Overview of negative triangularity experiments with strongshaping in ASDEX Upgrade

ORAL

Abstract

The Negative Triangularity (NT) is a regime where shaping appears to provide an edge-localized modes (ELMs) free scenario, while maintaining high confinement [1]. Complete ELM avoidance has been consistently achieved in strongly shaped plasmas on TCV [2] and DIII-D [3]. In contrast, early NT experiments in ASDEX upgrade resulted in H modes with weak ELMs, regardless of the ion ▽B drift configuration [5]. This outcome is attributed to the weak shaping with triangularity levels of δupp ≈ -0.33 and δlow ≈ +0.01. In this work, we report on a series of the latest ASDEX Upgrade experiments with stronger shaping of δupp ≈ -0.5 and δlow ≈ 0. An ideal MHD BALOO code calculation is in agreement with experimental observations and shows the closure of the second stability for those shapes, concomitant with the absence of ELMs. In addition, experience from TCV with similar plasma shapes suggested that these triangularity values would be adequate for ELM avoidance. This new shape served as a basis for various scans where experiments with increased density (via gas fueling and pellet injection), power levels up to 10 MW of pure Neutral Beam Injection (NBI) heating and combined with ECRH, and impurity seeding were conducted. There is evidence of strong power degradation; however, confinement improvement H98 ≈ 1 was observed with nitrogen seeding. Confinement qualities and the stability boundaries of the plasma edge, in those various cases, are discussed.

[1] A Marinoni 2021 RMPP

[2] S Coda 2022 PCF

[3] M Austin 2019 PRL

[4] T Happel 2023 NF

[5] B Vanovac 2024 PPCF

*This work is supported by the US DOE under Award DE-SC0014264. This work has been carried out within the frame-work of the EUROfusion Consortium, partially funded by the European Union via the Euratom Research and TrainingProgramme (Grant Agreement No 101052200 EUROfusion). The Swiss contribution to this work has been funded by theSwiss State Secretariat for Education, Research and Innovation (SERI). Views and opinions expressed are however those ofthe author(s) only and do not necessarily reflect those of the European Union, the European Commission or SERI. Neitherthe European Union nor the European Commission nor SERI can be held responsible for them.

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Presenters

  • Branka Vanovac

    • MIT PSFC

Authors

  • Branka Vanovac

    • MIT PSFC

  • Joerg Hobirk

    • Max Planck Institute for Plasma Physics, Garching, Germany

  • Thomas Puetterich

    • Max-Planck Institut für Plasmaphysik Division Plasma Dynamics
    • Max Planck Institute for Plasma Physics

  • Olivier Sauter

    • EPFL Swiss Plasma Center
    • EPFL, Swiss Plasma Center (SPC)
    • École Polytechnique Fédérale de Lausanne, Swiss Plasma Center, CH-1015 Lausanne, Switzerland
    • SPC-EPFL

  • Michael Faitsch

    • Max Planck Institute for Plasma Physics
    • Max-Planck-Institut für Plasmaphysik, Boltzmannstr. 2, 85748 Garching, Germany

  • Michael G Dunne

    • Max-Planck Institut für Plasmaphysik
    • Max–Planck–Institut fuer Plasmaphysik

  • Andrew O Nelson

    • Columbia University

  • Paola Mantica

    • Istituto per la Scienza e Tecnologia dei Plasmi, CNR, Milano

  • Rainer Fischer

    • Max Planck Institute for Plasma Physics, Garching, Germany

  • Dirk Stieglitz

    • Max-Planck Institut für Plasmaphysik

  • Tim Happel

    • Max-Planck-Institut für Plasmaphysik, Boltzmannstr. 2, 85748 Garching, Germany

  • Lorenzo Aucone

    • Department of Physics 'G. Occhialini', University of Milano-Bicocca, Milano