TOKAMAK DIVERTOR MAPS

A mapping method is developed to investigate the problem of determinat ion and control of heat-deposition patterns on the plates of a tokamak divertor. The deposition pattern is largely determined by the magneti c field lines, which are mathematically equivalent to the trajectories of a single-degree-of-freedom time-dependent Hamiltonian system. Maps are natural tools to study the generic features of such systems. The general theory of maps is presented, and methods for incorporating var ious features of the magnetic field and particle motion in divertor to kamaks are given. Features of the magnetic field include the profile o f the rotational transform, single- versus double-null divertor, rever se map, the effects of naturally occurring low M and N, and externally imposed high-M, high-N perturbations. Particle motion includes radial diffusion, pitch angle and energy scattering, and the electric sheath at the plate. The method is illustrated by calculating the stochastic broadening in a single-null divertor tokamak. Maps provide an efficie nt, economic and elegant method to study the problem of motion of plas ma particles in the stochastic scrape-off layer.