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10-15 May 2021
Nice, France
Europe/Vienna timezone
The Conference will be held virtually from 10-15 May 2021

Runaway electron experiments and model validation on ASDEX Upgrade and TCV

12 May 2021, 14:00
4h 45m
Nice, France

Nice, France

Regular Poster Magnetic Fusion Experiments P4 Posters 4

Speaker

Dr Gergely Papp (Max Planck Institute for Plasma Physics)

Description

Introduction
Disruptions in tokamaks can lead to the generation of a relativistic runaway electron (RE) beam - up to several megaamperes of current in a large tokamak - that may cause serious damage to the first wall. The issue of RE beam avoidance and mitigation is of prime importance for ITER [1]. RE dynamics are governed by a complex interplay of effects such as atomic processes, penetration of the high-Z material injected for mitigation, disruption dynamics (MHD), kinetic phenomena and quantum mechanical effects. The EUROfusion consortium is executing a coordinated research program to better understand the generation [2], control [3] and mitigation [4] of disruption-born REs following massive material injection.

Latest experimental results
TCV achieved RE beam control up to a pre-disruption elongation of $\kappa \approx 1.5$. RE beam experiments were also carried out at various triangularities, including negative triangularity discharges. Our results indicate that increasing elongation or changing triangularity has no significant impact on the post-disruption RE beam evolution, and the main challenge is position control.

ASDEX Upgrade (AUG) has developed RE beam scenarios in a wide range of magnetic fields ($B_t$ = 1.9 T to 2.9 T) and plasma currents ($I_p$ = 0.7 MA to 1.2 MA). A 12-point scan in this range of parameters demonstrated that post-disruption RE beam generation is only possible on AUG if the pre-disruption edge safety factor is $q_{95}>3$ (Fig. 1), a phenomenon to be investigated employing nonlinear MHD modeling.

$I_p$ - $B_t$ scan of RE generation on AUG.

High frequency (100 kHz to 1000 kHz) wave activity has been observed in the current quench (CQ) and RE beam stage in $\sim$ 85% of AUG RE discharges. The waves start in the CQ, last up to 7 ms, have an average sweep rate of 150 kHz/ms, have low toroidal mode numbers n<5 and appear to propagate in the ion diamagnetic direction. The presence, amplitude, frequency, mode number or chirp rate of the waves show no clear correlation with post-disruption RE beam evolution, unlike observations on other tokamaks.

Kinetic model validation
RE studies on ASDEX Upgrade and TCV are carried out using massive gas injection of neon, argon and krypton. The scaling of the initial RE current on plasma and injection parameters and the subsequent dissipation is analysed using 1D disruption-runaway simulations [5,6] along with state-of-the-art kinetic models [7] solving for the complete electron distribution (full-f). The high-Z dissipation model was validated for both pre- and post-disruption injections, on both AUG and TCV for neon, argon and krypton [4].

A 1:4 argon-deuterium mixture has prevented RE beam formation in the most commonly used RE scenario on ASDEX Upgrade (Fig 2). Modeling using the GO code [5] demonstrates that the scaling of RE current with deuterium fraction can only be explained if the latest models on Dreicer [9] and avalanche [8] generation are used. The improved growth rates, which include the impact of high-Z interaction and radiaton, are extracted from a full-f kinetic model and implemented using a combination of analytical formulas [8] and a neural network [9].

The effect of argon-deuterium mixture injections on RE generation, and comparison with modeling. The argon pressure was kept constant while increasing deuterium pressure in the mixture.

Experimental synchrotron images (Fig. 3e-h) of a vertically moving runaway electron beam sweeping past a filtered camera in the TCV tokamak agree well with predictions from the synthetic synchrotron diagnostic SOFT (Fig. 3a-d) [10,11]. Significant non-collisional pitch angle scattering as well as radial transport of REs - an indication of high-frequency modes - would be needed to explain the detected synchrotron emission. This experimental validation lends confidence to the theory underlying the synthetic diagnostics which are used for benchmarking theoretical models of and probing runaway dynamics.

