Low temperature Thomson scattering on MAST-U.

Area of Science:

• Fusion energy research
• Plasma physics diagnostics

Background:

• Tokamak divertors are crucial for plasma exhaust and heat dissipation.
• Accurate electron density and temperature measurements are vital for understanding plasma behavior in divertor regions.

Purpose of the Study:

• To develop and implement an advanced divertor Thomson scattering system for the MAST-U tokamak.
• To enhance electron density and temperature profile measurements along the Super-X divertor leg.
• To achieve measurements at lower electron temperatures and densities than previously possible.

Main Methods:

• Adaptation of an existing polychromator design for low-temperature measurements.
• Addition of a new 1061 nm channel with a 2 nm bandwidth.
• Implementation of OD6 optical filters and a 1064.1 nm laser line filter to minimize stray light.
• Application of a novel averaging technique to scattered signal traces for noise reduction.

Main Results:

• Successful development of a new divertor Thomson scattering system for MAST-U.
• Enabled electron density and temperature measurements down to approximately 5 eV.
• Demonstrated improved data accuracy in the scrape-off layer due to noise reduction.
• Achieved radial profiles down to densities of ~1 x 10^18 m^-3.

Conclusions:

• The new divertor Thomson scattering system significantly enhances diagnostic capabilities for MAST-U.
• The system provides valuable data for understanding plasma physics in divertor regions, particularly at low densities.
• The developed techniques contribute to more accurate plasma characterization in fusion devices.