In the maintenance procedure of fusion DEMO reactor, used in-vessel components are removed from the reactor vessel to be replaced. The temporally storage area for the used blanket segments is necessary. In the present work, the temporally storage area is conceptually designed as the used segments are stored dispersively in the plural compartments in the hot cell for the following dismantling procedure. The space dose rate of the compartment, where more than one segment is installed, was evaluated by means of the gamma ray transport calculation with PHITS Monte Calro analysis code. The space dose rate in the compartment decreases with time. For example, by the temporally storage of five used segments in one compartment for 20 years, the space dose rate in the compartment becomes lower than 250 Gy/hr, which is the limited value proposed for the remote handling in the ITER. The decay heat of the segments during the temporally storage is removed by flowing He. The segments are cooled at the temperature lower than 550 ^◦C. Then, the used back plates can be reused in the other operation of the reactor, since the mechanical properties of the back plates are not affected by the heat treatment during the temporally storage.

To stably control and operate a deuterium-tritium (DT) fusion reactor, it is important to accurately obtain the fuel ion ratio n_t/n_d (n is the number density). Previously, fuel ion ratio diagnostic methods using deuterium-deuterium (DD) and DT neutron emission rates have been studied. The reaction rate coefficients and neutron emission spectra, i.e., the shape and peak value, are strongly influenced by external plasma heating such as neutron beam injection (NBI) heating. In this paper, we consider the fuel ion ratio diagnostics by directly measuring the neutron emission spectra, including both beam-thermal and beam-beam fusion reactions, in deuterium beam-injected DT plasma. We also evaluate the slowing-down neutron component, i.e., noise, to examine whether the above method can be used for plasma diagnostics. On the basis of Boltzmann-Fokker-Planck and Monte Carlo neutron transport analyses, the applicability of the method to the beam-injected DT plasma is discussed. It is shown that the feasible plasma parameter regions of measuring for fuel ion ratio diagnostics is increased by beam injection and by adopting neutron detector channels shifted to the high-energy side.

ITER diagnostic lower ports will be used to exchange divertor cassettes and install diagnostic systems. In-vessel components of diagnostic lower port #02 (LP#02) will be mounted on a divertor cassette and a support structure, so-called a diagnostic rack, to be removed and reinstalled collectively. Japan Domestic Agency is responsible for procurements of an integration engineering of LP#02 and a divertor impurity monitor, a main tenant system in LP#02. This paper presents preliminary thermal analyses for two critical components in LP#02, the diagnostic rack and a mirror box on the divertor cassette, which will be exposed to the harsh thermal load from plasma. Realistic fabrication methods for cooling the diagnostic rack and a required cooling path layout of the mirror box on the divertor cassette have been assessed to implement the preliminary design from the viewpoint of thermal analysis.

The characteristics of a 230-mm-diameter radio-frequency (rf) negative hydrogen ion source are investigated by the measurements of electron density and temperature. A hydrogen plasma is produced by an inductively coupled discharge operated with an rf frequency of 300 kHz and a power of a few tens of kW, where a field-effect-transistor-based inverter power supply is used as an rf generator. The ion source has a magnetic filter for reduction of the electron temperature near the plasma grid used for the extraction of a negative ion beam. A high electron density greater than 10¹⁸ m⁻³ is successfully obtained for an operating gas pressure of 0.3 Pa. The electron temperature near the plasma grid is observed to decrease to about 1 eV with increasing magnetic field strength of the magnetic filter.

ACT2 (Active Cooling Teststand 2), a high heat flux test facility using electron beam has been upgraded from ACT facility and started the operation. A new electron gun enables the steady state and transient heat load on actively cooled samples. ACT2 can achieve large loaded area with steady state reactor relevant heat flux (∼20 MW/m²) up to 200 × 200 mm² and simulation of edge localized modes with short pulse length (∼100 µs). Beam profile was obtained about 9 mm with graphite probes. The heat flux is obtained by water calorimetry and measurement of the current through the samples.