Full-f kinetic simulations were carried out for the first time on AUG for the complete duration of the thermal and current quench. The resulting RE distribution functions are validated using synthetic diagnostics for synchrotron (SOFT) and hard X-ray radiation [12].

Simulated (a-d) and measured (e-h) synchrotron emission from a vertically translated runaway electron beam in TCV.

Acknowledgements
This work was supported by the EUROfusion - Theory and Advanced Simulation Coordination (E-TASC). This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014-2018 and 2019-2020 under grant agreement No 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission.

References
[1] B.N. Breizman et al., NF 59 083001 (2019)
[2] G. Pautasso et al., PPCF 59 014046 (2017)
[3] D. Carnevale et al., PPCF 61 014036 (2018)
[4] G. Papp et al., EPS I4.105 (2019)
[5] G. Papp et al., NF 53 123017 (2013)
[6] E. Fable et al., NF 56 026012 (2016)
[7] L. Hesslow et al., PRL 118 255001 (2017)
[8] L. Hesslow et al., NF 59 084004 (2019)
[9] L. Hesslow et al., JPP 85 475850601 (2019)
[10] M. Hoppe et al., NF 58 026032 (2018)
[11] M. Hoppe et al., NF submitted (2020)
[12] A. Shevelev et al., this conference

Affiliation Max Planck Institute for Plasma Physics
Country or International Organization Germany

