Two-photon polymerization is a recently developed technique that is used to print millimeter-size cellular structures with micrometer resolution. The two-photon polymerization process discussed in this paper is used to build structures to stabilize direct-drive targets that are imploded at cryogenic temperatures. These targets are supported by a very thin stalk (10 to 18 µm diameter) that can be broken (or dislodged) by vibrations that occur when the target is transported or when the cryogenic shroud is removed. And any vibration at the moment of implosion affects how precisely the target is aligned to the focus of the laser beams. This study investigates the mechanical properties of different millimeter-sized cellular auxetic structures (~0.2 g/cm3) at room and cryogenic temperatures (20°C and −140°C) and how well the most promising structure dampens vibrations at room temperature.

Neutronics calculations of fusion systems require accurate neutron transport simulations to predict quantities such as shielding effectiveness, material damage and transmutation, and reaction rates. Evaluated nuclear data from the U.S. Evaluated Nuclear Data Library (ENDF), the Joint Evaluated Fission and Fusion File (JEFF), or the Fusion Evaluated Nuclear Data Library (FENDL) are frequently used for these calculations. Therefore, the results from these calculations are highly dependent on the accuracy of the cross sections and angular distributions provided in these evaluated nuclear data libraries. The quasi-differential neutron scattering method was developed to validate the accuracy of evaluated cross sections and angular distributions. These measurements are particularly well suited to validate nuclear data pertaining to nuclear fusion applications. The incident neutron energy region of the measurement, 0.5 to 20 MeV, corresponds with the neutron energy range most relevant to fusion systems where neutron scattering reactions dominate. Modeling neutron scattering reactions accurately is important since neutrons will only have a few interactions before being absorbed or leaking from a system. In quasi-differential neutron scattering experiments, a white pulsed neutron beam is scattered from a thick sample and neutrons are detected by an array of detectors surrounding the sample. The experimental data are then compared with detailed radiation transport simulations using multiple evaluated nuclear data sets. This comparison provides information about the accuracy of these evaluated data for the sample of interest. The advantage of such a method is the high sensitivity to the nuclear data of the measured sample material with minimal interference from other materials. This method has been successfully utilized to obtain nuclear reaction data of several materials that are important to nuclear fission reactors and criticality safety applications, such as Be, Pb, Fe, Ta, Mo, 238U, Zr, and F. Moreover, data from these measurements informed certain evaluations in the ENDF/B-VIII.0 and ENDF/B-VIII.1 nuclear data libraries. We propose that quasi-differential neutron scattering will be of great value for the validation of fusion-related materials, such as Si, W, Li, Ti, Nb, and O, and that additional measurements are needed for more materials of interest.

In this paper we provide an overview of the vision and strategy of FuseNet for fusion education and training in Europe. We bring into perspective the educational role of FuseNet in the European fusion landscape and how it addresses the needs of its different stakeholders. We give particular attention to the events the association organizes. We conclude with future plans for the network.

A gross electricity–producing compact pilot plant (PP) is essential in addressing the science and technology gap between present-day tokamaks including ITER to a DEMO and power plant in the staged approach to DEMO. Key driving features for nuclear analysis requirements for a compact fusion PP of 3.6-m major radius, 300-MW fusion power with 0.8 electric gain and 20% (75 days) availability are presented. Modular blanket maintenance requirements and compactness require a gap between the outboard blanket and vacuum vessel for allowing maintenance through the vertical ports, and a scheme is presented. The requirements arising from the plant layout, breeding and shielding blankets, and maintenance scheme and the regulatory considerations are discussed. Because of the space constraints, a breeding blanket is possible only on the outboard, and a preliminary one-dimensional nuclear analysis of the plant is carried out with a helium-cooled solid breeder. For 75 days of continuous operation, the displacement damage in the first wall is about 1.5 displacements per atom (dpa), and the neutron fluence at the magnet insulator is 9.1 × 1017 n/cm2. The total dpa of the structural material in a campaign of 3 full-power years (FPY) were about 22, which is almost the limiting dpa of reduced-activation ferritic-martensitic steel. The analysis indicates that further optimization of the shield blanket is essential for the target operational lifetime of 3 FPY. The total tritium breeding ratio (TBR) obtained is 0.92, which could be reduced to 0.5 to 0.6 by considering the reduction in the blanket coverage area. The target TBR is set to 0.6 for the analysis. To meet this target TBR, an initial tritium inventory of about 2.7 kg is required for 1 calendar year of operation (0.2 FPY) where the exhaust processing time is about 1 day and the time for tritium extraction from the blanket is about 10 days.

Shattered pellet injection (SPI), currently the most effective method of disruption mitigation, is currently implemented on tokamaks worldwide for experimental purposes. Cryogenic pellets are formed and fired into an angled surface before entering the plasma. The impact with the angled surface causes the pellets to fragment into a cloud of particles with the purpose of increasing the surface area for ablation. As pellets traverse guide tubes, depending on design, there is a chance of an off-normal pellet impact. Pellet impacts are also, depending on design, possible in the plasma chamber if not fully ablated and assimilated, or if the fragment plume is not directed in the proper direction. This paper outlines a series of pellet impact tests on various tiles and components relevant to the ITER, JET, and ASDEX Upgrade SPI systems. Testing was done to assess the potential damage from pellet and fragment plume impacts through high-speed imaging and the visual inspection of components.

