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• RF conditioning of RFQ of IFMIF/EVEDA accelerator (LIPAc) reached stable CW at 80 % of nominal voltage at the end of 2021. • Conditioning towards nominal voltage at CW was stopped in March 2022 because of vacuum leak from one of the O-Ring of the RF windows, damaged by high temperature. • Several coupled RF and thermal simulations of the couplers of the RFQ were performed with FEM codes. Thermal weak point was identified in the contact between the anchor of the RF window and the cooled inner conductor of the coupler. • A solution to improve cooling of the RF window that could be implemented quickly with minor modifications of the RF windows parts of the couplers was found. • After the testing and validation of the modification in a prototype, the couplers with the modified parts were successfully installed in RFQ and RF conditioning of RFQ resumed in June 2023. Under the Broader Approach (BA) agreement, the Accelerator Facility validation activities aim at demonstrating the acceleration of 125 mA D+ beam up to 9 MeV. This is the main goal of the Linear IFMIF Prototype Accelerator (LIPAc) under installation and commissioning in Rokkasho, Japan [ 1 , 2 ]. The LIPAc commissioning by accelerating the beam through the entire line is currently on-going at Rokkasho Fusion Institute [ 3,4 ]. Other than the beam commissioning, in 2021 and 2022 extensive conditioning experimental campaigns have been carried out on the Radio Frequency Power System (RFPS)-RFQ system to reach CW [5]. The RFPS-RFQ is composed of 8 RF-RFQ tetrode based chains injecting RF power into the RFQ by 8 couplers. The target of the RFQ conditioning campaigns is to reach CW operation at nominal vane-voltage of 132 kV. RFQ could achieve CW field of 105 kV at the end of 2021 [ 5,8 ]. During the RFQ conditioning campaigns in 2022, the conditioning was stopped because of abnormal increase of vacuum pressure due to a leak from one O-Ring of the couplers. The 8 couplers are equipped with a ceramic window (vacuum barrier) using O-ring for sealing purposes [ 9 ]. Extensive simulation and design studies have been carried out and an upgraded design of the parts near the RF window of RFQ coupler has been proposed and validated for implementation. This paper will focus on the RFQ couplers technical issue, analysis of the design upgrade, implementation of the upgraded solution and perspective for future improvements of the RFQ couplers designs in view of FNS and DONES application. [ABSTRACT FROM AUTHOR]

• The blanket testing facility for WCCB TBM was newly built in Rokkasho Fusion Institute, Japan. • An apparatus for flow accelerated corrosion testing under coolant condition of TBM was installed. • An apparatus for high heat flux testing under cooling with pressurized water using electron beam gun was installed. • An apparatus for ingress testing of pressurized water inside TBM was installed. • An apparatus for evaluating characteristics of beryllium-water reaction was installed. Intensive research and development activities have been conducted for designing a water-cooled ceramic breeder (WCCB) blanket system. In this system 325 °C/15.5 MPa of pressurized water removes heat injected and accumulated in blanket containers made of a reduced activation ferritic/martensitic steel, F82H. The container has lithium ceramics and beryllium pebbles as tritium breeder and neutron multiplier, respectively. In order to demonstrate performance of the system, especially for high-temperature pressurized water coolant, experimental apparatus have been installed in Rokkasho Fusion Institute, National Institutes for Quantum Science and Technology, Japan. These apparatuses enable to conduct the following experiment on full-scale mockups: 1) high heat flux (HHF) test to demonstrate heat removal of surface heat flux by electron beam gun simulating plasma, 2) flow assisted corrosion, 3) coolant ingress into dummy pebble beds, and 4) beryllium-water reaction between the coolant and the pebbles. In this paper, overviews, specifications, early results of these apparatus are reported. [ABSTRACT FROM AUTHOR]

