Modelling of Electron Cyclotron Radiative Transport in Fusion Plasmas: The new Code RAYTEC (Approach and Applications)

As it was recognised that local electron cyclotron (EC) wave power losses can be a competitive contribution to the 1D electron power balance for reactor-grade tokamak plasmas with core temperatures of 35 keV or higher as anticipated for steady-state operation in ITER and DEMO 1 and, therefore, have an impact on the temperature profile of these plasmas, a systematic effort is ongoing to improve the modelling capability for the radial profile of EC wave emission. This effort aims at generating and validating a hierarchy of codes that cover the non-local behaviour of EC wave transport with good accuracy and also provide sufficient computational efficiency for being usable in 1D transport studies 2 . To cover the effects of a non-circular plasma cross-section and of toroidicity for plasmas with arbitrary density and temperature profile, a new code, RAYTEC, which traces the change of the EC radiation intensity along the rays, has been developed and applied to ITERlike plasmas 3 . The motivation for this work was to provide an alternative to SNECTR which is no longer in active use. In its present form, the code addresses specular reflection (which allows tracing rays without having to rely on Monte-Carlo methods as does SNECTR) of straight rays at an ideally toroidal wall with elliptical cross section, and covers plasmas in thermodynamic equilibrium. The efficiency of the computations was enhanced by adopting Robinson’s approach 4, 5, 6 for the calculation of the EC absorption coefficient as well as by an appropriate modelling of the inner hot plasma for the lower frequencies for which the plasma effectively behaves as a black body and which contributes little to the net EC wave power density dP/dV that is emitted from the plasma. RAYTEC has been used to (i) investigate to which extent elongation of the plasma cross section and toroidicity affect the angular distribution of the radiation field I, (ii) determine the radial profile of the net EC wave power density dP/dV that is emitted from the plasma for