EC beam tracing in fusion plasmas

The aim of the beam tracing technique is to include in the description of s hort-wavelength electromagnetic wave beams the effects of diffraction, whic h are neglected by the standard ray tracing method, but can play a signific ant role in focused or collimated wave beams. Beam tracing is, from a physi cal point of view, very close to other similar approaches, such as the para bolic equation and the complex eikonal description. In the beam tracing met hod, however, the problem is greatly simplified, since the full wave equati on is reduced to a set of ordinary differential equations that describe the behaviour of the beam axis, the width of the beam and the curvature of the wave front. The propagation of an electromagnetic wave beam in a simplifie d (slab) geometry can be studied analytically. These calculations allow inv estigation of situations in which the role of diffraction becomes significa nt, and clarification of the basic mathematical features of the formalism. In order to solve the problem for realistic plasma geometries and arbitrary launching conditions for the wave beam, a numerical approach is necessary. A new code is presented, in which the beam tracing equations are integrate d. Examples of absorption and current drive profiles are shown for RTO/RC I TER. (C) 2001 Elsevier Science B.V. All rights reserved.