The Broader Approach (BA) activities aim to complement the ITER project and to promote the early realization of fusion energy through research, development, and tests of technologies supporting the future demonstration fusion reactor (DEMO). These activities are implemented under the BA agreement, which was signed and ratified in 2007 between Euratom and the Government of Japan. In essence, the BA activities consist of three projects: a) The Satellite Tokamak Programme Project JT-60SA, the world's largest superconducting tokamak until ITER starts, aims to support the assembly, commissioning and preliminary operation of ITER, and carry out demonstration and optimisation of steady-state operation of advanced plasma configurations for DEMO; b) The International Fusion Energy Research Centre (IFERC), which comprises three different sub-projects: the DEMO Design Research and Development Coordination Centre to coordinate design and R&D on materials and components for DEMO, the Fusion Computer Simulation Centre for the simulations of fusion plasmas, the analysis of experimental data, modelling of ITER operation, and contribution to the design of DEMO, and the Remote Experimentation Centre to allow scientists to participate remotely in fusion experiments from its control room in Japan; c) The Engineering Validation and Engineering Design Activities for the International Fusion Materials Irradiation Facility (IFMIF/EVEDA) focused on the design and validation of key components needed for the future Fusion Neutron Source facilities to characterize materials envisioned for DEMO. After 13 years of fruitful collaboration, Euratom and Japan launched the second phase of the BA activities in 2020. It is focused on exploiting and enhancing the facilities that have already been built and on working more closely than ever with ITER as the latter advances towards the first plasma. This paper will present a synthesis of the achievements already obtained thanks to the three BA projects and will address the future developments planned in 2023 and beyond. [ABSTRACT FROM AUTHOR]

In a fusion reactor, the plasma based on a deuterium-tritium reaction generates high energy neutron flux interacting with the materials of the plasma facing components. In order to study the irradiated behavior of these materials, the International Fusion Materials Irradiation Facility (IFMIF) was conceived to generate these fusion relevant neutrons through d -Li stripping source. IFMIF is presently in its Engineering Validation and Engineering Design Activities (EVEDA) phase under the Broader Approach agreement signed between EURATOM and Japanese Government in 2007. This agreement mandates the IFMIF/EVEDA project to validate the design of the different systems of IFMIF and to produce an integrated engineering design of IFMIF, together with the data necessary for future decisions on its construction and operation. While the Engineering Validation Activity (EVA) of the Lithium Target Facility and the Test Facility was completed by constructing prototypes, the EVA of the Accelerator Facility with the Linear IFMIF Prototype Accelerator (LIPAc) is still on-going at the Rokkasho Fusion Institute, Japan. This paper overviews the achievements in the previous phase ended on 31 March 2020 and the progress in the current phase to complete the commissioning of the LIPAc. [ABSTRACT FROM AUTHOR]

JT-60SA is a joint international fusion experiment being built and operated in Japan under the framework of the Broader Approach Agreement and Japanese National Fusion Programme, aiming at an early realization of fusion energy by conducting supportive and complementary work for the ITER project, all towards supporting the basis for DEMO. In this context, a collaboration has been established via EUROfusion between Fusion for Energy and CEA to develop actively cooled targets of the JT-60SA divertor. The first Actively Cooled Divertor (ACD) target, planned to be operated in 2029, has graphite as armour material and TZM as heat sink material. To be DEMO relevant, ACD target with tungsten armour is planned to be operated in 2033, with either CuCrZr or TZM as heat sink material. This paper focusses on the choice of the design (material, dimensions) of these targets. Results of thermal and structural analysis of these targets are presented. The calculations, carried out in the environment of Ansys 2021R2 code, have taken into account the heat loading under plasma operation (with a peak heat flux of 10 MW/m2) and the electromagnetic loads from a representative plasma disruption (VDE 30 ms). In order to check the compliance with nuclear requirements, RCC-MRx 2015 has been used for the mechanical assessment of metallic components, while for the graphite the comparison between the maximum stress and the yield stress has been considered. The performed analyses show that the thermal load on target during the plasma heat loading drives target designs due to differential expansion at the interface between the heat sink and the flat tiles. Additionally, on-going assessments on these divertor targets are presented, focussing on experimental High Heat Flux testing, as well as computational thermal-hydraulic studies on enhanced target configurations. [ABSTRACT FROM AUTHOR]

