Sparking potentials and ionisation coefficients in SF6

Steady-state ionisation currents under uniform field conditions have been measured in SF6 over the range 110 ≤E/p≤1000V cm−1torr−1 with gas pressures varying from 1 to 10 torr, at 20°C. Sparking potentials Vs were also measured for a range 1≤pd≤20 torr-cm. Townsend's primary ionisation (α/p) and electron-attachment (η/p) coefficients were found to depend on E/p only. The values of secondary-ionisation coefficient (γ) were also determined over the range 140≤E/p≤600 V cm−1 torr−1. Measurements of Vs of SF6 have shown that the deviations from Paschen's law rise up to ±3.5% at values of pd near the Paschen minimum.