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 (j_ECCD) for NTM suppressionmore » by 70%, as predicted by the modified Rutherford equation. Furthermore, this beneicial effect of fueling pellets can be important as j_ECCD 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:

Bardoczi, Laszlo  ^[1];

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Choi, Minjun J.  ^[2];

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Bañon-Navarro, Alejandro ^[3]; Shiraki, Daisuke  ^[4];

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La Haye, Robert John ^[5]; Park, S. H. ^[2]; Knölker, M.  ^[6];

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Evans, Todd E.  ^[7];

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McKee, George R.  ^[8];

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Woo, Minho ^[2]; Park, B. H. ^[2]; Jenko, Frank  ^[9]

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+ 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:

2019-10-23

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