Electron Transport Coefficients and Effective Ionization Coefficients in SF ₆ -O ₂ and SF ₆ -Air Mixtures Using Boltzmann Analysis

The electron drift velocity, electron energy distribution function (EEDF), density- normalized effective ionization coefficient and density-normalized longitudinal diffusion velocity are calculated in SF ₆ -O ₂ and SF ₆ -Air mixtures. The experimental results from a pulsed Townsend discharge are plotted for comparison with the numerical results. The reduced field strength varies from 40 Td to 500 Td (1 Townsend=10 ⁻¹⁷ V·cm² ) and the SF ₆ concentration ranges from 10% to 100%. A Boltzmann equation associated with the two-term spherical harmonic expansion approximation is utilized to gain the swarm parameters in steady-state Townsend. Results show that the accuracy of the Boltzmann solution with a two-term expansion in calculating the electron drift velocity, electron energy distribution function, and density-normalized effective ionization coefficient is acceptable. The effective ionization coefficient presents a distinct relationship with the SF ₆ content in the mixtures. Moreover, the E/N cr values in SF ₆ -Air mixtures are higher than those in SF ₆ -O ₂ mixtures and the calculated value E/N cr in SF ₆ -O ₂ and SF ₆ -Air mixtures is lower than the measured value in SF ₆ -N ₂ . Parametric studies conducted on these parameters using the Boltzmann analysis offer substantial insight into the plasma physics, as well as a basis to explore the ozone generation process.