from 31 January to 2 February, 32 experts in Plasma Wall Interaction (pwi) and plasma edge physics gathered in tervaniemi, finland to discuss computer simulation tools. the meeting was organised by two EFDA PWI Task Force special expert working groups and hosted by the Association EURATOM-TEKES.

Probably the most positive news reported at the meeting concerned the JET ITER-Like-Wall, which will consist of beryllium and tungsten. One of its critical issues is the fact that tungsten atoms reduce the plasma performance when they enter the plasma centre. Two independent simulations now predict that the plasma core is well screened from tungsten at very low fuelling rates.

PWI models develop rapidly.

The meeting also concluded that simulation tools are developing with giant leaps and moving towards a comprehensive modelling of PWI issues. Several models were presented, which connect to other plasma models, calculate several plasma particles simultaneously, or integrate the CADmodels of the vessel walls into their calculations. This is an important step forward, as the plasma wall interaction effects have until now been just one of many uncertainties in plasma modelling. They have been reliably approximated since the current experiments do not challenge the walls to their limits. Due to the extreme heatand particle loads expected in ITER, designers will, for the first time, depend on data from the most sophisticated plasma models.

Urgent issues.

The experts also identified topics that require urgent attention: The boundary conditions at the wall need to be improved by combining the models with data from experiments and chemical simulations. Important are also the flows in the outermost plasma layer which tends to peel off and flow to the divertor or the limiter of the tokamak. At the moment, most codes are unable to represent the flows measured in this layer. Some codes appear to overcome this issue for limiter tokamaks, but have thus far failed to give realistic flow patterns for divertor tokamaks.

Markus Airila, VTT