A Numerical Investigation on a c.w. High-power, Electron-beam, Pre-ionized He : N 2 : CO 2 : CO Laser

We studied some kinetic, fluid-dynamic and electrical problems arising in the numerical modelling of a c.w.TE high power CO2 laser operating with N2, He and CO additives. We adapted a five-temperature pulsed laser model to the c.w. case by coupling a set of fluid-dynamic equations to the kinetic set. We added the rate equation for the secondary electron density. We calculated in some detail the ionization term and fitted experimental results to determine attachment and recombination coefficients in the discharge chamber. In order to solve our equations a numerical code has been developed. By this means we investigated the effects of temperature, density and velocity variations in the flowing mixture on the small signal gain of the device. We obtained profiles in the laser chamber of the sustainer current, small signal gain and fluid-dynamic parameters. A simple (Fabry-Perot) optical cavity model has been used to calculate output power and electrical efficiency of the device. A comparison of numerical code predictions and experimental results is presented.