Monte Carlo model for electron degradation in xenon gas

Abstract

We have developed a Monte Carlo model for studying the local degradation of electrons in the energy range 9-10 000 eV in xenon gas. Analytically fitted form of electron impact cross sections for elastic and various inelastic processes are fed as input data to the model. The two-dimensional numerical yield spectrum (NYS), which gives information on the number of energy loss events occurring in a particular energy interval, is obtained as the output of the model. The NYS is fitted analytically, thus obtaining the analytical yield spectrum (AYS). The AYS can be used to calculate electron fluxes, which can be further employed for the calculation of volume production rates. Using the yield spectrum, mean energy per ion pair and efficiencies of inelastic processes are calculated. The value for mean energy per ion pair for Xe is 22 eV at 10 keV. Ionization dominates for incident energies greater than 50 eV and is found to have an efficiency of approximately 65% at 10 keV. The efficiency for the excitation process is approximately 30% at 10 keV.

Effects of secondary γ-electrons from accelerator grid under ion impingement in gridded ion sources

“…The calculated total excitation and ionization cross-sections in reference [30] were based on the recent experimental and theoretic studies, and consistent with the previous values. The small deviations of the total excitation and ionization cross-sections from their true values cannot result in the overestimated distances that are one order higher than the gap.…”

“…The gas pressure P calculated using equation ( 3) is 0.48 Pa, and the corresponding Xe atom density n 0 in equation ( 2) is 1.16 × 10 20 m −3 . Based on the digitized electron-impact ionization and excitation cross-sections of Xe atom in reference [30], the ionization and excitation distances calculated using equation ( 1) are shown in figure 9. At the energetic secondary γ-electron energy of 1350 eV, the calculated ionization and excitation distances are 518.5 and 2333.6 mm (see figure 9), respectively.…”

“…Therefore, the calculated excitation and ionization distances by equation (1) are overestimated. The reasons for overestimates are as follows: (1) the total excitation and ionization cross sections in reference [30] are incorrectly low; (2) the calculated n 0 is unreliably small; (3) the assumptions made in deriving the formula in equation (1) are invalid.…”