Reactor requirements can be put in a clearer perspective if they are seen together with those of the preceding steps, i.e. JET, NET and DEMO. Extrapolation from JET is moderate in plasma size, considerable in machine size and large in plasma performance and machine endurance. Extrapolation from the present understanding of tokamak plasma physics, to be developed further both in JET and elsewhere and, from technologies that we plan to develop for NET, can lead to a viable reactor, but with uncertainties regarding economic performance. Although overall economic predictions for fusion may be premature, consideration of capital costs at least indicates the desirable direction and incentive for further progress in plasma physics and technology. Among physics issues the plasma power density (which is directly related to operational limits on beta, plasma density and plasma current), the power and particle loads on the walls of the device as well as the plasma exhaust requirements, and the prospects for steady-state operation, are of primary importance. Technologically the most severe requirements are on operational reliability, lifetime of plasma-facing components, and remote handling.
Magnetic island formation in a tokamak plasma from helical perturbations of the plasma current
