Speaker
Dr
Florian M. Laggner
(Princeton University)
Description
For wide ranges of operational parameters and in machines with different wall materials, the inter-ELM pedestal profile evolution was robustly linked to characteristic fluctuations, indicating that universal instabilities dominate the pedestal structure and its dynamics in between edge localized modes (ELMs). The presented results substantially advance the comprehension of the underlying instabilities that determine the pedestal structure because ion and electron density as well as temperature gradients were found to become clamped in different phases of the ELM cycle. The general behavior of the inter-ELM fluctuations supports that similar mechanisms determine the pedestal of future fusion devices, and stresses the necessity that predictive models need to incorporate a robust mechanism, which describes the clamping of individual profile gradients across wide ranges of pedestal parameters.
The inter-ELM fluctuations exhibit a similar sequence of their onsets in ASDEX Upgrade and DIII-D. This gives strong evidence that their origin is the same, although both machines usually operate in different parameter regimes. Generally, low fluctuation amplitudes are found during the initial recovery of the maximum electron density gradient. After this phase, maximum electron density gradient saturates. The electron temperature pedestal evolves further and the saturation of maximum electron temperature gradient correlates with the onset of high frequency fluctuations.
Fast vertical plasma oscillations were utilized as a tool to probe the pedestal fluctuations as well as the pedestal stability. Such oscillations perturb the edge current. To make them an effective ELM pacing method, the pedestal must evolve close to its gradient saturation. This state of saturated gradients is stable, but marginal to the stability limit. If a perturbation, e.g. of the edge current, is applied, it is highly probable that an ELM crash is triggered.
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 under grant agreement No 633053. The views and opinions expressed herein do not necessarily reflect those
of the European Commission.
This work was supported by the US Department of Energy under DE-FC02-04ER54698, DE-SC0015878 and DE-SC0015480.
| Country or International Organization | United States of America |
|---|---|
| Paper Number | EX/P6-4 |
Primary author
Dr
Florian M. Laggner
(Princeton University)
Co-authors
Dr
Ahmed Diallo
(PPPL)
Dr
B.A. Grierson
(Princeton Plasma Physics Laboratory)
Prof.
Egemen Kolemen
(Princeton University)
Dr
Elisabeth Wolfrum
(Max Planck Institut fuer Plasmaphysik)
Mr
Felician Mink
(Max Planck Institut fuer Plasmaphysik)
Mr
Georg Friedrich Harrer
(Institute of Applied Physics, TU Wien, Fusion@OEAW)
Dr
Kshitish Kumar Barada
(UCLA, Los Angeles, USA)
Dr
Marco Cavedon
(Max Planck Institut fuer Plasmaphysik)
Dr
Philip B. Snyder
(General Atomics)
Dr
R.J. Groebner
(General Atomics)
Dr
Thomas H. Osborne
(General Atomics)
