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 (¿/p) and electron-attachment (¿/p) coefficients were found to depend on E/p only. The values of secondary-ionisation coefficient (¿) 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.