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

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 E_R/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.