Collisional-Radiative and Transport Modelling of Hydrogen and Helium for ITER

The current ITER computational engineering activities for edge plasma and plasma surface interaction (divertor) issues are carried out with the B2-EIRENE code, version SOLPS 4.3. Atomic and molecular data are brought into this integrated edge plasma tool mostly via the kinetic (Monte Carlo) Boltzmann solver EIRENE. The relevance of precise and comprehensive hydrogenic A and M processes within this computational model is obvious, as only those processes and their associated friction, plasma cooling effects etc. provide access to the favourable 'detached divertor' regime, on which the planned ITER operation is based. This regime is characterized by a (hydrogen-) chemical complexity not otherwise encountered in fusion plasmas. Helium is the ash of the fusion process and without control of its concentration the fusion flame in ITER would be choked by its own ash within 100 seconds, well short of the planned 600 - 1000 seconds of plasma operation per discharge. Edge and divertor plasma modelling for ITER falls already into the category of 'computational engineering', whereas all other applications of edge transport modelling codes today, e.g. to the ASDEX-Upgrade and JET tokamaks (2D) or the LHD and W7X stellarators (3D), etc. are largely 'computational science' activities still. This necessarily leads to particular consequences also for atomic and molecular databases within the B2-EIRENE code package. Computational parameter scans in the multi-dimensional parameter space of the ITER divertor are extremely slow and expensive, both with respect to human and to computational resources. One single data point (i.e. one single run with B2-EIRENE on a particular set of ITER input parameters) takes about 3 months on current computers. (This figure is a constant since about 15 years: the increasing complexity of the physical model compensates rapid speedup and availability of CPUs.) Exchanges of code modules or of A and M databases are only carried out if either missing physics has been clearly identified or if significant improvement of the data quality is to be expected. The A and M databases of the EIRENE code are upgraded continuously and these updates are activated in many applications in Europe, mainly JET, TEXTOR, ASDEX-Upgrade, Tore Supra, etc., but they are activated in the ITER engineering activities only if the additional benefits over the old model are obvious, for reasons of above mentioned ITER code database management and necessity of backward compatibility in the computational design process. The B2 part (and atomic data in it) is about 15 years old, despite more recent heavy development (e.g., B2 to B2.5, fully developed ADAS interfaces for impurity flow, etc.); the EIRENE part, and related A and M databases used by ITER, are more recent