• Dogleg type beam transport line design for preventing the contamination of the superconducting linac system from the free surface liquid metal target system. • Moderate pressure gradient design to establish a vacuum system for satisfying the different required pressure. • Quantitative estimation of the reduction of the contamination for the newly designed dogleg beam line. The Advanced Fusion Neutron Source (A-FNS) project is progressing at the QST Rokkasho institute, Japan. The A-FNS will conduct fusion neutron irradiation tests of materials for a fusion demonstration reactor (DEMO reactor). For these tests a high intensity deuteron beam accelerator is used to produce a high neutron flux with the neutron energies around 14 MeV. The accelerator system accelerates a deuteron beam to a beam energy of 40 MeV, guides the beam towards a liquid lithium target and shapes the uniform beam at the Li target using a magnet system. Two of the main considerations for the A-FNS high energy beam transport (HEBT) design are protection of the Superconducting Radio-Frequency linear accelerator (SRF) and vacuum system design for the interface of the HEBT and the target system. For the A-FNS, back streaming of Li vapor from the windowless free surface of the Li target is a concern. In addition, widely different vacuum pressure must be maintained between the accelerator system and the target system. This paper shows the detailed design of the A-FNS HEBT section regarding these considerations. [ABSTRACT FROM AUTHOR]

• Temporal variation of atmospheric concentration of tritiated water vapor (HTO) in the vicinity of Fukushima Daiichi nuclear power plant is reported for the first time. • Monthly atmospheric HTO concentration during a period 2017–2019. • The atmospheric HTO concertation at different two sampling sites are compared. Continuous measurement of tritium in the atmosphere is important to evaluate the environmental impact of nuclear facilities and fusion facilities as well as to elucidate tritium behavior in the environment. A passive type sampler is powerful tool to conduct long-term monitoring because this does not require any power supply. This paper demonstrated the effectiveness of the passive type sampler for continuous measurement and characterized temporal variation of atmospheric concentration of tritiated water vapor around the Fukushima Daiichi nuclear power plant. The atmospheric concentrations were successfully obtained at two sampling sites and ranged within the variation in past observation although the concentration at one of the two sites was slightly higher than that of background level in Japan. Additionally, we measured the tritium concentrations of soil pore water and free water in pine needles. These values indicated the validity of the measured atmospheric tritium concentrations. [ABSTRACT FROM AUTHOR]

• Experimental campaign on MTF carried out in QST lab in Naka, Ibaraki, Japan. • Opera, SLACCAD, COMSOL, EAMCC3D correctly predict beam divergence. • Semi-empirical Opera model with current density asymmetry correctly predicts the beam deflection. • COMSOL and EAMCC3D slightly underestimate heat loads on the grids. It is a widely recognized phenomenon that, in negative ion sources for NBI, the magnetic fields in the source cause an asymmetry of the current density at the meniscus, which affects the beam optics. In order to achieve a more realistic estimation of the negative ion beam optics, the ion current density profile at the beamlet meniscus is sometimes assumed to be non-symmetric with respect to the beamlet axis. The new hypothesis tested in this paper is an empirical law obtained by recent investigations on a similar Kamaboko ion source, which relates this asymmetry to the magnetic field strength at the meniscus and to the power injected in the ion source. For the first time this hypothesis is used to directly and correctly predict the value of the beamlet deflection. The MeV ion source Test Facility (MTF) is a high voltage negative ion beam accelerator dedicated to fusion experiments in QST, Naka, Ibaraki, Japan. MTF can be operated as a three- or five-stage multi-aperture accelerator with a configuration and beam energy comparable to the future ITER NBI. In 2019, experiments were conducted on MTF aiming at accelerating a H- beam with high energy and good optics for a long duration of the beam (around 100 s). These experiments allowed to measure the beamlet divergence and deflection as well as the heat loads due to particle impinging on the accelerator grids, over a wide range of operating parameters. The predictions of several beam simulation codes (Opera, COMSOL, SLACCAD, EAMCC3D) have been compared to the experimental measurements, which allows to obtain a good agreement in terms of beam optics and a fair agreement in terms of heat loads. [ABSTRACT FROM AUTHOR]