VELOCITY DISTRIBUTION OF CARBON AND OXYGEN-ATOMS IN FRONT OF A TOKAMAK LIMITER

From the Doppler-broadened emission profiles of a CI line (P-3(2) --> P-3(2)0, lambda = 909.5 nm) and of an OI line (P-3(2,1,0) --> S-3(1)0, lambda = 844.6 nm), the velocity distribution of carbon and oxygen atoms in front of a graphite limiter has been deduced. For the pi-component of the CI line, the Zeeman splitting is negligible, but for the pi-components of the OI line, the Paschen-Back effect has to be taken into account. The contribution of chemical and physical sputtering to the release of impurities under various experimental conditions has been investigated at the tip of the limiter. For C atoms, chemical sputtering dominates at low boundary temperatures, and physical sputtering at high temperature. For oxygen, chemical sputtering is always indicated to be the more efficient process.