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The D(d, n)3He reaction is one of the common monoenergetic neutron sources. We compile the Frag Data table of D(d, n)3He reaction from the literature as an external cross-section data for PHITS. We confirm the validity of the Frag Data table by the calculation of the total and angular neutron yield calculations for an ideal deuterium thin target. Finally, PHITS with the Frag Data table is applied to the angular neutron yield and spectrum calculations of the gas target and the deuterium-loaded titanium target of the Tohoku University Fast Neutron Laboratory.

The absolute calibration of the detection efficiency for the total neutron yield in the whole plasma is one of the most important issues in the neutron diagnostics such as a neutron flux monitor (NFM). The possibility of a partial neutron calibration is investigated based on the in-situ neutron calibration data of the Large Helical Device (LHD), JT-60U, and other tokamaks. In the case of NFM using a 235U fission chamber located outside of the vacuum vessel on the equatorial plane, more than 90% of the detector counts are contributed by neutrons in the toroidal angle range of −60° to +60°. The detection efficiency for the neutron source located at one toroidal position on the magnetic axis (called point efficiency) decreased exponentially with the absolute toroidal angle of the neutron source. We found that a partial calibration in the toroidal angle range of −60° to +60° combined with exponential extrapolations to -180° and +180°can estimate total detection efficiency within 5% uncertainty. In the case of point efficiency measurement at the limited number of the toroidal locations, the total detection efficiency for the whole plasma can be estimated within 4% uncertainty with the assistance of the MCNP simulation.

InfraRed imaging video bolometer (IRVB) is a powerful diagnostic for the plasma radiation measurement. Study on plasma radiation phenomena, e.g., plasma detachment, is one of the crucial issues to realize a fusion reactor. In order to apply the IRVB to such a study, a shielding is required to protect an IR camera from neutron irradiation. In the large helical device (LHD), deuterium experiment has started in 2017. Then, the shielding was designed using MCNP6 code with the 3-D modeling of LHD. The guideline of the neutron flux for the design was determined by the operational experience in JT-60U tokamak and by the result of the irradiation in OKTAVIAN. The strong neutron flux due to the location close to the vacuum vessel and the influx through the lens hole were reduced sufficiently. The designed shielding was applied to the LHD deuterium experiments and the IRVB with the shielding could be operated successfully without any dead pixels in the neutron emission rate up to 3.3×10 15 n·s -1 , which is the maximum rate in the first experimental campaign and in the total neutron emission of 3.6×10 18 n. These correspond to the neutron emission rate of 2.9×10 7 n·s -1 and the total neutron emission of 3.2 × 10 10 n at around the IR camera.

In the Large Helical Device (LHD) of the National Institute for Fusion Science, the experiments using deuterium plasma were performed from March 2017. Neutrons with the energy of 2.45 MeV are generated by d (d, n) 3He reactions. The evaluation of the neutron flux in the torus hall as well as the LHD vessel is very important for designing the decommissioning of the LHD in the future, and the radiation shielding for workers and components around LHD. In this study, we performed the activation experiments using multiple activation foils to obtain a neutron spectrum in the vacuum vessel of the LHD. The reaction rate of each activation foil was generally consistent with the calculation result by MCNP6. As a result of the unfolding with SAND-II code, we experimentally obtained the neutron spectrum in the vacuum vessel of the LHD for the first time.

For the estimation of the neutron field generated by deuterium plasma operation in the Large Helical Device (LHD), the first measurement of the thermal neutron distribution on the floor level of the LHD torus hall was carried out. For the thermal neutron detection, indium was used as activation foils. The radioactivity of these foils were evaluated by a high-purity germanium detector (HPGe) and an imaging plate (IP). The major components of radioactive isotope of indium was 116mIn. The mapping of thermal neutron distribution in the torus hall was performed. The interactions between neutron and components around LHD were observed in the thermal neutron distribution. Also, the borated polyethylene blocks effectively absorbed the thermal neutron. The thermal neutron distribution evaluated in this work can be helpful to predict the amount of radioactive waste in the torus hall proceeding with deuterium experiment in LHD.

