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Title: Determination of current and rotational transform profiles in a current-carrying stellarator using soft x-ray emissivity measurements

Abstract

In this research, collimated soft X-ray (SXR) emissivity measurements from multi-channel cameras on the Compact Toroidal Hybrid (CTH) tokamak/torsatron device are incorporated in the 3D equilibrium reconstruction code V3FIT to reconstruct the shape of flux surfaces and infer the current distribution within the plasma. Equilibrium reconstructions of sawtoothing plasmas that use data from both SXR and external magnetic diagnostics show the central safety factor to be near unity under the assumption that SXR iso-emissivity contours lie on magnetic flux surfaces. The reconstruction results are consistent with those using the external magnetic data and a constraint on the location of q = 1 surfaces determined from the sawtooth inversion surface extracted from SXR brightness profiles. The agreement justifies the use of approximating SXR emission as a flux function in CTH, at least within the core of the plasma, subject to the spatial resolution of the SXR diagnostics. Lastly, this improved reconstruction of the central current density indicates that the current profile peakedness decreases with increasing external transform and that the internal inductance is not a relevant measure of how peaked the current profile is in hybrid discharges.

Authors:
ORCiD logo [1]; ORCiD logo [2];  [1];  [1]; ORCiD logo [1]; ORCiD logo [3];  [1];  [1]; ORCiD logo [1];  [1]
  1. Auburn Univ., AL (United States). Physics Department
  2. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  3. Auburn Univ., AL (United States). Physics Department ; Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1422574
Alternate Identifier(s):
OSTI ID: 1418890
Grant/Contract Number:  
AC05-00OR22725; FG02-00ER54610
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Physics of Plasmas
Additional Journal Information:
Journal Volume: 25; Journal Issue: 1; 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; 46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY

Citation Formats

Ma, X., Cianciosa, M. R., Ennis, D. A., Hanson, J. D., Hartwell, G. J., Herfindal, J. L., Howell, E. C., Knowlton, S. F., Maurer, D. A., and Traverso, P. J. Determination of current and rotational transform profiles in a current-carrying stellarator using soft x-ray emissivity measurements. United States: N. p., 2018. Web. doi:10.1063/1.5013347.
Ma, X., Cianciosa, M. R., Ennis, D. A., Hanson, J. D., Hartwell, G. J., Herfindal, J. L., Howell, E. C., Knowlton, S. F., Maurer, D. A., & Traverso, P. J. Determination of current and rotational transform profiles in a current-carrying stellarator using soft x-ray emissivity measurements. United States. doi:10.1063/1.5013347.
Ma, X., Cianciosa, M. R., Ennis, D. A., Hanson, J. D., Hartwell, G. J., Herfindal, J. L., Howell, E. C., Knowlton, S. F., Maurer, D. A., and Traverso, P. J. Wed . "Determination of current and rotational transform profiles in a current-carrying stellarator using soft x-ray emissivity measurements". United States. doi:10.1063/1.5013347. https://www.osti.gov/servlets/purl/1422574.
@article{osti_1422574,
title = {Determination of current and rotational transform profiles in a current-carrying stellarator using soft x-ray emissivity measurements},
author = {Ma, X. and Cianciosa, M. R. and Ennis, D. A. and Hanson, J. D. and Hartwell, G. J. and Herfindal, J. L. and Howell, E. C. and Knowlton, S. F. and Maurer, D. A. and Traverso, P. J.},
abstractNote = {In this research, collimated soft X-ray (SXR) emissivity measurements from multi-channel cameras on the Compact Toroidal Hybrid (CTH) tokamak/torsatron device are incorporated in the 3D equilibrium reconstruction code V3FIT to reconstruct the shape of flux surfaces and infer the current distribution within the plasma. Equilibrium reconstructions of sawtoothing plasmas that use data from both SXR and external magnetic diagnostics show the central safety factor to be near unity under the assumption that SXR iso-emissivity contours lie on magnetic flux surfaces. The reconstruction results are consistent with those using the external magnetic data and a constraint on the location of q = 1 surfaces determined from the sawtooth inversion surface extracted from SXR brightness profiles. The agreement justifies the use of approximating SXR emission as a flux function in CTH, at least within the core of the plasma, subject to the spatial resolution of the SXR diagnostics. Lastly, this improved reconstruction of the central current density indicates that the current profile peakedness decreases with increasing external transform and that the internal inductance is not a relevant measure of how peaked the current profile is in hybrid discharges.},
doi = {10.1063/1.5013347},
journal = {Physics of Plasmas},
issn = {1070-664X},
number = 1,
volume = 25,
place = {United States},
year = {2018},
month = {1}
}

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Figures / Tables:

FIG. 1 FIG. 1: Rendering of the last closed flux surface of a CTH plasma. Poloidal slices (highlighted in grey) indicate the toroidal locations of SXR cameras used for 3D equilibrium reconstructions.

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    Figures/Tables have been extracted from DOE-funded journal article accepted manuscripts.