記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1103/PhysRevLett.116.015002

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1585/pfr.3.031

その他リンク： http://www.jspf.or.jp/PFR/PFR_articles/pfr2008/pfr2008_03-031.html

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The characteristics of geodesic–acoustic-mode (GAM) are investigated through direct and simultaneous measurement of electrostatic and density fluctuations with a heavy ion beam probe. The amplitude of the GAM changes in relation to the radial position; it is small near the separatrix, reaches a local maximum at 3 cm inside the separatrix and then decreases again to 5 cm inside the separatrix. The frequency is constant in the range, though the predicted GAM frequency varies according to the temperature gradient. The correlation length is about 6 cm and comparable to the structure of the amplitude of the GAM. The results indicate the GAM has a radial structure which reflects the local condition at about 3 m inside the separatrix. The phase relation between the GAM oscillation indicates that the GAM is a radial propagating wave.
The interaction between the GAM and the ambient density fluctuation is shown by the high coherence between the GAM oscillation and the temporal behaviour of the ambient density fluctuation. Moreover, the phase relation between the electric field fluctuation of the GAM (E˜r,GAM) and the amplitude of the density fluctuation indicates that the modulation of the ambient density fluctuation delays the E˜r,GAM. The causality between the GAM and the modulation of the density fluctuation is revealed.

DOI： 10.1088/0741-3335/48/4/S04

その他リンク： https://iopscience.iop.org/article/10.1088/0741-3335/48/4/S04

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The electrostatic and density fluctuation are measured simultaneously with a heavy ion beam probe. The electrostatic fluctuation with the geodesic acoustic mode (GAM) frequency is observed in L-mode plasmas and not in H-mode plasmas. The poloidal and radial structure is consistent with the GAM. So the fluctuation is concluded to be the GAM. The amplitude of the GAM changes in the radial direction; it is small near the separatrix, has a maximum at 3 cm inside the separatrix and decreases again to 5 cm inside the separatrix. The GAM and the temporal behaviour of the ambient density fluctuation show a significant coherence, and the phase of modulation of the ambient density fluctuation tends to delay the potential oscillation of the GAM. It is clearly verified that the GAM affects ambient fluctuation and also the local particle transport through modulation of the amplitude of the ambient fluctuation.

DOI： 10.1088/0029-5515/46/5/003

その他リンク： https://iopscience.iop.org/article/10.1088/0029-5515/46/5/003

出版者・発行元：Nuclear Fusion  

Recently, experiments on basic plasma physics issues for solving future problems in fusion energy have been performed on a Large Helical Device. There are several problems to be solved in future devices for fusion energy. Emerging issues in burning plasma are: alpha-channeling (ion heating by alpha particles), turbulence and transport in electron dominant heating helium ash exhaust, reduction of the divertor heat load. To solve these problems, understanding the basic plasma physics of (1) wave-particle interaction through (inverse) Landau damping, (2) characteristics of electron-scale (high-k) turbulence, (3) ion mixing and the isotope effect, and (4) turbulence spreading and detachment, is necessary. This overview discusses the experimental studies on these issues and turbulent transport in multi-ion plasma and other issues in the appendix.

DOI： 10.1088/1741-4326/ad3a7a

Web of Science

Scopus

出版者・発行元：Plasma Physics and Controlled Fusion  

A comparative investigation was conducted to assess the impact of high-field side (HFS) extraordinary (X) mode (HFS X) injection and low-field side (LFS) ordinary (O) mode (LFS O) injection of 8.2 GHz radio frequency (RF) power in the Q-shu University experimental steady-state spherical tokamak. In the case of the HFS X injection, the ratio of electron plasma frequency and RF frequency f pe / f RF was 1.3, indicating an overdense plasma, whereas in the LFS O injection, this ratio was 0.9. Distinctive features emerged in the electron temperature and density profiles between the two injection scenarios. In the HFS X injection, the profiles peaked between the fundamental electron cyclotron resonance (ECR) layer and the upper hybrid resonance layer. Conversely, in the LFS O injection, the peaks were situated near the 1st ECR layer. This implies effective excitation of the electron Bernstein wave (EBW) in the case of the HFS X injection, with the wave power being absorbed through the doppler-shifted ECR of the EBW. Density and temperature oscillations were observed only in the start-up phase of the HFS X injection, which may correlate with the presence of the left-hand cutoff of the X-mode. These findings will be contributed to understand the distinctive characteristics associated with plasma heating through EBW excitation in the HFS X injection.

