A systematic and general nonlinear optimization strategy for integrated structural-sealing design of large and complex vacuum components in fusion reactors

Abstract

The standardization of fusion engineering technologies is a major trend in the development of the fusion field. One of the key technologies is the reliable design of large and complex vacuum components (LCVCs) under intricate loads, which determines the safe and stable operation of fusion devices. To meet the requirements for accurate, efficient, and systematic design of LCVCs in future fusion reactors, this paper proposes a systematic optimization method called the NOVACS strategy. It establishes a general phased nonlinear multi-objective optimization approach for both the LCVC body and its seals, collaboratively planning the optimization process by leveraging a parameter input set to drive structural updates, thereby improving design accuracy, efficiency, and integrity. To demonstrate the advantages of the strategy, the cryostat of the ITER Magnet Cold Test Bench (MCTB) is chosen for systematic optimization. Compared to the trial-and-error method, it can enhance optimization efficiency by approximately 33% through an established multi-computer linkage mode for multi-objective experimental design and analysis, even when the optimization process is nonlinear. Additionally, the optimization results concerning mass and deformation objectives are improved, yielding an economical design while ensuring structural reliability. Further design is conducted on the seal at the largest interface of the cryostat using this strategy, resulting in an O-ring with a profile diameter of Φ45 mm and approximately 55.8 m in circumference, optimized according to the leakage rate function. It exhibits good contact characteristics, effectively sealing large flanges with a maximum flatness tolerance of up to 4 mm. Moreover, even in the worst-case sealing scenario, the O-ring will not fail, with a maximum leakage rate of 6.26 × 10⁻⁷ Pa·m³/s. The proposed NOVACS strategy provides feasible technical guidance for the full-process optimization design of LCVCs in fusion devices, facilitating the establishment of its standardized design.