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Takao FUKUYAMA, Naoki NISHIDA
原稿種別: Rapid Communications
2022 年 17 巻 p.
1201002
発行日: 2022/01/07
公開日: 2022/01/11
ジャーナル
フリー
A chaos control system based on the time delayed-feedback method was constructed using the LabVIEW system in a laboratory plasma. When the appropriate delay-time and proportionality constant are set as control parameters, the chaotic oscillations are stabilized to be periodic. However, if they are not, the system makes the transition to a more chaotic state. The constructed chaos control system can be widely applied to laboratory plasma by feeding the system back to the dominant location in an electric circuit.
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Ryosuke NISHIO, Shin KAJITA, Hirohiko TANAKA, Koji ASAOKA, Takayoshi T ...
原稿種別: Rapid Communications
2022 年 17 巻 p.
1201004
発行日: 2022/01/21
公開日: 2022/01/26
ジャーナル
フリー
For the development of a high nitrogen atom density source, we produced nitrogen plasmas and measured the nitrogen atom density using vacuum ultraviolet absorption spectroscopy (VUVAS) at high neutral gas pressure (>1.5 mTorr) and discharge power (>500 W) in the NAGDIS-T, which could generate spiral-shaped dissociative recombining plasmas. It was seen that the nitrogen atom density increases with increasing neutral gas pressure and discharge power, and it reached 6.2 × 1017 m−3. In the low gas pressure case, the estimated atom density was confirmed to be consistent with that measured by the actinometry method.
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Masaomi AIZAWACARANZA, Makoto SASAKI, Hiroki MINAGAWA, Yuuki NAKAZAWA, ...
原稿種別: Rapid Communications
2022 年 17 巻 p.
1201048
発行日: 2022/05/13
公開日: 2022/06/14
ジャーナル
フリー
Prediction of time evolution of multi-scale turbulence is performed by using Long-short term memory networks. The time series data is obtained by Langmuir probes in a linear magnetized plasma device, PANTA. The simultaneous prediction of high and low frequency components of turbulence is shown to be possible within several tens percent accuracy. The prediction accuracy depends on the initial network, which can be controlled by reducing the learning rate.
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Naohiro KASUYA, Makoto SASAKI
原稿種別: Rapid Communications
2022 年 17 巻 p.
1201053
発行日: 2022/05/13
公開日: 2022/06/14
ジャーナル
フリー
Ion mass dependence of the resistive drift wave instability is investigated to understand wave number spectra in magnetized cylindrical plasmas. Modes with larger axial mode numbers are linearly unstable in the case of smaller mass ions as helium. Analytical expression is obtained, which shows that not only the azimuthal mode number but also the axial mode number has the preferable one depending on the mass number. Therefore, 3-D observation of the spatial structure is important to capture the variation including this parameter.
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Keigo YOSHIMURA, Hiroyuki TAKAHASHI, Tomohiro SEINO, Kaoru KUSABIRAKI, ...
原稿種別: Rapid Communications
2022 年 17 巻 p.
1201082
発行日: 2022/06/22
公開日: 2022/07/01
ジャーナル
フリー
The rollover of electron density, a common indicator for the onset of volumetric recombination, was observed in hydrogen plasma, for the first time in the DT-ALPHA. Electron density and electron temperature were measured near the plasma production region and secondary gas feeding position with various conditions regarding the amount of hydrogen secondary gas. A rollover of electron density was observed at the secondary gas feeding position, whereas electron density near the plasma production region remained nearly constant. This behavior indicates an enhancement of hydrogen molecular-activated recombination.
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Masayuki YOSHIKAWA, Yousuke NAKASHIMA, Junko KOHAGURA, Yoriko SHIMA, H ...
原稿種別: Rapid Communications
2022 年 17 巻 p.
1202093
発行日: 2022/08/15
公開日: 2022/08/19
ジャーナル
フリー
The study of pellet ablation mechanisms is an important subject for plasma fueling in fusion plasmas. In GAMMA 10/PDX, sub-millimeter hydrogen pellet injection experiments are conducted in the higher electron density plasma for detached plasma experiments. We observed the pellet ablation cloud by two-directional simultaneous photography during the GAMMA 10/PDX pellet injection experiments. The three-dimensional pellet ablation cloud and its trajectory were clearly obtained for the first time.
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Motoki NAKATA, Seikichi MATSUOKA
原稿種別: Rapid Communications
2022 年 17 巻 p.
1203077
発行日: 2022/06/22
公開日: 2022/07/01
ジャーナル
フリー
The impact of magnetic geometry on zonal-flow generation in ion temperature gradient driven turbulence is investigated by means of linear and nonlinear gyrokinetic simulations. The modulation of geodesic curvature on various configurations has revealed amplification of the zonal-flow intensity in relatively smaller geodesic curvature. Based on these findings, a nonlinear proxy model for explorations of novel magnetic geometry to activate the zonal-flow dynamics is proposed.
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Motoki NAKATA
原稿種別: Rapid Communications
2022 年 17 巻 p.
1203078
発行日: 2022/06/22
公開日: 2022/07/01
ジャーナル
フリー
Ion- and electron-scale microinstabilities and the linear zonal-flow response in mixture plasmas with the medium-Z impurity and He-ash are investigated by means of a multi-species gyrokinetic model. In addition to the charge and dilution effects, stabilization/destabilization by nonthermal He-ash ions is clarified.
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Takayuki KOBAYASHI, Hibiki YAMAZAKI, Shinichi HIRANAI, Masayuki SAWAHA ...
