3D Physics and Pedestal Transport

The research group investigates the physical mechanisms of toroidal asymmetries at the plasma edge and their influence on transport in the pedestal region.

The world is not ideal, and the same applies to the toroidal symmetry of a tokamak. Due to inaccuracies in the design or external influences such as coil feed-throughs, so-called intrinsic magnetic perturbation fields can arise, which lead to deviations from the toroidal symmetry of the tokamak plasma. These perturbations can affect the stability of the plasma edge and cause additional heat, particle and momentum transport, or in the worst case can lead to sudden disruptions. However, magnetic perturbations can also have positive effects. For example, deliberately applied external magnetic perturbaton can suppress eruptive edge instabilities, which is important for future fusion power plants.

The colours in the graphic represent the 3D deformation of the surface of the Tokamak plasma (red shows an outward bulge, blue an inward indentation), which is caused by perturbation coils (black coils). In addition, a small magnetic island is generated, the structure of which was successfully detected using high-resolution electron temperature measurements.

Graphic: Adapted by M. Willensdorfer, et al. Nat. Phys. (2024), under a Creative Commons license CC BY 4.0

The colours in the graphic represent the 3D deformation of the surface of the Tokamak plasma (red shows an outward bulge, blue an inward indentation), which is caused by perturbation coils (black coils). In addition, a small magnetic island is generated, the structure of which was successfully detected using high-resolution electron temperature measurements.

Graphic: Adapted by M. Willensdorfer, et al. Nat. Phys. (2024), under a Creative Commons license CC BY 4.0

The research group is investigating the following topics:

Operation and development of diagnostics: Implementation of methods such as Thomson scattering in the core, edge and divertor, electron cyclotron emission profiles and imaging in the plasma edge region.
Application of real-time measurements: Development and use of real-time measurements for profile control and stability monitoring.
Influence of asymmetries on instabilities: Non-axial magnetic perturbation fields can influence the behavior and symmetry of magnetohydrodynamic (MHD) instabilities. To this end, we compare measurements with 3D MHD codes such as CASTOR3D and JOREK, which are also used in stellarators.
Influence of external magnetic perturbations on transport: Small symmetry deviations can have a large effect on transport, in particular on momentum transport. Since each tokamak has a different intrinsic perturbation field, it is important to know and be able to describe this effect. The comparison between measurements and codes is essential here.
Physics of the suppression of edge instabilities: Investigation of ELM suppression (Edge Localized Modes) by applied magnetic perturbations. We are investigating the necessary conditions and the physics behind it.