Pushered single shell (PSS) has emerged as an alternative platform of implosion to ease the stability issue at the ablation front. The design consists of a thin inner Be layer, a 50% Cr:Be plateau region, an S-curve gradient, a low Cr (1.5%) tamper layer, and followed by a pure Be outer layer. General Atomics has developed a way to fabricate the higher-Z Cr to lower-Z Be gradients on glow discharge polymer mandrels with a designed S-shape profile for optimal implosion stability using magnetron sputtering. Microstructure analysis of the gradient coating indicated that at lower Cr concentration a short order or amorphous structure was formed. These fabricated PSS capsules were subsequently built into capsule fill tube assemblies, verified to be leak tight at both ambient and cryogenic conditions, and delivered to Lawrence Livermore National Laboratory for the shots. The capsule thermal stability was demonstrated by invariable Cr profiles before and after pyrolysis. However, cracking at inner Cr layers was observed, which has been attributed to thermal stress.

With the rapid growth and development of potential commercial fusion power plants, the urgency of building a skilled workforce is increasing. Therefore, it is necessary to train and educate early-career scientists and engineers to be able to work for current and future employment in fusion-related fields. In the Inertial Fusion Science and Technology (RISE) Hub, efforts are underway to address this urgency. Specifically in the RISE Hub, we train the next generation of “fusioneers” by involving them in every level of Hub activities. Here, we describe several training, outreach, and educational activities that are led by early-career scientists and engineers, graduate students, and postdoctoral researchers, under the supervision of Hub professionals. These activities educate and train students on key aspects of fusion systems, from the laser driver technologies to the target design, manufacturing, simulation, and validation. In addition, several of these initiatives are being supported by industry partners, national laboratories, and universities, facilitating the transition of knowledge between fusion experts and students. The goals of these outreach efforts led by the RISE Hub are not only to train and educate a skilled workforce but to grow young leaders and broaden their participation in developing commercial fusion power plants.

The development of effective neutron shielding materials is of paramount importance for the progression of fusion technologies with the aim of producing clean and sustainable energy for future generations. This study demonstrates the successful fabrication of a promising candidate material for shielding applications, hafnium hydride, through the powder metallurgy process. Powder metallurgy fabrication resulted in the production of 91% dense, crack-free, ε-phase HfH2 pellets with a hydrogen-to-metal ratio of 1.89 to 2.00. Resonant ultrasound spectroscopy (RUS) was used to measure a Young’s modulus of 34.52 ± 2.70 GPa and a shear modulus of 12.25 ± 0.18 GPa. Nanoindentation techniques have been used to establish a hardness value of 4.45 ± 1.63 GPa, and a Young’s modulus of 47.8 ± 6.4 GPa was determined using Poison’s ratio from RUS. Hydrogen release was measured using thermogravimetric analysis and appeared to occur in three different regimes as the sample transitioned through the ε- and δ-phases. Heat capacity matched literature data up to 600 K, after which a rapid increase was observed due to phase transformations occurring with hydrogen loss.

This paper reports calculated surface heat load owing to plasma thermal radiation, which will be applied to the surfaces of Equatorial Port 09 (EP09) diagnostic shield modules (DSMs) for thermal analysis during normal operation. The calculation assumes that the thermal energy will deposit uniformly in all directions from the plasma to the adjacent components and environment (i.e. gray body radiation). Assuming the temperature for the plasma surface, calculated view factors are used to determine the allocation of thermal energy to each component. The analysis provides an initial assessment of the thermal radiation heat load on the DSMs to be checked in structural/thermal analyses to verify significance. The designs of the EP09 components are still in the early preliminary phase, and changes are expected in the future.

Boron carbide (B4C) is an attractive inertial confinement fusion ablator material. The fabrication of B4C ablators by magnetron sputtering requires process optimization. To increase process flexibility, here we explore high-power impulse magnetron sputter (HiPIMS) deposition of B4C in pure Ar and mixed Ar-Ne plasmas. The results show that higher plasma discharge currents can be reached with a mixed Ar-Ne plasma in the entire working pressure range studied ( 5 to 50 mTorr). At 45 mTorr with 10% of Ne in the Ar-Ne mix, high peak target current densities of ~1 A cm−2 were demonstrated. Films deposited with such a mixed Ar-Ne plasma with a full-face erosion magnetron source on substrates biased at −25 V exhibited higher density and improved mechanical properties, albeit with higher compressive residual stresses compared to the case of HiPIMS deposition in a pure Ar plasma. This work demonstrates additional process flexibility of the HiPIMS discharge mode for the deposition of B4C coatings.