The time evolution of an electron-beam-controlled high-pressure discharge in CO2 laser gas mixtures

The rate coefficients of recombination and attachment processes in electron-beam-sustained high-pressure discharges in N2, CO2, or 1:1 N2/CO2 are determined experimentally by measuring the time course of the discharge current. A discharge volume 1 x 1 x 10 cm at 1.0 or 0.5 atm pressure is subjected to an electron beam of maximum electron density (controlled by the thickness of the separating Lenard window) (2 or 20) x 10 to the 13th/cu cm from a cold-cathode electron-beam gun powered by a 1.64-nF 230-kV (maximum) Tesla transformer and to an electric field of reduced strength 1-12 kV/cm atm from a capacitor bank with maximum voltage 10 kV, capacitance 6.1 microF, and discharge-circuit inductance less than 50 nH. The results are presented in graphs and discussed. A rapid decrease in the recombination rate (despite constant field strength) is observed immediately after the discharge ignites in N2, but not in CO2; CO2 discharges are found to become unstable as soon as they are no longer recombination-determined, and the N2/CO2-mixture results are shown to be consistent with these findings. The implications for the operation of tunable high-pressure gas lasers are indicated.