Optimizing confinement in a tokamak

Significant progress has been made in recent years in achieving levels of energy confinement in existing tokamaks which scale to that required for ITER. In particular, high confinement is achieved routinely in the plasma edge and in the plasma core, leading to steep density and temperature gradients. These gradients can drive non-inductive currents which could reduce significantly the requirements for externally applied current drive in a steady state tokamak. However, high confinement can also lead to deleterious effects related to pressure and current driven magnetohydrodynamic instabilities and to impurity accumulation. Experimental effort is now turning to the real time control of plasma and current profiles to facilitate the achievement of high confinement and to prevent the deleterious effects which could otherwise inhibit the development of a fully coherent operating scenario for a reactor.