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Title: Controlled neoclassical tearing mode (NTM) healing by fueling pellets and its impact on electron cyclotron current drive requirements for complete NTM stabilization

Abstract

Controlled partial stabilization of core m/n – 2/1 Neoclassical Tearing Modes (NTMs) by fueling deuterium pellets is reported in DIII-D and KSTAR H-mode plasmas (m=n are the poloidal/toroidal mode numbers). Analyses of DIII-D data exploring possible physics origins show that an explanation is offered by NTM-turbulence multi-scale interaction, triggered by a sudden increase of local gradients near q–2 caused by the pellet. Pellet injection from the high-field side allows deep fueling which reaches the island region. In turn, low-k turbulent density fluctuations (ñ) increase by 30% in the island region. This ñ can drive transport across the island separatrices, reducing the pressure at spot at the O-point and diminishing the NTM drive. The Mirnov probe array detects the reduction of the 2/1 magnetic amplitude by up to 20%. Causality between elevated gradients outside of the island, turbulence spreading into the island and reduced NTM drive is qualitatively supported by non-linear gyrokinetic turbulence simulations. These demonstrate increased penetration of ion-scale ñ from the background plasma to the O-point region when the background gradient is increased. This interaction has potentially far reaching consequences as it can can lead to a reduction of the required electron cyclotron current density (jECCD) for NTM suppressionmore » by 70%, as predicted by the modified Rutherford equation. Furthermore, this beneicial effect of fueling pellets can be important as jECCD is the anticipated active NTM control technique for the International Thermonuclear Experimental Reactor (ITER), but its efficiency will be lowered by third harmonic absorption in Pre-Fusion Power Operation-1 (PFPO-1) at half magnetic field.« less

Authors:
ORCiD logo [1]; ORCiD logo [2];  [3]; ORCiD logo [4];  [5];  [2]; ORCiD logo [6]; ORCiD logo [7]; ORCiD logo [8];  [2];  [2]; ORCiD logo [9]
+ Show Author Affiliations
  1. Univ. of California, Los Angeles, CA (United States)
  2. National Fusion Research Inst., Daejeon (Republic of Korea)
  3. Max Planck Institute for Plasma Physics, Garching (Germany)
  4. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  5. General Atomics, San Diego, CA (United States)
  6. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
  7. Univ. of California - San Diego, San Diego, CA (United States)
  8. Univ. of Wisconsin, Madison, WI (United States)
  9. Max-Planck-Inst. of Plasma Physics, Bayern (Germany)
Publication Date:
Research Org.:
General Atomics, San Diego, CA (United States); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Fusion Energy Sciences (FES); Ministry of Science, ICT and Future Planning (MSIT)
OSTI Identifier:
1569040
Alternate Identifier(s):
OSTI ID: 1657912
Grant/Contract Number:  
FC02-04ER54698; AC05-00OR22725
Resource Type:
Accepted Manuscript
Journal Name:
Nuclear Fusion
Additional Journal Information:
Journal Volume: 59; Journal Issue: 12; Journal ID: ISSN 0029-5515
Publisher:
IOP Science
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; ntm; magnetic island; eccd; control; turbulence; gyrokinetic

