The Conversion of Metastable Helium from the Singlet to the Triplet State by Electron Collision

Marriott, R. A.

doi:10.1088/0370-1298/70/4/306

Cited by 25 publications

(6 citation statements)

References 4 publications

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“…Helium has two metastable species: the He-I 2 1 S 1 singlet metastables and the He-I 2 3 S 1 triplet metastables. In the plasma the population of triplet metastables prevails over that of the singlet metastables because of an efficient conversion channel of superelastic collisions of the singlet metastables with thermal electrons [72,73]:…”

Section: Effect Of the Number Of Consecutive Driving Harmonicsmentioning

confidence: 99%

Helium metastable species generation in atmospheric pressure RF plasma jets driven by tailored voltage waveforms in mixtures of He and N₂

Korolov

Leimkühler

Böke

et al. 2020

J. Phys. D: Appl. Phys.

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Spatially resolved tunable diode-laser absorption measurements of the absolute densities of He-I (23S1) metastables in a micro atmospheric pressure plasma jet operated in He/N2 and driven by ‘peaks’- and ‘valleys’-type tailored voltage waveforms are presented. The measurements are performed at different nitrogen admixture concentrations and peak-to-peak voltages with waveforms that consist of up to four consecutive harmonics of the fundamental frequency of 13.56 MHz. Comparisons of the measured metastable densities with those obtained from particle-in-cell/Monte Carlo collision simulations show a good quantitative agreement. The density of helium metastables is found to be significantly enhanced by increasing the number of consecutive driving harmonics. Their generation can be further optimized by tuning the peak-to-peak voltage amplitude and the concentration of the reactive gas admixture. These findings are understood based on detailed fundamental insights into the spatio-temporal electron dynamics gained from the simulations, which show that voltage waveform tailoring allows to control the electron energy distribution function to optimize the metastable generation. A high degree of correlation between the metastable creation rate and the electron impact excitation rate from the helium ground state into the He-I ((3s)3S1) level is observed for some conditions which may facilitate an estimation of the metastable densities based on phase resolved optical emission spectroscopy measurements of the 706.5 nm He-I line originating from the above level and metastable density values at proper reference conditions.

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Section: Effect Of the Number Of Consecutive Driving Harmonicsmentioning

confidence: 99%

Helium metastable species generation in atmospheric pressure RF plasma jets driven by tailored voltage waveforms in mixtures of He and N₂

Korolov

Leimkühler

Böke

et al. 2020

J. Phys. D: Appl. Phys.

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“…We carried out calculations for the zero-order partial wave cross sections at thermal energies and present the results in table 8. Comparison is made with similar calculations by Marriot [13]. It should be mentioned that in order to compare our results we evaluated the cross section with the data reported by Marriot [13] and found out that the cross section at 0.026 eV should be 158.29 a 2 0 instead of 180 a 2 0 reported in the paper.…”

Section: Resultsmentioning

confidence: 57%

“…Comparison is made with similar calculations by Marriot [13]. It should be mentioned that in order to compare our results we evaluated the cross section with the data reported by Marriot [13] and found out that the cross section at 0.026 eV should be 158.29 a 2 0 instead of 180 a 2 0 reported in the paper. The present results agree very well with those obtained by Marriot.…”

Section: Resultsmentioning

confidence: 57%

“…In this paper, as a test case, we have carried out calculations of the contributions to the cross section for both elastic and inelastic scattering of electrons from hydrogen, and helium atoms, and also helium ions for few partial waves retaining coupling between two, three and a few more channels. The reliability of the present extended MCHF method is assessed by comparison of the present results with previous calculations [10][11][12] for hydrogen, [13] for helium atom, and [14][15][16] for helium ions including same number of open channels for both elastic and inelastic scattering of electrons.…”

Section: Introductionmentioning

confidence: 92%

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Extension of the single-channel MCHF method to include multichannels

