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Title: Exploration of the parameter space of quasisymmetric stellarator vacuum fields through adjoint optimisation
Contributors: Nies, Richard
Paul, Elizabeth J.
Panici, Dario
Hudson, Stuart R.
Bhattacharjee, Amitava
U. S. Department of Energy contract number DE-AC02-09CH11466
U. S. Department of Energy contract number DE-SC0016072
U. S. Department of Energy contract number DE-AC02–76CH0307
Simons Foundation (Hidden Symmetries collaboration)
Issue Date: 2024
Publisher: Princeton Plasma Physics Laboratory, Princeton University
Abstract: Optimising stellarators for quasisymmetry leads to strongly reduced collisional transport and energetic particle losses compared to unoptimised configurations. Though stellarators with precise quasisymmetry have been obtained in the past, it remains unclear how broad the parameter space is where good quasisymmetry may be achieved. We here study the range of aspect ratio and rotational transform values for which stellarators with excellent quasisymmetry on the boundary can be obtained. A large number of Fourier harmonics is included in the boundary representation, which is made computationally tractable by the use of adjoint methods to enable fast gradient-based optimisation, and by the direct optimisation of vacuum magnetic fields, which converge more robustly compared to solutions from magnetohydrostatics. Several novel configurations are presented, including stellarators with record levels of quasisymmetry on a surface, three field period quasi- axisymmetric stellarators with substantial magnetic shear, and compact quasisymmetric stellarators at low aspect ratios similar to tokamaks.
Appears in Collections:Plasma Science & Technology

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