Measurement of electron swarm coefficients in C2F4-Xe and evidence of Penning ionization in C2F4-Ar

We have measured the electron drift velocity, the effective ionization coefficient, and the longitudinal diffusion coefficient of electrons in the C2F4-Xe mixtures with 1% and 5% amount of C2F4. The electron drift velocity curves show a well defined region of negative differential drift velocity, and a similar effect is found for the density-normalized longitudinal diffusion coefficients at low E/N values. Previous findings of possible Penning ionization effects on the pulse shapes in the C2F4-Ar mixtures were not found in C2F4-Xe. This effect is further explored in this paper and fully supported by the simulation of avalanche development in the C2F4-Ar mixtures in which, apart from electron transport and effective ionization, the formation of metastable Ar∗ followed by ionization of C2F4 has been included. In most cases the comparison between simulations and measurements is very good, thereby giving further support to the original hypothesis.