Combined plasma–coil optimization algorithms. (3rd April 2021)

• Record Type: Journal Article
• Authors: Henneberg, S. A.; Hudson, S. R.; Pfefferlé, D.; Helander, P.
• Is Part Of: Journal of plasma physics. Volume 87:Number 2(2021)
• Publication Date: 2021-04-03
• Subjects: fusion plasma; Plasma (Ionized gases) -- Periodicals; 530.4405
• DOI: 10.1017/S0022377821000271
• Languages: English
• ISSNs: 0022-3778

Abstract

Abstract : Combined plasma–coil optimization approaches for designing stellarators are discussed and a new method for calculating free-boundary equilibria for multiregion relaxed magnetohydrodynmics (MRxMHD) is proposed. Four distinct categories of stellarator optimization, two of which are novel approaches, are the fixed-boundary optimization, the generalized fixed-boundary optimization, the quasi-free-boundary optimization, and the free-boundary (coil) optimization. These are described using the MRxMHD energy functional, the Biot–Savart integral, the coil-penalty functional and the virtual casing integral and their derivatives. The proposed free-boundary equilibrium calculation differs from existing methods in how the boundary-value problem is posed, and for the new approach it seems that there is not an associated energy minimization principle because a non-symmetric functional arises. We propose to solve the weak formulation of this problem using a spectral-Galerkin method, and this will reduce the free-boundary equilibrium calculation to something comparable to a fixed-boundary calculation. In our discussion of combined plasma–coil optimization algorithms, we emphasize the importance of the stability matrix.