原稿種別: Rapid Communications
2022 年 17 巻 p.
1205015
発行日: 2022/03/30
公開日: 2022/04/23
ジャーナル
フリー
We developed a prototype low reflection dummy load for calorimetric power measurements in high-power millimeter wave systems. The dummy load is featured by low reflection of millimeter waves by an internal cylinder designed for increasing the length of the ray trajectory in the dummy load. This structure prevents the millimeter wave reflection from the dummy load by absorbing the waves by the inner surface of the cylinder. Initial tests at high powers of up to 0.5 MW for 0.25 s were successfully able to measure output power with lower reflection back to the source than that of conventional short pulse dummy loads used in the past.
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Hiroki KAWASE, Hiyori UEHARA, Ryo YASUHARA
原稿種別: Rapid Communications
2022 年 17 巻 p.
1205057
発行日: 2022/06/06
公開日: 2022/06/28
ジャーナル
フリー
Liquid phase H2O and D2O were measured with mid-IR lasers with wavelengths of 2.9 µm and 3.9 µm. The laser power change over time was observed when the water isotope specie was continuously replaced. Additionally, the concentration ratio of H2O and D2O as a function of time was obtained. These results indicate that quantitative measurement of water isotopes using mid-IR lasers in real-time has been successful.
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Yoshiyuki WATANABE, Kazunori MORISHITA, Takashi NOZAWA, Hiroyasu TANIG ...
原稿種別: Rapid Communications
2022 年 17 巻 p.
1205105
発行日: 2022/11/24
公開日: 2022/12/07
ジャーナル
フリー
Size and temperature dependence of the point defect binding free energy has numerically evaluated for self-interstitial atom (SIA) clusters and vacancy clusters in bcc Fe by using continuum models based on thermodynamics and linear elasticity. The estimated binding free energy of SIAs to SIA-clusters is much higher than that of vacancies to vacancy clusters, indicating that SIA-clusters are more thermally stable than vacancy clusters. For relatively small clusters, the estimated binding free energy at 0 K is comparably consistent with atomistic calculation data; and then, the SIA binding free energy at 850 K is averagely about 35% lower than that at 0 K, while the vacancy binding free energy is about 6% lower; which may remarkably affect the formation kinetics of those defect clusters under irradiation. These kinds of information will be one of the basic parameters for a theoretical model of the microstructural evolution of Fe-based materials in the nuclear fusion DEMO environment.
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Takuma MINE, Ryohei MASAI, Mizuki KAWAGUCHI, Yusuke KIKUCHI
原稿種別: Rapid Communications
2022 年 17 巻 p.
1206031
発行日: 2022/03/30
公開日: 2022/04/23
ジャーナル
フリー
A diamond-like carbon film with a film hardness of 12 GPa was prepared at a low substrate temperature of 60◦C using a repetitive nanosecond pulsed glow hydrogen/methane discharge plasma operated in burst mode under a gas pressure of 1.2 kPa. As the peak electrical power of the pulsed discharge increased, the hydrogen content in the films estimated by Raman spectroscopy decreased and the film hardness increased. The ion irradiation to the substrate is considered to be the main factor determining the film properties, since the hydrogen abstraction reaction and the etching of graphite components by hydrogen radical irradiation are weakened in the low-temperature deposition.
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Xingyu GUO, Ryo ASHIDA, Yuto NOGUCHI, Hitoshi TANAKA, Masaki UCHIDA, T ...
原稿種別: Regular Articles
2022 年 17 巻 p.
1401024
発行日: 2022/04/08
公開日: 2022/04/29
ジャーナル
フリー
In order to detect the wave pattern of electron Bernstein waves (EBWs), an excitation and detection system has been developed in Low Aspect ratio Torus Experiment (LATE). The system consists of a waveguide launcher with arbitrary polarization, a specially designed five-pin probe antenna, a two-dimensional (2-D) mechanical probe driving system, and a homodyne-type mixer circuit. The excitation and detection system has been tested in the air and shows reliable results.
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Tetsuya AKITSU, Masaaki INUTAKE
原稿種別: Regular Articles
2022 年 17 巻 p.
1401081
発行日: 2022/07/22
公開日: 2022/07/30
ジャーナル
フリー
A surface-localized mode governing resistive drift-Alfvén mode is experimentally observed in a collisional, current-carrying finite-β plasma, accompanied by an electron diamagnetic-drift frequency spectrum. The half-wavelength travelling along the plasma column with the Alfvén velocity determines the Alfvén mode. The spatial distribution and the phase relation of magnetic components are presented.
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Hiroki MINAGAWA, Shinji YOSHIMURA, Kenichiro TERASAKA, Mitsutoshi ARAM ...
原稿種別: Regular Articles
2022 年 17 巻 p.
1401099
発行日: 2022/09/14
公開日: 2022/09/30
ジャーナル
フリー
The particle flux onto a material is an important parameter in the study of the plasma-material interaction. With conventional Doppler spectroscopy, it is difficult to measure the flow velocity perpendicular to the material because only the velocity component projected on the wave number vector can be measured. To overcome the limitation, we are developing a transverse flow measurement method using the azimuthal Doppler shift of a Laguerre-Gaussian (LG) beam absorption spectroscopy. In this paper, the feasibility of this spectroscopy method has been examined by numerical analysis. The LG beam is anisotropically absorbed in the transverse flow due to the azimuthal Doppler shift. Since the anisotropic LG beam rotates with propagation, the spatial structure of resonance absorption in plasma and the intensity structure of the LG beam that has propagated through the plasma are inevitably different in the LG beam absorption spectroscopy. It was shown that the deviation from the original azimuthal Doppler shift is reduced to several percent at the position where the intensity distribution of the LG beam reaches its maximum value. Therefore, the transverse flow can be measured with sufficient accuracy by properly selecting the position on the beam cross-section used to evaluate the azimuthal Doppler shift.
