Measurement of Ionization and Attachment Coefficients in Carbon Dioxide in Uniform Fields

The growth of pre-breakdown currents in uniform field conditions has been studied in carbon dioxide at different pressures in the E/p range of 1200 to 26 v cm-1 (mm Hg)-1. Experimental measurements of the Townsend ionization coefficient α show good agreement with the earlier measurements in the E/p range of 1200 to 100 v cm-1 (mm Hg)-1 and with the recent measurements in the E/p range of 70 to 50 v cm-1 (mm Hg)-1. The results show that earlier measurements neglecting attachment may be in error below E/p = 50 v cm-1(mm Hg)-1. It is suggested that the mechanism of negative ion formation is due to dissociative attachment, consequently the growth of current at constant E/p can be represented by the appropriate modification of the Townsend equation. Employing this equation, values of α and the dimensionally equivalent attachment coefficient η have been computed. Further, static breakdown potentials have been measured up to pd (pressure × gap length) similar 1500 mm Hg cm and the values of secondary coefficient γ have been calculated using the modified Townsend breakdown criterion.