Ion aging effects on the dissociative-attachment instability in CO2 lasers

Onset of the dissociative-attachment instability requires that the rate coefficient for electron detachment (k _d) from negative ions be below a critical value. The predominant negative and positive ions in a CO₂N₂He gas-discharge plasma are known to change with time. As secondary by-products form and the predominant negative-ion species changes from CO ₃ ^– to NO ₂ ^– , a decrease ink _d occurs destabilizing the discharge. Since NO ₂ ^– and NO ₃ ^– are largely unreactive with respect to associative detachment,k _d depends in a sensitive fashion on the concentration of certain minority negative ions (O^–, O ₂ ^– ) and neutrals (CO, O, N). The sufficient conditions for the dissociative-attachment instability are much less sensitive to changes in the electron-ion and ion-ion recombination rate coefficients resulting from the ion aging process.