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#36
Runaway Electron Studies Within the WPTE Framework Oral
Umar Sheikh (Ecole Polytechnique Federale de Lausanne (EPFL), Swiss Plasma Center (SPC))
U. Sheikh, J. Decker, O. Ficker, M. Hoppe, G. Papp, G. Pautasso, C. Paz-Soldan, C. Reux, L. Simons, T. Wijkamp and the WPTE team
SCHEDULED This contribution is scheduled to be presented on Monday 2nd 11:45-12:15
Abstract
The proposed talk will provide an overview of the runaway electron (RE) research program within WPTE. This will cover the experiments recently conducted on ASDEX Upgrade and TCV, diagnostic collaborations and modelling results. An outlook for the near-term future will also be presented. The primary experimental focus in the past year has been on the benign termination of a RE beam. This approach requires “flushing” of the impurity injected to create the RE beam, followed by a modification of the q-profile that results in an MHD instability, which expels all of the REs over a large wetted area. On TCV, the experimental plan has been designed to decouple the physics phenomena involved. Experiments have explored the flushing of Neon, used to create the RE beam, via deuterium and hydrogen injection. The flushing efficacy has been explored through variations in injected hydrogen and deuterium quantity, staggered multiple injections and variation of the original impurity content. A strong correlation between plasma state and neutral pressure was observed, leading to a novel approach of flushing using the fueling valves. This has allowed the plasma dynamics to be slowed down in the discharge phases of interest, enabling better diagnosis and finer control. Studies of MHD instabilities leading to the expulsion of suprathermal electrons are being conducted on TCV using the RE seed population created in the low-density scenarios. In this context, the current profile can be modified using actuators such as gyrotrons, which would normally not be usable after a disruption. Through this approach, the impact of sawteeth, NTMs and low q95 values on RE expulsion have been explored. In coordination with the flushing studies, benign termination attempts have begun. Benign termination studies are also being carried out in AUG. Comparisons between MGI flushing and fueling pellets have recently been conducted, however, low q95 values required for kink mitigation have not yet been achieved. The generation of RE beams with high Te, via an internal transport barrier, have also been explored. Numerous diagnostic collaborations have been initiated through this work program. These include the REAGARDS system, REIS-Upgrade, MANTIS-II diagnostic and an RF antenna. The status and outcomes of these diagnostics will be summarized in the presentation. Modelling of these WPTE experiments is ongoing. Kinetic codes such as LUKE calculate the RE population dynamics and global disruption simulators such as DREAM are used to interpret the flushing and benign termination experiments. Synthetic diagnostics such as SOFT (ECE and synchrotron radiation) and R5X2 (fast electron bremsstrahlung) enable direct comparison with measurements and model validation. An overview of this work with connections to other presentations will be presented.
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