MEASUREMENTS OF THE DRIFT VELOCITY OF ELECTRONS IN MIXTURES OF NITROGEN AND CARBON-DIOXIDE FROM 100 TO 1000 TD

The arrival-time spectra (ATS) of electrons in mixtures of nitrogen (N -2) and carbon dioxide (CO2) have been measured for reduced electric f ields (E/N) from 100 to 1000 Td (1 Td = 10(-17) V cm(2)) at room tempe rature by using a double-shutter drift tube. The drift velocity (W-m) of the electrons in N-2 and CO2 mixtures was evaluated from a previous ly reported ATS method. In mixtures of N-2 and CO2, we found that W-m is larger than the value predicted by a linear combination of the drif t velocities of the pure gases based on the mole fraction (partial pre ssure) of CO2 in the mixture, k, in the range of low E/N (less than or equal to 200 Td). We refer to this as the 'mixing effect'. In contras t, a linear combination of the drift velocities of the pure gases base d on k was found to accurately predict the drift velocities in N-2/CO2 mixtures in the higher E/N region (greater than or equal to 250 Td). In addition to the experimental evaluation, calculations of W-m in the se gas mixtures were carried out by a Boltzmann equation analysis, and the results were compared with those from the ATS measurements. The r atio (D-L/mu) of the longitudinal diffusion coefficient (D-L) to the e lectron mobility (mu) was also estimated. The value of D-L/mu, called the characteristic energy, also shows a small mixing effect with incre asing k in the range of low E/N (less than or equal to 150 Td) and inc reases monotonically in the range of 200 less than or equal to E/N les s than or equal to 450 Td, while the value decreases linearly as k inc reases in the higher E/N (greater than or equal to 500 Td) range.