The Thomson scattering system at Wendelstein 7-X.

Area of Science:

• Plasma physics
• Fusion energy research
• Stellarator technology

Background:

• The Wendelstein 7-X (W7-X) stellarator is a leading experimental facility for magnetic confinement fusion research.
• Accurate plasma diagnostics are crucial for understanding and optimizing stellarator performance.
• The initial operation campaign required a robust Thomson scattering system for plasma characterization.

Purpose of the Study:

• To detail the design and implementation of the Thomson scattering diagnostic system for the W7-X stellarator.
• To establish a reliable method for measuring plasma electron temperature and density profiles.
• To validate the system's performance during the initial operational phase.

Main Methods:

• A 10-spatial channel Thomson scattering system was designed and installed.
• The system utilizes a Nd:YAG laser, observation optics, fiber bundles, and polychromators with silicon avalanche diodes.
• Spectral calibration employed a super continuum laser, and density calibration used Raman scattering in nitrogen gas.

Main Results:

• The Thomson scattering system successfully measured plasma profiles during the first operation campaign.
• Observed plasma characteristics included peaked temperature profiles and flat density profiles.
• The system demonstrated effective data acquisition using high dynamic range analog-to-digital converters.

Conclusions:

• The designed Thomson scattering system is effective for characterizing plasma in the W7-X stellarator.
• The system's calibration methods ensure accurate measurements of electron temperature and density.
• The observed plasma profiles provide valuable insights for fusion energy research at W7-X.