Deterioration and improvement of hot plasma confinement in magnetic fusion devices

Abstract
A simple physical picture of plasma transport in magnetic fusion devices allows us to deduce the decreasing energy confinement time with added heating power and the increasing confinement time with added plasma current. The first is due to Bohm-like diffusion and the second is due to the characteristics of Z pinches and a decrease of deposited power due to enhanced radiation loss. The addition of momentum into a plasma by flowing current that includes noninductive current drive may lead to a Z-pinch effect that compensates for the decrease in confinement time caused by the heating.