Speaker
Jan Mlynar
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I1.002.pdf
Runaway Electron experiments at COMPASS in support
of the EUROfusion ITER physics research
J. Mlynar1 , O. Ficker1,2 , E. Macusova1 , V. Plyusnin3 , J. Urban1 , M. Vlainic4 , V. Weinzettl1 ,
the COMPASS team1 & the EUROfusion MST1 Team*
A more detailed list of co-authors shall be provided in the contribution.
1 Institute of Plasma Physics of the CAS, 18200 Prague, Czech Republic
2 FNSPE, Czech Technical University in Prague, 11519 Prague, Czech Republic
3 IST - IPFN, Av. Rovisco Pais 1, 1049-001 Lisbon, Portugal
4 Institute of Physics, University of Belgrade, P.O. Box 68, 11080 Belgrade, Serbia
* See the author list of H. Meyer et al., Nuclear Fusion 57 (2017) 102014
Research into generation, confinement and mitigation of Runaway Electrons (REs) in tokamaks
presents one of the key tasks of the fusion energy development due to the risk of damage of the
ITER plasma facing components by post-disruption RE beams. Two major groups of experi-
ments aimed at improved understanding and control of REs were carried out on the COMPASS
tokamak. In the first group, the effects of Massive Gas Injection (MGI, Ar or Ne, ∼ 1020 par-
ticles) and impurity seeding (∼ 1019 particles) were studied systematically. The observed phe-
nomena include generation of the post-disruption RE beam, current conversion from plasma
to REs, and formation and decay of RE filaments. Studies of the penetration of impurity gas
puff into RE dominated discharges complement this work. Differences between Ar and Ne
penetration into the RE beam were mainly attributed to their ionisation potentials and atomic
masses in accordance with spectral measurements. A distinctive drop of the background plasma
temperature and electron density was observed following an additional deuterium injection into
the RE beam. This change slowed down the RE current dissipation significantly. The second
group of experiments was focused on the role of the magnetic field in the physics of REs.
In particular, the RE currents formation and decay were studied depending on the plasma elon-
gation, magnetic field strength, feedback on plasma current and, most importantly, on multiple
sources of the magnetic field perturbations. Special attention was given to the effects of the
Resonant Magnetic Perturbation (RMP) on the RE current formation and decay. The benefit of
the RE experiments on COMPASS was reinforced by diagnostic enhancements (fast cameras,
Cherenkov detector, vertical ECE etc.), the loop voltage control and the modelling efforts (for
example, the CODE and the MARS-F codes). The current status of the art in the RE studies on
COMPASS will be given in the framework of results achieved in the coordinated EUROfusion
RE research programme. Major challenges linked to the planned RE research shall be outlined.
