Search

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., source:Takeo Nishitani, Sachiko Yoshihashi, Kunihiro Ogawa, Misako Miwa, Shigeo Matsuyama & Akira Uritani (2022) Neutron yield calculation of thin and thick d-D targets by using PHITS with frag data table, Journal of Nuclear Science and Technology, 59:4, 534-541, DOI: 10.1080/00223131.2021.1981475, source:https://doi.org/10.1080/00223131.2021.1981475, identifier:0000-0003-2254-3164

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., source:https://doi.org/10.1585/pfr.16.1405018, identifier:0000-0002-7959-6155

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., source:https://doi.org/10.1585/pfr.14.1202159, identifier:0000-0003-4555-1837

The compact neutral particle analyzer (CNPA) combined with the impurity pellet measurement is one of the few instruments that can directly measure the radial high energy particle distribution in the Large Helical Device (LHD). For this purpose, it is suitable to set CNPA near LHD. On the other hand, sufficient and heavy shielding against DD-neutrons, generated in deuterium experiment, is required, especially when the deuterium neutral particle beam injection heating is applied. The shield is insufficient due to the weight limitation on the stage. However, if the neutron energy is thermalized on the detector, the neutron noise can be estimated only from the total neutron yield, which is monitored by the 235U fission chamber, etc. In the experiments, the pure neutron noise on the CNPA has been measured by closing the gate-valve to avoid the charge exchange neutral particle signals. The neutron noise on the CNPA has been proportional to the total neutron yield over three-order magnitudes. This means that the neutron noise can be estimated from the total neutron yield. Therefore, the calibrated charge exchange neutral signal can be obtained simply by subtracting the estimated neutron noise from the measured signal in ordinary experiments., source:https://doi.org/10.1585/pfr.14.3402142

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., source:https://doi.org/10.1585/pfr.14.3403123

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., source:https://doi.org/10.1585/pfr.14.3405162, identifier:0000-0002-3415-4775

Neutronics aspects of a compact D-D neutron generator as a neutron source for the neutron calibration in magnetic confinement fusion devices are assessed by the MCNP calculation. The neutron emission distribution of the compact D-D neutron generator has a large anisotropy not only due to the scattering with the neutron generator body but also due to the intrinsic anisotropy of the differential cross-section of the d(d,n)3He reaction. The angular neutron distribution at the target of the compact D-D neutron generator is calculated with the PHITS code where the slowing down on the accelerated deuterons in the target material is considered. The calibration experiments are simulated by using the MCNP-6 code for the ITER neutron flux monitor (NFM) to be installed in the equatorial port. The detection efficiency of NFM is calculated for a D-D plasma neutron source, an idealistic D-D neutron source, a 252Cf neutron source and the compact neutron generator. It is found that the detection efficiency of NFM for the compact neutron generator is approximately 50% larger than that for the idealistic D-D neutron source. The discrepancy is improved to be 25% by the intention of the target 20 cm from the body of the compact neutron generator., source:https://doi.org/10.1585/pfr.15.2402017, identifier:0000-0003-2254-3164

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., source:https://doi.org/10.1585/pfr.15.2405043, identifier:0000-0003-0920-2154

Measurements of radial DD neutron emission profiles by the vertical neutron camera (VNC) are performed in neutral beam-heated deuterium plasmas in the Large Helical Device. The time evolution of the neutron counting rate obtained by VNC is consistent with that of the total neutron emission rate measured by the fission chamber. The radial peak position of line-integrated neutron emission profile shifts outward according to preset magnetic axis positions (Rax_vac) from 3.60 m to 3.90 m. The line-integrated neutron emission profiles measured in the experiment at Rax_vac of 3.60 m, 3.75 m, and 3.90 m are compared with that estimated by a calculation using FIT3D-DD code with considering the line-integration effects. The radial position of the peak in calculation is almost the same as that of in the experiment. However, the profile measured in experiment is wider than that of the calculated profile., source:https://doi.org/10.1585/pfr.13.3402122, identifier:0000-0003-1799-5406

