Hitoshi Tamura

A novel method, called Advanced Multi-Step Brazing, was developed to fabricate a new type of divertor heat removal component with W armor and an oxide-dispersion-strengthened copper (GlidCop®) heat sink in the initial phase of our work. Later, a new type of divertor heat removal component, which has a rectangular-shaped cooling channel with a V-shaped staggered-rib structure in the GlidCop heat sink, was developed. This new component showed an extremely high heat removal capability during a ~30 MW/m² steady-state heat loading condition in our previous work. In this work, the new component was installed in the divertor strike position of the Large Helical Device and exposed to neutral beam injection–heated plasma discharges with 1180 shots (~8000 s) in total. Though submillimeter-scale damage, such as unipolar arc trails and microscale cracks, was identified on the W surface, the extremely high heat removal capability did not show any sign of degradation over the experimental period. On the other hand, remarkable sputtering erosion and redeposition phenomena, due to the strong influx of the divertor plasma, was confirmed on the W armor.

Superconducting magnets in fusion reactors are subjected to a huge electromagnetic force of >100 MN/m. The magnets have to be sustained with a strong-body structure to avoid high stress and deformation. The total weight of the magnet system in the fusion reactor is estimated to be more than 20,000 tons. We applied topology optimization technique to the magnet support structure to reduce the weight of fusion reactors. Compared with the conventional design, we achieved a weight reduction of >25%. Static and seismic analyses were carried out to validate the soundness of the topology-optimized design. Consequently, the stress against the electromagnetic force in the structure was within the permissible range. It was discovered that using seismic isolation structure can adequately prevent the damage to the magnet system even when directly subjected to a massive earthquake.

The applicability of tokamak, helical and laser fusion reactors as a volumetric fusion neutron source has been examined using the systems codes that have been utilised for the conceptual design of DEMO and commercial reactors in Japan. This study has clarified the characteristics of reactor-based volumetric neutron sources that can be designed based on the current physics and engineering basis with a reasonable running cost (∼5B Yen/year). Although the achievable neutron flux is 2–3 orders lower than that of accelerator driven neutron sources, tokamak and helical neutron sources can provide a much larger irradiation area for the test of large components. Laser neutron sources have both high operability and tritium breeding capacity. These reactor-based neutron sources also serve as an integrated test bed of the entire reactor system.

The purpose of this paper is to investigate the through-thickness stresses of woven glass fiber reinforced polymer (GFRP) composite laminates under combined tensile and shear loading. Tensile tests were carried out with cross specimens at room temperature under various stacking angles, and the through-thickness strength properties of the woven GFRP laminates were evaluated. The failure characteristics of the woven GFRP laminates were also studied by optical microscopy observations. A three-dimensional finite element analysis (FEA) was carried out to calculate the stress distributions in the cross specimens, and the failure conditions of the specimens were examined. The numerically determined interlaminar tensile and shear stresses at failure location were consistent with Hoffman and Mohr-Coulomb failure criteria when the stacking angle was relatively small. This work is the first attempt to quantify the relation between interlaminar tensile and shear strengths of GFRP composite laminates under tensile and shear loading simultaneously using a combined numerical and experimental approach. A method based on finite element stress analysis was developed for estimating the through-thickness strength of the composite laminates using the experimentally determined fracture load and location. The results suggest that the through-thickness strength under combined tensile and shear loading can be determined effectively by this approach for relatively small stacking angles.

In magnetic-confinement-type fusion reactors, the strong electromagnetic force generated by the superconducting coil is of the order of several tens of MN/m. To support this huge force, a strong and heavy coil support structure is required. The total weight of each magnet designed for conventional fusion reactors or experimental devices is several times greater than the ideal value. In recent years, structural optimization has advanced, owing to improvements in computer-aided design and finite-element analysis. For instance, the topology optimization method contributes novel designs that overturn common sense. In the present study, topology optimization is applied to the design of the magnet system used in a helical fusion reactor to reduce the weight of the magnet while maintaining the mechanical soundness of the component. A weight reduction of more than 25% from the conventional design could be achieved.