DOI： 10.1088/1361-6587/ad802e

Web of Science

Scopus

出版者・発行元：Nuclear Fusion  

The plasma current start-up experiment is conducted through electron cyclotron (EC) heating in the QUEST spherical tokamak. During the EC heating, the application of a toroidal electric field in the opposite direction to the plasma current effectively inhibits the growth of energetic electrons. Observations show rapid increases in plasma current and hard x-ray count immediately following the cancellation of the retarding electric field. When a compact tokamak configuration maintains equilibrium on the high field side, along with the retarding field, it leads to effective bulk electron heating. This heating achieved an electron temperature of Te ≈ 1 keV at electron density ne > 1.0 × 1018 m−3. Ray tracing of the EC wave verifies that more power absorption into plasma through a single-pass occurs around the second resonance layer with higher values of electron density and temperature.

DOI： 10.1088/1741-4326/ad6914

Web of Science

Scopus

出版者・発行元：Nuclear Fusion  

Electron cyclotron wall conditioning with neon gas (Ne-ECWC) has been performed on the normal conducting spherial tokamak QUEST with metal walls under a trapped particle configuration with O-mode EC waves including X-mode polarization with a frequency of 8.2 GHz and an injection power of 16 kW. The Ne-ECWC removes hydrogen from the wall with small neon retention. The Ne-ECWC decreases hydrogen recycling at the following tokamak discharges, contributing to an improvement of the following tokamak plasma start-up: the plasma current increases and the start-up timing of the plasma current shifts forward. However, defects such as voids and bubbles are formed on tungsten surface exposed to the Ne-ECWC plasma.

DOI： 10.1088/1741-4326/ad3d6e

Web of Science

Scopus

記述言語：英語   出版者・発行元：Transdisciplinary Research and Education Center for Green Technologies, Kyushu University  

During the early phase of tokamak plasma start-up prior to the formation of a closed magnetic surface, various plasma current profiles are expected to be observed. Especially, the noninductive current drive (CD) by the electron Bernstein wave (EBW) is likely to be the most dominant, and the current profile is expected to focus on a local area predicted by the theoretical model. In addition, the EBWCD direction could be affected by a horizontal magnetic field induced by a toroidal magnetic field coil and feed-through. The magnetic flux data cannot be fitted by using a previous model described by Yoshinaga23), and hence, this model needs improvement. Consequently, an improved model is introduced in this paper based on the theoretical prediction of EBWCD. This model can be applied to reproduce the complex plasma current profile accurately during the early phase of the tokamak plasma start-up.

DOI： 10.5109/7183306

CiNii Research

出版者・発行元：Physics of Plasmas  

Electron and impurity ion density profiles have been controlled by using tangential and perpendicular neutral beams for plasma heating in a stellarator/heliotron for the first time. Reduced anisotropy of stored energy for energetic ion En⊥/Enǁ has resulted in an inward electron and impurity transport, forming a core electron density peaking. Increased anisotropy leads to a flat or hollowed electron density profile with an impurity exhaust in a core region [Yoshinuma et al., Nucl. Fusion 49, 062002 (2009)]. A high confinement state of particles in LHD has yet to be achieved, except for a temporal state of an electron density peaking created by a pellet injection. As a pioneering and crucial research result, the operation of energetic ion anisotropy by neutral beams has newly demonstrated that the direction of the radial transport of bulk and impurity ions can be controlled. At the same time, the overall plasma performance rises in neutron flux and stored energy. On the other hand, the increase in the anisotropy flattens the density profile. This new finding holds promise for a control knob of nuclear fusion reactors to enhance fusion power output.

DOI： 10.1063/5.0201440

Web of Science

Scopus

記述言語：英語   出版者・発行元：Scientific Reports  

A symmetry-breaking in rotational spatial pattern of quasi-periodic solitary oscillations is revealed with tomography measurement of plasma emission, simultaneously with background asymmetry in stationary plasma structure. Although the oscillatory pattern deformation is a natural course in the presence of asymmetry, elaborate analyses identify existence unfeatured nonlinear effects of the background asymmetry, i.e., its nonlinear couplings with harmonic modes of rotational symmetry, to produce non-harmonic mode to break the symmetry and cause the oscillatory pattern to be chaotic. The findings suggest the unrecognized fundamental process for plasmas to be turbulent.

