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Title: Role of Microtearing Turbulence in DIII-D High Bootstrap Current Fraction Plasmas

Abstract

We report the first direct comparisons of microtearing turbulence simulations to experimental measurements in a representative high bootstrap current fraction ( f BS) plasma. Previous studies of high f BS plasmas carried out in DIII-D with large radius internal transport barriers (ITBs) have found that while the ion energy transport is accurately reproduced by neoclassical theory, the electron transport remains anomalous, and not well-described by existing quasilinear transport models. A key feature of these plasmas is the large value of normalized pressure gradient, which is shown to completely stabilize conventional drift-wave and kinetic ballooning mode instabilities in the ITB, but destabilizes the microtearing mode. Nonlinear gyrokinetic simulations of the ITB region performed with the CGYRO code demonstrate that the microtearing modes are robustly unstable and capable of driving electron energy transport levels comparable to experimental levels for input parameters consistent with the experimental measurements. These simulations uniformly predict that the microtearing mode fluctuation and flux spectra extend to significantly shorter wavelengths than the range of linear instability, representing significantly different nonlinear dynamics and saturation mechanisms than conventional drift-wave turbulence, also consistent with the fundamental tearing nature of the instability. In conclusion, the predicted transport levels are found to be mostmore » sensitive to the magnetic shear, rather than the temperature gradients more typically identified as driving turbulent plasma transport.« less

Authors:
ORCiD logo [1];  [1];  [2];  [2];  [2];  [2];  [3]
  1. Univ. of California, San Diego, La Jolla, CA (United States)
  2. General Atomics, San Diego, CA (United States)
  3. Oak Ridge Associated Univ., Oak Ridge, TN (United States); Chinese Academy of Sciences, Anhui (China)
Publication Date:
Research Org.:
Univ. of California, San Diego, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Fusion Energy Sciences (FES) (SC-24)
OSTI Identifier:
1576791
Report Number(s):
DOE-UCSD-18287-1
Journal ID: ISSN 0031-9007; PRLTAO
Grant/Contract Number:  
SC0018287
Resource Type:
Accepted Manuscript
Journal Name:
Physical Review Letters
Additional Journal Information:
Journal Volume: 123; Journal Issue: 22; Journal ID: ISSN 0031-9007
Publisher:
American Physical Society (APS)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; Plasma; Turbulence; Gyrokinetics

Citation Formats

Jian, Xiang, Holland, Christopher, Candy, Jeff, Belli, Emily, Chan, Vincet, Garofalo, Andrea M., and Ding, Siye. Role of Microtearing Turbulence in DIII-D High Bootstrap Current Fraction Plasmas. United States: N. p., 2019. Web. doi:10.1103/PhysRevLett.123.225002.
Jian, Xiang, Holland, Christopher, Candy, Jeff, Belli, Emily, Chan, Vincet, Garofalo, Andrea M., & Ding, Siye. Role of Microtearing Turbulence in DIII-D High Bootstrap Current Fraction Plasmas. United States. doi:10.1103/PhysRevLett.123.225002.
Jian, Xiang, Holland, Christopher, Candy, Jeff, Belli, Emily, Chan, Vincet, Garofalo, Andrea M., and Ding, Siye. Tue . "Role of Microtearing Turbulence in DIII-D High Bootstrap Current Fraction Plasmas". United States. doi:10.1103/PhysRevLett.123.225002.
@article{osti_1576791,
title = {Role of Microtearing Turbulence in DIII-D High Bootstrap Current Fraction Plasmas},
author = {Jian, Xiang and Holland, Christopher and Candy, Jeff and Belli, Emily and Chan, Vincet and Garofalo, Andrea M. and Ding, Siye},
abstractNote = {We report the first direct comparisons of microtearing turbulence simulations to experimental measurements in a representative high bootstrap current fraction (fBS) plasma. Previous studies of high fBS plasmas carried out in DIII-D with large radius internal transport barriers (ITBs) have found that while the ion energy transport is accurately reproduced by neoclassical theory, the electron transport remains anomalous, and not well-described by existing quasilinear transport models. A key feature of these plasmas is the large value of normalized pressure gradient, which is shown to completely stabilize conventional drift-wave and kinetic ballooning mode instabilities in the ITB, but destabilizes the microtearing mode. Nonlinear gyrokinetic simulations of the ITB region performed with the CGYRO code demonstrate that the microtearing modes are robustly unstable and capable of driving electron energy transport levels comparable to experimental levels for input parameters consistent with the experimental measurements. These simulations uniformly predict that the microtearing mode fluctuation and flux spectra extend to significantly shorter wavelengths than the range of linear instability, representing significantly different nonlinear dynamics and saturation mechanisms than conventional drift-wave turbulence, also consistent with the fundamental tearing nature of the instability. In conclusion, the predicted transport levels are found to be most sensitive to the magnetic shear, rather than the temperature gradients more typically identified as driving turbulent plasma transport.},
doi = {10.1103/PhysRevLett.123.225002},
journal = {Physical Review Letters},
number = 22,
volume = 123,
place = {United States},
year = {2019},
month = {11}
}

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