担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Contributions to Plasma Physics  

In order to simulate hydrogen (H) plasma in the linear plasma device NAGDIS-II, we have modified the fluid code LINDA-NU to allow the simultaneous calculation of multiple ion species consisting of hydrogen atomic ions ((Formula presented.)) and molecular ions ((Formula presented.)). In this simulation, H and (Formula presented.) neutrals are assumed to be uniformly distributed in space in order to obtain initial qualitative results. The fraction of (Formula presented.) ions increases as the (Formula presented.) molecular density increases, and the recombination process between (Formula presented.) and electrons is observed to reduce the particle flux to the target plate. With an increase in H density, the electron density increases due to the decrease in ion flow velocity due to the change exchange process, and the electron temperature decreases to less than 1 eV, leading to the detached plasma formation attributed to the electron-ion recombination process.

DOI： 10.1002/ctpp.202300150

Scopus

担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Nuclear Materials and Energy  

The tungsten (W) fuzzy structure was widely observed in linear plasma devices under the fusion-relevant condition. This type of structure can be used in many application fields benefiting from its larger surface area and high optical absorbance. However, W fuzz can be barely formed when the sample temperature is lower than 900 K. This study decreased the threshold to ∼800 K using W co-deposition on a Si nanocones substrate. It suggests that the conventional threshold temperature is only necessary for He bubble rupture to create a rough surface that induces the uneven trapping of the adatom diffusion.

DOI： 10.1016/j.nme.2024.101668

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Nuclear Fusion  

ZrC dispersion-strengthened W exhibits high strength/ductility, low ductile-to-brittle transition temperature, and excellent thermal shock resistance, making it a promising candidate plasma-facing material for future fusion devices. In this study, surface modification of 0.5 wt.% ZrC dispersion-strengthened W (WZrC) under low energy and high fluence He plasma irradiation at high temperature was presented. Under the energy of 90 eV and fluence ranging from 6 × 1024 He·m−2-2 × 1026 He·m−2 He irradiation at 920 °C, a typical fuzz nanostructure appeared on the W matrix of WZrC. The thickness of fuzz layer is proportional to the square root of He irradiation fluence. The fuzz showed comparable thickness and structural features to pure W, indicating limited effects of the particle’s addition on resistance to high fluence He irradiation at high temperatures. Under continuous He injection, the fuzz would grow extending onto the particle area, making the particle obscured. Besides, the erosion behavior of particles under He plasma irradiation has been investigated, which is thought to be dominated by a sputtering process. Under the He influence of 6 × 1024 He·m−2, only nanopores were observed in the surface region. With fluence increasing to 5 × 1025 He·m−2, the surface became relatively uneven with larger holes. W aggregated in spots and distributed on the surface of the particle, which might be the result of subthreshold sputtering and deposition. When fluence further increased to 2 × 1026 He·m−2, the particles were eroded completely and covered by the extended fuzz, forming cavities. In addition, distinctive layered nanotendrils were observed above the cavities, which were characterized to consist of inner W-riched skeletons and outer Zr-riched layers. It indicates that the layered nanotendrils should be the result of fuzz extension combined with particle sputtering/deposition.

DOI： 10.1088/1741-4326/ad2f4c

Scopus

出版者・発行元：Applied Physics Letters  

This study reports on the formation of self-organized silicon (Si) nanostructures by 75 eV helium (He) plasma irradiation at normal incidence without the presence of impurities. In contrast to the featureless surface after normal incidence argon (Ar) ion beam irradiation without the co-deposition of impurities, the Si surface exhibits the development of faceted nanostructures under 75 eV He plasma irradiation. The faceted structures are interspersed with valleys that extend in two orthogonal directions, imparting a mountain-like morphology to the surface. Our investigation verifies that the He bubbles align themselves along the direction perpendicular to the surface underneath these valleys. Furthermore, the presence of He bubbles induces distortion in the surface layer and leads to the formation of an amorphous Si layer. The underlying mechanism driving this surface evolution could be attributed to the instability induced by the presence of He bubbles.

DOI： 10.1063/5.0186756

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Applied Physics  

Low-energy ion beam irradiation, combined with the introduction of impurities, presents a promising approach for nanopatterning silicon (Si) surfaces. In this research, we investigate the surface evolution of Si (100) surfaces irradiated by 75 eV helium (He) plasma, in the presence of tantalum (Ta), traditionally regarded as an impurity incapable of initiating pattern formation, as evidenced in prior studies. The Ta impurities are pre-deposited onto the Si surfaces using the magnetron sputtering method, which offers a more controlled and quantifiable approach compared with the conventional co-deposition route. After irradiation at 800 K, dense cone arrays are produced on the Si surface. The growth of the cones is explored for fluence spanning (1-10) × 1025 m−2. The cross-sectional scanning electron microscope images indicate that the cone lengths and base width are well characterized by t1/2 dependence. The kinetics of the cone growth follow Fick’s law, characterized by an effective diffusive mechanism with the coefficients of diffusion: D = 6.49 ± 0.83 × 10−16 m−2 s−1. Transmission electron microscope observations reveal that the cone has distinct inner and outer parts with different microstructures and a clear interface. The growth mechanism of these cones is elucidated as a composite process involving preferential sputtering, the destabilizing influence of He bubbles, and the migration of adatoms.

DOI： 10.1063/5.0187265

Scopus

担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Plasma  

Plasma-driven science is defined as the artificial control of physical plasma-driven phenomena based on complex interactions between nonequilibrium open systems. Recently, peculiar phenomena related to physical plasma have been discovered in plasma boundary regions, either naturally or artificially. Because laboratory plasma can be produced under nominal conditions around atmospheric pressure and room temperature, phenomena related to the interaction of plasma with liquid solutions and living organisms at the plasma boundaries are emerging. Currently, the relationships between these complex interactions should be solved using science-based data-driven approaches; these approaches require a reliable and comprehensive database of dynamic changes in the chemical networks of elementary reactions. Consequently, the elucidation of the mechanisms governing plasma-driven phenomena and the discovery of the latent actions behind these plasma-driven phenomena will be realized through plasma-driven science.

DOI： 10.3390/plasma7010011

Scopus

担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IEEE Transactions on Plasma Science  

Fuzzy nanostructured tungsten (W) is formed by helium (He) plasma irradiation. In fusion devices, the thermophysical properties are important to consider the response to pulsed heat load from the plasma. In this work, the thermal conductivity of the W fuzz is measured using a pulsed light heating thermoreflectance method. A detailed model was developed to explain the entire temporal evolution of the thermoreflectance signal. It was found that the thermal conductivity of the nanostructured layer was deduced to be in the range of 0.18%–0.21% of the pure (ideal) W and lower than the previously reported highly porous metallic materials. In addition to the porosity, the specific nonuniform nanofiber structure is likely to contribute to the low effective thermal conductivity.

DOI： 10.1109/TPS.2023.3348465

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Japanese Journal of Applied Physics  

Nano-tendril bundles (NTBs) are nanostructures formed on the surface of tungsten under helium plasma irradiation with impurities. Upon annealing, NTBs of different sizes exhibit distinct morphological changes. This study aims to elucidate the underlying reasons for the different morphological changes observed in NTBs through the analysis of their thermal responses. A simulation approach was employed to investigate the temperature distribution of NTBs with different heights, aspect ratios, and porosities during annealing experiments. The simulation results revealed varying degrees of impact of height, aspect ratio, and porosity on the temperature distribution of NTBs during annealing. This finding contributes to a better understanding of the thermal properties and reactions of NTBs.

DOI： 10.35848/1347-4065/ace6ac

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physica Scripta  

Volumetric plasma recombination in a detached deuterium (D) plasma was experimentally studied in the linear plasma device NAGDIS-II. The radial distributions of the electron temperature (Te) and the electron density (ne) were measured by upstream and downstream laser Thomson scattering (LTS) systems and D-atom excited states of the Balmer series (n = 3-7) were measured by optical emission spectroscopy (OES). The results indicated that the electron static pressure, particle flux and heat flux present a two-step reduction with an increasing neutral pressure, suggesting that molecule activated recombination (MAR) and electron-ion recombination (EIR) were activated, respectively. The difference in the distributions of the atomic state population densities was observed to be a feature of the transition from the MAR-dominant phase to the EIR-dominant phase. The transition between the two phases had a distinct boundary at Te ∼0.7 eV, which was considered a transition point between the phases. The ratios of the atomic state population densities showed different features in the two phases, and are expected to be useful in characterizing the phase and degree of plasma detachment.

