SCALING OF DIVERTOR CONDITIONS IN NEXT STEP DEVICES WITH DIVERTOR DEPTH AND UPSTREAM PLASMA CONDITIONS

From 2-D modelling of the scrape-off plasma of a next step device, the scaling of key divertor parameters with density, power, transport coefficients and geometry (pitch, size) is derived. In high-recycling conditions, both power density and electron temperature at the divertor plate decrease strongly with increasing upstream density and decreasing input power. When the upstream density is adjusted to obtain constant, low electron temperature at peak power load, the peak power per unit area is proportional to the input power, and the scaling with connection length and transport coefficients is relatively benign. When divertor depth increases, the temperature still increases strongly with decreasing upstream density and both electron temperature and peak power per unit area decrease. Only for a very short divertor, a thermally unstable region is found (i.e. the upstream density is a multivalued function of plasma temperature at the divertor plate).