Equilibrium of Tokamak Plasma

The first extraordinary equilibrium to be considered is the so-called “advanced tokamak” scenarios aiming at obtaining internal transport barriers (ITBs) in tokamak plasmas. The second extraordinary equilibrium is the equilibrium obtained in “spherical tokamaks” at record high values of plasma β, β ∼ 1. In this case, plasma pressure expels magnetic field from the centre of plasma and may form a diamagnetic well. The ITB scenarios are obtained by applying high power of an auxiliary heating to tokamak plasma early in the discharge and well before the inductive current diffuses to the plasma centre. Plasma equilibria in tokamaks are usually described by the Grad–Shafranov equation pretty well, so this approach is used in a majority of tokamak discharges in present-day machines. Due to the incomplete penetration of the inductive current to the central region at the start of main heating, a hollow current profile is often created with non-monotonic safety factor-profile.