The Density Dependence of Edge-Localized-Mode Suppression and Pump-out by Resonant Magnetic Perturbations in the DIII-D Tokamak

Journal Article · 10 December 2019 · Physics of Plasmas

DOI: https://doi.org/10.1063/1.5134767 · OSTI ID:1575408

Hu, Q.M.  ^[1]; Nazikian, R.  ^[2]; Grierson, B.  ^[2]; Logan, N.C.  ^[2]; Park, J-K  ^[2]; Paz-Soldan, C.  ^[3]; Yu, Q. ^[4]

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1. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States); General Atomics
2. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
3. General Atomics, San Diego, CA (United States)
4. Max Planck Society, Garching (Germany)

Here, the density dependence of edge-localized-mode (ELM) suppression and density pump-out (density reduction) by $$n$$ = 2 resonant magnetic perturbations (RMPs) is consistent with the effects of narrow well-separated magnetic islands at the top and bottom of the H-mode pedestal in DIII-D low-collisionality plasmas. Nonlinear two-fluid MHD simulations for DIII-D ITER Similar Shape (ISS) discharges show that, at low collisionality ($$v^*_e<0.5$$), low pedestal density is required for resonant field penetration at the pedestal top ($$n_{e,ped} ≈ 2.5x10^{19}$$ m^-3 at $$Ψ$$N≈0.93), consistent with the ubiquitous low density requirement for ELM suppression in these DIII-D plasmas. The simulations predict a drop in the pedestal pressure due to parallel transport across these narrow width ($$Δ_{ΨN}≈0.02$$) magnetic islands at the top of the pedestal that is stabilizing to Peeling-Ballooning-Modes (PBMs), and comparable to the pedestal pressure reduction observed in experiment at the onset of ELM suppression. The simulations predict density pump-out at experimentally relevant levels ($$Δn_e/n_e≈-20%$$) at low pedestal collisionality (n*e≈0.1) due to very narrow ($$Δ_{ΨN}≈0.01-0.02$$) RMP driven magnetic islands at the pedestal foot at $$Ψ$$N$≈0.99$. The simulations show decreasing pump-out with increasing density, consistent with experiment, resulting from the inverse dependence of parallel particle transport on collisionality at the foot of the pedestal. The robust screening of resonant fields is implicated between the top and bottom of the pedestal during density pump-out and ELM suppression, consistent with the preservation of strong temperature gradients in the edge transport barrier as seen in experiment.

• Research Organization: General Atomics, San Diego, CA (United States); Princeton Plasma Physics Laboratory (PPPL), Princeton, NJ (United States); Princeton Univ., NJ (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Fusion Energy Sciences (FES) (SC-24)
• Grant/Contract Number: AC02-09CH11466; FC02-04ER54698; SC0015878
• OSTI ID: 1575408
• Journal Information: Physics of Plasmas, Journal Name: Physics of Plasmas Journal Issue: 12 Vol. 26; ISSN 1070-664X
• Publisher: American Institute of Physics (AIP)Copyright Statement
• Country of Publication: United States
• Language: English