Influence of recombination and ion chemistry on the stability of externally sustained molecular discharges

Abstract

The causes of thermal instability in high-pressure-low-temperature molecular discharges have been investigated with special emphasis placed on externally sustained CO laser discharges. Analysis shows that cw discharges of the type used in high-power CO lasers are inherently unstable, having thermal instability growth times on the order of 0.1 msec. The single most important factor affecting the instability growth rate at a specific power-density level was found to be electron-ion recombination. Changes in the recombination process as a consequence of positive-ion kinetics were found to result in order-of-magnitude variations in the instability growth rate. For this reason ion clustering reactions and water ion chemistry were investigated for conditions generally similar to those of high-pressure laser discharges. Analysis of high-pressure ion chemistry showed that conversion of clustered ions to molecular ions can have a significant impact on both the steady-state and stability characteristics of molecular discharges.