The Compact Neutral Particle Analyzer (CNPA) is an E//B type neutral particle energy analyzer using permanent magnets. CNPA is installed on the diagnostic platform and connected to the outside horizontal port. Based on the preliminary shielding design, 15 cm thick borated polyethylene shields were installed before the fast deuterium plasma campaign. However, neutron induced noises could not be ignored in plasmas with the neutron emission rate higher than ∼1 × 1014 n/s. We carried out the detailed neutronics analyses for the original neutron shield by using the MCNP6 code, which takes into account the detailed structure. The neutron streaming from the beam inlet and the penetration of the bulk shield are approximately 60% and 40% contribution to the neutron flux at the detector array, respectively. Consequently, 5 cm borated polyethylene plates are added to the bulk shield and an extension shield of borated polyethylene cylinder shield with 20 cm in diameter and 35 cm in length is added around the beam inlet, where the neutron flux is expected to be 1.9 × 106 n/cm2⋅s at the detector array for the plasma with the neutron emission rate of 1.9 × 1016 n/s., source:https://doi.org/10.1585/pfr.14.3405048

To obtain rapid change of the neutron emission rate caused by magnetohydrodynamic (MHD) instabilities, measurements of the neutron flux with the high temporal resolution are made on the Large Helical Device (LHD) with a fast-neutron scintillation detector called neutron fluctuation (NF) operated in current modes. The time response of this detector is up to 5 microseconds. We checked the unwanted signal level caused by neutrons/gamma-rays inside the PMT. The intensity of the unwanted signal was negligibly small compared with the intensity of the scintillation signal as expected. The signal of NF has linear dependence with total neutron emission rate measured by neutron flux monitor in MHD quiet discharges. Rapid decreases of the neutron flux associated with bursting MHD modes excited in a neutral-beam-heated LHD plasma are observed with NF. We found that the neutron flux rapidly decreases within 2 ms., source:https://doi.org/10.1585/pfr.13.3402068, identifier:0000-0003-4555-1837

The deuterium plasma experiments have been conducted since March 2017 on the Large Helical Device. The neutron yield per shot has reached up to 7 × 1014 and 3.5 × 1015 in the first phase where NBI #1, 2, and 3 used hydrogen and NBI #4 and 5 used deuterium, and in full D-D phase, respectively. For the triton burnup study in this campaign, the neutron activation system (NAS) has been used to measure 14 MeV neutrons and 2.45 MeV neutrons. The triton burnup ratio of 0 ∼ 0.34% are obtained by the NAS measurement. Triton burnup ratio increases with electron density when line-averaged electron density is below about 2.5 × 1019 m−3, and decreases with electron density above 2.5 × 1019 m−3. Meanwhile, the triton burnup ratio decreases as the magnetic axis positions shift outward, which can likely be explained by the orbit of helically trapped energetic tritons. In addition to the NAS measurement, the phenomenon of the 14 MeV neutron emission lagging at the 2.45 MeV neutrons emission has been observed by the time evolution measurement with scintillating-fiber detectors and neutron flux monitor., source:https://doi.org/10.1585/pfr.13.3402121, identifier:0000-0001-9473-3747

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., source:https://doi.org/10.1585/pfr.14.3402129

Total neutron emission rate from Large Helical Device plasmas is measured by using a neutron flux monitor newly installed for deuterium operations. Deuteron temperature is derived from the total neutron emission rates in electron cyclotron heated Large Helical Device plasmas. Time evolution of central deuteron temperature obtained by the neutron flux monitor approximately agrees with central impurity ion temperature measured by the EUV spectrometer., source:https://doi.org/10.1585/pfr.12.1202036, identifier:0000-0003-4555-1837

The precise estimation of the radiation field is required to evaluate the soundness of the diagnostic and control components for the LHD deuterium experiment. Monte Carlo neutron calculations are carried out with three-dimensional modeling of LHD using MCNP-6 code with the cross-section library of ENDF B-VI. Three-dimensional map of the total neutron flux, neutron and gamma-ray spectra, and the dose rate profile are obtained. Neutron and gamma fluxes by MCNP-6 code are about 2/3 of those by DORT code, which is probably due to the two-dimensional modeling of the DORT calculation. The gamma-ray absorbed dose for Si is 20 - 70 Gy during nine years operation, where high integrated electric devices such as the programmable logic controller (PLC) may survive if we consider the gamma-ray effect only., source:https://doi.org/10.1585/pfr.11.2405057, identifier:0000-0003-2254-3164