DOI： 10.1038/s41598-024-62969-1

Web of Science

Scopus

PubMed

出版者・発行元：Plasma Physics and Controlled Fusion  

The electron temperature and density profiles in the midplane of a spherical tokamak plasma produced by electron cyclotron heating (ECH) in Q-shu University experiment with steady-state spherical tokamak (QUEST) are measured by the helium line intensity ratio method. The measured profiles are compared with those obtained by the Thomson scattering method, and the measured temperatures and densities are found to agree within factors of ∼2 and ∼6, respectively. Taken together with the previous results of comparisons performed in the scrape-off layers of several toroidal devices, the same degree of agreement between the helium line intensity ratio method and other methods is obtained in the ranges of 7-100 eV for temperature and 4 × 1016-1 × 1019 m−3 for density.

DOI： 10.1088/1361-6587/ad2c2a

Web of Science

Scopus

記述言語：英語   出版者・発行元：一般社団法人 プラズマ・核融合学会  

A new method is proposed to analyze plasma image of tomography using modified Fourier-Bessel Functions (FBF) instead of the original FBF analysis. The application of the method to an assumed plasma image shows that the difference between the original and the fitting image is improved considerably to that of FBF, owing to giving a better fitting inside the plasma and eliminating the ghost values outside the plasma, without any disadvantages in analysis of plasma structures and patterns.

DOI： 10.1585/pfr.19.1201014

Web of Science

Scopus

CiNii Research

出版者・発行元：Nuclear Fusion  

Results from the successful solenoid-free plasma startup using the method of transient coaxial helicity injection (transient CHI) in the QUEST spherical tokamak (ST) are reported. Unlike previous applications of CHI on HIT-II and on NSTX which required two toroidal insulating breaks to the vacuum vessel, QUEST uses a first of its kind, floating single biased electrode configuration, which does not use such a vacuum break. Instead, the CHI electrode is simply insulated from the outer lower divertor plate support structure. This configuration is much more suitable for implementation in a fusion reactor than the previous configurations. Transient CHI generated toroidal currents of 135 kA were obtained. The toroidal current during the formation of a closed flux configuration was over 50 kA. These results bode well for the application of transient CHI in a new generation of compact high-field STs and tokamaks in which the space for the central solenoid is very restricted.

DOI： 10.1088/1741-4326/ad0dd6

Web of Science

Scopus

出版者・発行元：Nuclear Fusion  

A novel divertor biasing by four biasing plates distributed toroidally (TDDB) on the upper divertor target plate is applied to low density tokamak plasmas started-up by 28 GHz 2nd harmonic electron cyclotron current drive (ECCD) in a quasi-double null configuration of the QUEST spherical tokamak (ST). In the ST plasmas of line averaged electron density < n e > ∼0.7-1 × 1018 m−3, about 20%-40% of the current I bias driven by ∼85 V sawtooth bias voltage reaches the lower divertor plate along the biased scrape-off-layer (SOL) flux tube as the SOL current I SOL . The fact I SOL is noticeably lower than I bias indicates an appreciable leakage of parallel current from the biased SOL flux tube. The leakage currents in the toroidal and radial directions are confirmed by detection of them using the unbiased plates in the TDDB experiments. From the ion saturation current density profile obtained by a divertor Langmuir probe array, the fall-off lengths of divertor particle flux are estimated together with the strike line position. Total particle flux to the upper divertor, evaluated by the integrated ion saturation current density profile is reduced by up to 45% during positive biasing of the TDDB, depending on the position of the strike line to the biased plate. In addition, the TDDB also induces a noticeable loss of fast electrons produced by ECCD, leading to an ∼2% reduction in the maximum toroidal current of the ST plasma compared to a shot without the TDDB. Reduction of the divertor particle flux and enhancement of the fast electron losses are thought to be dominantly caused by E × B drift induced by the TDDB. In the present experimental conditions, the effects of magnetic perturbations produced by the SOL currents on the fast electron losses can be neglected because of a too small SOL current.

DOI： 10.1088/1741-4326/acee13

Web of Science

Scopus

出版者・発行元：Journal of Applied Physics  

This article presents a method to estimate the rotational velocity of a cylindrical plasma from its two-dimensional images by an extended use of the Fourier-rectangular function transform, which was proposed to analyze the structure and dynamics of a cylindrical plasma [K. Yamasaki e t a l ., J. Appl. Phys. 126 , 043304 (2019)]. The proposed method is applied to tomography images of plasmas produced in a linear cylindrical device and succeeds in obtaining the radial distribution of rotational velocity and its fluctuations, providing an interesting finding, that is, the existence of flow modulation associated with m = 1 mode fluctuations.

