Author: Tünde Fülöp
Requested Type: Poster
Submitted: 2018-02-27 08:06:11
Co-authors: L. Hesslow, O. Embreus, G. Wilkie, M. Hoppe, G. Papp
Chalmers University of Technology
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
In this contribution, we review recent results on RE dynamics obtained with the relativistic finite-difference Fokker-Planck solver CODE [Landreman et al, CPC 2014] and its nonlinear counterpart NORSE [Stahl et al, CPC 2017]. The latter includes a fully nonlinear relativistic collision operator, making it possible to consider scenarios where the electric field is comparable to the Dreicer field (or larger), or the electron distribution function is otherwise far from a Maxwellian, which can be the case already in present-day runaway experiments.
We show that accounting for the presence of partially ionized impurities in combination with synchrotron and bremsstrahlung radiation losses leads to an effective critical field that is drastically larger than the classical Connor-Hastie field, and even exceeds the value obtained by replacing the free electron density by the total electron density (including both free and bound electrons). Using CODE with a self-consistent inductive electric field, we show that the runaway current decay after an impurity injection is expected to be linear in time and proportional to the effective critical electric field in highly inductive tokamak devices.