Prior to the deuterium experiments of the Large Helical Device (LHD), an in situ neutron calibration experiment was carried out by using an 800 MBq 252Cf neutron source in November 2016, where a neutron flux monitor, a neutron activation system and a vertical neutron camera are calibrated. This paper concentrates on the in situ calibration for the neutron flux monitor. The neutron flux monitor based on 235U fission chambers and 10B and 3He proportional counters are positioned at three locations outside the LHD cryostat. The counts are measured during continuous rotation of the 252Cf neutron source on the typical magnetic axis of the plasma by a toy train, where the neutron source can be regarded as a ring neutron source. Detection efficiencies for the 252Cf ring source are derived by (total counts)/(total emitted neutron number) in the continuous rotation of the neutron source. Detection efficiencies for the real plasma neutron source are obtained from the measured detection efficiencies with the correction factor taking account of the deference between the 252Cf ring source and the real plasma neutron source evaluated by MCNP calculations with the three-dimensional model of the LHD. Finally, the uncertainty of the total neutron emission rate measurement is discussed.

The neutral beam (NB) fast ion confinement in the Large Helical Device (LHD) is studied for several full field ( $B_{t}\sim 2.75~\text{T}$ ) magnetic configurations by a combination of neutron measurement and simulations. To investigate the NB fast ion confinement, we have performed a series of short-pulse NB injection experiments. The experiment results are analysed by the integrated code TASK3D-a. From this investigation, the effective particle diffusion coefficients of the tangential and perpendicular NBs are approximately $D^{\text{eff}}\sim 0.1~\text{m}^{2}~\text{s}^{-1}$ and $D^{\text{eff}}\sim 1~\text{m}^{2}~\text{s}^{-1}$ in the standard configuration. It is clarified that the NB fast ion confinement improves when the plasmas are shifted inward. Moreover, it is also found that the simulation, which considers the deuteron dilution effect due to the presence of impurity ions, can describe a neutron emission rate consistent with the measurement.

In the large helical device (LHD) deuterium plasma experiment, the neutron emission rate and the shot-integrated neutron yield are measured with the neutron flux monitor (NFM) and the neutron activation system (NAS), respectively, where the neutron emission is assumed to be isotropic in the plasma. The differential cross section of the D(d,n) 3 He reaction has a large anisotropy for the forward direction of the incident deuteron direction. LHD has intensive tangential neutral beam injectors (NBIs), which may cause an anisotropic neutron emission in the plasma. The angular distribution of the neutron emission is calculated from the fast-ion distribution function evaluated by a code that solves Fokker-Plank equations for the 180-keV tangential NBI. The effect of the anisotropic neutron emission on the NFM and NAS measurements is estimated by a general-purpose Monte Carlo N-particle (MCNP) code calculations. Also, the effect is confirmed experimentally. The neutron emission rate measured with the NFM near the equatorial port is about 10% larger than that with the NFM at the top of the LHD center axis. The shot-integrated neutron yield measured with NAS is 25% larger than that with NFM at the top of the LHD center axis in the case of the tangential neutral beam injection, which is consistent with the MCNP calculation.

The deuterium operation of the large helical device (LHD) began in March 7, 2017, after long-term preparation and commissioning of apparatuses necessary for execution of the deuterium experiment. A comprehensive set of neutron diagnostics was developed and installed onto LHD through numerous efforts in preparation. Neutron diagnostics play an essential role in both neutron yield management for the radiation safety and extension of energetic-particle physics study in LHD. Neutron flux monitor (NFM) characterized by fast-response and wide dynamic range capabilities is successfully working. Total neutron emission rate reached $3.3 \times 10^{15}$ (n/s) in the first deuterium campaign of LHD. The highest neutron emission rate was recorded in inward shifted configuration. Neutron yield evaluated by neutron activation system agrees with neutron yield measured with NFM. Performance of vertical neutron camera was demonstrated. Neutron emission profile was inwardly shifted in the inwardly shifted configuration, whereas it was outwardly shifted in the outwardly configuration. Secondary deuterium-tritium neutrons produced by triton burnup in LHD deuterium plasmas were detected for the first time in stellarator/heliotron devices in the world. Similar to total neutron emission rate, the inward shifted configuration provided highest triton burnup ratio.

The Large Helical Device (LHD) plans to start deuterium experiments in March 2017. The expected performances of the neutron flux monitor and the vertical neutron camera have been investigated by neutron Monte Carlo simulations using the MCNP-6 Monte-Carlo neutronics code and the cross-section library FENDL-3.0. Three neutron flux monitors using 235 U fission chambers are located on the center axis of LHD and at two toroidal locations on the horizontal plane outside the cryostat. The detection efficiency for the neutron emission in the plasma has been evaluated. This is almost insensitive to the neutron source profile and the plasma position. The vertical neutron camera consists of 11 channels of stilbene detectors with a parallel collimator embedded in the concrete floor slab. The response function of the stilbene detector has been evaluated with PHITS code. Based on the response function, the count rate of the stilbene detector is estimated to be ∼6 × 10 4 cps for maximum neutron yield shots. Also, the spatial resolution is estimated to be 70 mm, which is smaller than the pitch of adjoining channels.

