Divertor-plasma studies on DIII-D

This paper presents an overview of recent results from divertor physics studies in DIII-D. Heat flux measurements at input power levels up to 20 MW show that steady divertor heat loads of up to 4 MW/m2 are obtained in H-mode discharges with ELMs. No carbon blooms are observed. The heat flux profile is highly peaked at the outside strike point in single-null discharges, and is up/down asymmetric in double-null discharges. Recent experiments with gas injection below the X-point have demonstrated a factor of two reduction in the peak divertor heat flux for H-mode plasmas at these power levels. These heat flux data, along with measurements of the ne and Te profiles at the divertor are being used to help interpret the first reported measurements of the erosion profile for a set of graphite divertor tiles exposed to several months of high power tokamak operation. We have now modified the divertor hardware in order to carry out experiments with divertor biasing, baffling, and pumping. 26 refs., 8 figs