62nd Annual Meeting of the APS Division of Plasma Physics
Volume 65, Number 11
Monday–Friday, November 9–13, 2020;
Remote; Time Zone: Central Standard Time, USA
Session NI02: Invited: Magnetic Fusion: ELMs
9:30 AM–12:30 PM,
Wednesday, November 11, 2020
Chair: Ahmed Diallo, PPPL
Abstract: NI02.00004 : Predicting operational windows of ELMs suppression by Resonant Magnetic Perturbations in the DIII-D and KSTAR tokamaks.*
11:00 AM–11:30 AM
Live
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Abstract
Author:
Qiming Hu
(Princeton Plasma Physics Laboratory)
A newly developed plasma response model, combining the nonlinear two-fluid
MHD code TM1 and toroidal ideal MHD code GPEC, quantitatively predicts the
narrow isolated $q_{\mathrm{95}}$ windows ($\Delta
q_{\mathrm{95}}\approx $ 0.1) of ELM suppression by $n=$ 1, 2 and 3
resonant magnetic perturbations (RMPs) in both DIII-D and KSTAR tokamaks
across a wide range of plasma parameters. The key physics that unites both
experimental observations and our simulations is the close alignment of key
resonant $q$-surfaces and the location of the top of the pedestal prior to an
ELM. This alignment permits an applied RMP to produce field penetration
rather than being screened due to the lower \textbf{E}x\textbf{B} rotation
at the pedestal top. The model successfully predicts that narrow magnetic
islands form when resonant field penetration occurs at the top of pedestal,
and these islands are easily screened when $q_{\mathrm{95}}$ moves off
resonance, leading to very narrow windows of ELM suppression (typically
$\Delta q_{\mathrm{95}}\approx $ 0.1). Furthermore, the observed
reduction in the pedestal height is also well captured by the calculated
collisional transport across the island. We recover the $q_{\mathrm{95}}$,
$\beta_{\mathrm{N}}$ and plasma shape dependence of ELM
suppression due to the effect of magnetic islands on pedestal transport and
Peeling-Ballooning-Mode (PBM) stability. Importantly, experiments do
occasionally observe wide windows of ELM suppression ($\Delta
q_{\mathrm{95}}\ge $ 0.5). Our model reveals that at low density multiple
islands open at the pedestal top, leading to wide operational windows of ELM
suppression consistent with experiment. The model indicates that wide
$q_{\mathrm{95}}$ windows of ELM suppression can be achieved at substantially
higher pedestal pressure with less confinement degradation in DIII-D by
operating at higher toroidal mode number ($n=$ 4) RMPs. This can have
significant implications for the operation of the ITER ELM control coils for
maintaining high confinement during ELM suppression.
*Work supported by US DOE contracts DE-FC02-04ER54698 and DE-AC02-09CH11466.