The time taken for an electron swarm to reach its equilibrium (or thermalise) with an instantaneously applied electric field (E/N) is very short, typically less than 10-9s for most medium and high-pressure plasmas (p=0.01-5bar). Thus, to undertake numerical modelling of the temporal evolution of plasmas driven by relatively slow time-varying voltage waveforms (>>10-9s), a steady-state Boltzmann code is usually sufficient to deduce the electron energy distribution function (EEDF) and the requisite electron swarm parameters as a function of E/N. Recently, however, plasmas driven by fast transient voltage pulses (e.g. risetimes >100V.ns-1, 1-10ns duration) are being rapidly developed, as reviewed in . It is not yet clear whether the EEDFs in these fast transient plasmas deviate significantly from “thermalised” due to the very rapidly varying E/N. To investigate this issue, we have calculated the time taken for electrons to become thermalised for a given E/N, over a range of fields applicable to most medium-high pressure plasma discharges, and for a variety of gases (Xe, Kr, Ar, Ne, He, N2). We have numerically solved the multi-term, spatially-homogenous Boltzmann equation, subject to a constant electric field, to follow the EEDF as it evolves from an initial room-temperature Maxwellian distribution toward thesteady-state. Transport quantities such as mean energy <> and drift velocity We were calculated at each time, and the <> was used to define thermalisation time th. Key results for Xenon are shown in fig.1. Our preliminary results for Xe and other gases suggest that th can be comparable with the voltage pulserisetimes for fast discharges , suggesting the EEDFs may not be fully thermalised.
|Number of pages||1|
|Publication status||Published - 24 Jun 2018|
|Event||The 20th Gaseous Electronics Meeting - Magnetic Island, Townsville, Australia|
Duration: 21 Jun 2018 → 24 Jun 2018
Conference number: XX
|Conference||The 20th Gaseous Electronics Meeting|
|Period||21/06/18 → 24/06/18|
- plasma physics
- Atomic processes
Boyle, G. J., Casey, M., White, R. D., & Carman, R. (2018). Thermalisation time of electron energy distribution functions in Xenon for electric fields in the range 1Td<E/N<1000Td. Session J. Abstract from The 20th Gaseous Electronics Meeting, Townsville, Australia.