The enhancement of the fusion reaction rate coefficient induced by energetic protons, which isone of the typical nuclear elastic scattering (NES) effects, was observed in the large helicaldevice (LHD) located at the National Institute for Fusion Science. An intense high purityhydrogen beam (the atomic ratio of the contained deuterium was less than 1 ppm) with∼170 keV-energy and ∼10 MW-power was injected into a deuterium plasma with the electrontemperature ∼9 keV and density ∼1019 m−3. After the hydrogen beam injection, the neutrongeneration rate by the D(d,n)3He fusion reaction immediately increased, and an increment ofover one order of magnitude was observed, even though there was no meaningful iontemperature variation. The reasons for the increment in the neutron generation rate arediscussed with reference to the Boltzmann–Fokker–Planck analysis along with LHDexperimental data. It is concluded that the increment was induced by the production ofenergetic deuterons due to the NES of energetic protons.

The fast deuteron (non-Maxwellian component) diagnostic method, which is based on the higher resolution optical spectroscopic measurement, has been developed as a powerful tool. Owing to a decrease in the D–H charge-exchange cross section, the diagnostic ability of conventional optical diagnostic methods should be improved for ∼MeV energy deuterons. Because the 3He–H charge-exchange cross section is much larger than that of D–H in the ∼MeV energy range, the visible light (VIS) spectrum of 3He produced by the dueteron–dueteron (DD) reaction may be a useful tool. Although the density of 3He is small because it is produced via the DD reaction, improvement of the emissivity of the VIS spectrum of 3He can be expected by using a high-energy beam. We evaluate the VIS spectrum of 3He for the cases when a fast deuteron tail is formed and not formed in the ITER-like beam injected deuterium plasma. Even when the beam energy is in the MeV energy range, a large change appears in the half width at half maximum of the VIS spectrum. The emissivity of the VIS spectrum of 3He and the emissivity of bremsstrahlung are compared, and the measurable VIS spectrum is obtained. It is shown that the VIS spectrum of 3He is a useful tool for the MeV beam deuteron tail diagnostics.

The single crystal CVD diamond detector (SDD) was installed in the torus hall of the Large Helical Device (LHD) to measure neutrons with high time resolution and neutron energy resolution. The LiF foil with 95.62 % of 6Li isotope enrichment pasted on the detector was used as the thermal neutron convertor as the energetic ions of 2.0 MeV alpha and 2.7 MeV triton particles generated in LiF foil and deposited the energy into SDD. SDD were exposed to the neutron field in the torus hall of the LHD during the 2nd campaign of the deuterium experiment. The total pulse height in SDD was linearly propotional to the neutron yield in a plasma operation in LHD over 4 orders of magnitude. The energetic alpha and triton were separately measured by SDD with LiF with the thickness of 1.9 μm, although SDD with LiF with the thickness of 350 μm showed a broadened peak due to the large energy loss of energetic particles generated in the bulk of LiF. The modeling with MCNP and PHITS codes well interpreted the pulse height spectra for SDD with LiF with different thicknesses. The results above demonstrated the sufficient time resolution and energy discrimination of SDD used in this work.

In the currently performed neutral beam (NB) -heated deuterium plasma experiments, neutrons are mainly produced by a beam-plasma reaction. Therefore, time-resolved measurement of the neutron emission profile can enhance the understanding of the classical and/or anomalous transport of beam ions. To measure radial neutron emission profiles as a function of time, the vertical neutron camera (VNC) capable of operation with a counting rate in the MHz range was newly installed on the Large Helical Device (LHD). This is the world’s first neutron camera for stellarator/heliotron devices. The VNC consists of a multichannel collimator, eleven fast-neutron detectors, and the digital-signal-processing-based data acquisition system (DAQ). The multichannel collimator having little cross talk was made from hematite-doped heavy concrete, which has a high shielding performance against both neutrons and gamma-rays. A stilbene crystal coupled with a photomultiplier having high-gain-stability in the high-count rate regime was utilized as a fast-neutron scintillation detector because it has a high neutron-gamma discrimination capability at high count rates. The DAQ system equipped with a field programmable logic controller was developed to obtain the waveform acquired with a 1 GHz sampling rate and the shaping parameter of each pulse simultaneously at up to 106 cps (counts per second). Neutron emission profiles were successfully obtained in the first deuterium campaign of LHD in 2017. The neutron emission profile was measured in tangentially co-injected NB-heated plasma with different magnetic axes (Rax). The neutron counts became larger in the inward-shifted configuration, which was consistent with the total neutron rate measured by the neutron flux monitor. The radial peak position of the line-integrated neutron profile which changed according to Rax showed that the VNC worked successfully as designed. The VNC demonstrated the expected performance conducive to extending energetic-particle physics studies in LHD.

