Development of Korea Superconducting Tokamak Advanced Researches (KSTAR) Lyman alpha diagnostics and its synthetic data algorithm

Characterizing the neutral density in the edge region of the magnetically confined plasma is critical for understanding power exhaust, fuel recycling, and the L–H transition. Lyman-α emission can offer two advantages over Balmer-α: higher emission intensity where the edge electron density is below 1019/m3, and simpler data analysis because the emissivity is directly tied to the ground-state atomic density, with a smaller molecular contribution at low temperatures near a divertor and the magnetic X-point. We report the Korea Superconducting Tokamak Advanced Research (KSTAR) Lyman Alpha Measuring Apparatus (KLAMA), a radial 20-channel system viewing the region near the magnetic X-point and lower divertor, with a radial channel separation of up to 1.3 cm. KLAMA uses three notch reflective filters designed to provide 13.02% transmission while suppressing the neighboring C-III line by a factor of ∼14. We have developed a synthetic data algorithm utilizing the Virtual KSTAR platform to optimize the optical design, quantify noise propagation, and build the transfer matrix. The synthetic data algorithm is also used for a Gaussian-process-regularized 2D reconstruction of the neutral density and is expected to be used to generate a forward model for a Bayesian inference analysis in future work. KLAMA has been manufactured and installed on KSTAR, and preliminary data acquired during a disruption are presented.