A practical globalization of one-shot optimization for optimal design of tokamak divertors

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• 作者：Maarten Blommaert^a ; ^{maarten.blommaert@kuleuven.be" class="auth_mail" title="E-mail the corresponding author} ; Wouter Dekeyser^b ; Martine Baelmans^b ; Nicolas R. Gauger^c ; Detlev Reiter^a
• 关键词：One-shot optimization ; Globalization strategy ; Continuous adjoint method ; Damped Hessian updates ; Magnetic divertor design ; Target heat load
• 刊名：Journal of Computational Physics
• 出版年：2017
• 出版时间：1 January 2017
• 年：2017
• 卷：328
• 期：Complete
• 页码：399-412
• 全文大小：649 K

文摘

In past studies, nested optimization methods were successfully applied to design of the magnetic divertor configuration in nuclear fusion reactors. In this paper, so-called one-shot optimization methods are pursued. Due to convergence issues, a globalization strategy for the one-shot solver is sought. Whereas Griewank introduced a globalization strategy using a doubly augmented Lagrangian function that includes primal and adjoint residuals, its practical usability is limited by the necessity of second order derivatives and expensive line search iterations. In this paper, a practical alternative is offered that avoids these drawbacks by using a regular augmented Lagrangian merit function that penalizes only state residuals. Additionally, robust rank-two Hessian estimation is achieved by adaptation of Powell's damped BFGS update rule. The application of the novel one-shot approach to magnetic divertor design is considered in detail. For this purpose, the approach is adapted to be complementary with practical in parts adjoint sensitivities. Using the globalization strategy, stable convergence of the one-shot approach is achieved.