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Title: Shrinking of core neoclassical tearing mode magnetic islands due to edge localized modes and the role of ion-scale turbulence in island recovery in DIII-D

Abstract

Experimental signature of long-wavelength turbulence accelerating the recovery of Neoclassical Tearing Mode (NTM) magnetic islands after they have been transiently reduced in size due to inter- action with Edge Localized Modes (ELMs) is reported for the first time. This work shows that per- turbations associated with ELMs result in peaking of the electron temperature (Te) in the O-point region of saturated core m/n 1/4 2/1 islands (m/n being the poloidal/toroidal mode numbers). In syn- chronization with this Te peak, the island width shrinks by as much as 30% suggesting a key role of the Te peak in NTM stability due to modified pressure gradient (rp) and perturbed bootstrap cur- rent (djBS) at the O-point. Next, this Te peak relaxes via anomalous transport (i.e., the diffusivity is 2 orders of magnitude larger than the neoclassical value) and the island recovers. Long-wavelength turbulent density fluctuations (n~) are reduced at the O-point of flat islands but these fluctuations are increased when Te is peaked which offers an explanation for the observed anomalous transport that is responsible for the relaxation of the Te peak. Linear gyrokinetic simulations indicate that n~ inside the peaked island is dominantly driven by the Ion Temperature Gradient instability. Thesemore » measure- ments suggest that n~ accelerates NTM recovery after an ELM crash via accelerating the relaxation of rp at the O-point. These observations are qualitatively replicated by coupled predator-prey equations and modified Rutherford equation. In this simple model, turbulence accelerates NTM recovery via relaxing rp and therefore restoring djBS at the O-point. The key physics of the rela- tionship between the Te peak and NTM stability has potentially far-reaching consequences, such as NTM control via pellet injection in high-b tokamak plasmas.« less

Authors:
 [1];  [1]; ORCiD logo [1];  [2]; ORCiD logo [1];  [3]
  1. Univ. of California, Los Angeles, CA (United States)
  2. General Atomics, San Diego, CA (United States)
  3. Univ. of Wisconsin, Madison, WI (United States)
Publication Date:
Research Org.:
General Atomics, San Diego, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
1361640
Alternate Identifier(s):
OSTI ID: 1361924
Grant/Contract Number:  
AC02-05CH11231; FC02-04ER54698; FG03-86ER53266; FG02-08ER54984
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Physics of Plasmas
Additional Journal Information:
Journal Volume: 24; Journal Issue: 6; Journal ID: ISSN 1070-664X
Publisher:
American Institute of Physics (AIP)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY

Citation Formats

Bardóczi, Laszlo, Rhodes, Terry L., Carter, Troy A., La Haye, Robert J., Bañón Navarro, Alejandro, and McKee, George R. Shrinking of core neoclassical tearing mode magnetic islands due to edge localized modes and the role of ion-scale turbulence in island recovery in DIII-D. United States: N. p., 2017. Web. doi:10.1063/1.4985078.
Bardóczi, Laszlo, Rhodes, Terry L., Carter, Troy A., La Haye, Robert J., Bañón Navarro, Alejandro, & McKee, George R. Shrinking of core neoclassical tearing mode magnetic islands due to edge localized modes and the role of ion-scale turbulence in island recovery in DIII-D. United States. doi:10.1063/1.4985078.
Bardóczi, Laszlo, Rhodes, Terry L., Carter, Troy A., La Haye, Robert J., Bañón Navarro, Alejandro, and McKee, George R. Thu . "Shrinking of core neoclassical tearing mode magnetic islands due to edge localized modes and the role of ion-scale turbulence in island recovery in DIII-D". United States. doi:10.1063/1.4985078. https://www.osti.gov/servlets/purl/1361640.
@article{osti_1361640,
title = {Shrinking of core neoclassical tearing mode magnetic islands due to edge localized modes and the role of ion-scale turbulence in island recovery in DIII-D},
author = {Bardóczi, Laszlo and Rhodes, Terry L. and Carter, Troy A. and La Haye, Robert J. and Bañón Navarro, Alejandro and McKee, George R.},
abstractNote = {Experimental signature of long-wavelength turbulence accelerating the recovery of Neoclassical Tearing Mode (NTM) magnetic islands after they have been transiently reduced in size due to inter- action with Edge Localized Modes (ELMs) is reported for the first time. This work shows that per- turbations associated with ELMs result in peaking of the electron temperature (Te) in the O-point region of saturated core m/n 1/4 2/1 islands (m/n being the poloidal/toroidal mode numbers). In syn- chronization with this Te peak, the island width shrinks by as much as 30% suggesting a key role of the Te peak in NTM stability due to modified pressure gradient (rp) and perturbed bootstrap cur- rent (djBS) at the O-point. Next, this Te peak relaxes via anomalous transport (i.e., the diffusivity is 2 orders of magnitude larger than the neoclassical value) and the island recovers. Long-wavelength turbulent density fluctuations (n~) are reduced at the O-point of flat islands but these fluctuations are increased when Te is peaked which offers an explanation for the observed anomalous transport that is responsible for the relaxation of the Te peak. Linear gyrokinetic simulations indicate that n~ inside the peaked island is dominantly driven by the Ion Temperature Gradient instability. These measure- ments suggest that n~ accelerates NTM recovery after an ELM crash via accelerating the relaxation of rp at the O-point. These observations are qualitatively replicated by coupled predator-prey equations and modified Rutherford equation. In this simple model, turbulence accelerates NTM recovery via relaxing rp and therefore restoring djBS at the O-point. The key physics of the rela- tionship between the Te peak and NTM stability has potentially far-reaching consequences, such as NTM control via pellet injection in high-b tokamak plasmas.},
doi = {10.1063/1.4985078},
journal = {Physics of Plasmas},
issn = {1070-664X},
number = 6,
volume = 24,
place = {United States},
year = {2017},
month = {6}
}

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