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Akira EJIRI, Hibiki YAMAZAKI, Yuichi TAKASE, Naoto TSUJII, Osamu WATAN ...
原稿種別: Regular Articles
2022 年 17 巻 p.
1402037
発行日: 2022/05/13
公開日: 2022/06/14
ジャーナル
フリー
In the TST-2 spherical tokamak (ST), non-inductive start-up by lower-hybrid waves (200 MHz) has been studied and a plasma current of 27 kA was achieved. For a comprehensive understanding of the wave sustained plasmas, a fast electron transport model combined with an X-ray emission model is constructed. The electrons in the model show a velocity random walk induced by the wave and collisional slowing down. Simultaneously, they show diffusion in real space. Electron generation and loss at the limiters are also considered. Using the model we can calculate the powers, such as the power from the wave to electrons (i.e., deposition power), collisional bulk electron heating power, power to the limiters. In addition, plasma current, electron density, neutral density, X-ray spectrum expected by a certain measurement system are obtained. Comparison with experimental data shows that a major part of the LHW deposition power is lost by fast electrons hitting the outboard limiter, while a minor part is used to heat cold bulk electrons. The diffusion in real space is well described by the RF induced radial transport, which is often used to interpret fast ion diffusion in ICRF heating. The present work suggests that the RF induced transport of fast electrons is the dominant loss mechanism.
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Masayuki YOSHIKAWA, Hirohiko TANAKA, Yuki HAYASHI, Shin KAJITA, Hennie ...
原稿種別: Regular Articles
2022 年 17 巻 p.
1402100
発行日: 2022/10/07
公開日: 2022/10/13
ジャーナル
フリー
With the help of the linear divertor simulation device Magnum-PSI, a fluctuation investigation of the impact of the target plate geometry was conducted. We simultaneously quantify coherent low-frequency fluctuations with a newly built 70-GHz microwave reflectometry system, a reciprocating probe, a light emission detector system, and a fast-framing camera system. The strong low-frequency fluctuations were observed at both the electron density and the plasma radiations by moving the target plate along the magnetic field line. Furthermore, a strong peak in fluctuation intensity and the influence of the target plate tilt angle on the fluctuation intensity were noted.
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Toshiki KINOSHITA, Kenji TANAKA, Yuki TAKEMURA, Shota TAKESHIDA, Hikon ...
原稿種別: Regular Articles
2022 年 17 巻 p.
1402107
発行日: 2022/12/09
公開日: 2022/12/28
ジャーナル
フリー
CO2 laser interferometers are a promising option for high-density plasma measurements. However, in low- and middle-density measurements, noise due to mechanical vibrations is a serious problem. To remove this noise, we developed a two-color laser imaging interferometer using a CO2 laser and quantum cascade (QC) laser, called the CO2/QC laser imaging interferometer, through benchtop experiments and installed it in the Large Helical Device (LHD). Benchtop experiments provided optical design guidelines for the CO2/QC laser imaging interferometer to minimize the influence of the unstable output wavelength of the QC laser. The optical system in LHD was designed according to this guideline, and the vibration noise was successfully reduced to 2.80 × 1018 m-3. We also demonstrate measurement examples of hollowed and peaked electron density profiles evaluated using Abel inversion and macro-scale instability. This is the first study to present the measurement results of high-temperature plasma using a CO2/QC two-color laser interferometer. The study outcomes provide important insights for the development of two-color laser interferometers in future fusion devices.
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Yoshihiro ITAKURA, Takaaki FUJITA, Atsushi OKAMOTO
原稿種別: Regular Articles
2022 年 17 巻 p.
1403016
発行日: 2022/05/13
公開日: 2022/06/14
ジャーナル
フリー
Edge transport barrier (ETB) models are developed and introduced into an integrated transport code TOTAL. The transitions between L-mode and H-mode are triggered by comparing the net heating power with the threshold powers. At the L to H transition, quick reduction in transport in the pedestal region causes back transition due to reduced net heating power and then gradual change in the transport in the pedestal region is needed. The pedestal pressure is adjusted to the value predicted by an empirical scaling. Three models, the PID control model, the ELM model, and the empirical continuous ELM model, are compared for the pedestal pressure control. The control is possible in all of three models but it is observed that larger pellet injection is needed to increase the density and a lower pedestal density is obtained in the ELM model. During tungsten injection, the pedestal pressure is well controlled in the empirical continuous ELM model and in the PID control model.
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Ryutaro KANNO, Gakushi KAWAMURA, Masanori NUNAMI, Seikichi MATSUOKA, S ...
原稿種別: Regular Articles
2022 年 17 巻 p.
1403029
発行日: 2022/04/22
公開日: 2022/05/17
ジャーナル
フリー
We develop a new simulation code for solving the Poisson equation, based on Monte Carlo methods. When static resonant magnetic perturbations (RMPs) are used in tokamak plasma to mitigate or suppress edge-localized modes, the RMPs generate an electric field in the ergodized edge region. The electrostatic potential should be calculated only in the edge region to reduce the computational cost of solving the Poisson equation in the complicated three-dimensional magnetic structure, which is assumed to be fixed in time. In this study, we propose a basic idea for evaluating an electrostatic potential given by the Poisson equation in only a part of the domain in curvilinear coordinates. This Poisson solver allows for the boundary condition to be set not only inside the selected region in which the potential is evaluated, but also outside the selected region. Several benchmarks for the developed code are also presented.