Two scintillating fiber (Sci-Fi) detectors have been operated in the first deuterium plasma campaign of the Large Helical Device in order to investigate the time evolution of the triton burnup through secondary 14 MeV neutron measurement. Two detectors use scintillating fibers of 1 mm diameter embedded in an aluminum matrix with a length of 10 cm connected to the magnetic field resistant photomultiplier. A detector with 91 fibers was developed in the Los Alamos National Laboratory and has been employed on JT-60U. Another detector with 109 fibers has been developed in the National Institute for Fusion Science. The signals are fed into a discriminator of 300 MHz bandwidth with a pulse counter module for online measurement and a digitizer of 1 GHz sampling with 14 bits to acquire pulse shape information for offline data analysis. The triton burnup ratio has been evaluated shot-by-shot by the 14 MeV neutron measurement of Sci-Fi detectors which are calibrated by using the neutron activation system and the total neutron measurement of the neutron flux monitor using 235U fission chambers.

The behavior of the 1 MeV triton has been studied in order to understand the alpha particle confinement property in the deuterium operation of toroidal fusion devices. To obtain time evolution of the deuterium-tritium (D-T) neutron emission rate where the secondary DT neutron emission rate is approximately 1012 n/s, we designed two high detection efficiency scintillating fiber (Sci-Fi) detectors: a 1 mm-diameter scintillation fiber-based detector Sci-Fi1 and a 2 mm-diameter scintillation fiber-based detector Sci-Fi2. The test in an accelerator-based neutron generator was performed. The result shows that the directionality of each detector is 15° and 25°, respectively. It is found that detection efficiency for DT neutrons is around 0.23 counts/n cm2 for the Sci-Fi1 detector and is around 1.0 counts/n cm2 for the Sci-Fi2 detector.

A wide-range neutron flux measurement instrument is developed herein for monitoring the total neutron emission rate and yield of the Large Helical Device (LHD) during deuterium experiments implemented from March 2017 in the National Institute for Fusion Science (NIFS), Japan. The instrument is designed for and installed on the Neutron Flux Monitoring (NFM) system, which measures the counting rate using a 235U Fission Chamber. By combining the pulse counting and Campbell methods, the Digital Signal Processing Unit (DSPU) realized a wide dynamic range of over six orders of magnitude from 1 × 103 counts/s (cps) to 5 × 109 cps. This study explains and discusses how the instrument is developed, including topics from the predevelopment activities to the verification test at the Kyoto University Critical Assembly (KUCA). Experimental results in the LHD using the finished products suggest that the NFM system works well during deuterium experiments.

Materials and structures of a collimator for a new neutron emission profile monitor in JT-60SA are examined through Monte Carlo simulations using the Monte Carlo N-Particle transport code. First, the shielding properties of various material combinations are compared in order to determine a combination with high shielding performances against both neutrons and gamma-rays. It is found that a collimator consisting of borated polyethylene and lead has a high shielding performance against neutrons. Moreover, a high shielding performance against gamma-rays is obtained when a lead pipe with a radial thickness of 0.01 m is inserted into a collimation tube. Second, we demonstrate that it is possible to improve the spatial resolution to a desired level by installing a thin tubular extension structure that fits into the limited space available between the main collimator block and the tokamak device. Finally, the collimator structures that meet both the targeted spatial resolutions (

