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Contact:
Phone: +46 31 7723180

Email: tunde_at_chalmers.se

Address:
Dept of Applied Physics
Chalmers University of Technology
SE-412 96 Göteborg
Sweden

Energetic electrons

The presence of fast particles in fusion plasmas has tremendous impact on the whole plasma and its performance. These particles may give rise to collective instabilities, that could result in deterioration of plasma confinement and damage to the wall, but they may also have positive effects, e.g. they may stabilise MHD modes, or improve plasma heating and ash removal.

Our main effort in the area of fast particles is focused on the dynamics of relativistic runaway electrons accelerated to high velocities by electric fields in tokamak disruptions. This is one of the most crucial problems facing ITER and similar machines. During a disruption a very quick cooling of the plasma takes place, which makes it increasingly difficult to drive the current. As a result, there will be a dramatic rise of the toroidal electric field. Such an electric field can detach a fraction of the electrons in velocity space from the bulk of the plasma and accelerate them to very high energies (tens of MeV). The detached electrons are normally referred to as runaway electrons. In the end, the beam of runaway electrons will intersect material surfaces of the mechanical structure of the tokamak and can potentially cause severe damage to vital parts.

We analyze the generation and subsequent dynamics of runaway electrons and means for suppressing the phenomenon. The central questions are: Under which conditions do RE beams form? If a RE beam forms, what are its characteristics, i.e. what is the energy spectrum? Is it possible to transport REs out of the plasma as soon as they are generated (e.g. via magnetic perturbations)? What is the effect of mitigation techniques such as massive material injection?

The projects are funded by Vetenskapsrådet via a project grant "Runaway electrons in fusion plasmas" (VR-grant 2014-5510, PI Tünde Fülöp) and by Eurofusion by an Enabling Research project "Kinetic modelling of runaway electrons".

Project participants: Adam Stahl, Ola Embreus, Mathias Hoppe, Linnea Hesslow, Taina Kurki-Suonio, Tünde Fülöp. Collaborators: Gergely Papp (Max-Planck-Princeton Center, Garching), Matt Landreman (University of Maryland).