Improved calculation of synchrotron radiation losses in realistic tokamak plasmas

Owing to the complexity of the exact calculation. synchrotron losses are us ually estimated in system studies, with expressions derived from a plasma d escription using simplifying assumptions on the geometry, radiation absorpt ion, and density and temperature profiles. In the present article, a comple te formulation of the transport of synchrotron radiation is performed for r ealistic conditions of toroidal plasma geometry with elongated cross-sectio n. using a quasi-exact method for the calculation of the absorption coeffic ients, and for arbitrary shapes of density and temperature profiles. The ef fects of toroidicity and temperature profile on synchrotron radiation losse s are analysed in detail. In particular, when the electron temperature prof ile is almost flat in the plasma centre as. for example, in internal transp ort barrier confinement regimes, synchrotron losses are found to be much st ronger than in the case where the profile is represented by its best genera lized parabolic approximation, though both cases give approximately the sam e thermal energy content. Such an effect is not included in presently used approximate expressions. As an illustration, it is shown that in the case o f an advanced high temperature plasma envisaged for a steady state commerci al reactor, synchrotron losses represent approximately 20% of the total los ses: so that this term becomes significant in the power balance of such a p lasma. Finally, the authors propose a seven variable fit for the fast calcu lation of synchrotron radiation losses. This fit is derived from a large da tabase which has been generated using a code implementing the complete form ulation, and is optimized for massively parallel computing.