Validity of models for Dreicer generation of runaway electrons in dynamic scenarios
Journal article, 2021

Runaway electron modelling efforts are motivated by the risk these energetic particles pose to large fusion devices. The sophisticated kinetic models can capture most features of the runaway electron generation but have high computational costs, which can be avoided by using computationally cheaper reduced kinetic codes. This paper compares the reduced kinetic and kinetic models to determine when the former solvers, based on analytical calculations assuming quasi-stationarity, can be used. The Dreicer generation rate is calculated by two different solvers in parallel in a workflow developed in the European integrated modelling framework, and this is complemented by calculations of a third code that is not yet integrated into the framework. Runaway Fluid, a reduced kinetic code, NORSE, a kinetic code using non-linear collision operator, and DREAM, a linearized Fokker-Planck solver, are used to investigate the effect of a dynamic change in the electric field for different plasma scenarios spanning across the whole tokamak-relevant range. We find that on time scales shorter than or comparable to the electron-electron collision time at the critical velocity for runaway electron generation, kinetic effects not captured by reduced kinetic models play an important role. This characteristic time scale is easy to calculate and can reliably be used to determine whether there is a need for kinetic modelling or cheaper reduced kinetic codes are expected to deliver sufficiently accurate results. This criterion can be automated, and thus it can be of great benefit for the comprehensive self-consistent modelling frameworks that are attempting to simulate complex events such as tokamak start-up or disruptions.

runaway electron

kinetic modelling


integrated modelling

Dreicer generation


S. Olasz

Budapest University of Technology and Economics

Hungarian Academy of Sciences

Ola Embréus

Chalmers, Physics, Subatomic, High Energy and Plasma Physics

Mathias Hoppe

Subatomic, High Energy and Plasma Physics PP

M. Aradi

Barcelona Supercomputing Center (BSC)

D. Por

Budapest University of Technology and Economics

T. Jonsson

Royal Institute of Technology (KTH)

Dimitriy Yadykin

Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics


Hungarian Academy of Sciences

Budapest University of Technology and Economics

Nuclear Fusion

0029-5515 (ISSN) 1741-4326 (eISSN)

Vol. 61 6 066010

Implementation of activities described in the Roadmap to Fusion during Horizon 2020 through a Joint programme of the members of the EUROfusion consortium (EUROfusion)

European Commission (EC) (EC/H2020/633053), 2014-01-01 -- 2019-01-01.

Subject Categories

Applied Mechanics

Bioinformatics (Computational Biology)

Fusion, Plasma and Space Physics



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