DOI： 10.1088/1402-4896/acfeb4

Scopus

担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Fusion Engineering and Design  

In this study, we applied machine learning to optical emission spectroscopy (OES) data and device parameters from the linear plasma device NAGDIS-II to explore the potential application of machine learning for predicting electron density, ne, and temperature, Te. The covered ranges of ne and Te, which were measured by an electrostatic probe, are 3.6 × 1017–2.4×1019 m−3 and 0.3–7.1eV, respectively. A three hidden layer neural network (NN) is introduced to model the relationship between ne/Te and the combination of line intensities, radial position, and device parameters. It is shown that the errors in ne and Te become 18.0 and 18.8%, respectively, which were almost the same level for the electrostatic probe, using all available data. Lasso regression and greedy algorithm are used to select the necessary line emissions. It is shown that four or five line intensities are sufficient to obtain almost the same quality as the one with all the other lines.

DOI： 10.1016/j.fusengdes.2023.114012

Scopus

担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Optics Express  

Optical diffusion is an essential process used to manage photons in a wide range of photoelectric systems. This work proposes an approach to fabricate novel optical diffusers by a plasma-processing technique, using fiberform nanostructures formed by helium plasma irradiation and subsequent annealing. After an annealing procedure in the air for oxidation, the optical properties and the light-diffusing abilities of these nanostructured thin films were studied. In addition to the morphology analysis and total transmittance measurement, the diffusion efficiency of the optical diffusers was analyzed using a transmitted scatter distribution function (TDF). It was revealed that the diffusion efficiency of a device with an irradiation time of 30 minutes could reach 97%. The results demonstrate the potential of these nanostructured optical diffusers for various photoelectric applications.

DOI： 10.1364/OE.493993

Web of Science

Scopus

担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Materials Research Express  

Nano-tendril bundles (NTBs) were formed on tungsten via helium (He) plasma exposure with various additional impurity gases, such as neon (Ne), nitrogen (N2), and argon (Ar). The sizes of the NTBs showed different distributions with different additional impurity gases. The field emission property of the NTBs formed with various additional impurity gases was measured. The field-emission property was significantly affected by the morphology of the NTBs, especially the tips of the fibers. In the Ne- and Ar-seeded cases, the NTBs were formed with sharp tips, and the onset electric field for field emission was ∼1 kV mm−1 for all the NTB samples. The Ne-seeded samples showed the most rapid increase in the emission current. In the N2-seeded case, two types of NTBs were formed. The NTBs were formed with sharp tips when the ratio of N2 impurity gas was 2.1%. With an increase in the ratio to 3.0% or higher, the fibers of the NTBs became thicker and the tips became rounder. In the Fowler-Nordheim (F-N) plot analysis, the field enhancement factors were approximately 6000-7000 without significant differences, for all NTBs with sharp tips. NTBs with round tips showed totally different field emission property, as the emission current was only several μA, which is one-tenth of that for the other samples. This suggests that the local morphology of NTBs, especially the geometrical shape of the tips, and not the general size of NTBs, is the main factor in determining the field emission property of NTBs.

DOI： 10.1088/2053-1591/acd1d4

Web of Science

Scopus

担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1038/s41598-023-32621-5

PubMed

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Plasma Science and Technology  

A fiberform nanostructure was synthesized by exposing high-density helium plasma to a 100 nm thick tungsten thin film in the linear plasma device NAGDIS-II. After helium plasma exposure, the cross-section of samples was observed by a scanning electron microscope, transmission electron microscope, and focused ion beam scanning electron microscope. It is shown that the thickness of the nanostructured layer increases significantly for only a short irradiation time. The optical absorptivity remains high, even though it is exposed to helium plasma for a short time. The usage of the thin film can shorten the processing time for nanostructure growth, which will be beneficial for commercial production.

DOI： 10.1088/2058-6272/ac9f2d

Web of Science

Scopus

出版者・発行元：Nuclear Fusion  

There are no changes to the fitting values in the original article.

DOI： 10.1088/1741-4326/acbbde

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 プラズマ・核融合学会  

We have applied the multivariable analysis technique called the proper orthogonal decomposition (POD) to both the divertor particle flux distribution and the electron pressure distribution in the core region of LHD. The cross-correlation analysis indicates that 3rd, 4th, and 5th POD modes of the electron pressure distribution are highly correlated with the divertor footprint index which is a measure of where the peak position of the particle flux distribution is located on the inner divertor plate. Both the 3rd and 4th modes seem to correspond to the shift of the electron pressure peak position from the magnetic-axis radius. In contrast, 5th mode has a strong influence on the peripheral gradient of the electron pressure distribution. Their relationships with the divertor footprint could be explained by the finite β and the Pfirsch-Schlüter current effects.

DOI： 10.1585/pfr.18.2402021

Web of Science

Scopus

CiNii Research

掲載種別：研究論文（学術雑誌）   出版者・発行元：Physics of Plasmas  

We have investigated the generation region of intermittent plasma structures, which could be due to the blob-like cross field transport around the divertor simulation experimental module (D-module) in the tandem mirror device GAMMA 10/PDX. A positive skewness of the ion saturation current was clearly seen when the electrode of the movable probe was located at the radial edge and just in front of the entrance limiter of the D-module. Fourier analysis and conditional averaging clarified that positive spikes intermittently appeared in the same region. This is the first indication that the phenomenon producing the high-density isolated plasma structures occurred in the upstream of the D-module. A negative skewness was also found, and large amplitude fluctuation was detected between regions showing positive and negative skewness. Furthermore, this and light emission fluctuations become stronger during the transient state from attached to detached state on the V-shaped target.

DOI： 10.1063/5.0129886

Web of Science

Scopus

出版者・発行元：ACS Applied Optical Materials  

The surface of GaN has been modified by a simple method that irradiates the substrate with Ar plasma and impurity codeposition, which is termed CoDE (Co-Deposition Etching). Unique structures were formed by the assistance of a small amount of Mo deposition without degradation of the crystal structure. The size of protrusions on the structure is influenced by the amount of deposited Mo particles. The mechanism for the structure formation is discussed based on transmission electron microscopy (TEM) observations and energy dispersive X-ray spectroscopy (EDS) measurements. Based on the GaN surface roughness, we have demonstrated random laser action in the UV region under photoexcitation. The lowest threshold (0.06 J/cm2) for random lasing was observed where the size of the structure is larger than 0.05 μm2, which was formed under conditions with the least amount of deposition. The correlation between the submicro/nanosize structures generated by plasma irradiation and lasing was evaluated in detail. The critical parameter to optimize the random lasing was determined to be the size of structures that can be modified by the Mo deposition rate. The results confirmed that the emission properties can be controlled by the processing conditions. This random laser fabrication technique is expected to be widely applicable to various direct-bandgap compound semiconductors.

DOI： 10.1021/acsaom.2c00085

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Japanese Journal of Applied Physics  

Arc spot motions on nanostructrued “fuzz” tungsten surfaces are investigated on the basis of a two-dimensional Monte Carlo random walk simulation. To compare with previous experimental results, the effects of self-avoiding, bifurcation and extinction of arc spots, as well as the fuzz thickness dependence, are included in the simulation. Under a given temporal arc current profile which is set as close as possible to the experiment, the results derived from the simulation reveal that the motion and the number of arc spots depend significantly on the fuzz thickness.

DOI： 10.35848/1347-4065/ac79fe

Web of Science

Scopus

出版者・発行元：Proceedings - International Symposium on Discharges and Electrical Insulation in Vacuum, ISDEIV  

Rod-like protrusion structures were formed on tungsten by helium plasma exposure with various impurity gases seeded as nitrogen (N2) and argon (Ar). Surface morphology observations and field emission current measurements were done for two samples. Cross-section observation shows that the inside of the protrusions was solid but not porous like conventional fuzz. Therefore, a new formation mechanism which is different from fuzz can be considered. The field emission current from N2-seeded case was slightly higher than that from fuzz, but much lower than that from NTBs, while the field emission current from Ar-seeded case was similar to that from NTBs. The difference in field emission current could be due to the different morphology of the tips between two samples.

DOI： 10.23919/ISDEIV55268.2023.10200357

Scopus

出版者・発行元：Proceedings - International Symposium on Discharges and Electrical Insulation in Vacuum, ISDEIV  

Thermophysical properties of the fuzzy nanostructured tungsten (W) layer formed by helium plasma irradiation (a) are measured using a pulsed light heating thermoreflectance method. A three layered model has been developed to explain the temporal evolution of the themoreflectance signal. The thermal conductivity of the nanostructured layer was deduced to be in the range of 0.14-0.26% of the pure (ideal) W.

