The motional Stark effect diagnostic on NSTX

Area of Science:

• Plasma Physics
• Fusion Energy Research
• Diagnostic Techniques

Background:

• The motional Stark effect (MSE) diagnostic is crucial for measuring magnetic field pitch in fusion plasmas.
• Low magnetic fields in devices like the National Spherical Torus Experiment (NSTX) pose challenges for traditional MSE diagnostics.
• Optimizing signal-to-noise ratio and minimizing Doppler broadening are key for accurate MSE measurements.

Purpose of the Study:

• To implement and report recent results from an improved MSE diagnostic on NSTX.
• To address the challenges posed by NSTX's low magnetic field for MSE measurements.
• To enhance the accuracy and temporal resolution of magnetic field pitch measurements.

Main Methods:

• Developed a novel optical design to reduce geometric Doppler broadening.
• Implemented a high-throughput, high-resolution spectral filter to improve signal quality.
• Utilized 16 operational sight lines for comprehensive plasma coverage.

Main Results:

• Achieved a polarization fraction of approximately 30%-40%.
• Obtained a time resolution of approximately 5 milliseconds.
• Successfully measured magnetic field line pitch from the plasma core to the outboard edge.

Conclusions:

• The novel optical and spectral filter design significantly enhances MSE diagnostic performance on NSTX.
• The improved diagnostic provides valuable data on magnetic field pitch distribution in low-field fusion environments.
• This work contributes to the advancement of diagnostic capabilities for magnetic confinement fusion research.