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See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1094.pdf
Measurements and modeling of DIII-D low collisionality (v*e~0.1-0.3) plasmas reveal pedestal-top locked modes as the probable trigger for Edge-Localized-Mode (ELM) suppression by n=2 and n=3 Resonant Magnetic Perturbations (RMPs) in a range of plasma conditions including neutral beam torque 3 - 6 Nm, plasma average triangularity delta=0.6-0.3 and edge safety factor q95=3.1-4.1. At the onset of ELM suppression in all these conditions, a rapid (< 1 ms) increase is observed in the high-field-side magnetic response concomitant with an increase in the co-Ip ExB rotation at the top of the pedestal. The nonlinear two-fluid MHD code TM1 [1] is used to simulate the onset of edge locked modes driven by RMPs for experimentally relevant profiles and transport parameters. The simulations reproduce the observed magnitude and time scale for changes in the pedestal ExB rotation and magnetic response of the plasma, strongly supporting the conjecture that ELM suppression is triggered by edge locked mode onset. Further evidence for magnetic island generation at the onset of ELM suppression comes from experiments designed to the hover near the threshold of ELM suppression. Near threshold conditions we observe cyclic magnetic pulsations with a slow toroidal rotation of the plasma magnetic response to the RMP [2], consistent with recent theoretical predictions of the limit cycle behavior of partially penetrated resonant fields [3]. The ELMs are suppressed cyclically in phase with the magnetic pulsations, consistent with the role of finite size magnetic islands in ELM suppression.
This work was supported in part by the US Department of Energy under DE-AC02-09CH11466, DE-FC02-04ER54698, DEAC05-06OR23100 and DE-FG02-04ER54761. DIII-D data shown in this paper can be obtained in digital format by following the links at https://fusion.gat.com/global/D3D_DMP. Disclaimer: This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.
[1] Hu, Q. et al. Nucl. Fusion 59, 016005 (2019),
[2] R. Nazikian et al Nucl. Fusion 58 106010 (2018)
[3] R. Fitzpatrick, Physics of Plasmas 25, 112505 (2018)
