Single Gaussian process method for arbitrary tokamak regimes with a statistical analysis. (1st October 2022)

• Record Type: Journal Article
• Authors: Leddy, J; Madireddy, S; Howell, E; Kruger, S
• Is Part Of: Plasma physics and controlled fusion. Volume 64:Number 10(2022)
• Publication Date: 2022-10-01
• Subjects: tokamak -- equilibrium reconstruction -- Gaussian process regression -- EFIT -- Thomson scattering; Plasma (Ionized gases) -- Periodicals; Controlled fusion -- Periodicals; 530.44
• DOI: 10.1088/1361-6587/ac89ab
• Languages: English
• ISSNs: 0741-3335

Abstract

Abstract: Gaussian process regression is a Bayesian method for inferring profiles based on input data. The technique is increasing in popularity in the fusion community due to its many advantages over traditional fitting techniques including intrinsic uncertainty quantification and robustness to over-fitting. This work investigates the use of a new method, the change-point method, for handling the varying length scales found in different tokamak regimes. The use of the Student's t-distribution for the Bayesian likelihood probability is also investigated and shown to be advantageous in providing good fits in profiles with many outliers. To compare different methods, synthetic data generated from analytic profiles is used to create a database enabling a quantitative statistical comparison of which methods perform the best. Using a full Bayesian approach with the change-point method, Matérn kernel for the prior probability, and Student's t-distribution for the likelihood is shown to give the best results.