Abstract Details
Abstracts
Author: Matt Landreman
Requested Type: Pre-Selected Invited
Submitted: 2019-02-21 06:35:45
Co-authors: W Sengupta, G G Plunk
Contact Info:
University of Maryland
8223 Paint Branch Drive
College Park, MD 20742
USA
Abstract Text:
Quasisymmetry, a remarkable property of some nonaxisymmetric magnetic fields that implies good confinement, has been the principle underlying stellarator designs such as HSX and NCSX. Historically, quasisymmetric magnetic field shapes have been found using numerical optimization. However a direct geometric construction of quasisymmetric fields, using equations derived by Garren and Boozer, is also possible. While the construction is limited to high aspect ratio, it has several advantages compared to optimization, such as orders-of-magnitude lower computational cost, and opportunities for analytic insight. For instance, the construction permits a precise understanding of how many unique quasisymmetric configurations are possible (close to the magnetic axis). We also demonstrate that the core regions of quasisymmetric fields obtained by optimization, including the HSX and NCSX experiments, match the construction. We show that the construction can be modified for a more general confinement condition, omnigenity. The speed of the construction enables wide and high-resolution numerical searches to identify and map the interesting regions of parameter space.
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