MICROWAVE-DISCHARGE IN H-2 - INFLUENCE OF H-ATOM DENSITY ON THE POWERBALANCE

We investigate a source of H atoms generated by a low-pressure surface wave discharge (2.45 GHz). We study the influence of microwave power both on the discharge characteristics and on the H atom density, which has been measured by actinometry. Dissociation levels of H-2 are much higher (75%) at low microwave power than at high power (10%). Unlike what has been found in oxygen surface wave plasmas, discharge characte ristics depend strongly on microwave power, due to an important coupli ng between discharge equilibrium and kinetics of the atomic hydrogen. These results are explained taking into account the effect of discharg e tube wall temperature on atomic recombination. The wall recombinatio n probability gamma is estimated as a function of the microwave power: it ranges from 6 x 10(-3) to 6 X 10(-2), which is very high in compar ison with values determined previously under post-discharge conditions .