Eikonal description of HF waves in toroidal plasmas

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Abstract
The authors discuss the use of the Eikonal approximation to describe the propagation and absorption of HF waves in toroidally confined plasmas. Particular attention is devoted to the derivation of a power transport equation in agreement with conservation of energy, and to the formulation of appropriate boundary conditions when the waves are launched by electrically short antennas. The ray equations are then applied to investigate the occurrence of radial reflections, which can affect the accessibility of the plasma core to HF heating; examples are given for waves in the Lower Hybrid and in the Ion Cyclotron frequency ranges. Finally, the use of the power transport equation for the evaluation of power deposition profiles during HF heating of Tokamak plasmas is illustrated by the example of Lower Hybrid waves launched by a phased waveguide array.