High-n Rydberg transition spectroscopy for heavy impurity transport studies in W7-X (invited)

Area of Science:

• Plasma Physics
• Atomic and Molecular Physics
• Spectroscopy

Background:

• Impurity transport is crucial for understanding and controlling high-temperature plasmas.
• Traditional methods for measuring impurity transport have limitations in localization and accuracy.
• High-n Rydberg states of impurity ions are not easily populated by impact excitation.

Purpose of the Study:

• To develop and validate a novel spectroscopy approach for investigating impurity transport.
• To determine impurity transport coefficients with high accuracy and documented confidence intervals.
• To demonstrate the utility of high-n Rydberg spectroscopy in plasma diagnostics.

Main Methods:

• Utilizing line-radiation following high-n Rydberg transitions.
• Employing charge exchange (CX) reactions along neutral beams to populate Rydberg states.
• Developing a technique to calculate effective emission coefficients using OPEN-ADAS database data.
• Comparing modeling results with new high-n Rydberg CX measurements and Bolometer data.

Main Results:

• Localized radiation of highly ionized impurities observed in the visible range.
• Effective emission coefficients calculated, reproducing energy dependence from databases.
• Impurity transport coefficients determined for the first time with 2σ confidence intervals.
• Error bars on transport coefficients reduced by incorporating Bolometer measurements.

Conclusions:

• High-n Rydberg spectroscopy provides significant constraints for determining impurity transport coefficients.
• The novel spectroscopy approach enhances the accuracy of plasma impurity analysis.
• Combined analysis with Bolometer measurements further refines impurity density and transport measurements.