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Shimpei ARAI, Yusuke KOSUGA
原稿種別: Regular Articles
2022 年 17 巻 p.
1403050
発行日: 2022/05/13
公開日: 2022/06/14
ジャーナル
フリー
In this study, in order to evaluate the SOL width of both density and temperature, we analyze Hasegawa-Wakatani model which includes the temperature fluctuations. Different instability regimes, i.e. drift waves and linearly unstable convective cells are studied. It is shown that convective cells are favorable in terms of the heat load reduction on the divertor. Implications on future devices, such as JT-60 SA, ITER, etc, are discussed.
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Keiji FUJITA, Shinsuke SATAKE
原稿種別: Regular Articles
2022 年 17 巻 p.
1403065
発行日: 2022/06/06
公開日: 2022/06/28
ジャーナル
フリー
Neoclassical transport is caused by the non-equilibrium distribution function produced by the driving forces due to quasi-steady but non-uniform plasma state parameters and electromagnetic fields as well as by the Coulomb interactions. In this article, we present a method to evaluate the impact of each driving force on neoclassical transport by a single global drift-kinetic simulation. This method can be used to evaluate the impacts of each driving force not only in one-dimensional forms as transport coefficients, but also in multidimensional forms as how the impacts of each driving force are distributed over the phase space. As an application of the method, we investigate the impacts of each driving force on particle density variations in an impurity hole plasma and demonstrate that the impact of the outward driving force of the temperature gradient on the radial impurity flux becomes as large as the impact of the inward driving force of the negative ambipolar radial electric field. Further, we show that the variation of electrostatic potential on each flux surface, Φ1, which is involved in several factors in a drift-kinetic equation, affects the density variations specifically through the radial E × B drift.
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Motoki NAKATA, Mitsuru HONDA
原稿種別: Regular Articles
2022 年 17 巻 p.
1403083
発行日: 2022/07/22
公開日: 2022/07/30
ジャーナル
フリー
Ion temperature gradient (ITG) and trapped electron modes (TEM) driven turbulent transport in an ITER-like plasma is investigated by means of multi-species gyrokinetic Vlasov simulations with D, T, He, and real-mass kinetic electrons including their inter-species collisions. Beyond the conventional zero-dimensional power balance analysis presuming the global energy and particle confinement times, gyrokinetic-simulation-based evaluation of a steady burning condition with He-ash exhaust and D-T fuel inward pinch is demonstrated. It is clarified that a significant imbalance appears in the turbulent particle flux for the fuel ions of D and T, depending on the D-T density ratio and the He-ash accumulation. Then several profile regimes to satisfy Reiters steady burning condition are, for the first time, identified by the gyrokinetic simulation. Also, the impacts of zonal flows and nonthermal He-ash on the optimal profile regimes are examined.
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Yushiro YAMASHITA, Yuji NAKAMURA, Akihiro ISHIZAWA, Kiyomasa WATANABE
原稿種別: Regular Articles
2022 年 17 巻 p.
1403104
発行日: 2022/11/24
公開日: 2022/12/07
ジャーナル
フリー
An electric current is induced on the vacuum vessel when the toroidal current of a tokamak plasma varies in time, and it is called the eddy current. During disruption, the eddy current becomes large and influences the process of disruption by interacting with the confined plasma. We have developed a new non-axisymmetric eddy current simulation code, the Keddy3D that solves the eddy current equation based on the thin-wall approximation. The Keddy3D is suitable for simulating long-term non-axisymmetric disruption processes with low computational costs.
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Ryusuke TSUJI
原稿種別: Regular Articles
2022 年 17 巻 p.
1404088
発行日: 2022/07/22
公開日: 2022/07/30
ジャーナル
フリー
A method is presented for controlling the trajectory of a vertically injected charged spherical laser fusion target. The position and time of the injected target in flight are measured in a position measurement unit using the Arago spot. After the target passes between the first pair of deflection plates, where there exists a constant electric field, the mass-to-charge ratio of the target in flight is obtained from the shift in its trajectory. The amplitude of the electric field applied between the second and third pairs of deflection plates is calculated using this ratio. After passing through the second and third pairs of deflection plates, the target deflects its trajectory to pass through the reactor center. The design parameters of the trajectory control system for a tabletop plasma device and a laser fusion reactor are presented.
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Shingo TAMAKI, Fajar PANUNTUN, Kazumichi UEDOI, Wang HAIDONG, Sachie K ...
原稿種別: Regular Articles
2022 年 17 巻 p.
1405001
発行日: 2022/01/21
公開日: 2022/01/26
ジャーナル
フリー
A deuterium-tritium (DT) neutron generator in Osaka University with a continuous intense neutron source emitting 3 × 1012 fusion neutrons per second has been in operation since 1981. However, radioactivation for the parts of the accelerator body is a serious issue. Hence, in this study, we investigated the radioactivation of the intense irradiation room containing the continuous intense neutron source. Core samples of the concrete wall were collected at various positions in the irradiation room and the radionuclides in them were determined by performing gamma-ray spectrometry. Major long-lived radionuclides found were 54Mn, 60Co, and 152Eu. The radioactivity of 152Eu may possibly be consistent with the result obtained using the simulation code. The radioactivities of 54Mn and 60Co were minimal compared with that of 152Eu. The tritium amount in the core sample was measured employing a tritium sampling system and a liquid scintillation detector and was found to be considerably larger than the amount estimated using the simulation code. Tritium diffused from the titanium-tritium target was attached to the wall surface. However, most of it did not penetrate the concrete wall. These results reveal the radioactivity issue of fusion neutron generator facilities and are expected to aid in the maintenance of their operation.