The hydrogen-release behavior of the molten salt FLiNaK containing directly synthesized 0.1 wt% nano-Ti powder was investigated. Hydrogen release was faster at higher temperatures, and the volume of released hydrogen from FLiNaK was significantly higher than that from pure FLiNaK. However, the ratio of released H/Ti in FLiNaK was smaller than that in µm-Ti powder.

High-power and long-pulse arc discharges of 150 kW for 100 s have been achieved for the first time by suppressing oxygen-induced-arcing which was one of the critical issues on JT-60SA negative ion source. Toward the realization of such arc discharge, the suppression of recycling of oxygen from the arc chamber wall was found to be a key issue in the large-size arc-driven negative ion source. Because the experimental results showed that this oxygen was derived from release of water due to high temperature chamber wall of heated by an arc discharge, the baking of the arc chamber was tried to reduce water adsorbing to the chamber before the long-pulse discharge. After the baking at 80 ^◦C for 8 hours, since the oxygen level was reduced to half of that before baking, the available pulse duration became twice longer. By combining this baking and long-pulse conditioning shots, the stable long-pulse arc discharge has been obtained. This result contributes to the improvement of availability of the large-size negative ion sources which require long-conditioning time.

The lithium target facility of IFMIF (International Fusion Materials Irradiation Facility) consists of target assembly, lithium main loop, lithium purification loops, the diagnostic systems, and remote handling system. Major impurities in the lithium loop are proton, deuterium, tritium, 7-Be, activated corrosion products and the other species (C, N, O). It is very important to remove nitrogen content in lithium loop during operation, in order to avoid the corrosion/erosion of the nozzle of lithium target for the stable lithium flow on the target assembly. Nitrogen in the lithium can be removed by N hot trap using Fe-5%Ti alloy at temperatures from 400 to 600^◦C. In this study, the specification and the detailed design were evaluated, and the component of N hot trap system was fabricated.

There is a need to develop ITER instrumentation and control (I&C) systems with high reliabilities. Interlock systems that activate machine protection functions are implemented on robust wired-logic systems such as programmable logic controllers (PLCs). We herein propose a software tool that generates program code templates for the control systems using PLC logic. This tool decreases careless mistakes by developers and increases reliability of the program codes. A large-scale engineering database has been implemented in the ITER project. To derive useful information from this database, we propose adding semantic data to it using the Resource Description Framework format. In our novel proposal for the ITER diagnostic control system, a guide words generator that analyzes the engineering data by inference is applied to the hazard and operability study. We validated the methods proposed in this paper by applying them to the preliminary design for the I&C system of the ITER edge Thomson scattering system.

Er₂O₃ is a high potential candidate material for tritium permeation barrier and electrical insulator coating for advanced breeding blanket systems with liquid metal or molten-salt types. Recently, Hishinuma et al. reported to form homogeneous Er₂O₃ coating layer on the inner surface of metal pipe using Metal Organic Chemical Vapor Deposition (MOCVD) process. In this study, the influence of thermal history on microstructure of Er₂O₃ coating layer on stainless steel 316 (SUS 316) substrate by MOCVD process was investigated using SEM, TEM and XRD. The ring and net shape selected-area electron diffraction (SAED) patterns of Er₂O₃ coating were obtained each SUS substrates, revealed that homogeneous Er₂O₃ coating had been formed on SUS substrate diffraction patterns. Close inspection of SEM images of the surface on the Er₂O₃ coating before and after thermal cycling up to 700^◦C in argon atmosphere, it is confirmed that the Er₂O₃ particles were refined by thermal history. The column-like Er₂O₃ grains were promoted to change to granular structure by thermal history. From the cross-sectional plane of TEM observations, the formation of interlayer between Er₂O₃ coating and SUS substrate was also confirmed.

Krylov subspace method and the variable preconditioned Krylov subspace method with communication avoiding technique for a linear system obtained from electromagnetic analysis are numerically investigated. In the k−skip Krylov method, the inner product calculations are expanded by Krylov basis, and the inner product calculations are transformed to the scholar operations. k−skip CG method is applied for the inner-loop solver of Variable Preconditioned Krylov subspace methods, and the converged solution of electromagnetic problem is obtained using the method.

