Modelling of anomalous Doppler broadened lines, thermalization of electrons and the role of radicals in discharges at high E/N

Abstract

Abstract. In this paper we show how Monte Carlo technique developed for swarm studies may be applied to model some real discharges or to provide data for realistic plasma models. In all cases discussed here the Monte Carlo technique without self consistent field is driven to a much greater level of complexity than usually found in swarm studies. We discuss three conceptually quite different situations that require exact modelling by Monte Carlo Simulations (MCS). The first is the case of transport in gases where degree of dissociation is large and thereby radicals formed by the discharge may affect the transport coefficients. Based on recent calculations for electron CF x radical cross sections we calculated how transport coefficients would be affected by the presence of radicals in pure CF 4 and CF 4 /Ar mixtures covering range of abundances often found in plasma etching devices. The second case studied here is modelling of thermalization of high energy electrons in the atmospheric gases as an attempt to provide the basis for detection of very high energy cosmic particles. In that case pressure dependent emission efficiency is studied as a function of electron energy and the system is developed to an arbitrary degree of secondary electron production. Finally we give some recent advances and current status of modelling of high E/N discharges operating in Townsend's regime in hydrogen where anomalous broadening was observed and explained by fast neutral excitation in both directions along and against the acceleration due to electric field.

Measurement and interpretation of swarm parameters and their application in plasma modelling

“…On the other hand, it is to be expected that fast neutrals may become relevant in modelling of micro discharges operating to the left of the Paschen minimum (Mariotti et al 2004, Wang et al 2005, Belostotskiy et al 2008, Petrović et al 2008c. (Petrović et al 1991(Petrović et al , 2008b for E/N = 10 kTd-comparison of MCS results (Petrović et al 2008b) and results in figure 1 of Petrović et al (1992). Unlike experiments, calculated profiles do not contain the central line induced by electrons.…”

“…Figure 28. Doppler profile(Petrović et al 1991(Petrović et al , 2008b for E/N = 10 kTd-comparison of MCS results(Petrović et al 2008b) and results in figure1ofPetrović et al (1992). Unlike experiments, calculated profiles do not contain the central line induced by electrons.…”

Experimental study of the evolution of H α line profile in a pulse hydrogen discharge

“…Profiles of hydrogen spectral lines at low pressure have been the subject of experimental and theoretical research for many years [1][2][3][4][5][6][7]. In various types of discharges (radio frequency (RF) [2,8], direct current (DC) [9], dielectric-barrier discharge [10], hollow cathode glow discharge [11][12][13] and others) their profiles often exhibit anomalous broadening in pure hydrogen [1-3, 5-9, 13, 14] and in mixtures with hydrogen [10,[13][14][15][16].…”

“…The H α profile, for example, consists of several components, each one of them appearing due to different excitation processes [1][2][3][4][5][6][7][8][10][11][12][13][14][15][16]. The central, narrowest component reflects the velocity distribution of the thermal excited * Author to whom any correspondence should be addressed.…”

Non-Maxwellian velocity distributions and non-Gaussian profiles of H atoms in low-pressure hydrogen discharges

“…There is a debate regarding the mechanisms of selective broadening of the spectral lines of atomic hydrogen. The most widespread class of models is known as the field ion acceleration and cathode reflection of ions and fast neutrals [5,10,[21][22][23][24][25]. According to these works, the H + , H + 2 and H + 3 ions accelerated in the cathode sheath region exchange their charge in collisions with H 2 molecules and, as a result of this process, fast H atoms and slow ions appear.…”