DOI： 10.1063/5.0165318

Web of Science

Scopus

出版者・発行元：Nuclear Fusion  

Spatially resolved rotational temperature of ground state hydrogen molecules desorbed from plasma-facing surface was measured in QUEST, LTX-β, and DIII-D tokamaks, and the increases of the rotational temperature with the surface temperature and due to collisional-radiative processes in the plasmas were evaluated. The increase due to collisional-radiative processes was calculated by solving rate equations considering electron and proton collisional excitation and deexcitation and spontaneous emission. The calculation results suggest a high sensitivity for the rotational temperature to electron and proton densities, but a negligible sensitivity to the electron, proton, and surface temperatures. In the three tokamaks with different plasma parameters and plasma-facing surface materials, the spatial profile of the rotational temperature was estimated using Fulcher-α emission lines (600-608 nm). In QUEST, the spatial profile of the rotational temperature was estimated from spatially resolved spectra. In the other tokamaks, the rotational temperature was evaluated assuming a single point emission with a location determined from the Fulcher-α emission profile as measured with a filtered camera. In metal-walled devices QUEST and LTX-β, the rotational temperature increased with the surface temperature, and the calculated collisional-radiative increase is consistent with measured increase assuming that the rotational temperature at the surface is approximately 500-600 K higher than the surface temperature. In DIII-D with carbon walls, a larger collisional-radiative increase than the other tokamaks was observed because of the higher density leading to a large difference from the calculated increase compared to the other smaller tokamaks. Measurement of the Fulcher-α emission profile with higher spatial resolution in DIII-D may reduce the difference and reveal the effect of the surface temperature on the rotational temperature. These results show the increases in the rotational temperature with the surface temperature and due to the collisional-radiative processes.

DOI： 10.1088/1741-4326/acd4d1

Web of Science

Scopus

記述言語：英語  

Spatially resolved rotational temperature of ground state hydrogen molecules desorbed from plasma-facing surface was measured in QUEST, LTX-β, and DIII-D tokamaks, and the increases of the rotational temperature with the surface temperature and due to collisional-radiative processes in the plasmas were evaluated. The increase due to collisional-radiative processes was calculated by solving rate equations considering electron and proton collisional excitation and deexcitation and spontaneous emission. The calculation results suggest a high sensitivity for the rotational temperature to electron and proton densities, but a negligible sensitivity to the electron, proton, and surface temperatures. In the three tokamaks with different plasma parameters and plasma-facing surface materials, the spatial profile of the rotational temperature was estimated using Fulcher-α emission lines (600–608 nm). In QUEST, the spatial profile of the rotational temperature was estimated from spatially resolved spectra. In the other tokamaks, the rotational temperature was evaluated assuming a single point emission with a location determined from the Fulcher-α emission profile as measured with a filtered camera. In metal-walled devices QUEST and LTX-β, the rotational temperature increased with the surface temperature, and the calculated collisional-radiative increase is consistent with measured increase assuming that the rotational temperature at the surface is approximately 500–600 K higher than the surface temperature. In DIII-D with carbon walls, a larger collisional-radiative increase than the other tokamaks was observed because of the higher density leading to a large difference from the calculated increase compared to the other smaller tokamaks. Measurement of the Fulcher-α emission profile with higher spatial resolution in DIII-D may reduce the difference and reveal the effect of the surface temperature on the rotational temperature. These results show the increases in the rotational temperature with the surface temperature and due to the collisional-radiative processes.

CiNii Research

出版者・発行元：Fusion Engineering and Design  

Various scenarios of electron cyclotron heating can be explored in a spherical tokamak with a high toroidal field. On the QUEST spherical tokamak, doubling the toroidal field results in the emergence of the fundamental resonance layer for 28 GHz electron cyclotron waves. The second-harmonic resonance layer shifts toward the plasma central area. To increase the coil current from 50 to 100 kA, a current source is designed with 125 modules in parallel. The module power supply comprises a bank of lithium-ion capacitors and a DC–DC buck converter. In the bench test of a single module, the current was found to increase linearly and maintained the flat-top as programmed.