Primary authors

Dr Gergely Papp (Max Planck Institute for Plasma Physics) Dr Gabriella Pautasso (Max Planck Institute for Plasma Physics) Dr Joan Decker (Ecole Polytechnique Fédérale de Lausanne – Swiss Plasma Center (SPC), Association Euratom-Confédération Suisse(EPFL) CH-1015 Lausanne, Switzerland) Umar Sheikh (Ecole Polytechnique Fédérale de Lausanne – Swiss Plasma Center (SPC), Association Euratom-Confédération Suisse(EPFL) CH-1015 Lausanne, Switzerland) Ondrej Ficker (Institute of Plasma Physics of the Czech Academy of Sciences) Mathias Hoppe (Chalmers University of Technology) Matthias Bernert (Max-Planck-Institut für Plasmaphysik) Patrick Blanchard (Ecole Polytechnique Fédérale de Lausanne – Swiss Plasma Center (SPC), Association Euratom-Confédération Suisse(EPFL) CH-1015 Lausanne, Switzerland) Dr Alexander Bock (Max Planck Institute for Plasma Physics) Tommaso BOLZONELLA (Consorzio RFX) Mr Luca Calacci (University of Rome Tor vergata) Daniele Carnevale (Universita' Roma Tor Vergata, Dipartimento di Ing. Civile ed Ing. Informatica) Dr Marco Cavedon (Max-Planck-Institut für Plasmaphysik) Jaroslav Cerovsky (Institute of Plasma Physics of the Czech Academy of Sciences) Dahye Choi (Ecole Polytechnique Fédérale de Lausanne – Swiss Plasma Center (SPC), Association Euratom-Confédération Suisse(EPFL) CH-1015 Lausanne, Switzerland) Dr Stefano Coda (Swiss Plasma Center (SPC), Ecole Polytechnique Fédérale de Lausanne (EPFL)) Dr Pierre David (Max-Planck-Institut f. Plasmaphysik) Dr Mathias Dibon (Max Planck Institute for Plasma Physics) Mike Dunne (IPP-Garching) Basil Duval (Ecole Polytechnique Fédérale de Lausanne – Swiss Plasma Center (SPC)) Ralph Dux (Max-Planck-Institut für Plasmaphysik, Garching, Germany) Dr Ola Embreus (Chalmers University of Technology) Michal Farnik (Institute of Plasma Physics of the Czech Academy of Sciences) Dr Michael Faitsch (Max-Planck-Institut für Plasmaphysik) Dr Rainer Fischer (Max Planck Institute for Plasma Physics) Christoph Fuchs (Max-Planck-Institut für Plasmaphysik) Marco Gobbin (Consorzio RFX, Associazione Euratom-ENEA sulla Fusione, Padova, Italy) CRISTIAN GALPERTI (Ecole Polytechnique Fédérale de Lausanne (EPFL), Swiss Plasma Center (SPC), CH-1015 Lausanne, Switzerland) Mr Luca Giacomelli (Institute for Plasma Physics and Technology, National Research Council, Milan, Italy) Dr Louis Giannone (Max-Planck Institut fuer Plasmaphysik) Dr Anja Gude (Max-Planck-Institute for Plasma Physics) Paul Heinrich (Max Planck Institute for Plasma Physics) Valentin Igochine (Max-Planck-Institut für Plasmaphysik) Ms Margarita Iliasova (Ioffe Insitute) Dr Klara Insulander Björk (Chalmers University of Technology) Filip Janky (Max Planck Institut für Plasmaphysik) Mr Eugeny Khilkevitch (Ioffe Institute) Luca Kosina (Max Planck Institute for Plasma Physics) Ondrej Kudlacek (Max Planck Institut für Plasmaphysik) BENOIT LABIT (Swiss Plasma Center (SPC) EPFL SWITZERLAND) Philipp Lauber (IPP Garching) Andrej Lier (Max Planck Institute for Plasma Physics) Oliver Linder (Max Planck Institute for Plasma Physics) Dr Tilmann Lunt (MPG-IPP) Dr Eva Macusoca (Institute of Plasma Physics of the CAS, Prague, Czech Republic) Dr Marc Maraschek (Max Planck Institute for Plasma Physics) Lionello Marrelli (Consorzio RFX) P. Marmillod (Ecole Polytechnique Fédérale de Lausanne – Swiss Plasma Center (SPC), Association Euratom-Confédération Suisse(EPFL) CH-1015 Lausanne, Switzerland) McCarthy Patrick (Department of Physics, University College Cork, Cork, Ireland) Jan Mlynar (Institute of Plasma Physics, Czech Academy of Sciences) Mr Andrea Dal Molin ( Dipartimento di Fisica “G. Occhialini”, Università di Milano-Bicocca, Milan, Italy) Massimo Nocente (Dipartimento di Fisica, Università di Milano-Bicocca) Mr Enrico Panontin (Dipartimento di Fisica “G. Occhialini”, Università di Milano-Bicocca, Milan, Italy) Ulrike Plank (Max-Planck-Institut für Plasmaphysik) Mr Artur Perek (Dutch Institute for Fundamental Energy Research) Gergo Pokol (NTI, Budapest University of Technology and Economics, Hungary) Dr Gabor Por (NTI, Budapest University of Technology and Economics, Hungary) Vladislav V Plyusnin (Instituto de Plasmas e Fusão Nuclear, Associação EURATOM-IST, Instituto Superior Tecnico) Mr Davide Rigamonti (Institute for Plasma Physics and Technology, National Research Council, Milan, Italy) Olivier Sauter (Ecole Polytechnique Fédérale de Lausanne – Swiss Plasma Center (SPC), Association Euratom-Confédération Suisse(EPFL) CH-1015 Lausanne, Switzerland) Bernhard Sieglin (Max Planck Institut für Plasmaphysik) Alexander Shevelev (Ioffe Institute) Wolfgang Suttrop (Max-Planck-Institut für Plasmaphysik) Dr Giovanni Tardini (IPP, Garching, Germany) Mr Marco Tardocchi (Institute for Plasma Physics and Technology, National Research Council, Milan, Italy) Dr Duccio Testa (EPFL Swiss Plasma Centre, Switzerland ) Markus Teschke (Max Planck Institute for Plasma Physics) Dr Wolfgang Treutterer (Max Planck Institute for Plasma Physics) Mr Lucas Unnerfelt (Chalmers University of Technology) Marco Valisa (Consorzo RFX) Mr Oskar Vallhagen (Chalmers University of Technology) Wijkamp Tijs (Dutch Institute for Fundamental Energy Research) ASDEX Upgrade team (Max Planck Institute for Plasma Physics) TCV team (Ecole Polytechnique Fédérale de Lausanne – Swiss Plasma Center (SPC), Association Euratom-Confédération Suisse(EPFL) CH-1015 Lausanne, Switzerland) the EUROfusion MST1 team

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