Divertors and impurity control: Where we stand, where we have to go

In the present paper we first recapitulate the maximum impurity concentrations compatible with the condition for ignition and with the restrictions on fuel dilution and state the requirements on particle exhaust and heat removal for an Intor size ignition experiment. We then discuss the potential of the divertor to meet these requirements by summarizing the results of present-day divertor experiments and the current theoretical understanding of divertor operation. In the last section we finally show how some divertor characteristics scale with heating power, and suggest experiments that have to be carried out before divertors can possibly be used in fusion reactors. (orig./RW)