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Title: Helical core formation and evolution during current ramp-up in the high-field tokamak Alcator C-Mod

Abstract

We report that large, spontaneous m/n = 1/1 helical cores are predicted in tokamaks with extended regions of low- or reversed-magnetic shear profiles in a region within the q = 1 surface and an onset condition determined by constant (dp/dρ)/B$$2\atop{t}$$ along the threshold. These 3D modes occurred frequently in Alcator C-Mod during ramp-up when slow current penetration results in a reversed shear q-profile. The onset and early development of a helical core in C-Mod were simulated using a new 3D time-dependent equilibrium reconstruction, based on the ideal MHD equilibrium code VMEC. The reconstruction used the experimental density, temperature, and soft-X-ray fluctuations. The pressure profile can become hollow due to an inverted, hollow electron temperature profile caused by molybdenum radiation in the plasma core during the current ramp-up phase before the onset of sawteeth, which may also occur in ITER with tungsten. Lastly, based on modeling, it is found that a reverse shear q-profile combined with a hollow pressure profile reduces the onset condition threshold, enabling helical core formation from an otherwise axisymmetric equilibrium.

Authors:
ORCiD logo [1]; ORCiD logo [1];  [2]; ORCiD logo [3]; ORCiD logo [4];  [3]; ORCiD logo [1]; ORCiD logo [1]
  1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  2. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
  3. Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)
  4. Univ. of Texas, Austin, TX (United States)
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Fusion Energy Sciences (FES) (SC-24)
OSTI Identifier:
1494895
Alternate Identifier(s):
OSTI ID: 1511782
Grant/Contract Number:  
AC05-00OR22725; AC02-09CH11466; FC02-99ER54512
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Physics of Plasmas
Additional Journal Information:
Journal Volume: 26; Journal Issue: 2; 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

Wingen, Andreas, Wilcox, Robert S., Delgado-Aparicio, L., Granetz, R. S., Houshmandyar, S., Shiraiwa, S., Cianciosa, Mark R., and Seal, Sudip K. Helical core formation and evolution during current ramp-up in the high-field tokamak Alcator C-Mod. United States: N. p., 2019. Web. doi:10.1063/1.5083055.
Wingen, Andreas, Wilcox, Robert S., Delgado-Aparicio, L., Granetz, R. S., Houshmandyar, S., Shiraiwa, S., Cianciosa, Mark R., & Seal, Sudip K. Helical core formation and evolution during current ramp-up in the high-field tokamak Alcator C-Mod. United States. doi:10.1063/1.5083055.
Wingen, Andreas, Wilcox, Robert S., Delgado-Aparicio, L., Granetz, R. S., Houshmandyar, S., Shiraiwa, S., Cianciosa, Mark R., and Seal, Sudip K. Mon . "Helical core formation and evolution during current ramp-up in the high-field tokamak Alcator C-Mod". United States. doi:10.1063/1.5083055.
@article{osti_1494895,
title = {Helical core formation and evolution during current ramp-up in the high-field tokamak Alcator C-Mod},
author = {Wingen, Andreas and Wilcox, Robert S. and Delgado-Aparicio, L. and Granetz, R. S. and Houshmandyar, S. and Shiraiwa, S. and Cianciosa, Mark R. and Seal, Sudip K.},
abstractNote = {We report that large, spontaneous m/n = 1/1 helical cores are predicted in tokamaks with extended regions of low- or reversed-magnetic shear profiles in a region within the q = 1 surface and an onset condition determined by constant (dp/dρ)/B$2\atop{t}$ along the threshold. These 3D modes occurred frequently in Alcator C-Mod during ramp-up when slow current penetration results in a reversed shear q-profile. The onset and early development of a helical core in C-Mod were simulated using a new 3D time-dependent equilibrium reconstruction, based on the ideal MHD equilibrium code VMEC. The reconstruction used the experimental density, temperature, and soft-X-ray fluctuations. The pressure profile can become hollow due to an inverted, hollow electron temperature profile caused by molybdenum radiation in the plasma core during the current ramp-up phase before the onset of sawteeth, which may also occur in ITER with tungsten. Lastly, based on modeling, it is found that a reverse shear q-profile combined with a hollow pressure profile reduces the onset condition threshold, enabling helical core formation from an otherwise axisymmetric equilibrium.},
doi = {10.1063/1.5083055},
journal = {Physics of Plasmas},
issn = {1070-664X},
number = 2,
volume = 26,
place = {United States},
year = {2019},
month = {2}
}

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Works referenced in this record:

Snake perturbation during pellet injection in the EAST tokamak
journal, August 2016


Persistent density perturbations at rational- q surfaces following pellet injection in the Joint European Torus
journal, November 1987


A nonlinear two-fluid model for toroidal plasmas
journal, November 2000

  • Sugiyama, L. E.; Park, W.
  • Physics of Plasmas, Vol. 7, Issue 11
  • DOI: 10.1063/1.1308083

Role of sawtooth in avoiding impurity accumulation and maintaining good confinement in JET radiative mantle discharges
journal, September 2003


Controlling sawtooth oscillations in tokamak plasmas
journal, November 2010


Self-Organized Stationary States of Tokamaks
journal, November 2015


Use of reconstructed 3D equilibria to determine onset conditions of helical cores in tokamaks for extrapolation to ITER
journal, January 2018


On the formation and stability of long-lived impurity-ion snakes in Alcator C-Mod
journal, April 2013


Role of a continuous MHD dynamo in the formation of 3D equilibria in fusion plasmas
journal, May 2017


JET snake magnetohydrodynamic equilibria
journal, June 2011


Sawtooth oscillations
journal, January 1986


Steepest-descent moment method for three-dimensional magnetohydrodynamic equilibria
journal, January 1983


The quiescent H-mode regime for high performance edge localized mode-stable operation in future burning plasmasa)
journal, May 2015

  • Garofalo, A. M.; Burrell, K. H.; Eldon, D.
  • Physics of Plasmas, Vol. 22, Issue 5
  • DOI: 10.1063/1.4921406

Snake-like phenomena in Tore Supra following pellet injection
journal, April 1997


Internal Kink Modes in Toroidal Plasmas with Circular Cross Sections
journal, December 1975


Electron critical gradient scale length measurements of ICRF heated L-mode plasmas at Alcator C-Mod tokamak
journal, April 2018

  • Houshmandyar, S.; Hatch, D. R.; Horton, C. W.
  • Physics of Plasmas, Vol. 25, Issue 4
  • DOI: 10.1063/1.5022180

NBI fast ion confinement in the helical core of MAST hybrid-like plasmas
journal, May 2014


Magnetic flux pumping in 3D nonlinear magnetohydrodynamic simulations
journal, October 2017

  • Krebs, I.; Jardin, S. C.; Günter, S.
  • Physics of Plasmas, Vol. 24, Issue 10
  • DOI: 10.1063/1.4990704

Tungsten as target material in fusion devices
journal, June 1996


MHD activity in JET hot ion H mode discharges
journal, April 1995


Helical core reconstruction of a DIII-D hybrid scenario tokamak discharge
journal, May 2017


Impact of ideal MHD stability limits on high-beta hybrid operation
journal, November 2016


Formation and Stability of Impurity “Snakes” in Tokamak Plasmas
journal, February 2013


Free boundary equilibrium in 3D tokamaks with toroidal rotation
journal, May 2015


Control of Neoclassical Tearing Modes by Sawtooth Control
journal, February 2002


Chapter 1: Overview and summary
journal, June 2007


V3FIT: a code for three-dimensional equilibrium reconstruction
journal, July 2009