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

Abstract

In this review paper, we discuss the current status of the physics of charged particle swarms, mainly electrons, having plasma modelling in mind. The measurements of the swarm coefficients and the availability of the data are briefly discussed. We try to give a summary of the past ten years and cite the main reviews and databases, which store the majority of the earlier work. The need for reinitiating the swarm experiments and where and how those would be useful is pointed out. We also add some guidance on how to find information on ions and fast neutrals. Most space is devoted to interpretation of transport data, analysis of kinetic phenomena, and accuracy of calculation and proper use of transport data in plasma models. We have tried to show which aspects of kinetic theory developed for swarm physics and which segments of data would be important for further improvement of plasma models. Finally, several examples are given where actual models are mostly based on the physics of swarms and those include Townsend discharges, afterglows, breakdown and some atmospheric phenomena. Finally we stress that, while complex, some of the results from the kinetic theory of swarms and the related phenomenology must be used either to test the plasma models or even to bring in new physics or higher accuracy and reliability to the models.

High-order fluid model for streamer discharges: II. Numerical solution and investigation of planar fronts

“…The limitations of the two-term approximation for solving Boltzmann's equation have been illustrated many times in past in the context of swarm studies [34,[49][50][51]. Here the question arises of whether a similar conclusion can be drawn for streamers taking into account that the streamer development is a non-linear, non-stationary and non-hydrodynamic problem where space charge effects are important and where the electron energy varies from thermal values in the streamer channel up to a few tens of eV in the outer region of the streamer for the fields considered here.…”

Simulation benchmarks for low-pressure plasmas: Capacitive discharges

“…This body of work has thus far had little impact on the low-temperature plasma physics community, whose literature shows slight evidence of interest in demonstrating the formal correctness of computer simulations, or quantifying the errors in simulation results. Partial exceptions are Lawler and Kortshagen [9] in which careful benchmarks for positive columns were developed, and the swarm physics community, which has historically been deeply engaged in questions of modelling accuracy [10]-but even there, modern ideas about systematic verification and validation have yet had little influence. Of course, many authors of low-temperature plasma physics computer simulations doubtless test their codes extensively, but such testing is of limited value while unpublished.…”

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.…”

“…While the issue of cross section degeneracy (i.e., different cross section sets capable of reproducing the measured transport coefficients) has limited their use in deriving cross sections, 22,23 swarm experiments do provide a test on the completeness and consistency of any cross section set proposed. 21,22 This paper revisits the issues surrounding computation of electron transport properties in water vapour as a function of E/n 0 in the range 0.01-1200 Td (1 Td = 1 townsend = 10 −21 V m 2 ). Various cross sections are incorporated into the Boltzmann equation and solved using similar procedures as described in Ref.…”