  Present divertor concepts for next step experiments such ITER and TPX rely
upon impurity and hydrogen radiation to transfer the energy from the edge
plasma to the main chamber and divertor chamber walls. The efficiency of these
processes depends strongly on the heat flux, the impurity species, and the
connection length. Using a database for impurity radiation rates constructed
from the ADPAK code package, we have developed criteria for the required
impurity fraction, impurity species, connection length and electron temperature
and density at the mid-plane. Consistent with previous work, we find that the
impurity radiation from coronal equilibrium rates is, in general, not adequate
to exhaust the highest expected heating powers in present and future
experiments. As suggested by others, we examine the effects of enhancing the
radiation rates with charge exchange recombination and impurity recycling, and
develop criteria for the minimum neutral fraction and impurity recycling rate
that is required to exhaust a specified power. We also use this criteria to
find the optimum impurity for divertor power exhaust.