DOI： 10.23919/ISDEIV55268.2023.10200254

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Nuclear Materials and Energy  

Optical emission spectroscopy (OES) of helium (He) line intensities has been used to measure the electron density, ne, and temperature, Te, in various plasma devices. In this study, a neural network with five hidden layers is introduced to model the relation between the OES data and ne/Te from laser Thomson scattering in the linear plasma device Magnum-PSI and compared to multiple regression analysis. It is shown that the neural network reduces the residual errors of prediction values (ne and Te) less than half those of the multiple regression analysis in the ranges of 2 × 1018<ne<8×1020 m−3 and 0.1<Te<4eV. We checked two different data splitting methods for training and validation data, i.e., with and without considering the unit of discharge. A comparison of the splitting methods suggests that the residual error will decrease to ∼10% even for a new discharge data when accumulating a sufficient data set.

DOI： 10.1016/j.nme.2022.101281

Web of Science

Scopus

出版者・発行元：2022 Conference on Lasers and Electro-Optics Pacific Rim, CLEO-PR 2022 - Proceedings  

Unique surface nanostructures were formed on semiconductors over a large area by Ar plasma irradiation with RF sample bias. As an application of these wavelength ordered size structure, we have demonstrated a random laser emission at UV region.

DOI： 10.1109/CLEO-PR62338.2022.10432590

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.13182/FST13-A16911

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.jnucmat.2010.12.237

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Web of Science

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/ctpp.2150320312

Web of Science

記述言語：日本語   出版者・発行元：九州大学大学院総合理工学研究科  

DOI： 10.15017/17680

CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Nuclear Fusion  

Superconducting (SC) tokamak JT-60SA plays an essential role in fusion research and development by supporting and complementing the ITER project, providing directions to the DEMO design activity and fostering next generation scientists and engineers. Since the short circuit incident at the terminal joints of equilibrium field coil #1 during the integrated commissioning (IC) in March 2021, both EU and JA implementing agencies (IAs) have examined how to ensure safe operation of JT-60SA by mitigating the risk of possible discharge occurrence inside the cryostat. Based on the experience of the global Paschen tests, the IAs have established a strategy of risk mitigation measures, which is a combination of (i) reinforcement of insulation, (ii) avoiding unnecessary voltage application to the coil systems and (iii) immediate de-energization of the coils when deteriorated vacuum conditions are detected. Thanks to the considerable efforts of the Integrated Project Team members, the IC restarted in May 2023. After confirmation of the SC state of the coil systems (TF, EF and CS), the coil energization test and the plasma operation phase 1 (OP-1) started. The first plasma was successfully achieved on 23 October 2023 with a limited value of voltage and current applied to the coils. The plasma configuration control was also confirmed with low plasma current and low auxiliary heating power conditions. Based on the IO-F4E-QST collaboration, activities of JT-60SA have been shared with the IO and provided an important lesson for ITER assembly and commissioning, and will provide an outstanding contribution to fusion research at large. After OP-1, maintenance & enhancement phase 1 (M/E-1) starts from January 2024, in which in-vessel components are installed, and heating and diagnostic systems are extensively upgraded to allow a high power heating experiment planned in OP-2. In order to make the best use of JT-60SA, a newly organized JT-60SA experiment team will refine the research plan for the future high heating power operation phase.

DOI： 10.1088/1741-4326/ad34e4

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： DOI: 10.1063/5.0129886

担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/aesr.202200141

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： doi.org/10.1021/acsaom.2c00085

担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： DOI: 10.1016/j.apsusc.2022.153668

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Plasma Physics and Controlled Fusion  

From pulsed plasma experiments focusing on neutral pressure dependence, the impacts of a transition from a low to a high recycling target on the particle load were investigated and discussed in the linear plasma device, Magnum-PSI. Time traces of the target ion flux were mitigated in high neutral pressure cases because of a plasma-neutral interaction. On the other hand, in low neutral-pressure cases, the target ion flux indicated partial suppression in the last part of the pulse. The Langmuir probe, located 200 mm upstream from the target plate, did not exhibit such a suppression. Pulse suppression can be expected from the localized interaction between recycled neutral flux and pulsed plasma in front of the target. The mean-free paths of recycled neutral particles regarding the charge exchange with pulse ions and elastic scattering with background neutral particles were compared. Modeling using a fluid code coupled with a neutral transport code was performed, and it was concluded that dynamic pressure induced by the transient recycled neutral flux caused sufficient momentum loss to stagnate the pulsed plasma toward the target plate.

DOI： 10.1088/1361-6587/ac8acb

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Nuclear Materials and Energy  

The bidirectional reflectance distribution function (BRDF) of recrystallized tungsten mono-blocks exposed to cyclic heat loading for ITER divertor outer vertical target was measured using a goniophotometer at a wavelength of 473 nm. Laser microscope observations revealed that the surface roughness of the mono-block increased by an order of magnitude after cyclic heat loads of approximately 20 MWm−2. Furthermore, the overall values of BRDF decreased with an increase in cyclic heat loading. A comparison between the modeled and measured BRDFs showed that an additional Lambertian component is necessary to a specular function (microfacet model or Gaussian function) to fit the measured BRDFs when the surface of the mono-blocks becomes rough.

DOI： 10.1016/j.nme.2022.101243

Scopus

担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 プラズマ・核融合学会  

Helium (He)-Tungsten (W) co-deposition experiments were conducted in the linear plasma device Co-NAGDIS at a temperature of 1223K to observe the characteristics of fuzz growth on theWsurface with auxiliary W deposition. The dependence on the deposition rate of W was investigated and a clear difference in fuzz thickness was found between He-only and co-deposition experiments. In addition, the fuzz structures on a single sample exhibited a spatially nonuniform distribution, which was probably caused by the nonuniformity in the deposition rate.

DOI： 10.1585/pfr.17.1302094

Scopus

CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： DOI: 10.1585/pfr.17.2405041

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 プラズマ・核融合学会  

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.

DOI： 10.1585/pfr.17.2402027

Scopus

CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： doi.org/10.1039/D2CP00289B

担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Nuclear Materials and Energy  

Nano-tendril bundles (NTBs) are known to be formed on tungsten by helium plasma exposure with additional neon impurity gas. In this study, the annealing experiments were conducted at the sample temperature of 1473 – 1673 K to investigate the changes of morphology and field emission property of NTBs. With NTBs formed on a W surface, the surface did not fully recover to a smoothed surface and the NTBs remained the fiber-form structures after the annealing at 1673 K for one hour. In addition, the onset electric field for field emission increased, while the emission current from NTBs significantly decreased after the annealing. When the samples were biased at −250 V during helium plasma exposure, arc ignition was confirmed on W surface with NTBs, whereas no arc ignition appeared on W with annealed NTBs.

DOI： 10.1016/j.nme.2022.101178

Scopus

担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1063/5.0079524

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Nuclear Fusion  

Construction of the JT-60SA tokamak was completed on schedule in March 2020. Manufacture and assembly of all the main tokamak components satisfied technical requirements, including dimensional accuracy and functional performances. Development of the plasma heating systems and diagnostics have also progressed, including the demonstration of the favourable electron cyclotron range of frequency (ECRF) transmission at multiple frequencies and the achievement of long sustainment of a high-energy intense negative ion beam. Development of all the tokamak operation control systems has been completed, together with an improved plasma equilibrium control scheme suitable for superconducting tokamaks including ITER. For preparation of the tokamak operation, plasma discharge scenarios have been established using this advanced equilibrium controller. Individual commissioning of the cryogenic system and the power supply system confirmed that these systems satisfy design requirements including operational schemes contributing directly to ITER, such as active control of heat load fluctuation of the cryoplant, which is essential for dynamic operation in superconducting tokamaks. The integrated commissioning (IC) is started by vacuum pumping of the vacuum vessel and cryostat, and then moved to cool-down of the tokamak and coil excitation tests. Transition to the super-conducting state was confirmed for all the TF, EF and CS coils. The TF coil current successfully reached 25.7 kA, which is the nominal operating current of the TF coil. For this nominal toroidal field of 2.25 T, ECRF was applied and an ECRF plasma was created. The IC was, however, suspended by an incident of over current of one of the superconducting equilibrium field coil and He leakage caused by insufficient voltage holding capability at a terminal joint of the coil. The unique importance of JT-60SA for H-mode and high-β steady-state plasma research has been confirmed using advanced integrated modellings. These experiences of assembly, IC and plasma operation of JT-60SA contribute to ITER risk mitigation and efficient implementation of ITER operation.

