Compact and multi-view solid state neutral particle analyzer arrays on National Spherical Torus Experiment-Upgrade

Area of Science:

• Plasma physics
• Fusion energy research
• Diagnostic instrumentation

Background:

• Fast-ion behavior is crucial for understanding plasma confinement in fusion devices.
• Existing diagnostics have limitations in spatial, temporal, and pitch-angle resolution.
• Neutral particle analyzers are key for measuring fast-ion distributions via charge exchange.

Purpose of the Study:

• To test a compact, multi-view solid-state neutral particle analyzer (SSNPA) diagnostic.
• To evaluate the SSNPA's capability for spatially, temporally, and pitch-angle resolved fast-ion measurements.
• To assess SSNPA performance on the National Spherical Torus Experiment-Upgrade.

Main Methods:

• Utilized three 16-channel subsystems (t-SSNPA, r-SSNPA, p-SSNPA) with varying viewing geometries and filter thicknesses.
• Detected fast neutral flux from charge exchange (CX) reactions during neutral beam modulation.
• Analyzed active and passive CX signals to differentiate particle populations and energy information.

Main Results:

• All SSNPA channels were operational with a signal-to-noise ratio typically >10, primarily limited by X-ray induced noise.
• Clear observation of active and passive CX signals during neutral beam modulation.
• Identified significant losses of passing particles during sawtooth events, with minimal impact on trapped particles.
• Observed fluctuations up to 120 kHz correlated with magnetohydrodynamics instabilities.

Conclusions:

• The solid-state neutral particle analyzer (SSNPA) is a viable diagnostic for fast-ion measurements in fusion plasmas.
• SSNPA data reveal insights into fast-ion transport and losses, particularly during plasma instabilities like sawteeth.
• The diagnostic successfully captured high-frequency fluctuations linked to magnetohydrodynamics, enhancing plasma behavior understanding.