To estimate the environmental transfer of tritium into the atmosphere and to establish tritium analysis techniques, this study improves our previous compartment model and proposes new analytical technique based on the microwave heating method and a water-sample purification technique using ion resin. This article introduces a new conceptual approach for estimating environmental tritium behavior.

The characteristics of the gas pressure measurement with the ASDEX type fast ionization gauge (AIG) in the mixture of Hydrogen and Helium is studied in this research. The calibration test stand capable of reproducing the mixture gas environment is assembled and used for the experimental calibration of the ionization gauge. In the experiment, the sensitivity of the AIG against pure hydrogen and pure helium is evaluated in order to eliminate the effect of individual differences among the AIG sensors. The mixture ratio of He in the test stand chamber is controlled from 3% to 15% to simulate the environment in divertor regions of fusion reactors. In the mixture gas, enhancement of the gauge sensitivity around 13% was observed. The enhancement of ionization due to the Penning Transferrer reactions, between the hydrogen atom and the metastable-helium atom is considered to be the main cause of the sensitivity change. Also it is found that the degree of enhancement of the AIG sensitivity can be changed drastically due to the condition of the AIG sensor. The monitoring or predicting the population of metastable-helium atoms will be important for the measurement of the mixture gas pressures.

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.

A calculation method is presented for the trajectory of a horizontally injected spherical laser fusion energy target in a reactor filled with residual gas. To evaluate the gas resistance and the placement error of the position measurement unit (PMU) set along the injection path, a test injection is successively made two times and the target positions in flight are measured by PMUs. Two unknown system parameters, gas resistance and placement error, are determined by solving an equation system. After determining the system parameters, the arrival position and arrival time of the newly injected fusion target at the reactor center can be calculated by simple arithmetic with the time data and position data of the injected target in flight.

This study shows the variation of the characteristics of a plasma bullet generated in impurity controlled working gas. Tunable diode laser absorption spectroscopy of metastable He atoms generated in the plasma bullet was performed. The metastable He atoms are generated in the plasma bullet and are quenched by impurities. The velocity and the size of the plasma bullet are derived from the arriving time and the shape of the rising phase of the absorbance. In addition, the impurity concentration was derived from the decay time of the absorbance. The impurity concentration in the working gas is controlled in a range of more than two orders of magnitude, and the impurity concentration reaches ppb level. We have observed the impurity dependence of the velocity and size of the plasma bullet. The velocity of the plasma bullet reaches a constant value and the bullet size dramatically increase below 20 ppm of the impurities. These results show the change of the propagation mechanism of the plasma bullet in the high purity working gas. In order to distinguish the plasma generated in the high purity gas from the standard plasmas, we would call it ultrapure plasma.

The advanced oxidation of 2, 4 - dinitrophenol (DNP), 2, 5 - DNP, and 3, 4 - DNP in aqueous solution has been investigated using a multi-gas, dielectric barrier discharge, and the degradation was measured by high performance liquid chromatography (HPLC). The acceleration of the advanced-oxidation has been investigated by the combination of the anion exchange polymer. The degradation pathway was suggested involving a rapid detachment of the nitro group followed by a slow opening of the aromatic-ring. The hydroxyl radical and the excited hydroxyl anion are responsible for the primary attack of the DNP with the production of dihydroxy-nitrobenzenes. The attack of hydroxyl radical occurs at the benzene ring carbon activated by the presence of a phenolic OH group and a nitro group. The reaction is dominated by a pseudo-first order kinetic reaction. The degradation process is interpreted using Molecular Orbital Theory.

Understanding edge impurity transport is one of the important issues for fusion devices to control edge radiation distribution for detachment operation and impurity influx to the confinement region. In LHD, the edge magnetic field structure becomes complex stochastic magnetic field. In order to study relation between impurity transport and the magnetic field geometry, 3D edge impurity emission distributions are obtained by a multichannel spectrometer system and tomography scheme. However, it is difficult to understand the three-dimensional (3-D) structure. Therefore, we propose a visualization system that employs a volume rendering method. With the proposed system, which can be used on a PC or mobile device, the user can observe a 3D structure in an arbitrary plane. To realize this function, we propose a volume visualization system comprising preprocessing and real-time rendering stages. Therefore, the visualization framerate can exceed 30 frames per second on PCs and approximately six frames per second on mobile devices, although the user frequently changes the position and direction of the camera.

The stability of an atmospheric pressure plasma source (APPS) for ion mobility spectrometer applications was investigated. Optimizations of the APPS for the operation conditions such as coil size and position for a plasma inductive excitation, and the ignition wire location were attempted. Ignition of Ar plasma is facilitated by the difference in electric potential inside the coil and the distance between the coil and the aluminum base attached to the ground terminal. Characterization of the ignition conditions, I-V measurements using a Gerdien condenser, and noise level in the ion current output signals were done for the developed APPS. The insertion of the ignition wire was found to affect the amplitude and value of the transported ion current through the Gerdien condenser.

Ion leakages from a Penning trap are studied in the BX-U linear trap [K. Akaike and H. Himura, Phys. Plasmas 25, 122108 (2018).]. The following leakage stops as the rise time of the upstream potential barrier sets to be longer. In the case, the number of trapped ions increases with the ion plasma still oscillating in the potential well of the Penning trap.