DOI： 10.1088/1741-4326/ac10e7

Scopus

担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 プラズマ・核融合学会  

DOI： 10.1585/pfr.17.1201004

Web of Science

CiNii Research

出版者・発行元：Optics InfoBase Conference Papers  

Unique surface nanostructures were formed on semiconductors over a large area by Ar plasma irradiation with RF sample bias. As an application of these wavelength ordered size structure, we have demonstrated a random laser emission at UV region.

DOI： 10.1364/CLEOPR.2022.CFP8J_02

Scopus

担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Surface Science  

Helium (He)-induced nanostructured tungsten sheets were synthesized by He plasma irradiation under different plasma exposure durations. After calcination, nanostructured tungsten oxide samples were used as photoelectrodes to test photoelectrochemical (PEC) performance. The results showed that nanostructured WO3 photoanodes have higher PEC performance compared to the sample without nanostructures. The 15 min irradiated sample had the highest photocurrent density of 3.5 mA/cm2 under the thermodynamic potential of water oxidation (1.23 V vs. RHE). It was found that the oxide layer thickness and exposed crystal facet have a significant impact on PEC performance. The plasma synthesis technique has proved to be an effective method for preparing nanostructured WO3 photoelectrodes.

DOI： 10.1016/j.apsusc.2021.151979

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 プラズマ・核融合学会  

<p>We performed helium (He) plasma irradiation to molybdenum (Mo) substrate with auxiliary Mo deposition. Different from W cases, large-scale fiberform nanostructure (LFN) growth did not occur easily. The experiments suggested that the experimental condition of Mo LFN growth has a much narrower conditional window than that of fuzz growth or another hidden control factor exists for LFN growth.</p>

DOI： 10.1585/pfr.16.1206105

Web of Science

担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physica Scripta  

Hydrogen isotope trapping at lattice defects in neutron-irradiated tungsten (W), a leading candidate as plasma facing material, is an important problem determining tritium (T) inventory in a vacuum vessel of a future fusion reactor. In this study, W samples were irradiated with neutrons in the Belgium Reactor 2 at 563 K to 0.06 or 0.016 displacement per atom (dpa). After characterizing defects by positron lifetime measurements, deuterium (D) penetration under exposure to D plasma was examined at 563-773 K. Positron lifetime showed the presence of dislocations, monovacancies and relatively large vacancy clusters. These defects trapped D atoms with different values of binding energy. Dependence of D retention on plasma exposure temperature and damage level indicated that the concentrations of weak traps with smaller binding energy increased more significantly with damage level than those of strong traps.

DOI： 10.1088/1402-4896/ac2c20

Scopus

その他リンク： https://iopscience.iop.org/article/10.1088/1402-4896/ac2c20/pdf

担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Physics D: Applied Physics  

Reducing the optical reflection of silicon (Si) material is a crucial issue on the surface of solar cells and other photonic applications. Fabrication of nanocone structures on the Si surface (black Si) by plasma (helium or argon) irradiation is a novel technique in recent decades with advantages, such as simple, economical, and harmless to the Si substrate. However, the uniformity and controllability of the surface remain problematic. In this study, uniform black silicon was obtained by low energy (<50 eV) helium ion irradiation with auxiliary Mo co-deposition. The characteristics of the nanocone show a clear relation with the Mo ratio. Deposited Mo was found to accumulate on the cone body, especially on the tip, and it worked as a nano mask to induce the formation of the nanocone and protect it from sputtering. The surface with high and large diameter nanocones possesses low reflectances of roughly 2%. The study of the relation between Mo ratio, characteristics of the nanostructure, and the reflectance of the surface raises a potential method of surface tailoring.

DOI： 10.1088/1361-6463/ac1190

Web of Science

Scopus

担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Photochemistry and Photobiology A: Chemistry  

In order to realize high-performance titanium dioxide (TiO2) photocatalysts for ethylene decomposition, titanium (Ti) thin film samples with fiberform nanostructures were prepared by helium (He) plasma treatment. Then, the oxidation condition for ethylene decomposition were optimized in terms of the oxidation temperature and duration. It is shown that He plasma irradiation with Ti deposition followed by oxidation in the air formed anatase-rich TiO2. The rutile anatase transition temperature increased to higher than 1000 K on the He treated samples and the best photocatalytic performance is twice higher than that on TiO2 sample formed in a magnetron sputtering device. Helium plasma treatment induces vacancies, He clusters, and He bubbles together with formation of nanostructures. The results suggested that those morphology changes lead to the formation of stable anatase structure, which is likely the key factor for the enhancement of photocatalytic activity. Based on the obtained ethylene decomposition rate, we will discuss the necessary light source and amount of photocatalysts to keep vegetables fresh in a long-distance transport cargo.

DOI： 10.1016/j.jphotochem.2021.113420

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physica Scripta  

Recent experiments have revealed that accelerated tungsten (W) nanostructure growth occurs during the exposure to helium (He) plasmas with an additional W deposition, and mm-thick large-scale fiberform nanostructures (LFNs) are formed when certain condition is satisfied. In order to reveal whether accelerated growth occurs in fusion device, it is important to understand the annealing process in addition to the growth process. In this study, we will perform thermal treatment of W LFNs. Detailed observation reveals that the LFNs shrink at a faster rate than that of conventional fuzz, though it takes longer time to fully be reintegrated to the surface because the thickness is orders of magnitude greater.

DOI： 10.1088/1402-4896/ac0866

Web of Science

Scopus

担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 プラズマ・核融合学会  

<p>Arcing was ignited on deformed tungsten (W) surfaces, where W <i>fuzz </i>and/or <i>nano-tendril bundles </i>(NTBs) were grown, by steady state helium (He) plasma exposures with impurity gas seeding. At the same sample potential of −250 V, the presence of NTBs enhanced the frequency of arc ignition, whereas no arc ignition appeared on typical fuzz surfaces without NTBs. After a series of arc ignitions on a sample surface with NTBs, the aspect ratio of NTBs decreased, indicating that protruded NTBs with larger aspect ratio tend to trigger arcing easily.</p>

DOI： 10.1585/pfr.16.2405069

Scopus

担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Plasma Science and Technology  

DOI： 10.1088/2058-6272/abea71

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 プラズマ・核融合学会  

<p>Influences of nitrogen ratio on plasma detachment and molecular activated recombination (MAR) processes during combined seeding with hydrogen have been investigated utilizing end-loss plasma in the GAMMA 10/PDX tandem mirror. Additional gases were injected under the condition that hydrogen partial pressure was fixed and nitrogen partial pressure was changed from 0% - 10% compared to that of hydrogen. Electron density and ion flux further decrease with increasing nitrogen ratio. In addition, it is suggested that the hydrogen-MAR process that begins with dissociative attachment is suppressed during combined seeding of nitrogen and hydrogen. Observed emission spectrum of NH radicals suggests that the density of NH increases as nitrogen ratio increases and nitrogen-induced MAR efficiently contributes to the reduction of particle flux.</p>

DOI： 10.1585/pfr.16.2402041

Scopus

担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 プラズマ・核融合学会  

<p>The computer tomography for divertor impurity monitor, which measures plasma emissions in the divertor region, for ITER has been conducted using a ray-tracing technique. We have attempted four different solution methods for the inversion problem and compared the results. The solution methods which minimize errors in logarithmic scale had better performance than the methods which minimize errors in linear scale. This is likely due to the fact that the values in the emission profile vary in a wide range of orders of magnitude. The accuracy of the reconstruction has been investigated by changing discharge conditions and the number of field-of-views used. The deterioration in accuracy was most noticeable when the emission profile was reconstructed using only two field-of-views. In addition, the accuracy deteriorated, making the estimation more challenging, under discharge conditions with low emission intensity because of the wider range of emission intensity under such conditions.</p>

DOI： 10.1585/pfr.16.2405019

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.35848/1347-4065/abe683

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 プラズマ・核融合学会  

<p>Time evolutions of the emission from helium (He) ion at 468.6 nm were observed in the magnetized co-axial plasma gun device NAGDIS-PG, and the broadening of the spectrum was analyzed in terms of Doppler and Stark broadenings to deduce the ion temperature and the electron density. A significant broadening of the He II spectrum was identified around a dip in the discharge current, suggesting that increases in the temperature and density occurred.</p>

DOI： 10.1585/pfr.16.1202013

Scopus

担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.35848/1347-4065/abe3a5

Web of Science

Scopus

担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.jnucmat.2021.152844

Scopus

担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1585/pfr.16.1206001

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.nme.2020.100848

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： doi.org/10.1016/j.nme.2020.100848