Citation Formats

Bardoczi, Laszlo, Choi, Minjun J., Bañon-Navarro, Alejandro, Shiraki, Daisuke, La Haye, Robert John, Park, S. H., Knölker, M., Evans, Todd E., McKee, George R., Woo, Minho, Park, B. H., and Jenko, Frank. Controlled neoclassical tearing mode (NTM) healing by fueling pellets and its impact on electron cyclotron current drive requirements for complete NTM stabilization. United States: N. p., 2019. Web. doi:10.1088/1741-4326/ab472d.
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Bardoczi, Laszlo, Choi, Minjun J., Bañon-Navarro, Alejandro, Shiraki, Daisuke, La Haye, Robert John, Park, S. H., Knölker, M., Evans, Todd E., McKee, George R., Woo, Minho, Park, B. H., & Jenko, Frank. Controlled neoclassical tearing mode (NTM) healing by fueling pellets and its impact on electron cyclotron current drive requirements for complete NTM stabilization. United States. https://doi.org/10.1088/1741-4326/ab472d
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Bardoczi, Laszlo, Choi, Minjun J., Bañon-Navarro, Alejandro, Shiraki, Daisuke, La Haye, Robert John, Park, S. H., Knölker, M., Evans, Todd E., McKee, George R., Woo, Minho, Park, B. H., and Jenko, Frank. Wed . "Controlled neoclassical tearing mode (NTM) healing by fueling pellets and its impact on electron cyclotron current drive requirements for complete NTM stabilization". United States. https://doi.org/10.1088/1741-4326/ab472d. https://www.osti.gov/servlets/purl/1569040.
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@article{osti_1569040,
title = {Controlled neoclassical tearing mode (NTM) healing by fueling pellets and its impact on electron cyclotron current drive requirements for complete NTM stabilization},
author = {Bardoczi, Laszlo and Choi, Minjun J. and Bañon-Navarro, Alejandro and Shiraki, Daisuke and La Haye, Robert John and Park, S. H. and Knölker, M. and Evans, Todd E. and McKee, George R. and Woo, Minho and Park, B. H. and Jenko, Frank},
abstractNote = {Controlled partial stabilization of core m/n – 2/1 Neoclassical Tearing Modes (NTMs) by fueling deuterium pellets is reported in DIII-D and KSTAR H-mode plasmas (m=n are the poloidal/toroidal mode numbers). Analyses of DIII-D data exploring possible physics origins show that an explanation is offered by NTM-turbulence multi-scale interaction, triggered by a sudden increase of local gradients near q–2 caused by the pellet. Pellet injection from the high-field side allows deep fueling which reaches the island region. In turn, low-k turbulent density fluctuations (ñ) increase by 30% in the island region. This ñ can drive transport across the island separatrices, reducing the pressure at spot at the O-point and diminishing the NTM drive. The Mirnov probe array detects the reduction of the 2/1 magnetic amplitude by up to 20%. Causality between elevated gradients outside of the island, turbulence spreading into the island and reduced NTM drive is qualitatively supported by non-linear gyrokinetic turbulence simulations. These demonstrate increased penetration of ion-scale ñ from the background plasma to the O-point region when the background gradient is increased. This interaction has potentially far reaching consequences as it can can lead to a reduction of the required electron cyclotron current density (jECCD) for NTM suppression by 70%, as predicted by the modified Rutherford equation. Furthermore, this beneicial effect of fueling pellets can be important as jECCD is the anticipated active NTM control technique for the International Thermonuclear Experimental Reactor (ITER), but its efficiency will be lowered by third harmonic absorption in Pre-Fusion Power Operation-1 (PFPO-1) at half magnetic field.},
doi = {10.1088/1741-4326/ab472d},
journal = {Nuclear Fusion},
number = 12,
volume = 59,
place = {United States},
year = {2019},
month = {10}
}
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Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record
https://doi.org/10.1088/1741-4326/ab472d
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Figures / Tables:

FIG. 1 FIG. 1: (a) Equilibrium reconstruction with pellet launch geometry. (b) Neutral beam power, (c) density (Thomson), (d) electron (T$e$, Thomson) and ion temperature (Ti, CER) inside the radial region of the 2/1 island, (e) normalized plasma beta, (f) n=1 magnetic RMS (Mirnov). Time trace of (g) ne, (h) Te andmore » Ti, (i) $n$ = 1 magnetic amplitude (thin orange line with circles: raw signal with 1 ms resolution, thick blue line: raw signal smoothed with 20 ms time constant), (j) raw poloidal magnetic field fluctuation at the tokamak wall (Mirnov) and (k) Divertor D$α$ signal during the injection of the largest pellet of the discharge.« less
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