Tokamak edge model validation and improvement

Because of the complexity of the physics in the edge of divertor tokamaks, extrapolation from present-day machines to future reactor or reactor-type devices is done using two-dimensional-edge codes. Amongst the issues which are important for future machines, are those of inboard/outboard divertor power asymmetries and the compression of hydrogen and helium. The issues driving the in-out power asymmetry are explored, and a reasonable match is found to existing experiments, as well as an 'adjustable knob' that could be used to further improve the match. In this work, one further effect that is known to play a role - that of ExB and diamagnetic drifts - is identified but not analysed, because the codes have not yet been able to include the drift terms in combination with the impurities and kinetic neutrals. It is also shown that the codes reproduce the fact the only small differences were seen on the ASDEX Upgrade experiment in the compression of helium when the DivII divertor was replaced by the DivIIb configuration. (author)