Speaker
Description
Understanding the MHD activity leading to runaway electron (RE) beam termination might al-
low a path to avoid localized first-wall damage in fusion-grade tokamaks such as ITER. Recent
experiments at JET demonstrated the possibility of benign termination of RE current [1], when
deuterium pellets were injected (via SPI) onto a plateau-phase RE beam with argon impurities in
the background plasma. This is the motivation of the present work, wherein through non-linear
MHD simulations, we aim to obtain some physical insight into the instabilities in the respective
JET experiments.
In this contribution, we present results of JOREK [2] simulations, that focus on the non-linear
interaction of resistive tearing modes with REs. Runaway electrons are modeled as a fluid that is
subjected to parallel transport and is electromagnetically coupled to the background plasma [3].
It is observed that the hollow current-profile of the equilibrium is conducive to the linear growth
of the unstable (m, n) = (4, 1) modes at the two q = 4 rational surfaces. In the non-linear phase,
this in turn leads to the growth of successively higher toroidal modes, eventually stochastising
the magnetic field in a large portion of the plasma cross-section and the corresponding expulsion
of REs. Both the timescales and the main qualitative dynamics in the simulations show close
resemblance to the experiment. The effect of runaway electrons and their transport velocity on the
linear and non-linear phases of this process is discussed.
References
[1] C. Reux et al., Manuscript in preparation (2020).
[2] G.T.A. Huijsmans et al., Nucl. Fusion 47.7, 659 (2007).
[3] V. Bandaru et al., Phys. Rev. E 99, 063317 (2019).
| Member State or International Organization | Germany |
|---|---|
| Affiliation | Max Planck Institute for Plasma Physics |