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Keisuke YAMAUCHI, Naoki SANO, Katsuaki TANABE
原稿種別: Regular Articles
2022 年 17 巻 p.
1405049
発行日: 2022/04/22
公開日: 2022/05/17
ジャーナル
フリー
We carried out a fundamental investigation of a uniaxial direct W-to-Cu bonding at relatively low temperatures in ambient air, which would potentially allow for simple preparation and maintenance of divertor wall components. W/Cu bonds formed at 500◦C with a bonding pressure of 0.1 MPa, but the mechanical interfacial strength was about 1 MPa, significantly lower than the state-of-the-art values for bonding around at 1000◦C in vacuum. Higher degree of interfacial oxidation and atomic interdiffusion were observed for higher bonding temperature, through x-ray photoelectron spectroscopy. The electrical conductivity across the bonded W/Cu interface, an indicator of thermal conductance, was measured to be lower for higher bonding temperature, presumably due to the interfacial oxidation.
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Haruya MASAKI, Masatoshi KONDO, Jae-Hwan KIM, Masaru NAKAMICHI
原稿種別: Regular Articles
2022 年 17 巻 p.
1405075
発行日: 2022/07/08
公開日: 2022/07/14
ジャーナル
フリー
Lithium titanate (Li2TiO3) pebble is a candidate tritium breeder of solid breeder blanket systems of fusion reactors. The oscillation of coolant tubes can be induced by the coolant flow. Fretting corrosion is caused between the Li2TiO3 pebbles and the coolant tubes which are made of reduced activation ferritic martensitic steel F82H. The purpose of the present study is to clarify the fretting behaviors at the temperatures of blanket conditions. The Li2TiO3 pebble produced by sol-gel method was pushed onto the surface of the oscillating F82H plate in the fretting tests which were performed for 10 min in an air atmosphere up to 573 K. The fretting scars of the Li2TiO3 pebble and the F82H plate were observed and analyzed by SEM/EDX and 3D laser scanning microscope. The fretting wear was mitigated at the temperatures of 373 K and 473 K due to the formation of the oxide layer, which might reduce the friction. The pebble was partially destructed by the fretting motion in the test performed at 573 K. The fretting wear of the pebble and the F82H plate was mitigated when the pebble was not fixed on the holder since the pebble could vibrate together with the oscillating plate.
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Yu-Ting LIN, Akira EJIRI, Kouji SHINOHARA, Yi PENG, Seowon JANG
原稿種別: Regular Articles
2022 年 17 巻 p.
1405098
発行日: 2022/09/14
公開日: 2022/09/30
ジャーナル
フリー
In order to control or suppress edge localized modes in nuclear fusion reactors, an accurate pedestal pressure profile measurement is necessary. A line integrated backward Thomson scattering measurement is an attractive method because of its long scattering length. Assuming that the first mirror is located far from the plasma to avoid degradation of the mirror due to erosion and impurity deposition, the measurement accuracies of density and temperature and pressure are estimated. For the target plasma, we adopt the pedestal profile with the shoulder density of 1019 - 1020 m-3 and the dimensions of the JA DEMO reactor. The calculation results show that, the Poisson noise due to finite detected scattered photon number is much larger than that due to bremsstrahlung emission. In addition, noise is enhanced by reconstruction process. The resultant total noise levels of reconstructed density, temperature and pressure profiles are at most 1.5%, 3%, 3%, respectively in the steep gradient region, and this method is feasible in the reactor.
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Shintaro ISHIYAMA, Akio SAGARA, Hirotaka CHIKARAISHI, Nagato YANAGI
原稿種別: Regular Articles
2022 年 17 巻 p.
1405103
発行日: 2022/12/02
公開日: 2022/12/28
ジャーナル
フリー
In the FFHR power reactor equipped with a supercritical CO2 gas turbine power generation system, an divertor cooling system is connected to this power generation system [S. Ishiyama et al., Prog. Nucl. Energy 50, No.12-6, 325 (2008)[1]]. In this paper, for the purpose of developing a diverter by supercritical CO2 gas cooling that can cope with a neutron heavy irradiation environment with a heat load of 15 MW/m2 or more, CFD heat transfer flow analysis was carried out for performance evaluation and its design optimization by a structural analysis models of a supercritical CO2 gas cooled divertors. As a result, in the supercritical CO2 gas cooled tungsten mono-block divertors (50 × 50 mm × 5 channel × 5,000 mL) with a flow path length of 5 m or less, the engineering designable range of these advanced diverters having the same cooling performance as the water cooling divertor was clarified, and its practicality is extremely high from the feature that the structural model has an extremely low risk during operation as compared with the water cooled divertor.
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Kunihiro KOJIMA, Masato GOTO, Hiroyuki HIGAKI, Kiyokazu ITO, Hiromi OK ...
原稿種別: Regular Articles
2022 年 17 巻 p.
1406003
発行日: 2022/02/02
公開日: 2022/02/09
ジャーナル
フリー
A detailed experimental study has been conducted to demonstrate the efficient confinement of ions in the popular four-rod configuration of a linear Paul trap without exciting the transverse radio-frequency (rf) quadrupole field. The three-dimensional (3D) ion confinement is achieved with an identical rf voltage applied to the end electrodes. The optimum operating region is visualized in the stability tune diagram, which indicates that a large number of ions can be stored by adjusting a few fundamental parameters. The lifetime of an ion cloud in the present linear trap is over a second (corresponding to a million rf cycles), long enough for various practical applications. It is also shown through 3D numerical simulations that one can easily extract ions from the trap at a low loss rate below 10%.