DOI： 10.1016/j.fusengdes.2023.113794

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.18.2402066

出版者・発行元：Fusion Engineering and Design  

Here, a versatile power supply system, consisting of two current sources, insulated-gate bipolar transistor stacks, and a capacitor bank, is proposed for application in various operations of the QUEST spherical tokamak. The central solenoid coil in this system can carrying a maximum current and voltage of ±8 kA and ±375 V, respectively. In plasma start-up experiments based on ohmic heating through double flux swing, a plasma current of over 100 kA is stably obtained. Moreover, the feedback control of the thyristor power supply is utilized to control the plasma current, plasma shape, and position. The oscillating central-solenoid current applies a bipolar loop voltage at constant time intervals, and the capacitor bank discharge facilitates a co-axial helicity injection as well as amplifies the toroidal current.

DOI： 10.1016/j.fusengdes.2023.113648

Web of Science

Scopus

出版者・発行元：Plasma Science and Technology  

A power-supply system was developed for Ohmic heating (OH) to double × 1018 the amount of change magnetic flux in the primary central solenoid (CS) on the QUEST spherical tokamak. Two power supplies are connected with stacks of insulated-gate bipolar transistors, and sequentially operated to generate positive and negative CS currents. This bipolar power-supply system is controlled via a field-programmable gate array, which guarantees the safety of the entire system operation. The new OH system, assisted by electron cyclotron heating, enables the stable generation of plasma currents exceeding 100 kA. Moreover, the achieved electron density over the wide range in the major radial direction exceeds the cut-off density for one of the high-power microwave sources in QUEST. This strategy yields target plasmas for future experiments with the electron Bernstein wave.

DOI： 10.1088/2058-6272/acafc2

Web of Science

Scopus

記述言語：英語   出版者・発行元：一般社団法人 プラズマ・核融合学会  

A design study of a line integrated Thomson scattering (TS) system with a complete backscattering configuration has been performed to clarify practical problems. Installation on the TST-2 spherical tokamak was assumed, and an optical system design with ready-made components, are adopted. Some practical aspects, such as aberration, masking effect of the laser combining mirror, misalignment are investigated by ray tracing calculations. The performance of density profile reconstruction was also investigated. It was found that a tangential-multi-chord measurement configuration on the midplane shows a good effective localization, and error enhancement in the reconstruction is small. In addition, the efficiency of the system is about an order of magnitude larger than the present conventional TS system in TST-2. The attractiveness of the line integrated TS measurements was demonstrated.

DOI： 10.1585/pfr.18.2402025

Web of Science

Scopus

CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1585/pfr.18.1305048

出版者・発行元：Fusion Engineering and Design  

An 8.56-GHz quasi-optical launcher system with incident-mode selectivity was developed for non-inductive electron cyclotron (EC) plasma ramp-up and long-pulse sustainment, and effective bulk-electron heating on the Q-shu University experiment with steady-state spherical tokamak (QUEST). A novel polarization-selective system was proposed to conduct fundamental and second harmonic EC heating and current drive experiments with ordinary and extra-ordinary mode waves, respectively. Selectivity of the incident modes or polarizations was confirmed using the whole developed system at a low power level. A large-sized mirror launcher was developed to inject the beam whose size was as small as possible near the QUEST major radius. The designed mirror performance was checked using a three-dimensional electromagnetic-wave simulator and a low-power test. Ultimately, 0.15-m sized beams for both the two polarizations were successfully attained near the QUEST major radius, even in low-frequency applications with long propagation.

DOI： 10.1016/j.fusengdes.2023.113479

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.7566/jpsj.92.033501

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1585/pfr.18.2405035

記述言語：英語   出版者・発行元：一般社団法人 プラズマ・核融合学会  

The Thomson scattering control system has been modified to measure the time evolution of the electron density and temperature profiles during long duration discharges in the QUEST spherical tokamak. The system consists of a signal generator and a control circuit. The former accepts a QUEST main trigger and provides multiple triggers, each of which starts a short-term (e.g. 15 s) measurement. The latter provides triggers to synchronize the oscilloscope and laser oscillation during a short-term measurement. The system was used in 1000 s long duration discharges in QUEST, and the temporal evolutions of density and temperature profiles were obtained successfully. It was found the profiles are stationary after about 300 s.

DOI： 10.1585/pfr.18.1405012

Web of Science

Scopus

CiNii Research

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1038/s41598-022-09526-w

出版者・発行元：Plasma Physics and Controlled Fusion  

In this paper, a phenomenology of competing behavior between the geodesic acoustic mode (GAM) and the limit-cycle oscillation (LCO) is presented. Before the LCO occurs, the GAM can grow to the observable amplitude via the turbulent Reynolds stress force. Approaching the L-H transition, the LCO is excited and the GAM decays. In the LCO phase, the GAM driving force is possibly suppressed by the nonlocal turbulence amplitude modulation by the LCO.

