Error correction associated with stray light for Faraday-effect polarimetry system on EAST

Area of Science:

• Plasma physics
• Fusion energy research
• Optical diagnostics

Background:

• Tokamak devices require accurate plasma measurements for operational control.
• Polarimeter-interferometer systems are crucial for electron density and plasma current profiling.
• Stray light from optical components and reflections introduces significant errors in Faraday rotation measurements.

Purpose of the Study:

• To develop and report a data processing approach to mitigate stray light influence on Faraday rotation measurements.
• To improve the accuracy of electron density and plasma current profile diagnostics in tokamaks.

Main Methods:

• Developed a theoretical model to analyze stray light effects.
• Extracted Faraday rotation angle by subtracting a deviation term calculated using a simplified model.
• Implemented a data processing technique to correct for spurious reflections and feedback light.

Main Results:

• Successfully reduced Faraday rotation oscillation from 2°-5° to 0.5°-1.5° during density ramp-up.
• Significantly decreased measurement errors caused by stray light.
• Demonstrated the effectiveness of the data processing approach for daily tokamak operation.

Conclusions:

• The developed data processing method effectively reduces stray light interference in polarimeter-interferometer systems.
• This approach enhances the reliability and accuracy of electron density and plasma current profile measurements.
• The technique is valuable for improving the operational performance of the Experiment Advanced Superconducting Tokamak.