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Hiroaki TOMURO, Mengran JI, Ryo NAGATA, Koichiro KOUGE, Tatsuya YANAGI ...
原稿種別: Regular Articles
2022 年 17 巻 p.
1406005
発行日: 2022/02/21
公開日: 2022/03/05
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フリー
Mo/Si multilayer mirrors are used for extreme ultraviolet (EUV) lithography. The formation of hydrogen-induced blisters in the Mo/Si multilayer is a problem that reduces the reflectance of the mirror. To evaluate the blister-resistance of EUV mirrors, the blister formation processes of Mo/Si multilayers with a capping layer were investigated using a high-frequency hydrogen plasma system as a hydrogen ion source under varying hydrogen ion exposure conditions. As a result, it was observed that blister formation by low-energy hydrogen ion irradiation of about 10 eV increases the blister-occupied area, depending on the amount of the ion dose. Furthermore, the sample was heated to promote the diffusion of hydrogen atoms, and the activation energy of blister formation was examined using the Arrhenius plot of the ion dose required for blister formation with respect to the heating temperature. The analysis showed that when the ion flux is known, the blister formation time can be predicted.
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Shinnosuke HOSOYAMA, Masahiro YAMAZAKI, Koichi SASAKI
原稿種別: Regular Articles
2022 年 17 巻 p.
1406070
発行日: 2022/06/15
公開日: 2022/06/28
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This paper demonstrates the estimation of vibrational temperatures of N2 and CO2 in low-pressure plasmas by threshold ionization mass spectrometry. The principle for the estimation is the decrease in the ionization potential by the vibrational excitation. We observed that the threshold ionization curves of N2 and CO2, which were measured using a quadrupole mass spectrometer with an energy-variable electron beam, shifted toward the low-energy side, when they were sampled from the plasmas. We constructed a model which assumed a Boltzmann distribution for the population densities of vibrational excited states and the same cross sections of electron impact ionization for vibrational excited states except the shifts of the threshold energies. The vibrational temperatures were estimated by fitting the experimental threshold ionization curves with the model.
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Yurika KOMORI, Hiroshi OKAWA, Tetsuya AKITSU
原稿種別: Regular Articles
2022 年 17 巻 p.
1406109
発行日: 2022/12/27
公開日: 2022/12/29
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In this study, we investigated the enhancement of cellular lipid that forms in Lipomyces starkeyi under the electro chemical stimulation by discharge in the dielectric barrier electrode at a gas-liquid boundary. The plasma injection sequence and composition of recovery media were optimized for the minimum deterioration of cellular density and maximum increase in the lipid volumes. Under optimum conditions, the volume of lipid globules increased to 1.35 and the count of cells per milliliter to 1.16.
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Yuki GOTO, Shin KUBO, Toru Ii TSUJIMURA, Toru KOBAYASHI
原稿種別: Regular Articles
2022 年 17 巻 p.
2401007
発行日: 2022/03/18
公開日: 2022/04/06
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In this paper, we measured the one-dimensional phase and polarization structure of a millimeter-wave with a helical wavefront (vortex beam) using a simultaneous heterodyne detection system at two spatial points. This is a novel approach, and it provides us with the relative phase of the vortex beam. We measured the phase discontinuity of the vortex beam by scanning the one-dimensional path where an antenna passes through the optical axis. It was found that relative phases gradually increase or decrease when the antenna does not pass through the optical axis. Additionally, we measured polarization parameters, which were indefinite near the optical axis. In other words, the optical axis of the vortex beam is a singular point about the phase.
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Haruhiko SAITOH, Itsuki TANIOKA
原稿種別: Regular Articles
2022 年 17 巻 p.
2401026
発行日: 2022/04/08
公開日: 2022/04/29
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フリー
Conditions for the emergence of chaotic orbit of low energy positrons are numerically calculated in a compact dipole trap for use in positron and electron-positron plasma experiments. Due to its relatively weak field strength and existence of magnetic null line near the confinement region, coupling between gyro and bounce motions is pronounced even for low energy particles in this trapping geometry. Breakdown of first and second adiabatic invariants and the resultant non-integrable chaotic motion are realized for positrons with kinetic energy below the order of 10 eV. This kinetic energy value is two orders of magnitude smaller than the threshold value for a chaotic orbit in the Ring Trap-1 (RT-1) experiment. The stochastic long orbit is potentially applicable for efficient injection and compression schemes of positrons in a compact levitated dipole experiment.
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Ryo MANABE, Hayato TSUCHIYA, Mayuko KOGA
原稿種別: Regular Articles
2022 年 17 巻 p.
2401072
発行日: 2022/06/22
公開日: 2022/07/01
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フリー
We perform the principal verification of reconstructing object surface images by using deep learning. Using the deep learning neural network based on convolutional neural networks, simple object surface images with 128×128 pixels are reasonably reconstructed with up-converting from rough microwave signal images with 16×16 pixels. The model captures large structural features of the object surface images even with small number of training data. As the number of training data increases, it captures small structures of objects. It is also found that noises of input signal images affect reconstructions of small structures of objects.
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Ayumu SAITOH
原稿種別: Regular Articles
2022 年 17 巻 p.
