POSITIVE-ION DRIFT VELOCITIES AND TOWNSEND PRIMARY IONIZATION COEFFICIENTS IN ETHANE

Positive-ion drift velocities have been measured in ethane gas, using the pulsed Townsend-discharge technique, over the range 40<or=E/p<or=1400 V cm-1 Torr-1. For 40<or=E/p<or=825 V cm-1 Torr-1 positive-ion drift velocities were determined by the balanced-pulse technique, and in the range 490<or approximately=E/p<or= 1400 V cm-1 Torr-1 by the positive-ion successor interval method. The experimental ion drift velocity was found to exhibit a linear dependence on E/p at low E/p changing to a square-root dependence at high E/p. Townsend primary ionisation coefficients have also been determined from balanced pulse measurements over the range 40<or=e/p<or=825 V cm-1 Torr-1. Experimental values of alpha /p are in moderate agreement with Townsend conductivity determinations, being lower at low E/p and higher at high E/p. In the range 100<or=E/p<or approximately=250 V cm-1 Torr-1 agreement is good. The effect of space-charge field distortion on the alpha coefficient, and hence the balanced pulse, is discussed. It is found that space-charge field distortion can produce different effects on the alpha coefficient in the pulsed and steady-state Townsend discharges.