Validation of density pump-out by pedestal-foot magnetic island formation prior to ELM suppression in KSTAR and DIII-D tokamaks

Journal Article · 24 July 2023 · Nuclear Fusion

DOI: https://doi.org/10.1088/1741-4326/ace5c0 · OSTI ID:1992382

Hu, Q. M. ; Park, J. -K. ; Yang, S. M. ; Kim, S. K. ; Logan, N. C. ; Nazikian, R. ; Kang, J. ; Paz-Soldan, C. ; Ko, W. H.; Park, G. Y.

Abstract TM1 nonlinear two-fluid simulations reveal key characteristics of density pump-out caused by pedestal-foot island formation when applying resonant magnetic perturbation (RMP). These characteristics include a bifurcation in pump-out with a low RMP coil current threshold, a sensitivity of pump-out magnitude to q ₉₅ , and the magnitude of pump-out scaling as the square root of the RMP coil current. Dedicated experiments are carried out in the KSTAR and DIII-D tokamaks to validate these features and show that: (1) a staircase bifurcation in density pump-out is observed when slowly ramping up the n = 1 RMP current, and the density fluctuations are found to be slightly decreased from the pedestal-foot to the pedestal-top; (2) the magnitude of density pump-out becomes weaker when decreasing q ₉₅ from 5.5 to 4.9, and a partial recovery of density pump-out is observed when q ₉₅ is ramped down to lower than 4.9; and (3) analysis of a DIII-D database of n = 3 RMP edge-localized mode control experiments finds that the magnitude of density pump-out is proportional to the square root of RMP coil current Δ n _e / n _e ∝ $I_{\text{RMP}}^{0.5}$ . These experimental observations are consistent with TM1 simulations.

• Research Organization: General Atomics, San Diego, CA (United States); Princeton Plasma Physics Laboratory (PPPL), Princeton, NJ (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES). Scientific User Facilities (SUF); USDOE Office of Science (SC), Fusion Energy Sciences (FES)
• Grant/Contract Number: AC02-09CH11466; AC52-07NA27344; FC02-04ER54698; SC0021968; SC0022270
• OSTI ID: 1992382
• Journal Information: Nuclear Fusion, Journal Name: Nuclear Fusion Journal Issue: 9 Vol. 63; ISSN 0029-5515
• Publisher: IOP PublishingCopyright Statement
• Country of Publication: IAEA
• Language: English