2401089
発行日: 2022/07/08
公開日: 2022/07/14
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フリー
The conjugate gradient (CG) method with the acceleration technique of using both H-matrix arithmetic and H-matrix-based preconditioning is applied to the linear system that appeared in the shielding current analysis of the uncracked high-temperature superconducting film and its performance is investigated numerically. The computational results show that the proposed acceleration technique is extremely effective for improving the speed of the CG method.
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Nandini YADAVA, Sachin S. CHOUHAN, Amulya SANYASI, Uttam SHARMA, Jay ...
原稿種別: Regular Articles
2022 年 17 巻 p.
2401095
発行日: 2022/08/24
公開日: 2022/09/03
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A capacitive coupled radio frequency (RF) plasma system has been developed for producing tungsten coated graphite tiles using plasma assisted chemical vapor deposition (PACVD) technique. To characterize the deposition chamber for optimal plasma parameters, small amount of air is released into the hydrogen plasma purposefully to measure its gas temperature using spectral bands of nitrogen molecule. Optical emission spectra in the wavelength range 350 to 900 nm have been recorded with a miniature spectrometer. Molecular spectral bands of N2 (B3Πg-A3 Σu+ ) have been observed and identified as three bands from the nitrogen 1PS (Δν = 2, 3 & 4). These bands are simulated using MATLAB code developed in-house by considering Boltzmann distribution of particles in the vibrational states. The experimental spectra have been modelled with the simulated spectrum through the best-fit technique by iterating the latter one with different temperature values. Boltzmann plot method is also utilized to evaluate plasma gas temperature using identified vibrational bands. The estimated temperature using spectral modelling method matches fairly well with Boltzmann plot method. The estimated vibrational temperatures are in the range of ∼7000 - 8000 K, an order higher than the room temperature ∼300 K.
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Mitsutaka ISOBE, Kunihiro OGAWA, Siriyaporn SANGAROON, Guoqiang ZHONG, ...
原稿種別: Regular Articles
2022 年 17 巻 p.
2402008
発行日: 2022/03/18
公開日: 2022/04/06
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フリー
The commissioning of three different types of D-D neutron energy spectrometer has been performed in the Large Helical Device (LHD) to accelerate energetic-ion physics studies in a non-axisymmetric system. Because the LHD is equipped with negative-ion-source-based tangential neutral beam injectors (N-NBs) characterized by high energy up to 180∼190 keV, a significant Doppler shift of D-D neutron energy from 2.45 MeV is expected. Two different compact neutron energy spectrometers, i.e., a conventional liquid organic scintillator, designated as EJ-301, and a newly developed Cs2LiYCl6:Ce with 7Li-enrichment called CLYC7, having tangential sightlines,have shown up- and/or down-shifted D-D neutron energy, as expected according to the direction of N-NB injection. In addition, with the aim of study on a perpendicular energetic ion tail, created by wave heating with ion cyclotron resonance frequency, a neutron energy spectrometer named the Time of Flight Enhanced Diagnostic (TOFED) is being developed. The TOFED is based on a time-of-flight technique and is characterized by high-energy-resolution and a high-counting-rate capability. Commissioning of the TOFED is now ongoing. Recent advances of neutron energy spectrometer development for LHD deuterium plasmas are described.
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Malay B. CHOWDHURI, Ranjana MANCHANDA, Joydeep GHOSH, Nandini YADAVA, ...
原稿種別: Regular Articles
2022 年 17 巻 p.
2402011
発行日: 2022/03/30
公開日: 2022/04/23
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フリー
Impurity behavior has been studied for the high performance Ohmically heated ADITYA tokamak plasmas operated with higher toroidal magnetic field and multiple gas puffs. The neutral hydrogen and impurity emissions in the visible range were monitored by photo multiplier tube (PMT) based system in which interference filter used for wavelength selection. The VUV spectral line emissions from impurities, such as C4+, O5+ and Fe14+, were also recorded by a VUV survey spectrometer operated in the 10 - 180 nm. It has been found that Hα, O1+, and C2+ emissions normalized with electron density (ne), and visible continuum normalized with ne2 show a gradual decrease with increase in density indicating lower impurity concentration in these discharges. The VUV emission also shows the similar trend with increasing ne. Indeed, the impurity transport study using iron emissions confirms that the iron concentration reduces with increasing ne. This is also corroborated by the observed reduction in plasma effective charge, Zeff and radiation power loss with the increase in ne. These results clearly indicate that the improved confinement for ADITYA plasma are correlated with reduction of impurities concentration in those discharges.
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Kunihiro OGAWA, Mitsutaka ISOBE, Ryosuke SEKI, Hideo NUGA, Hiroyuki YA ...
原稿種別: Regular Articles
2022 年 17 巻 p.
2402012
発行日: 2022/03/30
公開日: 2022/04/23
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フリー
A feasibility study for measuring a deuterium-deuterium (D-D) fusion reaction radial profile by promptly lost D-D fusion born 3 MeV protons, whose energy Larmor radius is the same as the minor radius of CFQS, was performed. The Lorentz orbit code was utilized to estimate the predicted signals of collimated proton detectors using the D-D fusion radial profile calculated by the analytical Fokker-Planck code for steady-state plasma FIT3D-DD code. The inversion of the D-D fusion profile using the estimated signals was performed using a linear matrix solution library. The coarse agreement between input and inverted profiles shows the possibility of D-D fusion profile diagnostics by a 3 MeV proton in CFQS.
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Akinobu MATSUYAMA, Ryuichi SAKAMOTO
原稿種別: Regular Articles
2022 年 17 巻 p.
