Effects of divertor geometry on tokamak plasmas

The design, construction and operation of advanced diverters have been the main topics of tokamak research during the last decade. The design of these diverters (carried out with two-dimensional plasma modelling codes) has been optimized to provide: a large operating density range for partially detached plasmas with large radiative losses; satisfactory particle control by efficient deuterium pumping; and He exhaust capability sufficient to remove fusion ashes when extrapolated to next step devices. This article explains the criteria that have guided this optimization process and then critically reviews the experimental evidence that confirms or refutes the physics-based design criteria on which the various existing advanced diverters have been based.