Time-dependent electron swarm parameters in RF fields in CH4 and H2

Abstract

The temporal behaviour of electron swarm transport in an RF field has been investigated for the electron non-conservative case in CH4, H2 and their mixture by using the first three terms in Legendre polynomials with a fourier expansion in time for the electron velocity distribution from the time-dependent Boltzmann equation. Calculations have been made for reduced RMS electric fields ER/N in the range 15 to 70 Td and reduced angular frequencies omega /N in the range 105/N0 to 1010/N0 cm2 s-1, where N0 is the number density at 1 Torr and 273 K. The temporal modulation of the isotropic part of the velocity distribution is essentially determined by the ratio between omega -1 and an energy relaxation time tau e. It is shown that in molecular gases with rotational and vibrational collisions at very low energy, the asymptotic form of the energy distribution at very high frequency field differs from a Maxwellian as in atomic gases. The phenomenon of negative differential conductivity in CH4 has been studied as a parameter of omega /N. The gas mixture effect in an RF field is also discussed.