Steady state D-T burning tokamak

The requirements of a steady-state, D-T burning tokamak in terms of energy and particle confinement are outlined. For a plasma with central fuelling there is a net radial flow of electrons across each magnetic surface. Borrass and Pfirsch have used plasma fluid equations to show that in such a case the instability responsible for the plasma transport must be manifest as an anomalous perpendicular resistivity. Otherwise the poloidal flux is convected out leading to a steady-state skin current which would be hydromagnetically unstable. For an edge fuelled plasma the mean radial flow of electrons is zero. But there are then limitations on the beta value and severe requirements on the diffusion rates inwards and outwards of fuel ions and alpha particles respectively. An experimental test of the physics involved requires current drive and a pulse length exceeding the skin-penetration time. However some deductions can be made from the results of present experiments and these are presented