担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/1361-6595/abc817

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1585/pfr.15.1505081

Web of Science

担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1585/pfr.15.1301082

Web of Science

担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.nme.2020.100843

Web of Science

Scopus

担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.nme.2020.100828

Web of Science

Scopus

担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/1361-6587/abb88f

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.vacuum.2020.109799

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.nme.2020.100812

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1063/5.0015912

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1585/pfr.15.1205061

Web of Science

Scopus

担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.35846/1347-4065/aba456

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/ppap.202000126

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/2053-1591/aba394

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1063/5.0010416

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.jnucmat.2020.152350

Web of Science

Scopus

担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/1361-6587/ab8e19

Web of Science

Scopus

担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1063/1.5134869

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.surfcoat.2020.125798

Web of Science

Scopus

担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Plasma and Fusion Research  

DOI： 10.1585/pfr.15.2402012

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/1402-4896/ab52c6

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1585/pfr.15.1201004

Web of Science

Scopus

担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.7567/1347-4065/ab5bbf

Web of Science

Scopus

担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/ctpp.201900114

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/1741-4326/ab73c3

Web of Science

Scopus

担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.7567/1347-4065/ab4601

Web of Science

Scopus

担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

© 2019 Acta Materialia Inc. Low-energy helium (He) plasma irradiations were conducted on ruthenium (Ru) and rhenium (Re), which have hexagonal close packed (HCP) crystal structures. Growth of linear shaped fiberform nanostructures were identified on the surfaces of the both metals after the He plasma irradiation. We also conducted He plasma irradiation while Re particles were deposited on tungsten substrate; 3-mm-thick large scale fiberform nanostructures were grown on the surface. The crystal orientation was analyzed using diffraction patterns of Re and Ru nanofibers together with detailed transmission electron microscope observations. It was found that the growth of linear nanofibers has a preferential crystal orientation in the growth direction and it is always in the c-direction of the HCP crystals. Potential growth processes and mechanisms are proposed based on the experimental observations.

DOI： 10.1016/j.actamat.2019.09.053

Web of Science

Scopus

担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1109/TPS.2019.2942725

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

© 2019 The Authors The objective of this study is to investigate the effects of neutron (n) irradiation on hydrogen isotope transport in tungsten (W). W samples were irradiated with neutrons in a fission reactor and then exposed to high flux deuterium (D) plasma at 563 K in a linear plasma device. The fraction of D release increased with increasing exposure time. In addition, the D retention in n-irradiated W increased in proportion to the square root of the plasma exposure time. These observations were explained by increase in the penetration depth of D with filling up displacement damages acting as strong trapping sites.

DOI： 10.1016/j.nme.2019.100699

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1585/pfr.14.1202135

Web of Science

担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/1361-6595/ab318d

Web of Science

Scopus

担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

© 2019 The Japan Society of Applied Physics. Ethylene decomposition via photocatalytic reaction using ultra-violet light was performed using an oxidized titanium (Ti) sheet and/or thin film samples fabricated by helium (He) plasmas treatments. We prepared nanostructured Ti samples formed by He plasma irradiation and additional thin film deposited samples using radio frequency magnetron sputtering. The samples prepared in this study had a slightly lower photocatalytic activity compared to the thin film deposited on tungsten nanostructure samples previously reported; the anatase formation was solely identified on Ti sheet samples and is hopeful for further improvement of photocatalytic activity of plasma treated titania.

DOI： 10.7567/1347-4065/ab2830

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

© 2019 The Japan Society of Applied Physics. Decomposition of ethylene gas by a photocatalyst is an environmentally friendly and sustainable process. We fabricated titanium dioxide thin films deposited on nanostructured tungsten substrates formed by exposure to helium plasma and evaluated their photocatalytic performance. The nanostructures were maintained even after sputtering and annealing, and the proportion of tungsten inside the thin film increased with increasing oxidation temperature. The photocatalytic activity was improved due to formation of the nanostructure.

DOI： 10.7567/1347-4065/ab09c8

Web of Science

Scopus

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

We have investigated detailed plasma structure around the recombination front region (RFR), where volume electron-ion recombination (EIR) strongly occurs in detached plasmas, by using two-dimensional (2D) movable probe system as well as laser Thomson scattering diagnostics. The 2D distribution of electron density, electron temperature, and plasma potential around the RFR, has been revealed for the first time. The spatial distribution of the particle loss rate due to EIR estimated from electron temperature and electron density profiles indicated that the three-dimensional structure of the RFR adopts a cone structure. Furthermore, in the peripheral region of the RFR, the radial profile of the electron density was widened locally with increasing cross-field transport caused by plasma fluctuation. From the heat transport analysis of electrons, it was found that the thermal relaxation process between electrons and ions is important for the cooling of electrons, and that the convection of electrons regulates electron heat transport near the RFR.

DOI： 10.1016/j.nme.2019.03.010

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1585/pfr.14.3401069

担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

© 2019 The Japan Society of Plasma Science and Nuclear Fusion Research. Helium induced nanostructures on tungsten were characterized by applying basic statistical analysis techniques to scanning electron microscope (SEM) images. As the analysis targets, pinhole- and fuzz-dominant surfaces irradiated with different ion fluences were employed. Although two-dimensional Fourier analysis of the normalized brightness of SEM images clarified several characteristic features, their differences are small to distinguish the dominant nanostructures. On the other hand, probability density functions (PDFs) of the normalized brightness indicate that hole- and fuzz-dominant surfaces have long tail and Gaussian-like shape, respectively. By using several indexes with considering the black and white saturation, it was found that kurtosis and Kullback- Leibler divergence could provide reasonable judgement as the characterization index.

DOI： 10.1585/pfr.14.3402049

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

© 1973-2012 IEEE. In nuclear fusion reactors, unipolar arcing is a longstanding plasma surface interaction issue. In this paper, short summaries of morphology changes by helium plasma irradiation under fusion relevant conditions and ignition of arcing on the He irradiated surfaces are given. Helium plasma irradiation leads to surface morphology changes, and arcing can be ignited on the surface in response to pulsed heat load accompanied by plasma instabilities. Then, we focused on arcing ignited on large-scale fiberform nanostructures (LFNs) formed with deposition of metallic particles together with helium-ion irradiation. Dusts release from the arc spot and the amount of material erosion are discussed based on the experiments.

DOI： 10.1109/TPS.2019.2908193

Web of Science

Scopus

担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.nme.2019.03.014

記述言語：英語   掲載種別：研究論文（学術雑誌）  

© 2019 The Japan Society of Plasma Science and Nuclear Fusion Research. It is important in divertor physics research to investigate thermal response process of beryllium deposited tungsten to high transient heat load such as ELMs. We investigated the heat load on aluminum-coated tungsten by comparing the measured back surface temperature and calculation results of the one-dimensional heat conduction equation. When the plasma power was low enough so that the evaporation did not occur sufficiently, the heat load on the aluminum-coated tungsten was higher than the virgin tungsten. It was caused by the reduction in the energy reflection coefficient due to the formation of aluminum layer. The results suggested that the beryllium deposited layer adversely affects the heat load on the divertor plate when the heat load was not high such as Grassy-ELM.

DOI： 10.1585/pfr.14.1401051

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

© 2019 WILEY-VCH Verlag GmbH &amp; Co. KGaA, Weinheim We have studied the validity of the double-probe method in recombining plasmas. Electron temperature (Te) measured with a double probe was quantitatively evaluated by taking into account the influences of plasma potential fluctuation, plasma resistivity, and electron density fluctuation on the current–voltage characteristics. Differential potential fluctuation and plasma resistivity between two electrodes have a minor effect on Te especially when the inter-distance is small (typically 1 mm). Scattering of measured Te due to the density fluctuation was sufficiently suppressed by making the data acquisition time long (typically 4 s) and taking the average. There is a good agreement between Te measured with the optimized double-probe method and that with laser Thomson scattering diagnostics.

DOI： 10.1002/ctpp.201800088

Web of Science

Scopus

担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

© 2019 The Japan Society of Plasma Science and Nuclear Fusion Research. A new laser Thomson scattering (LTS) measurement system in the upstream region of the linear plasma device NAGDIS-II is established in addition to the recently introduced LTS in the downstream. Further, horizontal distributions of the electron temperature and electron density were compared with those obtained from the Langmuir probe, indicating plasma disturbance due to the insertion of the probe head. We discuss the variation of the electron energy distribution function at upstream and downstream in the recombining plasma.

DOI： 10.1585/pfr.14.2405031

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

© 2019 The Authors Large-scale mm thick fiberform nanostructures are grown when materials are subjected to high flux helium ions with tungsten particles (ions and neutrals) precipitation. Observations of the large-scale fiberform nanostructures (LFNs) were conducted by scanning electron microscope (SEM) and transmission electron microscope (TEM) analyses. In particular, this study focuses on membrane nanostructures. Membranes that contain He bubbles were always observed when LFNs covered the surface. We discuss the growth process of the membrane structures based on detailed observations.

