Thickness of the scrape-off layer of a large tokamak with a poloidal divertor

Using a simple model, the thickness of a poloidal divertor scrape-off layer has been estimated for a tokamak of INTOR/NET size and for a demonstration tokamak reactor. The thickness is likely to be less than one centimetre and the temperature of the plasma at the target plate may exceed 100eV. Both the sputtering and the thermal loading of the target plate would be excessive. It may be possible to increase the scrape-off layer thickness and hence to decrease power loading and sputtering by increasing the edge density, but the improvement will suffice only if the ratio of perpendicular transport to parallel transport is larger than assumed here and/or if radiation is actively enhanced at the plasma edge. (author)