Determination of transport and reaction swarm coefficients from the analysis of complex transient pulses from the pulsed Townsend experiment

Bekstein, A.; Urquijo, J. de; Ducasse, Olivier; Rodríguez-Luna, J C; Juarez, Alfredo

doi:10.1088/1742-6596/370/1/012006

Cited by 5 publications

(4 citation statements)

References 7 publications

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“…If we substitute Fick's law expression (4) into the Brambring equation ( 13) (retaining 12 While the functional form of the current in the external circuit and its relation to the transport coefficients can be a source of uncertainty, these are distinct from the uncertainties that can typically be obtained from approximate analysis of the current in the external circuit. Indeed, some analyses have used quite simplified approaches to extract the various transport properties from the current in the external circuit [58,65,79,[83][84][85], which may lead to further issues. For example, extracting W, through dividing L by the measured electron transit time, T e , where the transit time is defined as the difference in times between the measured current's rise and fall to the respective half values.…”

Section: Relating Existing Pt Transport Properties To the Standard Tr...mentioning

confidence: 99%

“…This is the same expression as that from the original Brambring paper (see equation (12) of reference [1]) and used by the experimental groups [58,79,83,84], expressed using the PT transport properties. It is important to note that the W appearing in the first factor on the rhs of equation ( 26) is the flux drift velocity W, not the bulk drift velocity W B or the PT transport property W.…”

Section: Relating Existing Pt Transport Properties To the Standard Tr...mentioning

confidence: 99%

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Foundations and interpretations of the pulsed-Townsend experiment

Casey

Stokes

Cocks

et al. 2021

Plasma Sources Sci. Technol.

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The pulsed-Townsend (PT) experiment is a well known swarm technique used to measure transport properties from a current in an external circuit, the analysis of which is based on the governing equation of continuity. In this paper, the Brambring representation (1964 Z. Phys. 179 532) of the equation of continuity often used to analyse the PT experiment, is shown to be fundamentally flawed when non-conservative processes are operative. The Brambring representation of the continuity equation is not derivable from Boltzmann's equation and consequently transport properties defined within the framework are not clearly representable in terms of the phase-space distribution function. We present a re-analysis of the PT experiment in terms of the standard diffusion equation which has firm kinetic theory foundations, furnishing an expression for the current measured by the PT experiment in terms of the universal bulk transport coefficients (net ionisation rate, bulk drift velocity and bulk longitudinal diffusion coefficient). Furthermore, a relationship between the transport properties previously extracted from the PT experiment using the Brambring representation, and the universal bulk transport coefficients is presented. The validity of the relationship is tested for two gases Ar and SF 6 , highlighting also estimates of the differences.

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Section: Relating Existing Pt Transport Properties To the Standard Tr...mentioning

confidence: 99%

Section: Relating Existing Pt Transport Properties To the Standard Tr...mentioning

confidence: 99%

Foundations and interpretations of the pulsed-Townsend experiment

Casey

Stokes

Cocks

et al. 2021

Plasma Sources Sci. Technol.

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“…a fitting procedure. • Pulsed Townsend (PT) systems [36][37][38][39], where the experimental realization is similar to that of a TOF system, but in this case the time-dependent displacement current generated by all the moving electrons within the whole electrode gap is measured at fixed electrode separation, i.e. the measured current I(t) is:…”

Section: Introductionmentioning

confidence: 99%

Electron transport parameters in CO₂: a comparison of two experimental systems and measured data

