Sources for constellation errors in modulated dispersion interferometers.

Area of Science:

• Plasma physics
• Interferometry
• Fusion energy research

Background:

• Dispersion interferometry (DI) is crucial for measuring plasma density in fusion experiments, offering vibration resistance.
• High-density DI utilizes high-frequency phase modulation for accurate measurements, but temporal interferogram evaluation presents phase error challenges.
• Existing non-approximation-based methods for DI phase evaluation (Fourier spectrum ratio and sectioned integration) have limitations and cannot be used concurrently.

Purpose of the Study:

• To develop a technique enabling simultaneous use of two non-approximation-based DI phase evaluation methods.
• To compare the strengths and weaknesses of these methods under identical measurement conditions.
• To identify and analyze error sources in DI phase measurements, particularly polarization effects.

Main Methods:

• Implemented a novel technique combining two DI phase evaluation methods using quadrature correction.
• Conducted comparative measurements to assess method reliability in static and dynamic scenarios.
• Investigated phase measurement errors induced by polarization rotation and Faraday rotation.

Main Results:

• Successfully demonstrated the simultaneous application of Fourier spectrum ratio and sectioned integration methods for DI phase evaluation.
• Identified that one method is more reliable for static plasma conditions, while the other performs better in dynamic environments.
• Revealed polarization rotation as a significant error source impacting phase measurements.

Conclusions:

• The developed technique enhances the accuracy and reliability of plasma density measurements using DI.
• The findings have direct implications for the design of dispersion interferometer/polarimeter systems in current and future fusion reactors, including ITER and DEMO.
• Understanding and mitigating polarization-induced errors is critical for advancing fusion diagnostics.