Development of a forward model for Bayesian analysis of a single crystal dispersion interferometer

Area of Science:

• Plasma Physics
• Interferometry
• Fusion Energy Research

Background:

• Conventional heterodyne dispersion interferometers (DI) face challenges with beam overlap and alignment due to multiple nonlinear crystals.
• These challenges complicate data acquisition and system maintenance in fusion devices.

Purpose of the Study:

• To introduce the Single Crystal Dispersion Interferometer (SCDI), a novel DI system for KSTAR.
• To develop a forward model for analyzing SCDI data and estimating electron density with uncertainty.

Main Methods:

• The SCDI utilizes a single nonlinear crystal, replacing the second with a frequency doubler for simplified optical alignment.
• A forward model was developed, integrating optical and electronic systems, incorporating Gaussian and Poisson distributions for noise modeling (mechanical, electronic, photon).
• Bayesian-based data analysis routines were employed using the forward model as a likelihood function.

Main Results:

• The SCDI successfully obtained its first data on the KSTAR tokamak in January 2020.
• The developed forward model accurately infers line-integrated electron density and associated uncertainties from SCDI measurements.

Conclusions:

• The SCDI offers a simplified and more robust approach to dispersion interferometry compared to conventional systems.
• The validated forward model is crucial for accurate data analysis and provides a basis for future SCDI system design and improvements.