Using an Ar + CH₄ multi-hollow discharge plasma chemical vapor deposition (MHDPCVD) method, carbon nanoparticles (CNPs) are synthesized in a size range between 10 nm and 100 nm at gas pressures from 2 Torr to 5 Torr. The size of the nanoparticles increases from 45.42 nm³ at 2 Torr to 67.85 nm³ at 5 Torr. The size dispersion also increases. Conversely, the optical emission intensities and generation of carbon related radicals decrease with increasing pressure. The Raman measurements indicate that these CNPs are composed of polymer structures containing relatively high clustered and distorted sp2 sites.

When clusters of galaxies merge, shocks are formed that are characterized by a low (1-4) sonic Mach number and an Alfvénic Mach number that is typically an order of magnitude higher, giving the shocks a plasma β of approximately 100. The question we seek to answer is to what extent shocks can accelerate particles to relativistic speeds and thereby contribute to the cosmic ray spectrum. We use a combined particle-in-cell and magnetohydrodynamics code, which treats the thermal plasma as a fluid, but uses a kinetic approach to deal with non-thermal particles. This approach is computationally cheaper than the traditional PIC method while preserving the ability to deal with non-thermal particles. Our preliminary results confirm the ability of shocks in the low-Mach, high-β regime that characterizes galaxy cluster merger shocks to accelerate particles depends strongly on the input parameters, which was previously shown with PIC simulations.

We have investigated spatial structure of fluctuation of amount of nanoparticles in amplitude modulated VHF discharge reactive plasma in order to understand interaction fluctuations between plasma and nanoparticles. The interaction fluctuation appeared in the whole discharge region. Especially, the strong interaction fluctuation existed at the edge region. The behaviors of time evolution of intensity of spatial structure of interaction fluctuation at the center and edge regions were different with each other. Nanoparticles at the edge region were smaller than ones in the main discharge region. It suggested that the interaction fluctuation is related to the growth of nanoparticles.

Light-induced degradation is an important problem concerning hydrogenated amorphous silicon (a-Si:H) solar cells. A-Si:H films of lower Si-H₂ bond density exhibit less light-induced degradation. In this study, Raman spectroscopy measurements of a-Si:H films with P-layer/I-layer structure reveal that high-density Si-H₂ bonds exist in the I-layer within 60 nm of the P/I interface. These Si-H₂ bonds originate from surface reactions of SiH₃ radicals, as the alternative origin (i.e., cluster incorporation) is considerably suppressed by a multi-hollow discharge plasma chemical vapor deposition method. For an I-layer thickness of 20 nm, the density ratio of Si-H₂ and Si-H bonds in the I-layer decreases from 0.133 to 0.053 as the substrate temperature increases from 170^◦C to 250^◦C. Fine tuning of the substrate temperature during the initial stage of I-layer deposition is thus effective in suppressing Si-H₂ bond formation at the P/I interface.

We studied how the deposition of SiH₃ radicals, higher-order silane molecules, and clusters contributed to the bond configuration of hydrogenated amorphous silicon (a-Si:H) films. In our experiment, the deposition of three species was controlled using a multi-hollow discharge plasma chemical vapor deposition (MHDPCVD) method using a cluster-eliminating filter. We reduced the incorporation of higher-order silane (HOS) molecules into the films by increasing the gas flow velocity in the hollows from 1008 to 2646 cm/s. The results show that the lower incorporation of HOS molecules into the films reduced the SiH₂/SiH bond ratio, i.e., I_SiH2/I_SiH. Moreover,two-dimensional profiles of the I_SiH2/I_SiH ratio and the surface morphology suggest that the surface migration of HOS molecules is similar to that of the SiH₃ radicals, and the I_SiH2/I_SiH ratio is localized by the deposition of HOS molecules. Moreover, the results of optical emission spectroscopy show that HOS radical generation is irrelevant to the gas flow velocity.

Fusion plasmas are complex systems which involve a variety of physical processes interacting with each other across wide ranges of spatiotemporal scales. In the National Institute for Fusion Science (NIFS), we are utilizing the full capability of the supercomputer (Plasma Simulator) and propelling domestic and international collaborations in order to conduct the Numerical Simulation Reactor Research Project (NSRP). Understanding physical mechanisms of complex plasma phenomena for the systematization of fusion science, NSRP aims at realization of the Numerical Helical Test Reactor, which is an integrated system of simulation codes to predict behaviors of fusion plasmas over the whole machine range. In NSRP, eight task groups are organized to cover a wide range of fusion simulation subjects: plasma fluid equilibrium stability, energetic-particle physics, integrated transport simulation, neoclassical and turbulent transport simulation, peripheral plasma transport, plasma-wall interaction, multi-hierarchy physics, and simulation science basis. Verification and validation researches are in progress in these task groups collaborating with each other as well as with experimental and engineering groups. Successful examples of validations of large-scale simulations of energetic particle driven instabilities and neoclassical and turbulent transport against experimental results from tokamaks and helical systems are highlighted. In addition, recent achievements in advanced simulation studies on ion heating processes and plasma-wall interactions, as well as those in the application of Virtual-Reality (VR) technology to fusion engineering, are presented.