The Volumetric Neutron Source (VNS) is a pivotal facility proposed for advancing fusion nuclear technology, particularly for the qualification of breeding blanket systems, a key component of DEMO and future fusion reactors. This study focuses on the design and optimisation of the VNS Thermal Shield, adopting a multidisciplinary approach to address its thermal and structural behaviours. The Thermal Shield plays a crucial role in protecting superconducting magnets and other cryogenic components by limiting heat transfer from higher-temperature regions of the tokamak to the cryostat, which operates at temperatures between 4 K and 20 K. To ensure both thermal insulation and structural integrity, multiple design iterations were conducted. These iterations aimed to reduce electromagnetic (EM) forces induced during magnet charge and discharge cycles by introducing strategic cuts and reinforcements in the shield design. The optimisation process included the evaluation of various aluminium alloys and composite materials to achieve a balance between rigidity and weight while maintaining structural integrity under EM and mechanical loads. Additionally, an integrated thermal study was performed to ensure effective temperature management, maintaining the shield at an operational temperature of around 80 K. Cooling channels were incorporated to homogenise temperature distribution, improving thermal stability and reducing thermal gradients. This comprehensive approach demonstrates the viability of advanced material solutions and design strategies for thermal and structural optimisation. The findings reinforce the importance of the VNS as a dedicated platform for testing and validating critical fusion technologies under operationally relevant conditions.

The Wendelstein 7-X (W7-X) is the world largest stellarator with a sophisticated superconducting (SC) magnet system (MS) in operation since 2015. The W7-X components were designed in a framework of aspects: a plasma current decay of 100 kA and 2.7 MA with time constants of 140 and 50 ms for toroidal and diamagnetic currents, respectively, and a SC coil current decay of a 3T field on axis within 3s. However, during the second phase of operation in 2018, a fast plasma current decay event with a time constant of approximately 3 ms for toroidal current was observed. This observation has forced to reconsider the fast decay expectations and to initiate a massive W7-X torus components reanalysis campaign. One of the most critical components under higher induced eddy currents is the complex system of the MS thermal insulation (TI). The TI system separates the MS operated at ∼4K from the plasma vessel and outer vessel (PV TI and OV TI, respectively) and is located in the cryostat. The two main elements of the PV TI are actively cooled thermal panels and port shielding tubes. The multilayer thermal panels of the PV are connected to each other with clamps and attached to the PV by three different types of supports. Two complex finite element (FE) models have been developed to analyze the PV TI during postulated fast plasma current decay events with 1 ms time constant: an electromagnetic (EM) model to calculate eddy currents and EM forces on TI components [1], and a mechanical model to calculate the structural response of the PV TI. The paper presents main features of structural FE model and most important results from static and dynamic analyses of postulated fast plasma current decay events. Finally, required limitations for plasma currents for future W7-X operation are discussed.