The Pulse shape discrimination (PSD) technique for single crystal CVD diamond detector (SDD) was applied to the real-time thermal neutron measurement during the 3rd campaign of Deuterium-Deuterium (D-D) plasma experiment in the Large Helical Device (LHD). The PSD method is based upon the different shape of electrical pulses produced in diamond by gamma-ray (triangular-shaped pulse) and energetic ions (rectangular-shaped pulse), respectively. An improved PSD was developed which makes use of the full width at half maximum (FWHM) and the full width at 2/3 of the peak height (FW2/3 PH). These two parameters reflect the difference in the pulse shape produced by gamma-rays and energetic ions. The performance of this improved PSD technique was first tested irradiating the SDD by gamma-rays from 60Co and alphas from 241Am radiation sources, respectively. Then, using a 6LiF thermal neutron converter, a successful discrimination between gamma-rays and alpha particles and tritons generated by the 6Li(n,α)3H reaction induced by neutrons from 252Cf spontaneous fission neutron source was achieved. Thanks to this PSD processing technique, the thermal neutron detection efficiency increased about 1.7 times compared to previous measurements performed without the PSD technique. The real-time thermal neutron measurement by SDD with this enhanced PSD processing was also used during D-D plasma discharges in the Large Helical Device (LHD). It was found that both the time integrated counts and the time evolution count rate measured by the SDD reproduced well that of the fission chamber used as official LHD neutron monitor. The capability of the SDD detector using the PSD technique of precise real-time thermal neutron measurement in LHD was demonstrated.

Scintillating-fiber (Sci-Fi) detector has been employed to measure 14 MeV neutrons in the magnetic confinement fusion experiment. Design of the Sci-Fi detector reduces response to gamma-rays, compared to bulk scintillators, while at the same time enabling directional responses to energetic neutrons. Ability of gamma-ray rejection is an important parameter to judge the discrimination property for a fast neutron detector. In order to investigate the gamma-ray rejection abilities in the case of 2.45 MeV neutron and higher-energy neutrons, the pulse height spectra (PHS) of four different-head detectors in different diameter and with/without the aluminum (Al) matrix have been measured by using the accelerator-based neutron source with d–D reaction. Four different-head detectors show the different pulse height properties and the gamma-ray rejection abilities, which impact upon the neutron discrimination abilities. Meanwhile, simulations of detector responses have been performed using the Particle and Heavy Ion Transport code System (PHITS) to analyze the experimental results. Neutron discrimination abilities of small diameter Sci-Fi is better than that of large diameter Sci-Fi. Al matrix is beneficial to enhance 6.6–10 times difference of the gamma-ray rejection affecting the neutron discrimination ability in the case of Sci-Fi with/without Al matrix. It is also found that the neutron discrimination abilities of the Sci-Fi without the Al matrix and a plastic scintillator are the same.

The designs of neutron spectrum-shaping assembly (NSSA) composed with various shielding materials with natural isotopic abundance were evaluated to construct the neutron field dominated with thermal neutron or epi-thermal neutron for the application of neutron filed in the torus hall of LHD toward the BNCT research. According to the neutron transport calculation by MCNP6, the fast neutron moderation efficiency was higher in polyethylene (PE) compared to lithium fluoride (LiF) and magnesium fluoride (MF), although LiF showed relatively large epi-thermal and thermal neutron absorption. This comparison showed that the thermal neutron field can be effectively achieved with using PE. For constructing the NSSA which can provide the neutron field dominated with epi-thermal neutron, several NSSA designs were evaluated with respect to fast neutron flux, epi-thermal neutron flux, and gamma-ray dose. The combination of MF, lead (Pb) and cadmium (Cd) can provide the good epi-thermal neutron field with the mitigations of fast neutron flux and gamma-ray dose, which is also suitable for BNCT research in the torus hall of LHD.

A first attempt to observe a nuclear-elastic-scattering (NES) effect caused by energetic protons on deuteron slowing-down behaviour was made on the Large Helical Device located at the National Institute for Fusion Science. The NES effect on the slowing-down of fast ions can influence the confinement of fast ions, ion heating, fusion reaction rate coefficient, etc. An intense hydrogen beam was injected into a deuterium plasma to create a knock-on tail, i.e. a non-Maxwellian energetic component in the deuteron velocity distribution function. We conducted two types of experiment: (1) observation of the slowing-down of the knock-on tail and (2) observation of the NES effect on the slowing-down time of fast ions. The phenomena are discussed in terms of the difference in the decay process of the D(d,n)3He neutron generation rate after neutral beam heating is terminated between the cases when the knock-on effect is influential and not influential, and also from the difference in the neutron decay times. The results of a series of experiments indicate that the NES effect caused by energetic protons can have an impact on the slowing-down of fast deuterons.