The gas-liquid mixed phase plasma generated by a nanoseconds-pulsed discharge in bubbles was used for degradation of acetic acid in water. A Shirasu porous glass (SPG) membrane tube was adopted as micro-bubble generator and part of a discharge reactor. A large number of tiny bubbles are generated from dense micro-pores (average diameter of φ50 µm) of the SPG wall and a discharge through SPG membrane was initiated between high voltage electrode and bubble surface. Comparing with a resin tube reactor which has six mechanical holes (diameter of φ1 mm), the surface area of bubbles increased with the same gas flow rate. The hydrogen peroxide (H₂O₂) concentration in treated water using SPG membrane reactor increased by about 71% compared with that using the resin tube reactor, and the degradation amount of acetic acid was also promoted by about 82% when Ar gas was used with the flow rate of 2 L/min. Meanwhile the H₂O₂ production and degradation of acetic acid proportionally increased with the growth of gas flow rate in the SPG membrane reactor.

The thrust imparted by an applied-field magneto-plasma-dynamic thruster is enhanced by superimposing a convergent-divergent magnetic field called a magnetic Laval nozzle. The thrust increases up to 6.9 N by increasing the magnetic field strength at the Laval nozzle throat. It is observed that the plasma flow velocity increases and the ion temperature simultaneously decreases downstream of the throat. A major component of the measured Lorentz force arising from the plasma-induced current is identified to be in the radial direction, while a significant increase in the plasma density is observed upstream of the nozzle. These results imply that the plasma pressure increases upstream of the magnetic Laval nozzle due to an inhibition of the plasma loss, which contributes to the increase of the thrust.

In order to enhance the H⁻ surface production in hydrogen negative ion sources, it is important to increase the density of the H atoms dissociated from H₂ molecule and the resultant atomic flux towards the surface of the plasma grid. In this paper, the effect of the Electron Energy Distribution Function (EEDF) on the dissociation of H₂ in Linac4 H⁻ source has been studied using Electromagnetic Particle In Cell (EM-PIC) simulation with Monte Carlo method for Collision Processes (MCC). It has been shown that the rate coefficient of dissociation reactions can be enhanced in the lower H₂ gas pressure regime, while the H atom production rate becomes larger in the higher pressure regime. It is suggested that the optimal H₂ gas pressure to maximize the H atom production is determined by the balance of rate coefficient and the H₂ density.

This study aims to create an interface for visualizing numerical data on a head-mounted display (HMD) and introduce functions to allow control of this visualization via hand gestures. HMDs have the advantage of providing a user with a 360-degree field of view without taking up a lot of space. However, it is difficult to control visualized numerical data intuitively with this type of display because the user cannot see his/her own hand. We therefore introduced functions allowing the user to control the virtual scene with visualized virtual hands. We developed a system in which a virtual menu is presented to the users and they can change the visualization method by pushing virtual panels. The user can move freely in the visualized virtual scene. Moreover, to help users share their thoughts, we have introduced a drawing function that enables users to indicate points and areas of interest in the visualized scene.

A filament driven multi-cusp negative hydrogen ion source has been developed for proton cyclotrons. In order to increase the H⁻ beam current, the dependences of H⁻ beam current on various design/operating parameters has been studied experimentally and numerically. In this paper, the effects of arc-discharge voltage and current on H⁻ production via the volume production process are investigated by three-dimensional kinetic modeling of electrons in the source plasma and zero-dimensional rate equations. This numerical analysis reproduces the experimental results of H⁻ beam current dependence on the arc-discharge condition, and also gives reasonable explanations for their characteristics.

A W-band (75 - 110 GHz) oversized surface wave oscillator driven by weakly relativistic electron beams with energy in the range of 10 - 80 keV is studied. Rectangular corrugations are used as slow-wave structures (SWS) having surface waves with an upper cutoff frequency of approximately 100 GHz (W-band). Uniformly distributed annular electron beams are generated by a disk-type cold cathode and then are injected into the W-band oscillator. A longer SWS length causes the oscillator to function in both backward wave oscillator (BWO) and travelling wave tube (TWT) operations, and no meaningful oscillation occurs at the π-point or the Bragg condition. When the SWS length is short enough, oscillation occurs in all regions: BWO, π-point and TWT. The operations of the oscillator are strongly affected by the structure length. The maximum radiation power is estimated to be approximately 20 kW with the figure of merit of about 2 × 10² MW.GHz².

