A DESIGN STUDY FOR AN ADVANCED DIVERTOR FOR DIII-D AND ITER - THE RADIATIVE SLOT DIVERTOR

Reduction of the divertor heat load is an important issue for future tokamaks, particularly during the technology phase of ITER. We discuss a conceptual design for one type of advanced divertor: the radiative slot divertor. The goal of this divertor configuration is to enhance the radiation in the divertor region and thereby reduce the heat load at the strike points. At the same time, any effects on the core plasma must be minimized. Proof-of-principle experiments to enhance the radiation in the DIII-D divertor have been performed both with deuterium and impurity injection. We compare several computer models with results from these experiments to predict performance and thereby guide designs of radiative divertors for future machines. We have estimated impurity radiation using calculations of the background plasma with a two-dimensional fluid code (B2 or LEDGE) coupled with models of impurity radiation. The DEGAS code has been used to estimate hydrogenic transport, charge exchange, and radiation losses. Estimates of impurity transport are provided by 1 1/2-dimensional models and calculations of impurity frictional-force terms. These model results are in qualitative agreement with the approximately 1 MW reduction of measured divertor power in DIII-D during divertor impurity puffing experiments. Specific designs, including engineering details, for applications to DIII-D and ITER will be discussed.