DOI： 10.1016/j.nme.2019.02.004

Web of Science

Scopus

担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1585/pfr.14.2402036

担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

© 2019 The Authors Nano-tendril bundles (NTBs) were generated in DC He plasma with impurity gas-seeding (Ne and N 2 ) under sputtering-dominated conditions. NTB morphologies were characterized using the net erosion yield of samples. NTBs’ height and area were analyzed and ion fluence dependence was discussed. For both impurities, the number of NTBs increased steadily with increasing the fluence. It was revealed that NTB can be generated newly and continuously regardless of ion fluence. Surface observations suggested that micro-protrusions can evolve into NTBs. The effect of re-deposition of W was discussed based on SEM observations. Line-of-sight deposition seemed to play a key role of W feeder to enable NTBs to grow greater.

DOI： 10.1016/j.nme.2019.01.008

Web of Science

Scopus

担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1063/1.5081929

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.nme.2018.12.008

Web of Science

Scopus

担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1585/pfr.14.2402036

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1007/978-3-319-99834-3_12

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms  

© 2018 Elsevier B.V. Tungsten fuzz is a nanostructure formed on tungsten surface under helium plasma impact. In this work, we investigate this structure using the scattering of keV-energy protons. Energy spectra of scattered protons have double-peak shape that corresponds to the scattering from fuzz and underlying pure tungsten. The energy losses of protons in fuzz are estimated as the difference between primary beam energy and the energy corresponding to the local minimum between two peaks. Computer simulations with SRIM code also demonstrate double-peak shape of energy spectra of protons scattered from fuzzy target. Fuzz and pure tungsten stopping powers for protons are compared and fuzz density relative to pure tungsten is estimated and discussed. Evolution of H+energy spectra during fuzz irradiation by Ar+beam is measured and discussed.

DOI： 10.1016/j.nimb.2018.07.038

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Fusion Engineering and Design  

DOI： 10.1016/j.fusengdes.2018.04.104

Web of Science

Scopus

担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Plasma Physics and Controlled Fusion  

DOI： 10.1088/1361-6587/aae2d7

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Nuclear Fusion  

DOI： 10.1088/1741-4326/aad24e

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

© 2018 Wiley-VCH Verlag GmbH &amp; Co. KGaA, Weinheim Fiberform nanostructured niobium (Nb) was fabricated by one step helium (He) plasma irradiation. He ion implantation formed He nano-bubbles on a Nb plate and led to formation of protrusions while migrating in Nb matrix; fiberform nanostructures (FN) were grown when the fluence became high (&gt;1026 m−2). The necessary conditions for the formation of Nb FN were revealed to be the surface temperature range of 900–1100 K and the incident ion energy higher than 70 eV. The sample was oxidized at 573–773 K in an air atmosphere, and Pt nanoparticles were photo-deposited on the Nb2O5 samples. The surface was analyzed by scanning electron microscope, transmission electron microscope, x-ray photoelectron spectroscopy, and ultraviolet-visible spectrophotometry. Photocatalytic activity of the fabricated materials was studied using methylene blue (MB) decolorization process. An enhanced photocatalytic performance was identified on FN Nb2O5 substrate with Pt deposition.

DOI： 10.1002/cphc.201800769

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Nuclear Fusion  

DOI： 10.1088/1741-4326/aacd1f

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Plasma and Fusion Research  

DOI： 10.1585/pfr.13.1201099

Web of Science

Scopus

担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IEEE Transactions on Plasma Science  

IEEE Experimental data on the effect of the thickness of a nanostructured layer present on the surface of a tungsten cathode on its arcing properties have been analyzed. It has been shown that if the nanostructured layer is not completely destroyed as a result of the operation of a cathode spot cell, the spot ``sinks&#039;&#039; in the layer, the spot cells group together, and the trajectory of the spot motion becomes ``entangled.&#039;&#039; To interpret the experimental results, the grouping of arc spot cells was simulated using a random walk model based on the Monte Carlo method into which an attractive force was introduced and assuming that the cell plasma density, i.e., the cell initiation probability, is proportional to 1/r&amp;#x00B2;, where r is the distance between two spot cells. It has been demonstrated that spot cells are entangled, forming a group and moving together when the attractive force between them is strong enough. When this force decreases and the directionality of the cells increases as the cathode spot shifts to a lower thickness region of the nanostructured layer, the velocity of motion of the spot increases and its trace left on the surface becomes narrower.

DOI： 10.1109/TPS.2018.2859953

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER INST PHYSICS  

DOI： 10.1063/1.5040800

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

DOI： 10.1088/1361-6587/aac0d8

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Contributions to Plasma Physics  

DOI： 10.1002/ctpp.201700157

Web of Science

Scopus

担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physics of Plasmas  

DOI： 10.1063/1.5029414

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Plasma and Fusion Research  

DOI： 10.1585/pfr.13.3406065

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Plasma and Fusion Research  

DOI： 10.1585/pfr.13.1402033

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Physics D: Applied Physics  

DOI： 10.1088/1361-6463/aabe44

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Surface and Coatings Technology  

DOI： 10.1016/j.surfcoat.2018.02.026

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Plasma and Fusion Research  

DOI： 10.1585/pfr.13.1205001

Web of Science

Scopus

担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AIP Advances  

DOI： 10.1063/1.4997840

Web of Science

Scopus

記述言語：日本語   出版者・発行元：Plasma Physics and Controlled Fusion  

The stability with respect to a peelingballooning mode (PBM) was investigated numerically with extended MHD simulation codes in JET, JT-60U and future JT-60SA plasmas. The MINERVA-DI code was used to analyze the linear stability, including the effects of rotation and ion diamagnetic drift (w∗i), in JET-ILW and JT-60SA plasmas, and the JOREK code was used to simulate nonlinear dynamics with rotation, viscosity and resistivity in JT-60U plasmas. It was validated quantitatively that the ELM trigger condition in JET-ILW plasmas can be reasonably explained by taking into account both the rotation and w∗i effects in the numerical analysis. When deuterium poloidal rotation is evaluated based on neoclassical theory, an increase in the effective charge of plasma destabilizes the PBM because of an acceleration of rotation and a decrease in w∗i. The difference in the amount of ELM energy loss in JT-60U plasmas rotating in opposite directions was reproduced qualitatively with JOREK. By comparing the ELM affected areas with linear eigenfunctions, it was confirmed that the difference in the linear stability property, due not to the rotation direction but to the plasma density profile, is thought to be responsible for changing the ELM energy loss just after the ELM crash. A predictive study to determine the pedestal profiles in JT-60SA was performed by updating the EPED1 model to include the rotation and w∗i effects in the PBM stability analysis. It was shown that the plasma rotation predicted with the neoclassical toroidal viscosity degrades the pedestal performance by about 10% by destabilizing the PBM, but the pressure pedestal height will be high enough to achieve the target parameters required for the ITER-like shape inductive scenario in JT-60SA.

DOI： 10.1088/1361-6587/aa8bec

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Nature Publishing Group  

Helium plasma irradiation on metal surfaces leads to the formation of metallic fuzzy nanostructures accompanied by the growth of helium bubbles in metals. The mechanism of the growth process, its impact for fusion devices, and potential application have been explored. Here we show enhanced growth of large-scale fuzz by precipitating additional metallic particles during helium plasma irradiation. The growth rate of the fuzzy structures became orders of magnitude greater than conventional fuzz growth
in an hour of irradiation, 1 mm-thick visible tungsten and molybdenum fuzzy fur structures covered a tungsten metal substrate. Additional precipitation of metallic ions breaks the bottleneck diffusion process
moreover, further acceleration in the growth rate could have occurred if the electric sheath shape was influenced by the grown structure and the electric field that formed around the structure started collecting ions.

DOI： 10.1038/s41598-017-18476-7

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Plasma and Fusion Research  

DOI： 10.1585/pfr.13.3406074

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Nuclear Fusion  

This paper describes the recent progress in divertor simulation research using the GAMMA 10/PDX tandem mirror towards the development of divertors in fusion reactors. During a plasma flow generation experiment in the end cell of the GAMMA 10/PDX, ICRF heating in the anchor cell successfully extended the particle flux up to 3.3 1023 m2 s-1. Superimposing the short pulse of the ECH also attained a maximum heat flux of ∼30 MW m-2. We have succeeded in achieving and characterizing the detachment of the high-temperature plasma, which is equivalent to the SOL plasma of tokamaks, by using the divertor simulation experimental module (D-module) in the GAMMA 10/PDX end cell, in spite of using a linear device with a short magnetic field line connection length. Various gases (Ar, Xe, Ne and N2) are examined to evaluate the effect of radiation cooling against the plasma flow at the MW m-2 level in the divertor simulation region and the following results are obtained: (i) Xe gas was most effective in the reduction of heat and particle fluxes (1%, 3%, respectively) and has a stronger effect on electron cooling (down to ∼1.6 eV) in the used gas species. (ii) Ne gas was less effective. On the other hand, (iii) N2 gas showed more favorable effects than Ar in the lower pressure range. These results will contribute to the progress in detached plasma operation and in clarifying the radiation cooling mechanism towards the development of future divertors.

