Magneto-hydrodynamics and fast particles
The research unit Magneto-hydrodynamics and fast particles (MHD) is focused on theoretical studies of large-scale magneto-hydrodynamic instabilities and their interactions with supra-thermal particles in view of future burning plasmas. A priority lies in the development of fluid, hybrid, and kinetic models and codes for describing such phenomena. While most research is focused on tokamaks, also stellarator related questions are being addressed.
Transient magneto-hydrodynamic events and their control constitute a major challenge for fusion research in view of a successful implementation of ITER and DEMO. Theoretical models allow to establish a robust physics understanding and extrapolate to future devices after careful validation against experiments.
One of the most violent and problematic magneto-hydrodynamic events in tokamaks are major disruptions and the associated vertical displacement events (VDEs) and runaway electrons (REs). Our investigations include the development of efficient mitigation strategies to avoid excessive vessel forces and heat loads onto plasma facing components. Edge localized modes (ELMs), which can reduce the lifetime of divertor structures by large transient heat loads are studied as well, aiming at detailed physics understanding and to develop reliable ELM-free regimes and techniques for mitigation or suppression.
Predicting the physics of supra-thermal particles due to fusion-born alpha particles in a burning plasma requires theories and tools that address the multi-scale kinetic nature of the problem. For that purpose, the research unit is developing, verifying and validating a set of hierarchical models, that range from fast analytical estimates via hybrid models up to cutting-edge global gyrokinetic simulations. Linear stability thresholds, non-linear dynamics and overall transport of supra-thermal particles, mainly due Alfvénic or large scale MHD-type perturbations are investigated. A close collaboration with present-day experiments, in particular ASDEX Upgrade but also JT-60SA and JET ensures continuous progress in interpreting the increasingly complex plasma scenarios and refined measurements. Based on this process, the research unit aims to give input on optimal exploitation strategies and safe operation – e.g. avoiding first wall damage due to expelled energetic ions – of future tokamaks like ITER and DEMO.
Main codes used and developed in the research unit for studying MHD instabilities are the linear visco-resistive code CASTOR3D (tokamaks and stellarators), the extended non-linear two-fluid code TM1 (large aspect ratio limiter tokamaks), and the extended non-linear MHD code JOREK (divertor tokamaks). For kinetic physics problems, the research unit relies inter alia on LIGKA/HAGIS, HMGC, ORB5 and the full-f gyrokinetic TRIMEG code (divertor tokamaks).