TORBEAM, a beam tracing code for electron-cyclotron waves in tokamak plasmas Original Research Article

The beam tracing technique is used to describe the propagation and absorption of Gaussian wave beams with frequencies in the electron-cyclotron frequency range in a fusion plasma. Like in the standard ray tracing method, Maxwellʹs equations are reduced to a set of first-order ordinary differential equation. The technique employed here, however, allows for diffraction effects, neglected by the geometrical-optics procedure. The beam is specified in terms of the trajectory of the beam axis, the evolution of both the curvature of the wave front and the width of the field profile, as well as the absorption of the wave energy by the plasma. A Fortran code is presented, which solves the beam tracing equations in a tokamak geometry for arbitrary launching conditions and for both analytic and experimentally prescribed magnetic equilibria. Examples of wave propagation, power deposition and current profiles are computed and compared with ray tracing results.