Longitudinal electron diffusion coefficients in gases: Noble gases

Abstract

Values of the ratio of the longitudinal diffusion coefficient to mobility DL/μ for electrons in He, Ar, Kr, and Xe are derived from current waveforms obtained during earlier measurements of electron mobility. The electric field to gas density ratios E/N cover the wide range of 10−3 to 20 Td, thereby bridging previous experiments at low E/N to recent experiments at high E/N. Here 1 Td=1×10−21 V m2. The corresponding DL/μ values range from 0.0066 eV for thermal electrons at 77 K to 10 eV. In addition to the well-known peak in DL/μ for Ar at E/N between 0.01 and 0.1 Td caused by the Ramsauer minimum in the momentum transfer cross section, we find previously unreported low-energy peaks in DL/μ vs E/N in Kr and Xe and previously unreported pronounced leveling-off in DL/μ at E/N≳8 Td in Ar, Kr, and Xe. Calculations of transport coefficients using numerical solutions of the Boltzmann equation and cross section sets in the literature give good agreement with experiment from E/N producing thermal electrons up to average energies ≊10 eV and E/N up to 100 Td, the upper limit of our calculations. The leveling off of DL/μ at high E/N is caused by inelastic collisions.

Numerical effects on energy distribution functions in particle-in-cell simulations with Monte Carlo collisions: choosing numerical parameters

“…We employed a conventional particle-in-cell simulation with Monte Carlo collisions, using one space dimension, Cartesian coordinates, and periodic boundary conditions. A set of cross sections for electron collisions with helium was used [11]. In all cases, the ratio of the electron collision frequency, ν c , to the plasma frequency was ∼ 0.02.…”

A Monte Carlo study of photoelectron extraction efficiency from CsI photocathodes into Xe–CH4 and Ne–CH4 mixtures

“…In Xe, the elastic momentum transfer cross-section is based on [34][35][36] below ~2 eV and [37,38] above ~2 eV, the integral and partial cross-sections for excitation are obtained from [38] and [39], respectively, and the total ionization cross-section is from [40].…”

“…The calculations for Xe are shown together with the available experimental data in figure 2. Figure 3 [36,53,56] and [62,64,65], respectively. Similar good agreement was found in the case of CH 4 discussed in a previous paper [14].…”

Kinetic properties of particle-in-cell simulations compromised by Monte Carlo collisions

“…Collisions between electrons and neutrals were modelling using essentially the cross sections of Tachibana [43], with adjustments to the low-energy part of the momentum transfer cross section from Pack et al [44], and with isotropic scattering in the centre of mass frame. Ion-neutral collisions followed the recommendation of Phelps [45], with the anisotropic scattering cross section approximated by an isotropic scattering component and a backward scattering component.…”