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17–22 Oct 2016
Kyoto International Conference Center
Japan timezone

Kinetic modelling of runaways in fusion plasmas

19 Oct 2016, 14:00
4h 45m
Kyoto International Conference Center

Kyoto International Conference Center

Takaragaike, Sakyo-ku, Kyoto 606-0001 Japan
Poster THW - Magnetic Confinement Theory and Modelling: Wave–plasma interactions; current drive; heating; energetic particles Poster 4

Speaker

Prof. Tünde Fülöp (Chalmers University of Technology)

Description

Runaway electrons (REs) are a pressing issue for ITER due to their significant potential to cause damage. Improved knowledge of RE formation mechanisms, their dynamics and characteristics, as well as transport or loss processes that may contribute to RE suppression and control, will benefit the fusion community and contribute to a safe and reliable operation of reactor-scale tokamaks. In this work we discuss bremsstrahlung radiation emission and knock-on collisions, and describe an accurate theoretical framework for studying their effect on the RE distribution. These processes, together with synchrotron radiation reaction, have important implications for the understanding of many phenomena, such as the effective critical electric field for RE generation and the formation of non-monotonic features in the RE tail. Starting from the Boltzmann transport equation, we derive a collision operator for bremsstrahlung radiation reaction, fully accounting for the finite energy and emission angle of the emitted photons. The Boltzmann bremsstrahlung operator allows the REs to reach energies several times higher than the previously used mean-force model, and the emission of soft photons shifts part of the momentum-space distribution function towards higher perpendicular momenta. Avalanche runaway generation is the phenomenon whereby REs are generated due to large-angle collisions of already existing REs with thermal electrons, leading to an exponential growth of the runaway current. Here we describe a new large-angle collision operator, derived as the high-energy limit of the linearized relativistic Boltzmann collision integral. This operator generalizes previous models of large-angle collisions to account for the full momentum dependence of the primary distribution, and conserves particle number, momentum and energy, while also avoiding the double counting of small and large-angle collisions. We investigate the effect of the operator on the evolution of the RE distribution and find that the change to the RE growth rate can be large, especially during the early stages of the runaway acceleration process, and the likelihood of a given runaway seed transforming into a serious runaway beam can thus potentially be affected.
Country or International Organization Sweden
Paper Number TH/P4-1

Primary author

Prof. Tünde Fülöp (Chalmers University of Technology)

Co-authors

Mr Adam Stahl (Chalmers University of Technology) Dr István Pusztai (Chalmers University of Technology) Mr Ola Embréus (Chalmers University of Technology) Dr Sarah Newton (Chalmers University of Technology)

Presentation materials