Saha¹,

Murray

2005

J. Phys. B: At. Mol. Opt. Phys.

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The multiconfiguration Hartree–Fock (MCHF) method for single open channel has been extended to include multi-open channels. The coupled integro-differential equations satisfied by the radial wavefunctions of the multi-open channels associated with the scattering of electrons by atoms and ions at low energies are solved completely numerically self-consistently in the MCHF approximation to obtain the required linearly independent solutions. The asymptotic scattering parameters obtained from these solutions are used to calculate cross sections. The electron correlation and polarization effects which are very important for scattering of electrons at low energies can be obtained completely ab initio through the configuration interaction procedure. The extended method is now capable of performing calculations for both elastic and inelastic scattering processes. As a test case, we have calculated contributions to both elastic and inelastic cross sections for scattering of electrons from hydrogen and helium atoms as well as ionized helium at a few low energies for few partial waves including a few open channels. Our results are compared with similar data obtained by other existing approximate methods and are found to be in excellent agreement confirming a successful extension.

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“…In fact, the singlet state can be converted to the triplet through electron impact collisions, i.e. He(2 1 S) + e → He(2 3 S) + e + 0.78 eV [72,73]. This collision is not considered in the simulations.…”

Section: Resultsmentioning

confidence: 99%

Micro atmospheric pressure plasma jets excited in He/O₂ by voltage waveform tailoring: a study based on a numerical hybrid model and experiments

Liu

Korolov

Trieschmann

et al. 2021

Plasma Sources Sci. Technol.

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A hybrid simulation code is developed to treat electrons fully kinetically by the particle-in-cell/Monte Carlo collision (PIC/MCC) algorithm, while ions and neutral species are handled by a fluid model, including a time slicing technique to reduce the computational expenses caused by the responses of various species on different time scales. The code is used to investigate a capacitively coupled COST reference micro atmospheric pressure helium plasma jet with 0.1% oxygen admixture excited by a valley-type tailored voltage waveform with a fixed peak-to-peak voltage of 400 V, and a fundamental frequency of 13.56 MHz. The computational results are compared to experiments based on several sophisticated diagnostics, showing good agreement in the electron impact helium excitation rate, the helium metastable density, and the atomic oxygen density. The spatio-temporal electron heating dynamics, are found to be asymmetrical due to the specific shape of the driving voltage waveform. Tailoring the voltage waveform is shown to enable to control the electron energy probability function (EEPF) in distinct spatio-temporal regions of interest. As a consequence, the generation of reactive neutral species can be enhanced by increasing the number of consecutive harmonics. Based on a simplified two dimensional neutral transport model in the hybrid code, it is demonstrated that the transport between the electrodes, as well as the gas flow have different effects on various neutral species distributions due to the relevant chemical reaction rates for the generation and destruction of species.

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The Conversion of Metastable Helium from the Singlet to the Triplet State by Electron Collision

Cited by 25 publications

References 4 publications

Helium metastable species generation in atmospheric pressure RF plasma jets driven by tailored voltage waveforms in mixtures of He and N₂

Helium metastable species generation in atmospheric pressure RF plasma jets driven by tailored voltage waveforms in mixtures of He and N₂

Extension of the single-channel MCHF method to include multichannels

Micro atmospheric pressure plasma jets excited in He/O₂ by voltage waveform tailoring: a study based on a numerical hybrid model and experiments

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The Conversion of Metastable Helium from the Singlet to the Triplet State by Electron Collision

Cited by 25 publications

References 4 publications

Helium metastable species generation in atmospheric pressure RF plasma jets driven by tailored voltage waveforms in mixtures of He and N2

Helium metastable species generation in atmospheric pressure RF plasma jets driven by tailored voltage waveforms in mixtures of He and N2

Extension of the single-channel MCHF method to include multichannels

Micro atmospheric pressure plasma jets excited in He/O2 by voltage waveform tailoring: a study based on a numerical hybrid model and experiments

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Helium metastable species generation in atmospheric pressure RF plasma jets driven by tailored voltage waveforms in mixtures of He and N₂

Helium metastable species generation in atmospheric pressure RF plasma jets driven by tailored voltage waveforms in mixtures of He and N₂

Micro atmospheric pressure plasma jets excited in He/O₂ by voltage waveform tailoring: a study based on a numerical hybrid model and experiments