The diagnostic systems of DEMO that are mounted on or near the torus, whether intended for the monitoring and control functions of the engineering aspects or the physics behaviour of the machine, will have to be designed to suit the hostile nuclear environment. This will be necessary not just for their survival and correct functioning but also to satisfy the pertinent regulatory bodies, especially where any of them relate to machine protection or the prevention or mitigation of accidents foreseen in the safety case. This paper aims to indicate the more important of the reactor design considerations that are likely to apply to diagnostics for DEMO, drawn from experience on JET, the provisions in hand for ITER and modelling results for the wall erosion and neutron damage effects in DEMO.
