We are pleased to announce the publication of the paper First thermo-structural vacuum barrier design for the EU DEMO feeders, authored by Corrado Groth, Andrea Chiappa, and Marco Evangelos Biancolini, in Science Direct. This research is part of the collaboration between the University of Rome Tor Vergata and EUROfusion, contributing to advancements in fusion energy technology within the framework of the EU DEMO project.

Abstract

The vacuum barrier (VB) is a crucial component designed to separate the feeder into two distinct vacuum regions: the main cryostat vacuum and the feeder vacuum. This separation not only enhances thermal insulation but also facilitates maintenance and improves accessibility to feeder components. In addition to maintaining pressure integrity under both standard operational conditions and potential fault scenarios, the VB is essential for minimizing heat transfer to cryogenic systems.

This study presents the optimization of the VB design using a Radial Basis Functions-based mesh morphing technique. By incorporating simultaneous shape variations within structural and thermal simulations, the research enables parameterization of a complex, coupled nonlinear system. The structural model is evaluated under combined pressure and temperature loads, while the final VB configuration is determined through response surface optimization, ensuring an optimal balance between structural robustness and thermal efficiency.

Conclusions

This paper outlines the development of a preliminary vacuum barrier design tailored for the EU DEMO tokamak, taking into account its distinct operational requirements compared to ITER. In particular, variations in the number and temperature of penetrations, as dictated by the predefined process flow diagram for the toroidal field (TF) feeders, necessitated a unique design approach.

A double U-neck configuration was adopted to mitigate both thermal transmission to helium lines and mechanical stress levels. Additional thermal shielding was achieved through interception mechanisms utilizing helium-cooled thermal shields. The study integrated temperature and structural analyses, enabling the computation of the overall stress distribution arising from combined pressure loads and temperature differentials.

To ensure the structural and thermal efficiency of the VB, response surface-based optimization was performed, employing two shape parameters to regulate the U-neck length and the position of the vacuum barrier plate via mesh morphing. A design space exploration of 40 different configurations led to the identification of an optimal solution characterized by:

• Maximum stress of 160 MPa
• Operational temperature range of 104 K to 143 K

This final configuration effectively balances structural resilience and minimal thermal leakage, thereby reducing heat transfer to the superconducting bus bars while ensuring the mechanical integrity of the VB under various operational conditions, including vacuum loss scenarios in both the cryostat and feeder regions. This research marks a significant step forward in the thermo-structural design of critical components for the EU DEMO fusion demonstrator, contributing to the development of robust and efficient fusion energy systems.

🔗 Read the full paper here: https://www.sciencedirect.com/science/article/pii/S0920379625001073?dgcid=coauthor