Bayesian approach for validation of runaway electron simulations

Aaro E. Järvinen*, Tünde Fülöp, Eero Hirvijoki, Mathias Hoppe, Adam Kit, Jan Åström, JET Contributors

*Corresponding author for this work

    Research output: Contribution to journalArticleScientificpeer-review

    3 Citations (Scopus)
    51 Downloads (Pure)

    Abstract

    Plasma-terminating disruptions in future fusion reactors may result in conversion of the initial current to a relativistic runaway electron beam. Validated predictive tools are required to optimise the scenarios and mitigation actuators to avoid the excessive damage that can be caused by such events. Many of the simulation tools applied in fusion energy research require the user to specify input parameters that are not constrained by the available experimental information. The conventional approach, where an expert modeller calibrates these input parameters based on domain knowledge, is prone to lead to an intractable validation challenge without systematic uncertainty quantification. Bayesian inference algorithms offer a promising alternative approach that naturally includes uncertainty quantification and is less subject to user bias in choosing the input parameters. The main challenge in using these methods is the computational cost of simulating enough samples to construct the posterior distributions for the uncertain input parameters. This challenge can be overcome by combining probabilistic surrogate modelling, such as Gaussian process regression, with Bayesian optimisation, which can reduce the number of required simulations by several orders of magnitude. Here, we implement this type of Bayesian optimisation framework for a model for analysis of disruption runaway electrons, and explore for simulations of current quench in a JET plasma discharge with an argon induced disruption. We use this proof-of-principle framework to explore the optimum input parameters with uncertainties in optimisation tasks ranging from one to seven dimensions. The relevant Python codes that are used in the analysis are available via https://github.com/aejarvin/BO_FOR_RE_SIMULATIONS/.
    Original languageEnglish
    Article number905880612
    JournalJournal of Plasma Physics
    Volume88
    Issue number6
    DOIs
    Publication statusPublished - Dec 2022
    MoE publication typeA1 Journal article-refereed

    Funding

    The authors wish to acknowledge CSC-IT Center for Science, Finland, for computational resources. This work has been carried out within the framework of the EUROfusion Consortium, funded by the European Union via the Euratom Research and Training Programme (Grant Agreement No 101052200 – EUROfusion). This work was carried out under the EUROfusion E-TASC Advanced Computing Hub project. The work of Eero Hirvijoki was supported by the Academy of Finland grant no. 315278. The work was supported in part by the Swedish Research Council (Dnr. 2018-03911).

    Keywords

    • fusion plasma
    • plasma simulation
    • runaway electrons

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