Orbital effects on pitch angle diffusion of injected fast-ion beams in tokamaks

Abstract

The effects of ion orbits on pitch angle scattering of fast ion beam injection are investigated here for the magnetic equilibrium of the ITER tokamak. Two methods are used to calculate distributions in the presence of orbits, one applying boundary conditions a posteriori and one a priori. In both cases an orbit average of the Fokker-Planck equation is taken, yielding a solution in velocity space variables velocity and pitch angle. In the first case, conditions in the form of a linear combination of co, counter, and trapped distributions or fluxes are matched at the orbit transition value of pitch angle so that several distributions combine to form a solution. In the second case, an overall distribution is found which obeys boundary conditions derived from the trapped and passing regime essential behavior. Ultimately, both methods yield distributions which are essentially equivalent in character.