Imputation of faulty magnetic sensors with coupled Bayesian and Gaussian processes to reconstruct the magnetic equilibrium in real time

Semin Joung; Jaewook Kim; Sehyun Kwak; Kyeo-Reh Park; S H Hahn; H S Han; H S Kim; J G Bak; S G Lee; Y-C Ghim

doi:10.1063/1.5038938

Imputation of faulty magnetic sensors with coupled Bayesian and Gaussian processes to reconstruct the magnetic equilibrium in real time

Rev Sci Instrum. 2018 Oct;89(10):10K106. doi: 10.1063/1.5038938.

Authors

Semin Joung¹, Jaewook Kim¹, Sehyun Kwak¹, Kyeo-Reh Park¹, S H Hahn², H S Han², H S Kim², J G Bak², S G Lee², Y-C Ghim¹

Affiliations

¹ Department of Nuclear and Quantum Engineering, KAIST, Daejeon 34141, South Korea.
² National Fusion Research Institute, Daejeon 34133, South Korea.

PMID: 30399691
DOI: 10.1063/1.5038938

Abstract

A Bayesian with Gaussian process-based numerical method to impute a few missing magnetic signals caused by impaired magnetic probes during tokamak operations is developed such that the real-time reconstruction of magnetic equilibria, whose performance strongly depends on the measured magnetic signals and their intactness, is affected minimally. Likelihood of the Bayesian model constructed with Maxwell's equations, specifically Gauss's law for magnetism and Ampère's law, results in an infinite number of solutions if two or more magnetic signals are missing. This undesirable characteristic of the Bayesian model is remediated by coupling the model with the Gaussian process. Our proposed numerical method infers nine non-consecutive missing magnetic signals correctly in less than 1 ms suitable for the real-time reconstruction of magnetic equilibria during tokamak operations.