DOI： 10.1088/1741-4326/aa7cb4

Web of Science

Scopus

担当区分：筆頭著者   記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：社団法人 プラズマ・核融合学会  

<p>We have developed a compact divertor plasma simulator (CDPS) that can produce steady-state deuterium and/or helium plasmas with densities above ∼ 10¹⁸m⁻³for Plasma-Wall Interaction (PWI) studies of neutronirradiated materials. The maximum particle flux is about 10²²m⁻²s⁻¹. The CDPS was installed and is being operated in the radiation-controlled area of the International Research Center for Nuclear Materials Science, Institute for Materials Research, Tohoku University. We are able to control sample temperature within uncertainty of 5^◦C during plasma exposure by adjusting the cooling air flow rate to the sample holder. The CDPS has a sample-carrier system, which makes it possible to transfer a plasma-irradiated sample from the sample holder to an infrared heater for analysis using thermal desorption spectroscopy (TDS) without exposing it to the air. This avoids the oxidation of the sample and minimizes the time between the end of plasma exposure and TDS analysis. An ITER-like tungsten (W) sample (A.L.M.T. Corp.), which has been irradiated by neutrons to 0.06 dpa in a fission reactor, was exposed to a deuterium plasma in the CDPS. The experimental results clearly show that the total deuterium retention in the neutron-irradiated W sample increases significantly in comparison with a pristine W, as demonstrated by broadening of the TDS spectrum at high temperatures.</p>

DOI： 10.1585/pfr.12.1405040

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/1741-4326/aa867a

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Nuclear Fusion  

DOI： 10.1088/1741-4326/aa7fc2

Web of Science

Scopus

担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Nuclear Materials and Energy  

DOI： 10.1016/j.nme.2017.03.004

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Elsevier Ltd  

W samples were exposed to He plasma in the MAGPIE, NAGDIS-II and PISCES-A across a range of sample temperatures between 473–1123 K. GISAXS was used to quantify the effect of plasma fluence and W surface temperature on He nano-bubble size distributions. In NAGDIS-II at 873 K nano-bubbles are exponentially distributed with mean diameters μ=0.64±0.01nm, similar to the value of μ=0.62±0.01nmfound for the MAGPIE plasma device at the much lower temperature of 473 K. Above ∼900 K nano-bubbles followed an approximately exponential distribution with μ &gt
0.72 nm demonstrating a significant increase in nano-bubble sizes at higher temperatures.

DOI： 10.1016/j.nme.2016.11.025

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Nuclear Materials and Energy  

DOI： 10.1016/j.nme.2016.12.017

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Nuclear Materials and Energy  

DOI： 10.1016/j.nme.2017.02.025

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Nuclear Materials and Energy  

DOI： 10.1016/j.nme.2016.12.020

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Nuclear Materials and Energy  

DOI： 10.1016/j.nme.2017.05.001

Web of Science

Scopus

担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physics Letters, Section A: General, Atomic and Solid State Physics  

DOI： 10.1016/j.physleta.2017.05.028

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IEEE Transactions on Plasma Science  

DOI： 10.1109/TPS.2017.2679211

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1063/1.4990077

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1063/1.4986100

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Nuclear Fusion  

The JT-60SA project has been implemented for the purpose of an early realization of fusion energy. With a powerful and versatile NBI and ECRF system, a flexible plasma-shaping capability, and various kinds of in-vessel coils to suppress MHD instabilities, JT-60SA plays an essential role in addressing the key physics and engineering issues of ITER and DEMO. It aims to achieve the long sustainment of high integrated performance plasmas under the high β N condition required in DEMO. The fabrication and installation of components and systems of JT-60SA procured by the EU and Japan are steadily progressing. The installation of toroidal field (TF) coils around the vacuum vessel started in December 2016. The commissioning of the cryogenic system and power supply system has been implemented in the Naka site, and JT-60SA will start operation in 2019. The JT-60SA research plan covers a wide area of issues in ITER and DEMO relevant operation regimes, and has been regularly updated on the basis of intensive discussion among European and Japanese researchers.

DOI： 10.1088/1741-4326/aa5d01

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1585/pfr.12.1202027

Web of Science

担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/1741-4326/aa6dce

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

© 2017 IAEA, Vienna. The synergistic effects of steady-state and pulsed plasma irradiation to material have been investigated in the device NAGDIS-PG (Nagoya DIvertor Simulator with Plasma Gun). The duration of the pulsed plasma was ∼0.25 ms. To investigate the pulsed plasma heat load on the materials, we developed a temperature measurement system using radiation from the sample in a high time resolution. The heat deposited in response to the transient plasma on a tungsten surface was revealed by using this system. When the nanostructures were formed by helium plasma irradiation, the temperature increase on the bulk sample was enhanced. The result suggested that the amount of absorbed energy on the surface was increased by the formation of nanostructures. The possible mechanisms causing the phenomena are discussed with the calculation of a sample temperature in response to the transient heat load.

DOI： 10.1088/1741-4326/aa67ad

Web of Science

Scopus

担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.7567/JJAP.56.030303

Web of Science

Scopus

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/1361-6587/aa5394

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1585/pfr.12.1202007

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/ctpp.201500142

Web of Science

担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1585/pfr.11.1206125

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1038/srep30380

記述言語：英語   掲載種別：研究論文（学術雑誌）  

担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.7567/JJAP.55.056203

担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Nuclear Fusion  

DOI： 10.1088/0029-5515/56/4/046002

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1585/pfr.11.1202005

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1063/1.4940310

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

Web of Science

担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1585/pfr.10.1402083

担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms  

DOI： 10.1016/j.nimb.2015.07.035

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   出版者・発行元：Nuclear Fusion  

© 2015 IAEA, Vienna. This paper assesses the three-dimensional (3D) effects of the edge magnetic field structure on divertor/scrape-off layer transport, based on an inter-machine comparison of experimental data and on the recent progress of 3D edge transport simulation. The 3D effects are elucidated as a consequence of competition between transports parallel () and perpendicular () to the magnetic field, in open field lines cut by divertor plates, or in magnetic islands. The competition has strong impacts on divertor functions, such as determination of the divertor density regime, impurity screening and detachment control. The effects of magnetic perturbation on the edge electric field and turbulent transport are also discussed. Parameterization to measure the 3D effects on the edge transport is attempted for the individual divertor functions. Based on the suggested key parameters, an operation domain of the 3D divertor configuration is discussed for future devices.

DOI： 10.1088/0029-5515/55/10/104021

Scopus

担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/0031-8949/90/9/095604

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/0029-5515/55/8/083016

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/0029-5515/55/10/104018

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/0029-5515/55/7/073013

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j/jnucmat.2015.01.036

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1038/ncomms6816

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.jnucmat.2015.01.018

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.jnucmat.2015.01.068

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.jnucmat.2014.12.018

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.jnucmat.2014.12.011

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1063/1.4904917

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1585/pfr.9.3405136

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1063/1.4895718

担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1380/ejssnt.2014.343

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Contributions to Plasma Physics  

DOI： 10.1002/ctpp.201410074

Scopus

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physica Scripta  

DOI： 10.1088/0031-8949/89/02/025602

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Results in Physics  

DOI： 10.1016/j.rinp.2014.03.001

Web of Science

Scopus

担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.7567/JJAP.52.11NC02

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Fusion Engineering and Design  

DOI： 10.1016/j.fusengdes.2013.05.014

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Nuclear Fusion  

The JT-60SA project implemented by Japan and Europe is progressing on schedule towards the first plasma in March 2019. After careful R&D, procurements of the major components have entered their manufacturing stages. In parallel, disassembly of JT-60U has been completed on time, and the JT-60SA tokamak assembly is expected to start in January 2013. The JT-60SA device, a highly shaped large superconducting tokamak with a variety of plasma control actuators, has been designed in order to contribute to ITER and to complement ITER in all the major areas of fusion plasma development necessary to decide DEMO reactor construction. Detailed assessments and prediction studies of the JT-60SA plasma regimes have confirmed these capabilities: using ITER- and DEMO-relevant plasma regimes, heating conditions, and its sufficiently long discharge duration, JT-60SA enables studies on magnetohydrodynamic stability at high beta, heat/particle/momentum transport, high-energy ion physics, pedestal physics including edge localized mode control, and divertor physics. By integrating these studies, the project provides 'simultaneous and steady-state sustainment of the key performance characteristics required for DEMO' with integrated control scenario development.