2402017
発行日: 2022/03/30
公開日: 2022/04/23
ジャーナル
フリー
Cryogenic neon pellets of 3 mm in diameter were injected into neutral beam injection (NBI) heated discharges on the Large Helical Device (LHD). The time response of far infrared (FIR) interferometer has pointed out a relatively slow assimilation of the ablated materials compared to the cases of hydrogen injection. This is consistent with the neutral gas and plasma shielding (NGPS) model prediction, showing that strong line emission inside the ablation cloud limits the cloud temperature and the expansion velocity along the magnetic field line. Measured penetration depths were also compared, being well reproduced by the code prediction when the contribution from 180 keV fast ions produced by tangential NBI is taken into account.
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Tetsutarou OISHI, Masahiro KOBAYASHI, Hiromi TAKAHASHI, Yuki HAYASHI, ...
原稿種別: Regular Articles
2022 年 17 巻 p.
2402022
発行日: 2022/04/22
公開日: 2022/05/17
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フリー
In the Large Helical Device, the divertor detachment has been attempted by application of resonant magnetic perturbation (RMP) field and Ne gas puffing in electron cyclotron resonance- heated discharges for compatibility of high central electron temperature and low divertor heat load. Two kinds of divertor detachment phases were observed. The first one appeared transiently just after the Ne gas puffing (1st detachment), and the second one appeared steadily in the latter half of the discharge (2nd detachment). Space-resolved extreme ultraviolet spectroscopy revealed that NeVI-NeVIII emissions increased slightly outside the last closed flux surface (LCFS), while NeIX and NeX emissions increased inside the LCFS in the 1st detachment phase. Although in the 1st detachment the divertor heat load was significantly reduced, the central electron temperature also decreased because the Ne ions were penetrated inside the LCFS as a radiation source. In the 2nd detachment phase, NeVINeVIII emissions increased outside the LCFS while NeIX and NeX emissions kept low intensity inside the LCFS. In this phase, low divertor heat load and high central electron temperature were obtained simultaneously because the Ne ions were localized outside the LCFS as a radiation source. The profile measurements of Ne emission show that the edge island structure created by the RMP application impacts on the impurity emission distribution, where the peak of the emission shifts radially stepwise as the detachment proceeds.
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Hideo NUGA, Ryosuke SEKI, Kunihiro OGAWA, Shuji KAMIO, Yutaka FUJIWARA ...
原稿種別: Regular Articles
2022 年 17 巻 p.
2402023
発行日: 2022/04/22
公開日: 2022/05/17
ジャーナル
フリー
Tritium yields due to the deuterium-deuterium fusion reaction during the 22nd LHD experiment campaign are numerically estimated. As usual, the total tritium yields are assumed to be the same total neutron yields. In the Large Helical Device (LHD), however, it is considered that fusion reactivity of the D(d,p)T branch is lower than that of the D(d,n)3He one because the fusion reaction between a fast-deuteron and a thermal deuteron is dominant. By integrated simulation, considering the velocity distribution function of fast-deuteron, the ratio of the tritium yields to the neutron yields is estimated to be Yt/Yn ∼ 0.936. From the assumptions applied in the simulation, it is expected that this value should be still an over-estimation rather than the actual value.
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Xinyue GUO, Hirohiko TANAKA, Shin KAJITA, Noriyasu OHNO, Shogo HATTORI ...
原稿種別: Regular Articles
2022 年 17 巻 p.
2402027
発行日: 2022/05/13
公開日: 2022/06/14
ジャーナル
フリー
To investigate the isotope effect on the plasma detachment in helium (He) and hydrogen (H)/deuterium (D) mixture plasmas, we performed H2, D2 or He gas puffing into He plasma in the linear plasma device NAGDIS-II. Axial distributions of electron density (ne) and electron temperature (Te) were obtained using a movable Langmuir probe. Additionally, optical emission spectroscopy (OES) was applied to measure axial distributions of Balmer lines and He I lines. When the neutral gas pressure was high (ΔPn = 7 ∼10 mTorr), ne distribution in He-D2 mixture plasma was similar to that in pure He plasma, showing a sharp decrease at the downstream region where Te < 1 eV. In contrast, in He-H2 mixture plasma, a decrease in ne was confirmed from upstream region where Te > 1 eV. The upstream Hα/Hγ in He-H2 plasma was significantly larger than the Dα/Dγ in He-D2 plasma at the same Te. This result indicated that molecular activated recombination (MAR) processes significantly occurred in He-H2 plasma, while electron-ion recombination (EIR) processes were dominant in He-D2 and pure He plasmas.
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Dong LI, YunBo DONG, Wei DENG, WuLv ZHONG, Min XU
原稿種別: Regular Articles
2022 年 17 巻 p.
2402028
発行日: 2022/04/22
公開日: 2022/05/17
ジャーナル
フリー
An advanced tomography method based on Bayesian probability theory is presented in this article. In the method, Gaussian Process (GP) prior is adopted as an effective approach to smoothness regularization which can be optimized based on the balance between model complexity and data constraint. In particular, to address the problem of varying smoothness in space, a non-stationary version of the GP has been developed and resolved via Bayesian hierarchical algorithm to implement locally adaptive smoothness regularization such that the accuracy of the reconstruction can be improve significantly. The Bayesian formulism allows the reliability of the reconstruction result to be examined by the confidence interval of a posterior probability. Through a wide range of applications, this tomography method is proved to be a robust tool for the study of magnetohydrodynamics (MHD) activity and impurity transport during HL-2A experimental campaigns.
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