Characterisation of electron cyclotron wall conditioning plasma in ASDEX Upgrade

T. Wauters*, J. Buermans, J. Cavalier, E. Huett, R. Ragona, J. Svoboda, V. Bobkov, M. Griener, A. S. Jacobsen, A. Kallenbach, J. Likonen, T. Loarer, T. Lunt, S. K. Nielsen, R. A. Pitts, D. Ricci, V. Rohde, J. Stober, P. Schneider, M. UsoltsevaEUROfusion MST1 Team

*Corresponding author for this work

    Research output: Contribution to journalArticleScientificpeer-review

    4 Citations (Scopus)

    Abstract

    Electron cyclotron wall condition (ECWC) discharges are characterised in ASDEX Upgrade with full tungsten plasma facing components and X2 polarised waves launched from the equatorial ports, relevant to ECWC conditions in ITER Pre-Fusion Power Operation phase 1. The characterisation of the deuterium plasmas is based on experimental inputs such as electron density measurements, in-vessel pressure measurements, poloidal field maps obtained from the measured coil currents, as well as advanced tomographic methods on camera images filtered at the hydrogen Balmer lines. TOMATOR-1D simulations and collective Thomson scattering radiometer spectra complement the findings. The cold, high density and partially ionized toroidal plasmas show significant levels of stray radiation. The measured radiation includes waves at half of the gyrotron frequency suggesting the occurrence of parametric decay instabilities at 2nd harmonic upper hybrid resonance that locates at the low field side of the resonance. A displacement of the plasma emission along the resonance layer is observed at higher discharge power in discharges with a vertical poloidal magnetic field only. By optimizing the poloidal field pattern, along with the location of the electron cyclotron heating (ECH) resonance, the strongest surface interaction regions for the charged particles can be controlled. Directing plasma flux to inner wall surfaces, and same for the inner divertor apron, is found less effective in ASDEX Upgrade due to magnetic mirror effects and outward convective flows. Modeling however predicts the presence of an intense and uniform flux of low energy atoms produced at the ECH absorption layer that may be effective for conditioning the high field side surfaces after use of the disruption mitigation system.

    Original languageEnglish
    Article number066018
    JournalNuclear Fusion
    Volume63
    Issue number6
    DOIs
    Publication statusPublished - 17 Apr 2023
    MoE publication typeA1 Journal article-refereed

    Funding

    This work has been carried out within the framework of the EUROfusion Consortium, funded by the European Union via the Euratom Research and Training Programme (Grant Agreement No. 101052200—EUROfusion). Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or the European Commission. Neither the European Union nor the European Commission can be held responsible for them. Authors affiliated to the Institute of Plasma Physics of the Czech Academy of Sciences were also supported by the MEYS project number 9D22001. The work of S.K. Nielsen and A.S. Jacobsen was funded by research Grant 15483 from VILLUM FONDEN.

    Keywords

    • ECRH
    • ECWC
    • ITER
    • wall conditioning

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