Electron thermalization in rare gases and their mixtures

Abstract

A study of the parallel energy distribution of lost electrons from the central plasma of an electron cyclotron resonance ion source Rev.The time evolution and temperature dependence of electron energy distribution functions ͑EDFs͒ are studied in pure rare gases ͑He, Ne, Ar, Kr, Xe͒ as well as in their mixtures by using solutions of the Boltzmann equation. A clear difference between the gases having the Ramsauer-Townsend ͑RT͒ minimum in the momentum-transfer cross section, ͑RT gases: Ar, Kr, and Xe͒, and those without the RT minimum ͑non-RT gases: He and Ne͒ is pointed out. The influence of the position and the depth of the RT minimum on the EDF and time evolution is studied for three different initial electron energies. A formula proposed for describing thermalization time in a mixture is tested on ͑i͒ a non-RT-non-RT gas mixture, ͑ii͒ a RT-non-RT mixture and ͑iii͒ a RT-RT gas mixture. The linear combination of the reciprocal thermalization times in gas mixture with the component concentrations as weighting factors is found to be valid for gases with a similar energy dependence of the momentum-transfer cross section, m , and also for all rare-gas binary mixtures if the initial electron energy is sufficiently below the RT minimum. Conspicuous deviations from the linear relationship are observed in mixtures of gases whose energy dependence of m ͑or the stopping cross section͒ are different, and theoretical rationales for these findings are provided.

Modeling the thermalization of electrons in conditions relevant to atmospheric pressure He-O2 nanosecond pulsed discharges

“…The thermalization times for the cooling phase matches other work on helium, of around 80 ns [12]. No dependence on the initial EEDF was observed for the thermalization times in the cooling phase.…”

“…The definition of the thermalization time used in this work is the time taken to reach within 10% of the steady state value of the average electron energy, when being heated by an instantaneously applied electric field, or when cooling after a field is instantaneously removed. This definition is used in order to be consistent with earlier work on the thermalization of electron swarms in Helium [12,14].…”

“…Modeling of the electron thermalization process by means of the direct solution of the time-dependent electron Boltzmann equation, using the now well known twoterm approximation, was later demonstrated to be both sufficiently general and computationally inexpensive [11]. Solutions found using helium electron impact cross sections were first reported by Bronic and Kimura [12]. Modeling was performed of the evolution of electron swarms, from various Gaussian initial electron energy distribution functions (EEDF), cooling where no electric field was present.…”

Average Numbers of Scintillation Photons and Electrons Produced by an Alpha Particle in High-Density Xenon Gas

“…In contrast, our W ex -value is largely different from that of Saito et al 7) We expect that the ratio of the scintillation yield originating from the excitation luminescence to total scintillation yield, measured by Saito et al, 7) is excessively low because of the long STC (10 ms) of the main amplifier used in their work. In Miyajima et al's work, 4) the scintillation signals were shaped with a STC of 2 ms, which is shorter than the average thermalization time of e hot (3 ms 35) at 1 atm) in process (7). Most recombinations begin after the average thermalization time.…”

Electrons in rare-gas solids probed by EPR technique

“…Indeed, according to Ref. [13], a thermalization time in gaseous Ne is given by t th E(pt th 10 À6 ln(T w /T sub )/ ((1.1-1.0368)p) where pt th E1000 Torr Á ms. Using this result we estimated the thermalization time in our experimental conditions: t th E240 s. The corresponding quantity for the electrons of several eV is, in turn, several tens of seconds.…”