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A Faraday-effect polarimeter for fast magnetic dynamics measurement on DIII-D
J Chen1, W X Ding1, D L Brower1
1Physics and Astronomy, University of California Los Angeles, Los Angeles, California 90095, USA.
The Review of Scientific Instruments
|November 8, 2018
Summary
A new diagnostic tool measures fast magnetic field changes in DIII-D plasmas using a Faraday-effect-based radial-interferometer-polarimeter. This advancement allows for detailed observation of magnetic dynamics in high-performance fusion experiments.
Area of Science:
- Plasma Physics
- Fusion Energy Research
- Diagnostic Techniques
Background:
- Understanding fast magnetic dynamics is crucial for controlling high-performance plasmas in fusion devices like DIII-D.
- Existing diagnostic methods may have limitations in resolving rapid magnetic field perturbations.
Purpose of the Study:
- To develop and validate a novel Faraday-effect-based radial-interferometer-polarimeter diagnostic.
- To explore fast magnetic dynamics in high-performance DIII-D plasmas.
- To investigate and mitigate systematic errors in polarimetric measurements.
Main Methods:
- Utilized a Faraday-effect-based radial-interferometer-polarimeter with three chords near the magnetic axis.
- Employed newly developed solid-state sources operating at 650 GHz with low phase noise.
- Calibrated polarization distortion using a rotating quarter-wave plate and evaluated the Cotton-Mouton effect.
- Optimized alignment to minimize non-collinearity errors for electron densities up to 7 × 10^19 m^-3.
Main Results:
- Observed coherent and broadband high-frequency magnetic fluctuations in DIII-D H-mode plasmas.
- Successfully investigated and quantified various systematic errors, including optical component distortion and non-collinearity.
- Minimized measurement errors through alignment optimization and reduction of optical feedback.
Conclusions:
- The developed diagnostic is effective for exploring fast magnetic dynamics in fusion plasmas.
- The study provides a validated method for precise magnetic field perturbation measurements.
- The findings contribute to improved understanding and control of plasma behavior in fusion research.
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