Electron Cyclotron Resonance Heating and Current Drive

We contribute numerical codes for the modelling of electron cyclotron resonance heating and current drive to the EUROfusion Integrated Tokamak Modelling platform. We have co-developed the TORAY-FOM ray-tracing code for the description of EC wave propagation and absorption. Rays can be traced using either the cold or warm plasma dispersion relation. Options are provided for weakly or fully relativistic calculations of the dielectric tensor. In addition the current drive efficiency can be calculated using the adjoint technique. We have developed the bounce-averaged quasi-linear Fokker-Planck code RELAX, which allows to calculate the modified electron distribution function and current drive under conditions of high power ECRH and ECCD. We have provided both codes with options to model ECRH and ECCD in the presence of magnetic islands as created by tearing modes.

Neoclassical Tearing Modes and their control

We model the evolution of neoclassical tearing modes (NTMs) using models of increasing levels of accuracy and complexity. A zero dimensional description is provided by the generalized Rutherford equation which provides the evolution of the width of the magnetic island. We study the models for the most relevant contributions in the Rutherford equation including the classical stability, the neoclassical drive, and the stabilizing terms from local heating and current drive. In the next step of complexity, we have developed a 2D reduced MHD code. With this code we have provided the validation of the neoclassical and current drive terms in the generalized Rutherford equation (see Highlights). Finally, we are collaborating in the use of the 3D nonlinear MHD code JOREK for the modelling of tearing modes and their control by ECCD.

Fast particles and sawteeth

We have developed a numerical tool set for the study of fast particles and their interaction with MHD instabilities and perturbations. This tool set is centered around a full orbit particle tracking code with modules providing the toroidally symmetric equilibrium fields of a tokamak, the contributions from static resonant magnetic perturbation coils, and the time varying fields associated with a sawtooth crash or an Alfvén Eigenmode. We have studied in detail the redistribution of fast particles by sawteeth and have achieved good comparisons of the model predictions with measurements performed on the ASDEX-Upgrade tokamak (see Highlights).