The principal method of heating Wendelstein 7-X is through electron cyclotron resonance heating (ECRH). The ray-tracing code TRAVIS is built to model ECRH mathematically, as well as electron cyclotron current drive (ECCD) and emission (ECE). The code works with an arbitrary 3D magnetic configuration that is applicable for both stellarator and tokamak geometry. The wave field is calculated by weakly relativistic ray tracing, i.e. with thermal effects taken into account, while the absorption, current drive and emissivity are calculated fully relativistically. For ECCD, a so-called adjoint technique is applied for calculating the driven current in arbitrary geometry with approximately the same accuracy as in full Fokker-Planck simulations but with much less effort.
Macroscopic quantities such as the power deposition profile or the radiative temperature can be decomposed into contributions from trapped and passing particles. TRAVIS provides an understanding of these issues in stellarators, not only in interpreting the experiments, but also in choosing suitable target plasmas and magnetic configurations. The spatial width of the emission line, calculated together with the ECE spectrum, gives the theoretical upper limit to the spatial resolution of an ECE diagnostic. The energy range of emitting electrons calculated offers an additional possibility to analyse kinetic effects.
TRAVIS is a multi-beam and multi-pass ray-tracing code which can be used stand-alone (with user-friendly software) and coupled self-consistently with an 1D transport code. The code makes use of a specially designed graphical user interface, which allows the preparation of the input parameters and viewing the results in convenient (2D and 3D) form.