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Title: Improved performance of stellarator coil design optimization

Abstract

Following up on earlier work which demonstrated an improved numerical stellarator coil design optimization performance by the use of stochastic optimization (Lobsien et al., Nucl. Fusion, vol. 58 (10), 2018, 106013), it is demonstrated here that significant further improvements can be made – lower field errors and improved robustness – for a Wendelstein 7-X test case. This is done by increasing the sample size and applying fully three-dimensional perturbations, but most importantly, by changing the design sequence in which the optimization targets are applied: optimization for field error is conducted first, with coil shape penalties only added to the objective function at a later step in the design process. A robust, feasible coil configuration with a local maximum field error of 3.66 % and an average field error of 0.95 % is achieved here, as compared to a maximum local field error of 6.08 % and average field error of 1.56 % found in our earlier work. These new results are compared to those found without stochastic optimization using the FOCUS and ONSET suites. The relationship between local minima in the optimization space and coil shape penalties is also discussed.

Authors:
ORCiD logo [1];  [1];  [2]; ORCiD logo [1]; ORCiD logo [3];  [1]
  1. Max Planck Society, Garching (Germany). Max Planck Institute for Plasma Physics
  2. Univ. of Wisconsin, Madison, WI (United States)
  3. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
Publication Date:
Research Org.:
Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
Sponsoring Org.:
USDOE
Contributing Org.:
This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programs 2014–2018 and 2019–2020 under grant agreement no. 633053.
OSTI Identifier:
1615630
Grant/Contract Number:  
AC02-09CH11466
Resource Type:
Accepted Manuscript
Journal Name:
Journal of Plasma Physics
Additional Journal Information:
Journal Volume: 86; Journal Issue: 2; Journal ID: ISSN 0022-3778
Publisher:
Cambridge University Press
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY

Citation Formats

Lobsien, Jim-Felix, Drevlak, Michael, Kruger, Thomas, Lazerson, Samuel, Zhu, Caoxiang, and Pedersen, Thomas Sunn. Improved performance of stellarator coil design optimization. United States: N. p., 2020. Web. doi:10.1017/S0022377820000227.
Lobsien, Jim-Felix, Drevlak, Michael, Kruger, Thomas, Lazerson, Samuel, Zhu, Caoxiang, & Pedersen, Thomas Sunn. Improved performance of stellarator coil design optimization. United States. doi:https://doi.org/10.1017/S0022377820000227
Lobsien, Jim-Felix, Drevlak, Michael, Kruger, Thomas, Lazerson, Samuel, Zhu, Caoxiang, and Pedersen, Thomas Sunn. Wed . "Improved performance of stellarator coil design optimization". United States. doi:https://doi.org/10.1017/S0022377820000227. https://www.osti.gov/servlets/purl/1615630.
@article{osti_1615630,
title = {Improved performance of stellarator coil design optimization},
author = {Lobsien, Jim-Felix and Drevlak, Michael and Kruger, Thomas and Lazerson, Samuel and Zhu, Caoxiang and Pedersen, Thomas Sunn},
abstractNote = {Following up on earlier work which demonstrated an improved numerical stellarator coil design optimization performance by the use of stochastic optimization (Lobsien et al., Nucl. Fusion, vol. 58 (10), 2018, 106013), it is demonstrated here that significant further improvements can be made – lower field errors and improved robustness – for a Wendelstein 7-X test case. This is done by increasing the sample size and applying fully three-dimensional perturbations, but most importantly, by changing the design sequence in which the optimization targets are applied: optimization for field error is conducted first, with coil shape penalties only added to the objective function at a later step in the design process. A robust, feasible coil configuration with a local maximum field error of 3.66 % and an average field error of 0.95 % is achieved here, as compared to a maximum local field error of 6.08 % and average field error of 1.56 % found in our earlier work. These new results are compared to those found without stochastic optimization using the FOCUS and ONSET suites. The relationship between local minima in the optimization space and coil shape penalties is also discussed.},
doi = {10.1017/S0022377820000227},
journal = {Journal of Plasma Physics},
number = 2,
volume = 86,
place = {United States},
year = {2020},
month = {4}
}

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