Determination of Electron Swarm Parameters in Pure CHF₃ and CF₄ by a Time-Resolved Method

The density-normalized effective ionization coefficient (α-η)/N (α and η are the ionization and attachment coefficients respectively), the electron drift velocity Ve and density-normalized longitudinal diffusion coefficient NDL in trifluoromethane (CHF₃) and carbon tetrafluoride (CF₄) were measured using a pulsed Townsend technique over a wide E/N range. From the plots of (α-η)/N, we have derived the limiting field strength, (E/N)lim, which is valid for the analysis of insulation characteristics and applications to power equipment. Comparisons of the electron swarms parameters between CHF3 and CF4 have been performed, and the global warming potential (GWP) is also taken into account.