A NEW LOOK AT DENSITY LIMITS IN TOKAMAKS

The authors attempt to sort out the various limits and to extend the scaling law for one of them to include the important effects of plasma shaping, i.e. n¯e=kappaJ¯, where ne is the line average electron density (1020 m-3), κ is the plasma elongation and J¯(MA&middotm-2) is the average plasma current density, defined as the total current divided by the plasma cross-sectional area. In a sense, this is the most important density limit since, together with the q-limit, it yields the maximum operating density for a tokamak plasma. It is shown that this limit may be caused by a dramatic deterioration in core particle confinement occurring as the density limit boundary is approached. This mechanism can help explain the disruptions and Marfes that are associated with the density limit.