In order to study fast ion confinement and transport mechanisms both in quiescent plasmas and in the presence of magneto-hydrodynamic (MHD) activity, an electric field parallel to the magnetic field type neutral particle analyzer (E|B-NPA) was installed using Micro-Channel Plates (MCPs) in the Large Helical Device (LHD). The E|B-NPA is an established diagnostic used to measure the energy distribution of charge exchange neutral particles escaping from plasmas corresponding to hydrogen, deuterium, and tritium, respectively. The LHD deuterium experimental campaign started in 2017. To obtain more details of MHD behavior, we improved on time resolution performance of the E|B-NPA using a high-speed Pre-Amplifier and Discriminator (PAD) and Latching Scaler Module (LSM). For the last LHD experimental campaign, the E|B-NPA was installed on nearly the equatorial plane of the vacuum chamber to measure the passing energetic particles generated by tangentially injected neutral beams. As the results of the E|B-NPA commissioning, it is confirmed that the E|B-NPA successfully detected the energetic particles and obtained the energy distributions corresponding to hydrogen. Also, the effect of the neutron to E|B-NPA is estimated using the other neutron diagnostics during the experiments.

Lithium (Li) glass scintillation detectors were utilized by the neutron response of a 7Li glass subtracted from the neutron response of a 6Li glass to evaluate the tritium production rate (TPR) in the fusion blanket neutronics experiments, which is a so called Li glass method. TPRs in the Li2O blanket and the Li/V-alloy blanket were measured by a 6Li2O and a 6Li2CO3 pellet method, and by the Li glass method in the benchmark neutronics experiment with D-T neutrons at the Fusion Neutronics facility (FNS) of JAERI. TPRs measured by the Li glass method are lower than TPRs measured by the pellet method. The neutron responses of Li glass detectors have been calculated to study the discrepancies of two different methods by using the PHITS code. In the blanket, the neutron spectra change to harder from the backside to the front side of blanket. The reaction rate of several reactions, such as 6Li(n, n’α)D, 7Li(n, n’α)T, 7Li(n, 2n)6Li, and the elastic scattering of 6Li and 7Li increase with the neutron energy. The low-energy neutron peak was considered only for the calculation of TPR from Li glass, which loses the information of the 6Li(n, α)T reaction from high-energy neutron range. In addition, the reaction rate of this peak evaluated by the Li glass method is lower than real TPR of this peak for 6Li glass caused by weakened effect from other reactions. Therefore, the ratios of this peak reaction rate from the Li glass method against the total TPR of 6Li glass were evaluated to be a correction factor to correct Li glass method. After the correction, TPRs measured by Li glass method agree well with TPRs measured by pellet method.

In the Large Helical Device (LHD) of the National Institute for Fusion Science, a deuterium plasma experiment was performed in March 2017. Neutrons with an energy of 2.45 MeV are generated by d (d, n) 3He reactions. The evaluation of this neutron flux in the torus hall, as well as within the LHD vessel, is very important for the decommissioning of the LHD in the future and the radiation shielding for workers and components around the LHD. In this study, we evaluate the spatial distribution of thermal and epithermal neutron flux on the floor level of the LHD torus hall by measuring the neutron activation of gold foils. The flux information obtained in the experiment can be used for the evaluation of radio-activation and the shielding design.

In situ calibration of the neutron activation system on the Large Helical Device (LHD) was performed by using an intense 252Cf neutron source. To simulate a ring-shaped neutron source, we installed a railway inside the LHD vacuum vessel and made a train loaded with the 252Cf source run along a typical magnetic axis position. Three activation capsules loaded with thirty pieces of indium foils stacked with total mass of approximately 18 g were prepared. Each capsule was irradiated over 15 h while the train was circulating. The activation response coefficient (9.4 ± 1.2) × 10−8 of 115In(n, n′)115mIn reaction obtained from the experiment is in good agreement with results from three-dimensional neutron transport calculations using the Monte Carlo neutron transport simulation code 6. The activation response coefficients of 2.45 MeV birth neutron and secondary 14.1 MeV neutron from deuterium plasma were evaluated from the activation response coefficient obtained in this calibration experiment with results from three-dimensional neutron calculations using the Monte Carlo neutron transport simulation code 6.

Based on long-term research activities on fusion engineering, eleven key technologies for future fusion reactors, especially for demo reactor, were selected in the Working Group of fusion research ...

A neutron source for material and component tests is an essential tool for the DEMO reactor development. An accelerator-based neutron source such as IFMIF is regarded as the most promising one in J...