Vass

Egüz

Chachereau

et al. 2020

J. Phys. D: Appl. Phys.

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Two experimental apparatuses used to obtain electron transport coefficients in gases are compared based on measurements in CO2 over a wide range of E/N-values. The operation principles of the two experimental systems as well as their data acquisition methods are different. One operates under the time of flight (TOF) principle, where the transport coefficients are obtained by fitting the theoretical form of the electron density of a swarm in an unbounded region, n(x, t), to the measured current at different values of the drift length, I(L, t). The other experimental apparatus operates in the Pulsed Townsend (PT) mode, where the electron transport coefficients are obtained by fitting the spatial integral of n(x, t) over the drift region to the measured, time-dependent current signal, I(t). In both apparatuses, the measured E/N range was extended as much as possible to allow a large overlap for the comparison of the results. The bulk drift velocity, W, obtained by the two systems agrees well (within a few %) over a wide range of E/N values (100 Td ≤ E/N ≤ 1000 Td). The agreement between the data sets for the longitudinal component of the bulk diffusion tensor, D L , is less satisfactory, the TOF data show systematically higher values (by 10–50% depending on E/N) than the PT measurements. Significant differences are also found below 100 Td in case of the effective ionisation frequency, ν e f f , and the (steady state) Townsend ionisation coefficient, α e f f , where the TOF apparatus is unable to give accurate results. Our comparison justifies the correctness of the measured data over the range of agreement and also indicates the interval in E/N where the data obtained by each of the experimental systems can be taken to be reliable. The limits of the operating regimes of the two setups, stemming from the hardware and from the physical limits, are discussed.

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“…In the current programme on swarm transport in gaseous systems, we utilise a pulsed-Townsend (PT) experiment swarm technique to measure drift velocities, diffusion coefficients and various rate coefficients [90][91][92][93]. The primary aim is to build and then assess the completeness and accuracy of various electron-biomolecule cross-section sets.…”

Section: Towards Self-consistent Electron-biomolecule Cross-section Setsmentioning

confidence: 99%

Electron transport in biomolecular gaseous and liquid systems: theory, experiment and self-consistent cross-sections

White

Cocks

Boyle

et al. 2018

Plasma Sources Sci. Technol.

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Accurate modelling of electron transport in plasmas, plasma-liquid and plasma-tissue interactions requires (i) the existence of accurate and complete sets of cross-sections, and (ii) an accurate treatment of electron transport in these gaseous and soft-condensed phases. In this study we present progress towards the provision of self-consistent electron-biomolecule cross-section sets representative of tissue, including water and THF, by comparison of calculated transport coefficients with those measured using a pulsed-Townsend swarm experiment. Water-argon mixtures are used to assess the self-consistency of the electron-water vapour cross-section set proposed in de Urquijo et al (2014 J. Chem. Phys. 141 014308). Modelling of electron transport in liquids and soft-condensed matter is considered through appropriate generalisations of Boltzmann's equation to account for spatialtemporal correlations and screening of the electron potential. The ab initio formalism is applied to electron transport in atomic liquids and compared with available experimental swarm data for these noble liquids. Issues on the applicability of the ab initio formalism for krypton are discussed and addressed through consideration of the background energy of the electron in liquid krypton. The presence of self-trapping (into bubble/cluster states/solvation) in some liquids requires a reformulation of the governing Boltzmann equation to account for the combined localised-delocalised nature of the resulting electron transport. A generalised Boltzmann equation is presented which is highlighted to produce dispersive transport observed in some liquid systems.

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Determination of transport and reaction swarm coefficients from the analysis of complex transient pulses from the pulsed Townsend experiment

Cited by 5 publications

References 7 publications

Foundations and interpretations of the pulsed-Townsend experiment

Foundations and interpretations of the pulsed-Townsend experiment

Electron transport parameters in CO₂: a comparison of two experimental systems and measured data

Electron transport in biomolecular gaseous and liquid systems: theory, experiment and self-consistent cross-sections

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Determination of transport and reaction swarm coefficients from the analysis of complex transient pulses from the pulsed Townsend experiment

Cited by 5 publications

References 7 publications

Foundations and interpretations of the pulsed-Townsend experiment

Foundations and interpretations of the pulsed-Townsend experiment

Electron transport parameters in CO2: a comparison of two experimental systems and measured data

Electron transport in biomolecular gaseous and liquid systems: theory, experiment and self-consistent cross-sections

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Product

Resources

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Electron transport parameters in CO₂: a comparison of two experimental systems and measured data