A Monte Carlo simulation of ion transport at finite temperatures

We have developed a Monte Carlo simulation for ion transport in hot background gases, which is an alternative way of solving the corresponding Boltzmann equation that determines the distribution function of ions. We consider the limit of low ion densities when the distribution function of the background gas remains unchanged due to collision with ions. A special attention has been paid to properly treat the thermal motion of the host gas particles and their influence on ions, which is very important at low electric fields, when the mean ion energy is comparable to the thermal energy of the host gas. We found the conditional probability distribution of gas velocities that correspond to an ion of specific velocity which collides with a gas particle. Also, we have derived exact analytical formulas for piecewise calculation of the collision frequency integrals. We address the cases when the background gas is monocomponent and when it is a mixture of different gases. The developed techniques described here are required for Monte Carlo simulations of ion transport and for hybrid models of non-equilibrium plasmas. The range of energies where it is necessary to apply the technique has been defined. The results we obtained are in excellent agreement with the existing ones obtained by complementary methods. Having verified our algorithm, we were able to produce calculations for Ar$^+$ ions in Ar and propose them as a new benchmark for thermal effects. The developed method is widely applicable for solving the Boltzmann equation that appears in many different contexts in physics.Comment: 14 page

Measurements and modeling of electron energy distributions in the afterglow of a pulsed discharge in BF

In this paper we use experimental data (Radovanov S. and Godet L., J. Phys.: Conf. Ser., 71 (2007) 012014) for time-resolved electron energy distribution function in boron trifluoride (BF3) discharges together with cross-sections for electron excitation processes and attachment in order to explain electron dynamics in the pulsed plasma doping system. A Monte Carlo simulation (MCS) was used to perform calculations of the electron energy probability function (EEPF) in pulsed DC electric fields as found in practical implantation devices. It was found that in the afterglow, electric field in the plasma is not zero but still has a significant reduced electric field (E/N) albeit below the breakdown condition. Our analysis assuming free diffusion conditions in the afterglow led to the calculation of EEPF for a range of E/N corresponding to different afterglow times of a pulsed DC discharge. Calculated and experimental EEPF agree fairly well for a given set of cross-sections (see paper by Radovanov and Godet quoted above) and assumed initial distributions. In addition we have modeled the kinetics of production of negative ions in the afterglow as observed by experiment and found an increase in the production of negative ions in the early afterglow. Electron attachment in BF3 with 0.1% of F2 is a possible explanation for the observed rate of negative-ion production as predicted by our Monte Carlo simulation. However, the most likely cause for the increase in detected number density of ions is the collapse of the field-controlling electrons

Modeling of Electron Kinetics in BF3BF_{3}

In this paper we used the available data for the electron impact scattering cross sections $BF_{3}$ to calculate the transport coefficients for electrons. Monte Carlo simulation was used to perform calculations of the transport coefficients as well as the rate coefficients in DC electric fields, crossed electric and magnetic DC and RF fields

Electron and positron swarms: Collision and transport data and kinetic phenomena

A broad review of electron swarm studies completed recently is presented with a common thread of both being motivated by major applications which use swarm physics as part of their phenomenological foundation and also with a strong presence of nonconservative (electron number changing) collisions. The review is mainly based on the activities of Gaseous Electronics Laboratory Belgrade and it cannot cover all recent and ongoing activities in swarm physics but it attempts to cover the majority of topics covered by swarm physicists in general. Thus we start with recent determinations of the cross sections from the transport data and calculations of the transport data from the cross sections from other sources in gases such as NO, N2O and mixtures of Ar and N2. We proceed to show how the presence of radicals affects the transport coefficients in CF4, a gas with great potential for applications. The basic features of the transport are discussed for dc and rf electric and magnetic fields. In those two chapters we mainly focus on kinetic phenomena such as negative absolute mobility, non-conservative effects in particle transport and how angle between magnetic and electric field affects the transport coefficients. We also discuss application of semi empirical formulas. Finally we analyze positron transport and its difference from the transport of electrons. The Positronium formation cross section is significantly larger than that for analogous electron non-conservative processes (i.e. electron attachment). Thus transport of positrons gives a much stronger nonconservative effects including a new effect of the negative differential conductivity (NDC) in the bulk (WB - velocity of the center of the swarm that is relevant for the real space diffusion equation) drift velocity while the conditions required for NDC do not exist for the flux drift velocity (w F - mean velocity of particles in the swarm that is relevant for the calculations of flux when using continuity relation)

Electron and positron swarms: Collision and transport data and kinetic phenomena

A broad review of electron swarm studies completed recently is presented with a common thread of both being motivated by major applications which use swarm physics as part of their phenomenological foundation and also with a strong presence of nonconservative (electron number changing) collisions. The review is mainly based on the activities of Gaseous Electronics Laboratory Belgrade and it cannot cover all recent and ongoing activities in swarm physics but it attempts to cover the majority of topics covered by swarm physicists in general. Thus we start with recent determinations of the cross sections from the transport data and calculations of the transport data from the cross sections from other sources in gases such as NO, N2O and mixtures of Ar and N2. We proceed to show how the presence of radicals affects the transport coefficients in CF4, a gas with great potential for applications. The basic features of the transport are discussed for dc and rf electric and magnetic fields. In those two chapters we mainly focus on kinetic phenomena such as negative absolute mobility, non-conservative effects in particle transport and how angle between magnetic and electric field affects the transport coefficients. We also discuss application of semi empirical formulas. Finally we analyze positron transport and its difference from the transport of electrons. The Positronium formation cross section is significantly larger than that for analogous electron non-conservative processes (i.e. electron attachment). Thus transport of positrons gives a much stronger nonconservative effects including a new effect of the negative differential conductivity (NDC) in the bulk (WB - velocity of the center of the swarm that is relevant for the real space diffusion equation) drift velocity while the conditions required for NDC do not exist for the flux drift velocity (w F - mean velocity of particles in the swarm that is relevant for the calculations of flux when using continuity relation)