INFLUENCE OF VARIOUS PHYSICS PHENOMENA ON FAST WAVE CURRENT DRIVE IN TOKAMAKS

The paper presents an analysis of the influence of various physics phenomena (which are not necessarily independent) on current drive performance in tokamaks. Such phenomena include diffraction and other non-geometrical optics processes, k(parallel-to) modification, and multiple-pass absorption as well as antenna characteristics such as recessed cavity and septa geometry, poloidal extent and poloidal location of the current straps. The two-and-one-half-dimensional (2 1/2-D) full-wave code PICES is used for modelling ion cyclotron resonance heating and current drive. PICES is based on poloidal mode and reduced-order expansions. By 2 1/2-D, we mean that 3-D wave fields are calculated in axisymmetric geometry (2-D solution domain -rho, theta), while the correct toroidal dependence of the antenna source currents is obtained from a 2-D (rho, phi) recessed antenna code. The calculation includes the poloidal and toroidal structure of the antenna, modification of the k(parallel-to) spectrum due to the poloidal magnetic field and a complete solution for E(parallel-to). A semi-analytic model for current drive, including trapped electron effects, is employed. These calculations are used extensively to model fast wave current drive in DIII-D, ITER and other tokamaks.