Effect of hydrogen line radiation on the divertor target plate incident heat flux

Hydrogen resonance line radiation strongly interacts with the partially ionized plasma at the tokamak edge. As a result of these interactions, a nonlocal plasma energy transport channel opens, altering local atomic level populations by an order-of-magnitude, and affecting plasma transport. Understanding the effects of these interactions is essential to the design of future tokamak divertors, but previous models have not self-consistently treated this physical process. To model the interaction of hydrogen resonance photons with the plasma at the tokamak edge, a partially ionized plasma fluid transport code (PIP) has been developed and integrated into a nonlocal thermodynamics equilibrium (NLTE) code (CRETIN). The partially ionized plasma fluid transport model was derived from kinetic theory and includes the charge-exchange coupling of ions with neutral atoms, transport of internal atomic energy, as well as effective ionization, recombination, and energy loss rates determined by the NLTE model. We apply PIP and CRETIN to the modeling of an optically thick detached tokamak divertor both with and without the effects of line radiation interactions. While many characteristics of the detached divertor regime remain, e.g. the pressure drops in front of the target plate, several details change. Most importantly for the design of future divertors, line radiation interactions increase the divertor target plate incident plasma heat flux from 0.189 MW/m2 to 0.436 MW/m2. (copyright 2004 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)