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Title: Formation of a High Pressure Staircase Pedestal with Suppressed Edge Localized Modes in the DIII-D Tokamak

Abstract

We observe the formation of a high-pressure staircase pedestal (≈16–20 kPa) in the DIII-D tokamak when large amplitude edge localized modes are suppressed using resonant magnetic perturbations. The staircase pedestal is characterized by a flattening of the density and temperature profiles in midpedestal creating a two-step staircase pedestal structure correlated with the appearance of midpedestal broadband fluctuations. Here, the pedestal oscillates between the staircase and single-step structure every 40–60 ms, correlated with oscillations in the heat and particle flux to the divertor. Gyrokinetic analysis using the cgyro code shows that when the heat and particle flux to the divertor decreases, the pedestal broadens and the E × B shear at the midpedestal decreases, triggering a transport bifurcation from the kinetic ballooning mode (KBM) to trapped electron mode (TEM) limited transport that flattens the density and temperature profiles at midpedestal and results in the formation of the staircase pedestal. As the heat flux to the divertor increases, the pedestal narrows and the E × B shear at the midpedestal increases, triggering a back transition from TEM to KBM limited transport. The pedestal pressure increases during the staircase phase, indicating that enhanced midpedestal turbulence can be beneficial for confinement.

Authors:
ORCiD logo [1];  [1];  [2];  [2];  [2];  [1];  [1];  [1];  [3];  [4];  [2]
  1. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
  2. General Atomics, San Diego, CA (United States)
  3. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
  4. Univ. of Wisconsin-Madison, Madison, WI (United States)
Publication Date:
Research Org.:
Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States); General Atomics, San Diego, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Fusion Energy Sciences (FES) (SC-24)
OSTI Identifier:
1573786
Alternate Identifier(s):
OSTI ID: 1573794
Grant/Contract Number:  
FC02-04ER54698; AC02-09CH11466
Resource Type:
Accepted Manuscript
Journal Name:
Physical Review Letters
Additional Journal Information:
Journal Volume: 123; Journal Issue: 11; Journal ID: ISSN 0031-9007
Publisher:
American Physical Society (APS)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY

Citation Formats

Ashourvan, Arash, Nazikian, R., Belli, E., Candy, J., Eldon, D., Grierson, B. A., Guttenfelder, W., Haskey, S. R., Lasnier, C., McKee, G. R., and Petty, C. C. Formation of a High Pressure Staircase Pedestal with Suppressed Edge Localized Modes in the DIII-D Tokamak. United States: N. p., 2019. Web. doi:10.1103/PhysRevLett.123.115001.
Ashourvan, Arash, Nazikian, R., Belli, E., Candy, J., Eldon, D., Grierson, B. A., Guttenfelder, W., Haskey, S. R., Lasnier, C., McKee, G. R., & Petty, C. C. Formation of a High Pressure Staircase Pedestal with Suppressed Edge Localized Modes in the DIII-D Tokamak. United States. doi:10.1103/PhysRevLett.123.115001.
Ashourvan, Arash, Nazikian, R., Belli, E., Candy, J., Eldon, D., Grierson, B. A., Guttenfelder, W., Haskey, S. R., Lasnier, C., McKee, G. R., and Petty, C. C. Thu . "Formation of a High Pressure Staircase Pedestal with Suppressed Edge Localized Modes in the DIII-D Tokamak". United States. doi:10.1103/PhysRevLett.123.115001.
@article{osti_1573786,
title = {Formation of a High Pressure Staircase Pedestal with Suppressed Edge Localized Modes in the DIII-D Tokamak},
author = {Ashourvan, Arash and Nazikian, R. and Belli, E. and Candy, J. and Eldon, D. and Grierson, B. A. and Guttenfelder, W. and Haskey, S. R. and Lasnier, C. and McKee, G. R. and Petty, C. C.},
abstractNote = {We observe the formation of a high-pressure staircase pedestal (≈16–20 kPa) in the DIII-D tokamak when large amplitude edge localized modes are suppressed using resonant magnetic perturbations. The staircase pedestal is characterized by a flattening of the density and temperature profiles in midpedestal creating a two-step staircase pedestal structure correlated with the appearance of midpedestal broadband fluctuations. Here, the pedestal oscillates between the staircase and single-step structure every 40–60 ms, correlated with oscillations in the heat and particle flux to the divertor. Gyrokinetic analysis using the cgyro code shows that when the heat and particle flux to the divertor decreases, the pedestal broadens and the E × B shear at the midpedestal decreases, triggering a transport bifurcation from the kinetic ballooning mode (KBM) to trapped electron mode (TEM) limited transport that flattens the density and temperature profiles at midpedestal and results in the formation of the staircase pedestal. As the heat flux to the divertor increases, the pedestal narrows and the E × B shear at the midpedestal increases, triggering a back transition from TEM to KBM limited transport. The pedestal pressure increases during the staircase phase, indicating that enhanced midpedestal turbulence can be beneficial for confinement.},
doi = {10.1103/PhysRevLett.123.115001},
journal = {Physical Review Letters},
number = 11,
volume = 123,
place = {United States},
year = {2019},
month = {9}
}

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