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Title: Sawtooth oscillation behavior with varying amounts of applied stellarator rotational transform.

Abstract

In this study, tokamak-like sawtooth oscillations are observed in the Compact Toroidal Hybrid (CTH), a current-carrying stellarator. CTH has the unique ability to change the amount of the applied vacuum rotational transform from external stellarator coils relative to the rotational transform generated by the internal plasma current to investigate the effects of strong three-dimensional magnetic shaping on sawtooth behavior. The observed sawteeth in CTH, for plasmas with monotonically decreasing rotational transform profiles dominated by the plasma current, have characteristics of those observed on tokamaks including (1) a central emissivity rise and then a sudden crash with a well-defined inversion radius, (2) the presence of an m = 1 emissivity fluctuation, and (3) the normalized inversion surface radius scales with the total edge rotational transform. We explore the properties of an ensemble of discharges in CTH in which the fractional rotational transform, defined as the vacuum rotational transform divided by the total rotational transform, is systematically varied from 0.04 to 0.42 to observe changes in sawtooth oscillation dynamics. Over this range of the fractional rotational transform, the measured sawtooth period decreased by a factor of two. At a high fractional rotational transform, the sawtooth amplitude is observed to consist of onlymore » low-amplitude oscillations while the measured crash time of the sawtooth oscillation does not appear to have a strong dependence on the amount of the fractional transform applied. Lastly, experimental results indicate that the low-amplitude sawteeth are accompanied by a decrease in the sawtooth period and predominantly correlated with the mean elongation (due to the increasing fractional rotational transform) of the non-axisymmetric plasmas within CTH rather than other global equilibrium parameters.« less

Authors:
 [1];  [2];  [2];  [2];  [2];  [2];  [2];  [2];  [2];  [2]
  1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Auburn Univ., AL (United States)
  2. Auburn Univ., AL (United States)
Publication Date:
Research Org.:
Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
Sponsoring Org.:
USDOE National Nuclear Security Administration (NNSA)
OSTI Identifier:
1501627
Report Number(s):
SAND-2019-1053J
Journal ID: ISSN 1070-664X; 672006
Grant/Contract Number:  
AC04-94AL85000; FG02-00ER54610
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Physics of Plasmas
Additional Journal Information:
Journal Volume: 26; Journal Issue: 3; 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

Herfindal, Jeffery L., Maurer, David A., Hartwell, Greg J., Ennis, David A., Hanson, James D., Knowlton, Stephen F., Ma, X., Pandya, Mihir D., Roberds, Nicholas, and Traverso, Peter J. Sawtooth oscillation behavior with varying amounts of applied stellarator rotational transform.. United States: N. p., 2019. Web. doi:10.1063/1.5080242.
Herfindal, Jeffery L., Maurer, David A., Hartwell, Greg J., Ennis, David A., Hanson, James D., Knowlton, Stephen F., Ma, X., Pandya, Mihir D., Roberds, Nicholas, & Traverso, Peter J. Sawtooth oscillation behavior with varying amounts of applied stellarator rotational transform.. United States. doi:10.1063/1.5080242.
Herfindal, Jeffery L., Maurer, David A., Hartwell, Greg J., Ennis, David A., Hanson, James D., Knowlton, Stephen F., Ma, X., Pandya, Mihir D., Roberds, Nicholas, and Traverso, Peter J. Tue . "Sawtooth oscillation behavior with varying amounts of applied stellarator rotational transform.". United States. doi:10.1063/1.5080242. https://www.osti.gov/servlets/purl/1501627.
@article{osti_1501627,
title = {Sawtooth oscillation behavior with varying amounts of applied stellarator rotational transform.},
author = {Herfindal, Jeffery L. and Maurer, David A. and Hartwell, Greg J. and Ennis, David A. and Hanson, James D. and Knowlton, Stephen F. and Ma, X. and Pandya, Mihir D. and Roberds, Nicholas and Traverso, Peter J.},
abstractNote = {In this study, tokamak-like sawtooth oscillations are observed in the Compact Toroidal Hybrid (CTH), a current-carrying stellarator. CTH has the unique ability to change the amount of the applied vacuum rotational transform from external stellarator coils relative to the rotational transform generated by the internal plasma current to investigate the effects of strong three-dimensional magnetic shaping on sawtooth behavior. The observed sawteeth in CTH, for plasmas with monotonically decreasing rotational transform profiles dominated by the plasma current, have characteristics of those observed on tokamaks including (1) a central emissivity rise and then a sudden crash with a well-defined inversion radius, (2) the presence of an m = 1 emissivity fluctuation, and (3) the normalized inversion surface radius scales with the total edge rotational transform. We explore the properties of an ensemble of discharges in CTH in which the fractional rotational transform, defined as the vacuum rotational transform divided by the total rotational transform, is systematically varied from 0.04 to 0.42 to observe changes in sawtooth oscillation dynamics. Over this range of the fractional rotational transform, the measured sawtooth period decreased by a factor of two. At a high fractional rotational transform, the sawtooth amplitude is observed to consist of only low-amplitude oscillations while the measured crash time of the sawtooth oscillation does not appear to have a strong dependence on the amount of the fractional transform applied. Lastly, experimental results indicate that the low-amplitude sawteeth are accompanied by a decrease in the sawtooth period and predominantly correlated with the mean elongation (due to the increasing fractional rotational transform) of the non-axisymmetric plasmas within CTH rather than other global equilibrium parameters.},
doi = {10.1063/1.5080242},
journal = {Physics of Plasmas},
issn = {1070-664X},
number = 3,
volume = 26,
place = {United States},
year = {2019},
month = {3}
}

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