Dual-pass upgrade to the Thomson scattering diagnostic on the Prototype-Material Plasma Exposure eXperiment...

Area of Science:

• Plasma physics
• Fusion energy research
• Diagnostic techniques

Background:

• The Prototype-Material Plasma Exposure eXperiment (PMPX) requires precise measurements of plasma parameters.
• Understanding axial gradients is crucial for optimizing plasma confinement and performance.
• Previous diagnostics had limitations in spatial resolution and simultaneous multi-point measurements.

Purpose of the Study:

• To upgrade the Thomson scattering (TS) diagnostic system on PMPX.
• To enable simultaneous measurement of electron temperature (Te) and density (ne) at two axial locations.
• To improve the diagnosis of axial Te and ne gradients.

Main Methods:

• Implemented a double-pass laser beamline for Thomson scattering.
• Utilized an intensified CCD camera with double triggering to separate TS signals from background light.
• Increased the number of radial sampling points in both the central chamber and target regions.

Main Results:

• Successfully measured Te and ne at two axial locations (central chamber and target region).
• Observed distinct plasma parameter ranges: Te ≈ 4-15 eV and ne ≈ 2-4 × 10^19 m^-3 in the central chamber; Te ≈ 1-2 eV and ne ≈ 1-2 × 10^19 m^-3 in the target region.
• Enhanced measurement accuracy by subtracting plasma background light, including emission lines and bremsstrahlung.

Conclusions:

• The upgraded TS diagnostic effectively diagnoses axial electron temperature and density gradients.
• The enhanced spatial resolution and improved signal-to-noise ratio provide more reliable plasma characterization.
• Further optimization of the diagnostic setup can lead to even more precise plasma measurements.