Speaker
Ahmed Diallo
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1101.pdf
Studies of role of inter-ELM pedestal instabilities
on pedestal structure and ELM onset in DIII-D
A. Diallo1, J. Dominski1, F. Laggner2, K. Barada3, L. Zeng3, M. Brookman4,
M. Knolker1, M. Austin5, G. Canal6, B. Grierson1, E. Kolemen2, G. McKee7
1
Princeton Plasma Physics Laboratory, Princeton, NJ, USA: 2Princeton University,
Princeton, NJ, USA: 3UCLA, Los-Angeles, CA, USA: 4General Atomics, San Diego, CA
USA: 5University of Texas, Austin, USA: 6Plasma Physics Laboratory, Institute of Physics,
University of São Paulo, Brazil: 7University of Wisconsin, Madison, WI, USA
Experiments have been performed on DIII-D to study the role of inter-ELM pedestal
instabilities on both the pedestal structure and the onset of ELMs. In these experiments, we
scanned the NBI torque, puffed gas in the edge as well as varied the edge ECH heating to
study the impact of these actuators on the inter-ELM pedestal modes. We observe a
transition from a regime dominated at the beginning of the inter-ELM period by a single
mode located near q=5 which expands to a more balanced organization between this mode
and two secondary modes located near the q=6 surface just before the ELM onset. These
additional modes can couple energy from the pedestal into the separatrix, providing a
channel for the expulsion of energy and particles in the form of an ELM. More specifically,
a large majority of energy losses from the pedestal is thought to occur between ELMs [1].
The key players in this energy loss are instabilities localized in the pedestal such as kinetic
ballooning modes (KBM), electron temperature gradient (ETG), microtearing modes
(MTM), ion temperature gradient (ITG), etc. Many experiments have reported inter-ELM
pedestal modes (JET[2], C-Mod[3], DIII-D[4], AUG[5], EAST[6], and HL-2A[7]) that are
correlated with saturation of the pedestal gradients prior to the ELM onset. Recent
gyrokinetic calculations (GENE) have identified the pedestal modes on DIII-D to be
consistent with microtearing modes [9]. Here, we study the pedestal evolution between
ELMs to investigate the ELM onset mechanism. In addition, we report on pedestal
experiments where we extract the dynamics of the most dominant modes localized in the
pedestal during multiple inter-ELM periods and the effects of the various actuators on these
modes. This work was performed under US DoE contract DE-AC02-09CH11466,
DE-FC02-04ER5469, DE-FG02-08ER54984 and DE-FC02-04ER54698.
[1] A. Loarte ,et.al., Nucl. Fusion 54 (2014) 033007; [2] Perez et al., NF 2004; [3] Diallo et al. PRL 2014;
[4] Diallo et al., PoP 22, 056111 (2015); [5] Laggner et al., PPCF 2016; [7] Gao et al., NF 2015; [8] Zhong et
al., PPCF 2016. [9] M. Kotschenreuther et al., US-TTF 2017 “Fundamental considerations of gyrokinetic
pedestal transport”
