2 molecules excited by an RF discharge in an expanding thermal arc plasma. Comparison of the experimental results on relative electron-impact excitation cross sections for the transition H,(X',Z:, uo = 0) -+ H,(d3f7,, 0') with other experiments, and with calculations based on the Franck-Condon principle, shows good agreement. This means, that for plasma under investigation: 1) in the ground electronic state H,(X'X:), only the lowest vibrational level with uo = 0 is significantly populated, and 2) direct electron exictation of H,(d317,, u') state from the ground state H2(X1,Z;, uo = 0) dominates.
Experimental characterization of a hydrogen/argon cascaded arc plasma source
Review of Scientific Instruments, 1994
DOI to the publisher's website. • The final author version and the galley proof are versions of the publication after peer review. • The final published version features the final layout of the paper including the volume, issue and page numbers. Link to publication General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights. • Users may download and print one copy of any publication from the public portal for the purpose of private study or research. • You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal. If the publication is distributed under the terms of Article 25fa of the Dutch Copyright Act, indicated by the "Taverne" license above, please follow below link for the End User Agreement:
Composition of high current arc plasma in Ar-H2 mixture at moderate pressures
2017
Composition of the high current low pressure arc discharge in a large chamber (0.5 m in diameter) in Ar-H 2 mixtures was studied by optical emission spectroscopy methods and was modeled utilizing thermodynamic and fluid models. The dissociation degree of molecular hydrogen was estimated using I Hα /I H2 intensity ratio of H α line and Q1(0-0) line of the H 2 Fulcher's α-system. In addition, atomic hydrogen density was estimated using optical actinometry method from intensity ratio I Hα /I ArI of the H α and ArI 750 nm lines. Moreover, the H 2 dissociation degree across the discharge tube was modeled using LTE calculation based on minimization of isobaric-isothermal potential of the closed thermodynamic system with the help of commercial software TERRA. Alternatively, hydrogen thermal dissociation was calculated in an axially-symmetrical one fluid, one temperature approximation using commercial software COMSOL FEM; the thermal dissociation model relies on solving an advection-diffusion-reaction (ADR) equation for atomic hydrogen that is produced by Ar or H 2 impact and is lost in three-body recombination. The results of the comparison of hydrogen dissociation degree across the arc column demonstrate reasonably good agreement both with experimental findings and between two modeling approaches.
An arc discharge hydrogen atom source
Review of Scientific Instruments, 1993
A magnetically confined thermal electric arc gas heater of easy construction, handling, and maintenance has been designed, built, and tested as a suitable source of heat for dissociating hydrogen molecules. The plasma species in the gas discharge region are assumed to satisfy local thermodynamic equilibrium conditions. The average beam kinetic energy is determined to be 1 S eV, leading to an arc temperature of approximately 8700 K, the dissociation rate is 0.5 atoms per molecule and the total atom beam intensity in the forward direction is 1018 atoms/sr s. This novel atom source has been successfully ignited and operated with pure hydrogen during several hours of continuous performance, maintaining its characteristics and overcoming some of the difficulties previously found by researchers using other arc sources. The hyperthermal hydrogen atom beam obtained from this source is identified by MOO, chemical detectors, and analyzed and characterized by three different calorimetric sensors, Ni, Ta, and Teflon. The experimental results obtained with this dissociator agree with those published in the literature.
DOI to the publisher's website. • The final author version and the galley proof are versions of the publication after peer review. • The final published version features the final layout of the paper including the volume, issue and page numbers. Link to publication General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights. • Users may download and print one copy of any publication from the public portal for the purpose of private study or research. • You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal. If the publication is distributed under the terms of Article 25fa of the Dutch Copyright Act, indicated by the "Taverne" license above, please follow below link for the End User Agreement:
Plasma Expansion Dynamics in Hydrogen Gas
Atoms
Micro-plasma is generated in ultra-high-pure hydrogen gas, which fills the inside of a cell at a pressure of (1.08 ± 0.033) × 105 Pa by using a Q-switched neodymium-doped yttrium-aluminum-garnet (Nd:YAG) laser device operated at a fundamental wavelength of 1064 nm and a pulse duration of 14 ns. The micro-plasma emission spectra of the hydrogen Balmer alpha line, Hα, are recorded with a Czerny–Turner type spectrometer and an intensified charge-coupled device. The spectra are calibrated for wavelength and corrected for detector sensitivity. During the first few tens of nanoseconds after the initiation of optical breakdown, the significant Stark-broadened and Stark-shifted Hα lines mark the well-above hypersonic outward expansion. The vertical diameters of the spectrally resolved plasma images are measured for the determination of expansion speeds, which were found to decrease from 100 to 10 km/s for time delays of 10 to 35 ns. For time delays of 0.5 µs to 1 µs, the expansion speed of ...