In the Broader Approach (BA) framework, research and development on blanket related materials and technologies have been carried out between the EU and Japan. Those activities are implemented mainly at the Rokkasho BA site in collaboration with universities in Japan. In the R&D on SiCf/SiC composites for an advanced blanket material, mechanical properties of chemically vapor infiltrated (CVI) SiCf/SiC composites have been obtained in high temperature vacuum environment up to 1000 °C. As to R&D on the tritium technology, tritium retention of the fine-grained re-crystallized tungsten has been evaluated. On reduced activation of ferritic/martensitic (RAFM) steels as the blanket structural material, a 20-ton heat of the F82H RAFM steel has been successfully produced in an electric arc furnace. Advanced neutron multiplier pebbles of beryllide (beryllium–titanium alloy) have been fabricated using a dedicated rotating electrode apparatus followed by annealing from the beryllide rod produced with the plasma sintering method. Also advanced tritium breeder pebbles of lithium-rich lithium titanate have been fabricated by an emulsion method, where the grain size, confirmed by SEM, was less than 5 μm. Tritium recovery tests of advanced tritium breeder pebbles will be investigated under 14 MeV neutron irradiation as one of the new activities.

In the Broader Approach (BA) activities, cooperated work on the DEMO design is undertaken with the IFERC project team and home teams in the EU and Japan. System code benchmarking to establish the c...

We have developed a compact fast neutron camera based on a stack of nuclear emulsion plates and a pinhole collimator. The camera was installed at J-port of Korea superconducting tokamak advanced research at National Fusion Research Institute, Republic of Korea. Fast neutron images agreed better with calculated ones based on Monte Carlo neutron simulation using the uniform distribution of Deuterium-Deuterium (DD) neutron source in a torus of 40 cm radius.

New 14 MeV neutron detector using capillary plate with liquid scintillator has been developed aiming at the triton burn-up study on the deuterium plasma experiment of the Large Helical Device (LHD). A capillary plate with 25 mm in diameter, 10 mm in thickness, and 10 μm pitch honeycomb structure is used as a detector head. The scintillating light trajectory is measured by an Electron-Multiplying CCD (EMCCD) via relay lenses. The trajectories for neutrons and gamma-rays are simulated by the Particle and Heavy Ion Transport code System (PHITS). Maximum trajectory length is estimated to be 2 mm and 0.1 mm for 14 MeV neutron and 2.45 MeV neutron, respectively. The trajectory of a proton recoiled by a neutron is linear, and the trajectory length depends on the recoiled proton energy. On the other hand, the trajectory of an electron produced by gamma-ray is not straight due to the random walk of the electron in the scintillator. Therefore, we can identify 14 MeV neutrons from 2.45 MeV neutrons and gamma-rays by the trajectory length and the shape. The developed detector was installed in the basement of the LHD torus hall just under the vertical collimator embedded in the floor concrete for the second deuterium plasma campaign of LHD in 2018. We identify trajectory which is considered due to the proton recoiled by14 MeV neutrons on the LHD deuterium discharge.

A scintillating-fiber (Sci-Fi) detector has been employed to measure 14 MeV neutrons for the triton burnup study in the first deuterium plasma campaign of the Large Helical Device (LHD). The pulse-height spectra of the Sci-Fi detector are used to choose a suitable threshold for the discrimination of 14 MeV neutrons from a mix-radiation field of low-energy neutrons and gamma-rays. The measured pulse-height spectra of the Sci-Fi detector have two components with different decay slopes from the LHD experiment. To study the pulse-height property of the Sci-Fi detector, the pulse-height spectra on different energy neutrons have been measured by using the accelerator-based neutron source with d-D, p-Li, and d-Li reactions. Meanwhile, the simulations of the detector response have been performed by using the Particle and Heavy Ion Transport code System (PHITS). In the LHD experiment, the first decay component of the pulse-height spectra in low-pulse-height region has been found to correspond to the signals induced by 2.45 MeV neutrons and gamma-rays. In addition, the high-pulse-height region has been confirmed by both the accelerator experiment and the PHITS calculation to correspond to the recoil-proton edge induced by triton burnup 14 MeV neutrons. The detection efficiency of 14 MeV neutrons for the Sci-Fi detector calculated by the PHITS code agrees well with the detection efficiency of 14 MeV neutrons for the Sci-Fi detector evaluated in the LHD experiment. The Sci-Fi detector can work as a standard detector for the 14 MeV neutron measurement with a suitable threshold.

