Efficient design and verification of diagnostics for impurity transport experiments

Area of Science:

• Plasma physics and fusion energy research.
• Diagnostic development for magnetic confinement fusion devices.

Background:

• Previous experiments on Alcator C-Mod aimed to measure impurity transport using X-ray imaging crystal spectroscopy and laser blow-off injection.
• These attempts did not successfully yield unique reconstructions of impurity diffusion (D_Z) and convection (V_Z) profiles.

Purpose of the Study:

• To develop a fast, linearized model to estimate diagnostic requirements for impurity transport experiments.
• To assess the capability of existing spectroscopic diagnostics for inferring impurity transport coefficients.

Main Methods:

• Construction of a fast, linearized model for diagnostic requirement estimation.
• Analysis of spectroscopic diagnostic capabilities on Alcator C-Mod.
• Investigating the impact of spatial and temporal resolution on transport coefficient inference.

Main Results:

• Spectroscopic diagnostics on Alcator C-Mod are theoretically capable of inferring simple impurity diffusion (D_Z) and convection (V_Z) profiles with <10% uncertainty.
• The inadequacy of the experimental analysis procedure, not the diagnostics themselves, is likely the cause of previous failures.
• Sufficient spatial resolution can compensate for limited temporal resolution in transport experiments.

Conclusions:

• Existing spectroscopic diagnostics on Alcator C-Mod are adequate for impurity transport studies.
• Improved data analysis techniques are crucial for successful impurity transport coefficient reconstruction.
• The developed modeling approach is adaptable for designing and validating diagnostics on other fusion devices.