Kinetic phenomena in charged particle transport in gases, swarm parameters and cross section data

Abstract

In this review we discuss the current status of the physics of charged particle swarms, mainly electrons. The whole field is analysed mainly through its relationship to plasma modelling and illustrated by some recent examples developed mainly by our group. The measurements of the swarm coefficients and the availability of the data are briefly discussed. More time is devoted to the development of complete electron-molecule cross section sets along with recent examples such as NO, CF 4 and HBr. We extend the discussion to the availability of ion and fast neutral data and how swarm experiments may serve to provide new data. As a point where new insight into the kinetics of charge particle transport is provided, the role of kinetic phenomena is discussed and recent examples are listed. We focus here on giving two examples on how non-conservative processes make dramatic effects in transport, the negative absolute mobility and the negative differential conductivity for positrons in argon. Finally we discuss the applicability of swarm data in plasma modelling and the relationship to other fields where swarm experiments and analysis make significant contributions.

Transport coefficients and cross sections for electrons in water vapour: Comparison of cross section sets using an improved Boltzmann equation solution

“…18 One of the key discriminating tests on the completeness and accuracy of any given cross section set is provided through electron swarm experiments. [19][20][21] In swarm experiments, electrons are passed through a gas at known pressure and temperature under the influence of a uniform electric field. Currents are interpreted in terms of drift and diffusion and other transport coefficients.…”

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

“…On the other hand the effect on the drift velocity is significant and one example is shown for the mixture that includes argon in figure 2. The comparison between the two figures means that while mean energy is not perturbed much by the presence of radical and the shape of EEDF is not affected the elastic cross section for radicals which does not have a minimum fills the cross section in the region of the Ramsauer Townsend minimum in CF 4 and it changes the optimum conditions for the negative differential conductivity [16,18]. This is a proof that by selecting a mixture one may control independently the momentum and the energy balance and in particular the number balance.…”

“…We typically follow 100 000 electrons through hundreds of thousands of collisions and we have means to reproduce all observables with accuracy limited only by the quality of the cross sections and by statistical uncertainty. 4 Carbon tetrafluoride is commonly used in today's semiconductor industry for etching of dielectric materials, such as SiO 2 [1,2] and also for deposition of fluorinated polymer films.CF 4 has also an important role in a number of technological applications. CF 4 belongs to the Freon group of gases that unfortunately significantly contribute to the global warming of our planet with a lifetime of 50 000 years.…”

“…Some of the cross sections for electron-Cox radical scattering can be significantly larger than the cross sections for CF 4 itself especially in the region of the Ramsauer Townsend minimum and for the attachment cross section [13]. Until recently [14] no direct experimental measurements of these crosssections have been performed.…”

“…Perhaps the most promising future applications of non-equilibrium plasmas include massively parallel production of nanostructures for nanotechnologies (top down approach) and for medical treatments. Monte Carlo simulations are the best way to model such plasmas as they allow realistic treatment of complex boundary conditions [3], inclusion of recently found complex kinetic phenomena [4] and essentially 3 dimensional treatments of complex geometries. In this paper we show three examples of how extension of standard and exact Monte Carlo procedure as developed for studies of charged particle swarms [5] may be extended by making the model more complex by one step to include new phenomena required to explain realistic discharges in gases.…”