A study of the resonant magnetic perturbation (RMP) effect on transit beam ion behavior is performed using the total neutron emission rate (Sn) measurement of the deuterium plasma in the Large Helical Device. We conducted no RMP field, one-half RMP field, and full RMP field discharges and compared Sn that reflects the global beam ion confinement information. It is determined that owing to the RMP field, Sn decreased by approximately 15 - 30%. Numerical calculations based on the classical confinement of beam ions were performed to investigate the bulk plasma parameter effect on Sn. The calculated Sn shows that the degradation of Sn by RMP is mainly caused by the degradation of the electron temperature owing to island formation which results in a shorter slowing down time of beam ions.

The global flux distributions for thermal, epithermal and fast neutrons in the torus hall of large fusion devices were experimentally evaluated for the first time in the Large Helical Device (LHD) using the activation foil method measured by the imaging plate and high-purity germanium detector. It turned out that the thermal neutrons were effectively absorbed by borated polyethylene blocks placed beneath the LHD. This should reduce the radioactivity of the floor and would be beneficial in maintaining a good environment for radiation workers. Uniform distributions of epithermal and fast neutrons were observed near the LHD. In particular, the significant decrease in fast neutron flux with increasing distance from the LHD, due to the fast energy loss of fast neutrons, was observed.The neutron flux distribution measurement, with rough energy discrimination based on the threshold energy of the neutron activation foil, allows us to estimate the spatial radiation dose rate, as well as the radioactivity in components in the torus hall. The prediction of the radioactivity in the concrete floor indicated that radioactive isotope Fe will be a dominant source of radioactivity in the concrete after the nine-year deuterium experiment campaign finishes.

In order to investigate the confinement physics of the energetic particles (EPs) in the Large Helical Device (LHD), the neutral particle analyzer (NPA) array is newly developed using single crystal CVD diamond detectors. The diamond detectors are adopted because of their high radiation hardness which is suitable to withstand the high-neutron flux expected in the deuterium experiments. For the initial experimental campaign, two detectors were installed at z=−7.77 m for perpendicular lines of sight to measure helically trapped EPs generated by perpendicular neutral beam injectors (NBIs). As the result of the diamond NPA (DNPA) commissioning in the last LHD experimental campaign, the DNPA successfully detected the EPs. The signal pulse counting rate due to the neutron-induced noise is several kcps in the highest neutron flux discharge in LHD, this noise counting rate is sufficiently low compared to the neutral signal counting rate.

A tangential Fast-Ion D Alpha (FIDA) diagnostic is applied to the Large Helical Device (LHD) in order to observe energetic distribution of toroidal circulating energetic particles which are produced by tangential Negative Neutral Beams (NNB). A perpendicular Positive NB (PNB) is used as the diagnostic probe beam of the tangential-FIDA diagnostic in this observation geometry. In order to assess the appropriateness of the tangential-FIDA diagnostic, the experimental result was compared with a Silicon-diode-based Fast Neutral Analyzer (Si-FNA) which was installed on the same line of sight. As a result of the comparison, the tangential-FIDA and the Si-FNA experimental data obtained good linearity in the energy region from 60 keV to 180 keV. In addition, an enhanced FIDASIM was applied for analyzing the FIDA on the three-dimensional magnetic configuration fusion device.

We developed an analysis model to predict and describe neutron emission anisotropy caused by anisotropy of energetic deuterons in the large helical device (LHD), by considering energetic-ion distribution functions, the differential cross-section of fusion reactions, and the exact shape of the vacuum vessel of the LHD. Neutron emission anisotropy that can be observed by the neutron activation system is evaluated numerically assuming deuterium-beam-injected deuterium plasmas confined by the LHD using the model. We demonstrate the dependence of neutron emission anisotropy on the beam-injection direction and the electron temperature. Based on this estimation, we propose an experimental scenario to validate the analysis model and easily understand energetic-ion anisotropy caused by the neutral beam injection.

The fast ion confinement time in the Large Helical Device (LHD) is investigated by using the neutron measurement and simulations. To estimate the fast ion confinement time, a series of short pulse neutral beam (NB) injection experiments have been performed. Additionally, the NB heating simulation code, CONV_FIT3D, has been extended to estimate the neutron emission rate in LHD. We estimate the fast ion confinement time from the differences between the measured and the simulated neutron decay times after the NB is turned off. It is found that the fast ion confinement time of three tangential NBs have similar values τc ∼ 0.5 sec and the confinement time of the perpendicular NB is approximately τc ∼ 0.06 sec. Additionally, by using the confinement time and the ion ratio data estimated from the simulation result, we can obtain a simulation result similar to the measured data.