We have started a project of experimental generation of low Mach number collisionless shocks propagating into magnetized plasma, using high power lasers such as Gekko XII at Institute of laser engineering, Osaka University. We briefly present a result of our first experiments done in September 2014, in which Aluminum plane target was irradiated by main laser in ambient Helium gas with external magnetic field. Ejected Aluminum plasma had a bulk velocity of 430 km s⁻¹, which is sufficient enough to excite the magnetized collisionless shock in our experimental setup. However, the ejected Aluminum plasma was decelerated before the shock was excited.

Angular momentum changes due to nuclear-plasma interactions on highly-excited nuclei in high energy density plasmas created at the National Ignition Facility can be measured through a change in isomer feeding following gamma emission. We propose an experiment to detect these effects in ¹³³Xe^∗ in exploding pusher capsules.

Magnetic thrust chamber is a propulsion system controlling plasma by a magnetic field and is expected as a propulsion system of laser fusion rocket. This rocket obtains thrust due to the interaction between plasma and magnetic field in the system. We examine the plasma structure in a magnetic thrust chamber by observing the light emission from the plasma with several magnetic field strength. The experiments imply that anisotropic plasma expansion is induced by the applied magnetic field and the velocity is decreased at the magnetic field above 0.67 T.

The neutrino-nucleus interactions are important for understanding nucleosyntheses by neutrino-induced reactions as well as supernova explosion mechanisms. The M1 strength in atomic nuclei is important for estimation of neutrino-nucleus interactions. We have proposed a method using (γ, n) reactions with linear polarized laser Compton scattering (LCS) γ-rays to measure the M1 strength and verified a theoretical prediction for the first time. We have discussed experimental technique using the next generation of LCS beams.

In this overview, we explain methods to identify hysteresis in the gradient-flux relation for energy transport in a core plasma, which is revealed by a power modulation experiment. Two approaches to experimentally observe the hysteresis relation are discussed in detail. Advanced data analysis methods are also illustrated. A theoretical analysis of the process that couples heat to turbulence is also addressed.

The state of hydrogen plasma in the extraction region in a hydrogen negative-ion (H⁻) source for NBI has been investigated. We clearly observe an improvement of H⁻ density owing to the surface production effect with Cs seeding. H⁻ ions are widely distributed in the extraction region which is obtained by movable cavity ring down (CRD). We confirm a negative ion rich plasma with a few electrons in the extraction region, which state is important for reduction of electron contamination in extracting beam. An extraction area is reached 30 mm from the PG surface, which is measured by a 2D imaging diagnostic for H_α emission. We find the insensitive area for H⁻ extraction at the PG surface between the apertures. Negative ions produced at the surface are considered to have been supplied in the extraction region. The flow velocity of H⁻ ions is obtained by a four-pin Langmuir probe using a photodetachment technique with an Nd:YAG laser. H⁻ ion flows from the plasma grid surface, and its direction drastically changes at 20 mm from the production surface. This flow behavior is considered to be an important characteristic for improving H⁻ density in the extraction region.

Oxide dispersion strengthened (ODS) steels with nano-scaled oxide particles in high density in ferrite/martensite matrix and on grain boundaries of ultra-fine grains have excellent properties as structural material for fusion blankets, while some issues of fabrication processes are still remaining to be solved. In this overview, material properties of recently developed ODS steels are introduced in comparison to ferritic/martensitic (F/M) steels: 1) mechanical properties, 2) corrosion behavior and 3) radiation tolerance in ODS steels, which are outstandingly superior to the F/M steels. Coupling use of the ODS and F/M steels is effective to expand the design margin of fusion blankets. R&D of dissimilar joining of FM/ODS steels is indispensable.