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Tomographic inversion method to characterize coherent mode activity in the Wendelstein 7-X stellarator
C Büschel1, C Brandt1, H Thomsen1
1Max-Planck Institute for Plasma Physics, EURATOM Association, 17491 Greifswald, Germany.
The Review of Scientific Instruments
|May 21, 2026
Summary
A new method analyzes plasma coherent mode activity using soft x-ray tomography. This technique successfully reconstructs mode parameters, even with noisy data, aiding fusion energy research.
Area of Science:
- Plasma physics
- Fusion energy research
- Stellarator physics
Background:
- Coherent mode activity is crucial for understanding plasma behavior in fusion devices.
- Accurate analysis of these modes is essential for controlling plasma stability.
Purpose of the Study:
- To present a novel method for analyzing coherent mode activity in plasmas.
- To determine key mode parameters like frequency, location, and propagation.
Main Methods:
- Tomographic reconstruction of soft x-ray emissivity.
- Analysis of line-integrated, frequency-filtered soft x-ray signals from 360 photodiodes.
- Fitting reconstructed mode parameters to experimental data.
Main Results:
- Successfully reconstructed mode parameters, including frequency, poloidal mode number (m), and radial location.
- Demonstrated successful reconstruction even for modes near the noise level.
- Identified an m = 14 ± 2 mode in Wendelstein 7-X (W7-X) stellarator experiments.
Conclusions:
- The developed method provides accurate analysis of coherent mode activity.
- The identified mode characteristics align with theoretical predictions for kinetic ballooning modes at high plasma beta.
- This technique enhances plasma diagnostics for fusion research.
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