Measurement of Ionization and Attachment Coefficients in C3F8

The growth of pre-breakdown currents in uniform field conditions in C 3 F 8 at various pressures, for values of E/p in the range 90-300 V cm -1 mmHg -1 indicates large electron attachment processes. Assuming that the relevant mechanism of negative ion formation is dissociative attachment, values of the ionization and attachment coefficients (α and η) have been calculated from the semi-logarithmic plots of current against electrode separation employing the modified Townsend equation for the current growth and a process of curve fitting. Static breakdown potentials have also been measured up to a value of pd = 400 mmHg cm.