DOI： 10.1088/0029-5515/53/10/104010

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Nuclear Fusion  

It is found that resonant magnetic perturbation (RMP) fields have a stabilizing effect on the radiating edge plasma, realizing stable sustainment of radiative divertor (RD) operation in the Large Helical Device (LHD). Without RMP, thermal instability leads to radiative collapse. Divertor power load is reduced by a factor of 3-10 during the RMP-assisted RD phase, while maintaining relatively good core plasma confinement with confinement enhancement factor . It has also been demonstrated that the RMP field itself can initiate transition to RD operation by increasing perturbation strength, while keeping constant density and injection power. The results show a possibility of a new control knob for divertor power load in a 3D magnetic field configuration. It is also found that after the transition to RD, the energy confinement enhancement factor based on ISS04 scaling increases by a factor of 1.4 compared with the attached phase. The operation range of the RMP-assisted RD is identified in terms of RMP strength and radial location of the resonance layer of the RMP. A 3D edge radiation structure is analysed using the edge transport code EMC3-EIRENE and the results are compared with experiments. The comparison indicates that the application of RMP modulates the 3D edge radiation structure such that an intense radiation appears around the X-point of the m/n = 1/1 island in the case with RMP, while it is located at the inboard side without RMP. © 2013 IAEA, Vienna.

DOI： 10.1088/0029-5515/53/9/093032

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Nuclear Materials  

Be-seeded, high-flux, deuterium/helium mixture plasma exposure experiments on tungsten target materials have been performed to simulate ITER all tungsten divertor erosion/modification and deposition phenomena. The exposure conditions are kept fixed at a typical low-ion-energy of 60 eV and a flux of 3-6 × 1022/m2/s. Sample temperature is 1123 K and plasma exposure times spanning 1050-10,100 s are explored. The typical ratio of He/D ions is 0.2 and Be content is 0.2%. A He-induced nanostructure layer is formed on the exposure surfaces of tungsten materials and the surface of the nanostructure is covered by a thin layer of Be and O. A fraction of the re-eroded Be from the target is deposited on a glassy carbon plate with line of sight to the tungsten target. Rutherford backscattering spectrometry analyses show that the Be redeposit layer is in the form of laminae. Small amounts of Mo, W and C are also found in the redeposited Be layer. Elastic recoil detection analyses show that D, He and H are also included in the redeposited Be layer. © 2013 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jnucmat.2013.05.006

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/0029-5515/53/5/053013

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： doi.org/10.1063/1.4798597

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Contributions to Plasma Physics  

In this study, in order to clarify the influence of a probe electrode during probe measurements of an atmospheric pressure microwave plasma, simultaneous observations of probe current and the change of plasma shape using a high-speed camera have been done. Fast and random repetitions of attachment and detachment of the plasma torch to the probe electrode have been observed. It is found that the response time is related to ion sound speed. Different behaviors of the plasma torch for a floating metal electrode or an insulator have been observed. Probe current-voltage characteristics show asymmetric double probe shape © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

DOI： 10.1002/ctpp.201310014

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：プラズマ・核融合学会  

Sustaining a detached plasma is important for the reduction of the heat load on a divertor. The externally controlled methods such as gas puffing in the divertor region, etc. have been studied for maintaining detached plasmas. In the recent LHD experiments, a resonant magnetic perturbation (RMP) is utilized to establish the detached plasma, which is one of the candidates to reduce the divertor heat load. The finite plasma response field has been detected when the RMP is imposed, and its behavior is investigated from the viewpoint of the magnetic island dynamics. A parameter of the phase difference, Δ<i>θ</i> (defined as the phase difference between the plasma response field and the RMP), changes from antiphase to in-phase while the plasma transits from the attached to the detached states. Finally, when the Δ<i>θ</i> reaches at certain critical value, Δ<i>θ</i>_crit, the plasma enters the detached state. Since this critical value does not have a dependency on plasma beta and collisionality, Δ<i>θ</i>_critseems to be a threshold to establish the detached plasma. From the viewpoint of magnetic island dynamics, the behavior of Δ<i>θ</i> approaching in-phase implies the "trend" of island growth. The detached plasma might be established in the case of the tendency for the plasma response field to reinforce the island width.

DOI： 10.1585/pfr.8.1402058

担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Nuclear Materials  

The physical properties of tungsten with nanostructure on its surface are investigated focusing on the thermal radiation and cooling characteristics. First, direct evidence of substantial W surface cooling has been clearly shown with use of a very thin thermocouple inserted into W target, which solves an uncertainty associated with a radiation thermometer. Second, the above measurements of W surface temperature make it possible to estimate quantitatively the total emissivity from which we may evaluate the radiative power through the Stefan-Boltzmann equation, which is very important for mitigation evaluation of a serious plasma heat load to the plasma-facing component. © 2013 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jnucmat.2013.01.176

Scopus

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：39th EPS Conference on Plasma Physics 2012, EPS 2012 and the 16th International Congress on Plasma Physics  

In summary, we proposed saddle shaped stellarator system for vertical mode in toka-mak. These preliminary results demonstrate the feasibility of vertical stability, even if only two selected coils which are localized at one side of the torus. However as noted earlier, the experiment were conducted with the circular cross-section tokamak which is stable vertically. Further work is needed to confirm the improvement in the vertical stability in elongated tokamaks. In addition, very large coil current comparable to the plasma current are needed in our system. In order to reduce the current, future work also should focus on optimal configuration of the coils.

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1585/pfr.7.1402152

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1585/pfr.7.2405121

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/0741-3335/54/10/105015

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1585/pfr.7.1405100

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/ctpp.201210027

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1585/pfr.7.1202049

担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.cap.2012.04.024

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1585/pfr.7.1201033

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/0741-3335/54/3/035009

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.jnucmat.2011.11.044

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1143/JJAP.51.01AB03

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1143/JJAP.51.01AJ03

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We have measured ion temperature as well as electron temperature in plasma blobs observed in a linear plasma device by using an improved ion sensitive probe. Current-voltage characteristics of the ion sensitive probe inside and outside plasma blobs were re-constructed with a conditional sampling method. It is clearly found that both ion and electron temperatures in plasma blobs decrease more slowly in a cross-field direction than those in a bulk plasma without plasma blobs. © 2012 American Institute of Physics.

DOI： 10.1063/1.3681778

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：38th EPS Conference on Plasma Physics 2011, EPS 2011 - Europhysics Conference Abstracts  

The validation of current decay model during the current quench was investigated in high (3p disruptive discharges on JT-60U. It is experimentally confirmed that the electron temperature does not play an important role in the determination of the current decay time in the initial phase of current quench and that values obtained from L/R model are two orders of magnitude larger than the experimental current decay time. The current decay time predicted by the modified L/R model, in which the time derivative of plasma inductance is taken into account, is in fairly good agreement with the experimental data. In future work, we need to perform the MHD equilibrium code for free-boundary condition such as DINA [5] and TSC [6] code under the axisymmetric assumption in order to clear up the determination mechanism of time derivative of plasma inductance.

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physica Scripta T  

The status of ongoing research projects of tungsten R&D in Japan is summarized in this paper. For tungsten material development, a new improved fabrication technique, the so-called superplasticity-based microstructural modification, is described. This technique successfully improved fracture strength and ductility at room temperature. Recent results on vacuum plasma spray W coating and W brazing on ferritic steels and vanadium alloys are explained. Feasibility of these techniques for the manufacture of the blanket is successfully demonstrated. The latest findings on the effect of neutron damage in tungsten on T retention and on the change in mechanical and electrical properties are described. Retention characteristics for neutron-damaged W were different compared to those for ion-damaged W. Upon neutron irradiation, tungsten alloys containing transmutation elements of W (Re and Os) show changes in properties that are different compared with those shown by pure W. The effects of mixed plasma exposure (D/He/C) are described. Both D/He and D/C mixed ion irradiations significantly affect ion-driven permeation in W. He bubble dynamics play a key role in nano-structure formation on the W surface. © 2011 The Royal Swedish Academy of Sciences.

DOI： 10.1088/0031-8949/2011/T145/014029

Scopus