PLASMA-SURFACE INTERACTIONS IN THE ALCATOR C-MOD TOKAMAK

Alcator C-Mod is a high-field tokamak with which experiments were init iated in April 1993. The divertor and the first-wall have plasma-facin g surfaces of molybdenum. The divertor has a configuration which is cl osed in comparison to other, currently operating tokamaks, The combina tion of divertor geometry and high field (density) make Alcator C-Mod an ideal experiment to investigate dissipative (radiative/CX) divertor scenarios. Single-null divertor operation has become the standard mod e of operation. Relatively clean plasmas (Z(eff)less than or equal to 1.3) are obtained with short periods of baking and electron cyclotron discharge cleaning only. Impurity source rates and screening have been investigated with an extensive set of wavelength-filtered diode array s and spectrographs. Carbon and oxygen and molybdenum dominate the imp urity levels. The molybdenum source from the divertor proper is neglig ible.