Abstract Details
Abstracts
Author: Caoxiang Zhu
Requested Type: Poster
Submitted: 2019-02-22 12:33:55
Co-authors: D.A. Gates, S.R. Hudson, H. Liu, Y. Xu and S. Okamura
Contact Info:
Princeton Plasma Physics Laboratory
Princeton University, P.O. Box
Princeton, NJ 08543
United States
Abstract Text:
Error fields, which are predominantly attributed to mispositions in the coil geometry, could degrade plasma confinement and drive instabilities. To determine how coil misplacements drive error fields, previous investigations scanned all the possible displacements of coils to provide insights prior to construction. Difficulties in tight coil tolerance requires numerous time and cost during stellarator construction, even partly lead to the cancellation of NCSX and delay of W7-X.
Here we employ a Hessian matrix approach [C. Zhu et al., PPCF 60, 054016 (2018)] for rapidly identifying dangerous coil deviations. Two of the most common figures of merit, magnetic island size and quasisymmetry, are analytically differentiated over coil parameters to quickly compute the Hessian matrix. With the information from eigenvalues, we could directly identify the most sensitive coil deviation, which has the largest deterioration in magnetic islands or quasisymmetry. The new method is applied to analyze the possible errors fields in the CFQS experiment, which will be constructed in China. The results demonstrate that this method could exactly locate the perturbation scenario that opens n/m=4/11 island chain and deteriorates quasi-axisymmetry of the magnetic field. The sensitivity information suggests that each modular coil could have separate manufacturing/assembly precision. This would hopefully lead to significant reduce of time and cost.
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