Helium line ratio imaging in the C-2W divertor

Area of Science:

• Plasma physics
• Fusion energy research
• Diagnostic instrumentation

Background:

• Understanding plasma behavior in divertor regions is critical for fusion energy development.
• Previous diagnostic methods had limitations in spatial resolution and coverage.
• The C-2W ("Norman") device requires advanced diagnostics for plasma characterization.

Purpose of the Study:

• To develop and deploy a 2D imaging instrument for studying plasma in the expander divertor.
• To simultaneously measure three neutral helium spectral lines for plasma analysis.
• To obtain 2D maps of electron temperature and density with high spatial resolution.

Main Methods:

• Designed and deployed a 2D imaging instrument on the C-2W device.
• Utilized a custom-built supersonic gas injector for a neutral helium target.
• Employed a collisional-radiative model with helium spectral line ratios to reconstruct plasma parameters.
• Achieved mapping of the entire radial plasma cross-section (∼60 cm) with spatial resolution ≲1 cm.
• Data acquisition rates of up to 3 kHz are achievable.

Main Results:

• Successfully generated 2D maps of electron temperature and density in the divertor region.
• Presented images of helium emission and reconstructed plasma profiles.
• Demonstrated the capability to map plasma characteristics across a significant radial extent.
• Validated the diagnostic's potential for high-frequency measurements.

Conclusions:

• The 2D imaging instrument provides valuable, high-resolution measurements of electron temperature and density in the C-2W divertor.
• These measurements are essential for investigating the impact of electrostatic biasing and magnetic fields on plasma confinement and transport.
• The diagnostic contributes to improving the understanding and performance of fusion devices.