Fast-neutron directional detectors using scintillating optical fibers have been adopted for neutron emission profile measurement in magnetic confinement fusion devices. Because of their benefits of rapid response and directional properties to reduce restrictions on shielding, they are anticipated for installation in the Large Helical Device (LHD) of the National Institute for Fusion Science (NIFS). As described herein, the system design has been re-examined based on the results of recent experiments and simulations. Results show that fast neutrons with high energy of 14 MeV are attenuated by a self-shielding effect of scintillating fiber. Moreover, it has been demonstrated that the scintillation photons are attenuated in several centimeters before reaching the photon detector. The control of the photon transmission efficiency is important to enhance the directional property of the system. Along with reduced effects of the background gamma rays, adopting a thin scintillating fiber is effective. Further evaluation should be conducted to design a detector system considering the detecting efficiency, directional property, and gamma ray effect for application to an actual radiation field of the LHD., source:https://doi.org/10.1585/pfr.11.2405020, identifier:0000-0002-4058-2661

An energy transfer phenomenon between energetic ions, which cannot be explained only considering the Coulomb scattering process, was observed on a large helical device (LHD). This phenomenon often occurs in fusion reactivity enhancement and fast-ion slowing-down process that can be observed as a delay in the decay time of the D(d,n)3He neutron generation rate. The transferred energy required to induce such a reactivity enhancement or delay in the fast-ion slowing-down time (neutron decay time) was examined based on the Boltzmann−Fokker−Planck analysis in which a discrete energy transfer process, called nuclear elastic scattering (NES), is included. It was shown that even though the cross section of the NES is smaller than that of the Coulomb scattering, enough knock-on population appears in the energetic region in ion distribution function to induce the observable NES effects; thus, enough energy is transferred from beam ions to fast component of bulk ion distribution function indirectly and the transferred energy per unit time via NES is comparable to the Coulomb scattering rate. This study analytically demonstrates that the observed phenomena on LHD can be explained smoothly by considering the alternative indirect energy transfer channel between energetic ions, which can be comparable with the one via Coulomb scattering., source:https://doi.org/10.1063/5.0097720, identifier:0000-0002-7498-4191

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., source:https://doi.org/10.1109/TPS.2018.2879604, identifier:0000-0003-1586-1084

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., source:https://doi.org/10.1063/1.5032118, identifier:0000-0003-4555-1837

In a deuterium operation on the Large Helical Device, the measurement and control equipment placed in the torus hall must survive under an environment of radiation. To study the effects of gamma-ray irradiation on the equipment, an irradiation experiment is performed at the Cobalt-60 irradiation facility of Nagoya University. Transient and permanent effects on a personal computer, media converters, programmable logic controllers, isolation amplifiers, a web camera, optical flow meters, and water sealing gaskets are experimentally surveyed. Transient noise appears on the web camera. Offset of the signal increases with an increase of the integrated dose on the programmable logic controller. The DeviceNet module on the programmable logic controller is broken at the integrated dose of 72 Gy, which is the expected range of the integrated dose of the torus hall. The other equipment can survive under the gamma-ray field in the torus hall., source:Ogawa K, Nishitani T, Isobe M, Sato M, Yokota M, Hayashi H, Kobuchi T and Nishimura T 2017 Effects of gamma-ray irradiation on electronic and non-electronic equipment of Large Helical Device Plasma Sci. Technology 19 025601., source:https://doi.org/10.1088/2058-6272/19/2/025601, identifier:0000-0003-4555-1837

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., source:https://doi.org/10.1016/j.fusengdes.2018.09.013, identifier:0000-0003-0920-2154

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 (<10% of the plasma minor radius) and the targeted counting rate (105 cps order) are discussed., source:Review of Scientific Instruments 91, 113504 (2020); https://doi.org/10.1063/5.0025902, source:https://doi.org/10.1063/5.0025902, identifier:0000-0002-7371-9652

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., source:Review of Scientific Instruments 89, 10I105 (2018); https://doi.org/10.1063/1.5035290, source:https://doi.org/10.1063/1.5035290, identifier:0000-0001-9473-3747

The neutral beam (NB) fast ion confinement in the Large Helical Device (LHD) is studied for several full field (????????∼2.75 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 ????eff∼0.1 m2 s−1 and ????eff∼1 m2 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., source:Journal of Plasma Physics , Volume 86 , Issue 3 , June 2020 , 815860306 DOI: https://doi.org/10.1017/S0022377820000525[Opens in a new window] NASA ADS Abstract Service., source:https://doi.org/10.1017/S0022377820000525, identifier:0000-0003-3293-488X