Bulletin of the American Physical Society
64th Annual Meeting of the APS Division of Plasma Physics
Volume 67, Number 15
Monday–Friday, October 17–21, 2022; Spokane, Washington
Session GI02: Magnetic Confinement Fusion III
9:30 AM–12:30 PM,
Tuesday, October 18, 2022
Room: Ballroom 100 B
Chair: Carlos Paz-Soldan, Columbia University
Abstract: GI02.00005 : Internal plasma response measurements at the pedestal top in ELM suppressed plasmas in ASDEX Upgrade*
11:30 AM–12:00 PM
Presenter:
Matthias Willensdorfer
(Max Planck Institute for Plasma Physics)
Authors:
Matthias Willensdorfer
(Max Planck Institute for Plasma Physics)
Verena Mitterauer
(Max Planck Institute for Plasma Physics)
Guillermo Suarez
(Max Planck Institute for Plasma Physics)
Wolfgang Suttrop
(Max Planck Institute for Plasma Physics)
Mark R Cianciosa
(Oak Ridge National Lab)
Mike Dunne
(Max Planck Institute for Plasma Physics)
Rainer Fischer
(Max Planck Institute for Plasma Physics)
Matthias Hoelzl
(Max Planck Institute for Plasma Physics)
Tabea Gleiter
(Max Planck Institute for Plasma Physics)
Daniel Wendler
(Max Planck Institute for Plasma Physics)
Collaboration:
ASDEX Upgrade Team, MST1 team
To study the presence of a possible magnetic island limiting the pedestal pressure profile [1], we investigated the response of the pedestal electron temperature (Te) to external n=2 magnetic fields in ELM suppressed plasmas and plasmas with ELMs in ASDEX Upgrade [2]. Rigidly rotating MP-fields and high-resolution electron cyclotron emission measurements are combined to measure helical perturbations of the Te profile around the 7/2 rational surface, which is the rational surface at the pedestal top in the analysed scenario.
The measured radial displacement exhibits pronounced structures in its amplitude and phase profile around the 7/2 rational surface in ELM-suppressed plasmas, which are not seen in plasmas with ELMs. These structures are not captured by ideal magnetohydrodynamic (MHD) modelling using VMEC and suggest the presence of a magnetic island at the pedestal top in addition to ideal kink modes in ELM-suppressed plasmas. In contrast, the plasma response at the q=7/2 surface in ELMy plasmas is well described by ideal MHD modelling. Resistive structures are also observed at other rational surfaces (e.g. q=6/2) away from the pedestal top but in the presented cases not in conjunction with ELM suppression.
We further analysed the 3D ExB flow velocity (as determined from the radial force balance), which is close to zero at the rational surface where resistive structures are seen, in agreement with the observations of Ref. [3].
[1] R. Nazikian et al., Physical Review Letters, 2015
[2] W. Suttrop et al., Nuclear Fusion, 2018
[3] C. Paz-Soldan et al., Nuclear Fusion, 2019
*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.
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