Transport of electrons and propagation of the negative ionisation fronts in indium vapour

Abstract

We study the transport of electrons and propagation of the negative ionisation fronts in indium vapour. Electron swarm transport properties are calculated using a Monte Carlo simulation technique over a wide range of reduced electric fields E/N (where E is the electric field and N is the gas number density) and indium vapour temperatures in hydrodynamic conditions, and under non-hydrodynamic conditions in an idealised steady-state Townsend (SST) setup. As many indium atoms are in the first ( 5 s 2 5 p ) 2 P 3 / 2 metastable state at vapour temperatures of a few thousand Kelvin, the initial Monte Carlo code was extended and generalized to consider the spatial relaxation and the transport of electrons in an idealised SST experiment, in the presence of thermal motion of the host-gas atoms and superelastic collisions. We observe a significant sensitivity of the spatial relaxation of the electrons on the indium vapour temperature and the initial conditions used to release electrons from the cathode into the space between the electrodes. The calculated electron transport coefficients are used as input for the classical fluid model, to investigate the inception and propagation of negative ionisation fronts in indium vapour at various E/N and vapour temperatures. We calculate the electron density, electric field, and velocity of ionisation fronts as a function of E/N and indium vapour temperature. The presence of indium atoms in the first ( 5 s 2 5 p ) 2 P 3 / 2 metastable state significantly affects the characteristics of the negative ionisation fronts. The transition from an avalanche into a negative ionisation front occurs faster with increasing indium vapour temperature, due to enhanced ionisation and more efficient production of electrons at higher vapour temperatures. For lower values of E/N, the electron density behind the streamer front, where the electric field is screened, does not decay as one might expect for atomic gases, but it could be increased due to the accumulation of low-energy electrons that are capable of initiating ionisation in the streamer interior.

Scanning drift tube measurements and kinetic studies of electron transport in CO

“…Under non-hydrodynamic conditions in an idealized SST setup, the spatially resolved mean energy and average velocity are calculated via the so-called 'box-sampling' [55,58,62]. According to this method, the x-axis is divided into a large number of small boxes, each having a width of ∆x and being infinite in the other spatial directions.…”

“…where f SST (x, v) is the steady-state distribution function, ξ j k is the value of the quantity to be sampled when the jth electron is contained in the kth box, ∆t k j is the residence time of the electron in that box, and N e is the number of electrons that appear there. For more details on the Monte Carlo modeling of an idealized SST experiment, the reader is referred to [55,58,62,63].…”

“…The generalization of hydrodynamic conditions to non-hydrodynamic conditions allows a better understanding of the electron transport near the emitting electrode and the exact calculation of the effective SST ionization coefficient. In studies on the spatial relaxation of electrons under SST conditions using Monte Carlo and/or BE results, the primary focus has usually been on electrons in atomic gases [50][51][52][53][54][55][56][57][58][59][60][61][62][63]. Some results related to N 2 [52,64], CF 4 [56], CO 2 [59], CH 4 [65] and synthetic air [66] can also be found in the literature.…”

Current stage and future development of Belgrade collisional and radiative databases/datasets of importance for molecular dynamics

“…[10][11][12] Electron impact collision cross section databases over a wide range of impact energies are required to model and underpin the interactions in various applied fields 13 while total cross section data are useful for the study of electron transport properties in gases. 14,15 The last few decades have seen tremendous progress in both the computational and experimental techniques applied to study the scattering of electrons by biologically relevant molecules. Much ongoing effort has been undertaken to provide a deeper insight into the mechanisms related to the radiation damage of DNA, which includes many processes (ionization, electronic, rotational, and vibrational excitations, dissociation and dissociative electron attachment).…”