Coherence imaging spectroscopy at Wendelstein 7-X for impurity flow measurements

Area of Science:

• Plasma physics
• Spectroscopy
• Fusion energy research

Background:

• Coherence Imaging Spectroscopy (CIS) is crucial for measuring ion flow velocities in magnetically confined plasmas.
• Investigating impurity behavior in complex 3D magnetic island topologies, like at Wendelstein 7-X (W7-X), requires precise diagnostics.
• Existing CIS systems need highly accurate and stable calibration for reliable operation.

Purpose of the Study:

• To enhance the precision and stability of CIS systems at W7-X.
• To adapt a new calibration source for W7-X's specific requirements.
• To enable new investigations into CIS component performance.

Main Methods:

• Utilized a new, continuous tunable laser (commercially available since 2015) for calibration.
• Adapted a prototype laser model to meet W7-X's demanding specifications.
• Performed wavelength calibration with high accuracy (±0.01 pm) across a 450-650 nm spectral range.

Main Results:

• Achieved unprecedented precision and stability in CIS system calibration at W7-X.
• Successfully characterized and validated the W7-X CIS systems.
• Observed ion flow velocities of approximately 20-30 km/s during the W7-X experimental campaign.
• Corroborated CIS measurements with Mach probe data.

Conclusions:

• The new calibration method significantly improves CIS diagnostic reliability at W7-X.
• The enhanced CIS systems provide valuable data for understanding plasma edge physics.
• This work validates the CIS diagnostic's capability for future W7-X experiments.