Requirements for impurity control, exhaust and plasma-wall interaction in the next generation of tokamaks (JET, JT-60, T-15, TFTR) and in reactors (INTOR, etc.)

The overall conclusions of the Working Session were that (I) limiter solutions appear sufficient for the control of impurities and plasma-wall interaction in the next generation of large tokamaks, and that (II) for the more demanding conditions in reactors, including the helium exhaust requirements, divertor solutions, in particular a single-null poloidal divertor, seem more appropriate, although there is a possibility that schemes based on the use of pump limiters could also be suitable. Specific items on which further research and development work is needed include (I) improved diagnostics for the plasma edge region, also to allow for better plasma control, (II) sputtering data in a tokamak environment and specifically for tritium where data are lacking completely, (III) the question of redistribution of wall material after long-time operation which is important to decide whether it is admissible to use different materials for different wall components, as well as (IV) the techniques for helium pumping where an improved efficiency, both absolute and relative to the pumping of deuterium/tritium, could considerably diminish the effort needed in a reactor for exhaust and refuelling and reduce its tritium inventory. (orig./AH)