What is it about?
Fusion is a virtually inexhaustible, carbon-free energy source, but requires control of plasma turbulence. Phase contrast imaging (PCI) measures the average plasma turbulence along the line-of-sight of a laser beam. However, a PCI system can also measure turbulence in a smaller plasma region if it is equipped with a masking plate. This paper describes a new model of the PCI masking technique. The model is used to design optimized masks for the PCI system at the W7-X fusion device. Using the optimized masks, we found the location of the strongest plasma turbulence in W7-X experimentally.
Featured Image
Photo by FlyD on Unsplash
Why is it important?
Fusion in high-temperature plasmas can play a key role in solving the energy and climate crises of the 21st century. However, plasma turbulence has been a major obstacle to making fusion power a reality. We, therefore, need to understand and control plasma turbulence. Phase contrast imaging (PCI) provides data to helps us achieve this goal. Without masking plates, PCI measures the overall turbulence level which only provides a part of the picture. The new mask model presented here allows PCI to explore important details, such as the location of the strongest plasma turbulence. This greatly improves the usefulness of PCI.
Perspectives
This project was an exciting mixture of theory development, mask design work using the theoretical model, and experimental testing of the theoretical model and mask design. The product of this two-year process is a powerful new tool for exploring the location of plasma turbulence in W7-X, which is the largest fusion device of the stellarator type and the first stellarator where turbulence plays a dominant role. We have already used this to obtain a number of new physics insights. It will be very interesting to apply these results in future W7-X experiments with higher heating power and reduced plasma turbulence.
Søren Kjer Hansen
Massachusetts Institute of Technology
Read the Original
This page is a summary of: Localized phase contrast imaging at the Wendelstein 7-X stellarator, Physics of Plasmas, June 2024, American Institute of Physics,
DOI: 10.1063/5.0197958.
You can read the full text:
Resources
Development of a synthetic phase contrast imaging diagnostic for turbulence studies at Wendelstein 7-X
Publication on the synthetic phase contrast imaging model at W7-X which was used to interpret the mask results
Phase contrast imaging measurements and numerical simulations of turbulent density fluctuations in gas-fuelled ECRH discharges in Wendelstein 7-X
First publication inferring the location of the strongest turbulence observed by phase contrast imaging in W7-X, which has been confirmed using the masks
The Wendelstein 7-X phase contrast imaging diagnostic
Publication describing the W7-X phase contrast imaging system
Contributors
The following have contributed to this page
