Time of flight measurements of the ratio of radial diffusion coefficient and mobility for electron swarms in helium, argon, neon and krypton at high E/N

A time of flight pulse technique has been used for the measurement of the ratio of radial diffusion coefficient to mobility (D r / mu ) d for electron swarms in helium, argon, neon and krypton. The experimental range for helium and argon is 56.5<E/N<5650 Td (where E/N is the ratio of electrical field to gas number density), whilst the experimental range for neon and krypton is 1.41<E/N<5650 Td. The values of (D r / mu ) d increase with increasing E/N to a maximum value and then decrease in value. The values vary from 6.52 to 21.7 V in helium, 6.40 to 16.4 V in argon, 1.23 to 28 V in neon and 5.24 to 13.3 V in krypton. The results in helium and argon show good agreement with the result of Lakshminarasimha et al. (1977) obtained by using a steady-state technique over an experimental range which extended up to E/N=1300 Td. There are no experimental results in neon and krypton for comparison. The present results have been compared with theoretical values computed by various workers using the Boltzmann and Monte Carlo technique. Good agreement can generally be obtained between selected theoretical and the experimental results for the entire E/N region.