Design study of polychromators for ITER edge Thomson scattering diagnostics

Area of Science:

• Plasma Physics
• Fusion Energy Research
• Optical Engineering

Background:

• The ITER project requires advanced diagnostic systems for plasma measurement.
• Thomson scattering is a key diagnostic for electron temperature and density.
• Polychromators are crucial components for analyzing scattered light in Thomson scattering systems.

Purpose of the Study:

• To investigate and optimize polychromator designs for the ITER edge Thomson scattering system.
• To determine optimal optical filter transmission ranges and the number of filters.
• To evaluate the impact of different filter arrangements, including notch filters, on measurement accuracy.

Main Methods:

• Numerical calculations were employed to analyze polychromator designs.
• Five distinct filter arrangements were compared.
• Measurement accuracy was evaluated for a midplane port configuration.

Main Results:

• The optimal number of filters for cost-performance is determined to be 5 or 6.
• The inclusion of an optical notch filter to eliminate D(alpha) emission significantly improves measurement accuracy.
• A measurement accuracy increase of approximately 5% was observed with the use of a notch filter.

Conclusions:

• The study provides valuable insights into optimizing polychromator design for the ITER edge Thomson scattering system.
• The findings suggest that 5-6 filters offer the best balance between performance and cost.
• Implementing an optical notch filter is recommended for enhanced measurement accuracy.