Wendelstein 7-X
Promising stellarator principle
The Max Planck Institute for Plasma Physics in Greifswald operates Wendelstein 7-X, the world's largest stellarator. The stellarator principle is a promising alternative to the tokamak for the magnetic confinement of fusion plasmas. However, Wendelstein 7-X also poses new challenges with its complex geometry.
Wendelstein 7-X (Figure: MPG IPP)
Research goals at Wendelstein 7-X
The goal of the optimized Wendelstein 7-X stellarator is to demonstrate the good confinement of particles and energy in the fusion plasma. An important building block for this is the controlled decoupling of energy and particles in the edge region. The investigation of plasma-wall interactions is therefore an important element of the research program at Wendelstein 7-X.
The Jülich programme
Jülich has already played a part in the experimental setup in Greifswald by developing a superconducting bus system for coil feeding, and now contributes core competence in the areas of plasma-wall interactions and materials by developing diagnostics and simulation methods. Jülich is also developing a high-frequency heating system for the plasma together with Belgian partners.
Plasma-wall interactions in the three-dimensional boundary layer
A number of special diagnostics are being developed at Jülich for suitable observation of the processes in the plasma boundary layer. Among other things, helium is introduced selectively into the plasma boundary layer via a precisely controllable gas inlet. Local plasma parameters can be obtained from observation of the light produced by the interactions with the fusion plasma. A fast-moving manipulator was also installed on the propagation path of the gas injected into the plasma, which can be equipped with suitable measuring heads to briefly measure density, temperature and fluctuations as well as the magnetic field structure directly in the plasma boundary layer. The manipulator can also be used to expose materials to the plasma over a longer period of time and to analyze them directly afterwards in order to investigate erosion and deposition processes. A special Jülich method will be used to study local plasma structures and their motion from the reflection of microwaves. In a later phase, laser-based analysis methods for the wall will contribute to the understanding of deposition processes.
Model computations
The Jülich experimental program at Wendelstein 7-X is complemented by contributions to theory. The development of suitable simulation models for the plasma boundary layer and their application contribute to the interpretation of the measurement results and to the overall understanding of the processes in the plasma.
