Analysis of discharge parameters for applications in plasma devices

Abstract

Electron energy distribution is a fundamental parameter for proper understanding of electrical discharge processes. The discharge mechanism that should be considered depends upon the application, from the traditional low pressure discharge tubes to the more recent applications in medical sciences. The energy range of interest for this paper is 0.01–1000eV. The number density of electrons cover a range of 1020-1028 m−3. The general procedure adopted is to use the Boltzmann equation which takes in to account the energy gain and energy losses as the electron drifts under the influence of the electric field. Losses occur due to both elastic and inelastic collisions and a steady state is obtained when the two are equal. Elastic collisions are accounted for through momentum transfer cross section as a function of electron energy. Inelastic collisions are accounted for through the appropriate collision cross sections, also as a function of electron energy. Individual inelastic processes are ionization, excitation for each transition level of energy, rotational and vibrational excitation in molecular gases. The earliest attempt to take into account the inelastic collisions is due to Druyvesteyn whose method gave very good agreement for rare gases. With the advent of fast computers numerical methods were developed to take in to account individual elastic processes for several electronic and vibrational excitation levels. These methods are reviewed in the paper and a need for simplified method for engineering applications is pointed out. A simplified method is proposed and new results in krypton are discussed with good agreement with experimentally measured swarm properties.