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Graduate Student Seminar - 11/10/2017

"Gradient-Based Optimization of the Stellarator Coil-Winding Surface"

by Elizabeth Paul

Friday, November 10, 2017 -- 12:00 p.m.
Large Conference Room, 1207 Energy Research Facility

Advisor:  Professor William Dorland

Abstract: Toroidal plasmas are confined by magnetic fields that are twisted on closed surfaces of constant flux. For stellarators, this twisting is provided by external coils. Designing coils which can provide the desired magnetic surfaces while maintaining engineering feasibility has proven to be a significant challenge to the stellarator program. As stellarators are fully three-dimensional, the space of possible configurations is very large. Several computational tools have been developed to identify plasmas with good transport and stability properties. The coils to produce this plasma can then be optimized. The first computational tool developed for coil optimization assumed all coils to lie on a closed winding surface. We have extended this tool to optimize the geometry of the winding surface itself for both physics properties of the plasma and engineering constraints on the coils. Gradient-based optimization techniques are applied, using the adjoint method to efficiently evaluate sensitivity derivatives. We obtain results for the W7-X and HSX stellarators which simultaneously produce the desired plasma surface with better fidelity and increase the coil-plasma distance.

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