skip to main content
DOE PAGES title logo U.S. Department of Energy
Office of Scientific and Technical Information

This content will become publicly available on February 4, 2020

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:
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},
number = 2,
volume = 26,
place = {United States},
year = {2019},
month = {2}
}

Journal Article:
Free Publicly Available Full Text
This content will become publicly available on February 4, 2020
Publisher's Version of Record

Save / Share: