Magnetic divertors

The different needs for divertors in large magnetic confinement experiments and prospective fusion reactors are summarized, special emphasis being placed on the problem of impurities. After alternative concepts for reducing the impurity level are touched on, the basic principle and the different types of divertors are described. The various processes in the scrape-off and divertor regions are discussed in greater detail. The dependence of the effectiveness of the divertor on these processes is illustrated from the examples of an ASDEX/PDX-size and a reactor-size tokamak. Various features determining the design of a divertor are dealt with. Among the physical requirements are the stability of the plasma column and divertor throat and the problems relating to the start-up phase. On the engineering side, there are requirements on the pumping speed and energy deposition, and for a reactor, the need for superconducting coils, neutron shields and remote disassembly