Neoclassical tearing dynamo and self‐sustainment of a bootstrapped tokamak

The dynamo effect due to neoclassical tearing modes is considered. It is found that the global constraints on energy and helicity balance require a redefinition of the dynamo field in neoclassical magnetohydrodynamics. The parallel dynamo field is calculated from the boundary‐layer equations governing tearing modes. This dynamo effect can sustain a completely bootstrapped tokamak. A typical steady‐state current profile has a core region of weak pressure gradients surrounded by a region of strong pressure gradients, where the current profile is entirely due to the bootstrap effect.