MHD-Limits to Plasma Confinement

Ideal MHD restricts both the current and the pressure which can be stably confined in a Tokamak. A pressure profile optimisation is carried out for a variety of equilibria, which include JET and INTOR-like plasmas, in order to obtain the maximum β which can be stably confined at constant current. The current is limited to a value corresponding to a safety factor slightly above 2 at the plasma surface. A simple scaling law is found that fits well all the cases and which predicts a linear rise of 3 with the current.