DOI： 10.1088/1361-6587/ac9333

Web of Science

Scopus

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1063/5.0101723

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1109/TPS.2022.3193069

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1007/s10894-022-00338-4

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1063/5.0101632

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.fusengdes.2022.113199

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  

Geodesic acoustic modes (GAMs) are ubiquitous oscillatory flow phenomena observed in toroidal magnetic confinement fusion plasmas, such as tokamaks and stellarators. They are recognized as the non-stationary branch of the turbulence driven zonal flows which play a critical regulatory role in cross-field turbulent transport. GAMs are supported by the plasma compressibility due to magnetic geodesic curvature - an intrinsic feature of any toroidal confinement device. GAMs impact the plasma confinement via velocity shearing of turbulent eddies, modulation of transport, and by providing additional routes for energy dissipation. GAMs can also be driven by energetic particles (so-called EGAMs) or even pumped by a variety of other mechanisms, both internal and external to the plasma, opening-up possibilities for plasma diagnosis and turbulence control. In recent years there have been major advances in all areas of GAM research: measurements, theory, and numerical simulations. This review assesses the status of these developments and the progress made towards a unified understanding of the GAM behaviour and its role in plasma confinement. The review begins with tutorial-like reviews of the basic concepts and theory, followed by a series of topic orientated sections covering different aspects of the GAM. The approach adopted here is to present and contrast experimental observations alongside the predictions from theory and numerical simulations. The review concludes with a comprehensive summary of the field, highlighting outstanding issues and prospects for future developments.

DOI： 10.1088/1741-4326/ac0dd1

Web of Science

Scopus

researchmap

その他リンク： https://iopscience.iop.org/article/10.1088/1741-4326/ac0dd1/pdf

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.fusengdes.2021.112845

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1038/s41598-021-83191-3

記述言語：その他  

DOI： 10.1016/j.nme.2020.100872

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.nme.2021.100905

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1063/5.0031357

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/1741-4326/ab8a04

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.7566/jpsj.89.093501

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3390/atoms8030044

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/1741-4326/ab3a13

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/1741-4326/ab26e5

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.nme.2018.10.003

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）  

DOI： 10.1063/1.5048712

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/1741-4326/aad87e

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/1741-4326/aad611

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/1741-4326/aac699

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1103/PhysRevLett.120.045002

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1038/s41598-017-14821-y

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/1741-4326/aa800a

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/1741-4326/aa7fc2

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/1741-4326/aa754b

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/1741-4326/aa5d03

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1103/PhysRevLett.118.125001

記述言語：その他   掲載種別：研究論文（学術雑誌）  

2D spatial profile measurements of potential fluctuation with heavy ion beam probe on the Large Helical Device
© 2016 Author(s).Two-dimensional spatial profiles of potential fluctuation were measured with the heavy ion beam probe (HIBP) in the Large Helical Device (LHD). For 2D spatial profile measurements, the probe beam energy has to be changed, which requires the adjustment of many deflectors in the beam transport line to optimize the beam trajectory, since the transport line of LHD-HIBP system is long. The automatic beam adjustment system was developed, which allows us to adjust the beam trajectory easily. By analyzing coherence between potential fluctuation and magnetic probe signal, the noise level of the mode power spectrum of the potential fluctuation can be reduced. By using this method, the 2D spatial profile of potential fluctuation profile was successfully obtained.

DOI： 10.1063/1.4963908

記述言語：その他   掲載種別：研究論文（学術雑誌）  

Resistive interchange mode destabilized by helically trapped energetic ions and its effects on energetic ions and bulk plasma in a helical plasma
© 2016 IAEA, Vienna. A resistive interchange mode of the structure (, : poloidal and toroidal mode numbers, respectively) with a bursting character and rapid frequency chirping in the range less than 10 kHz is observed for the first time in the edge region of the net current-free, low beta LHD (Large Helical Device) plasmas during high power injection of perpendicular neutral beams. The mode resonates with the precession motion of helically trapped energetic ions (EPs), following the resonant condition. The radial mode structure is recognized to be similar to that of the pressure-driven resistive interchange mode, of which radial displacement eigenfunction quite localizes around the mode rational surface, and evolves into an odd-type (or island-type) during the late of frequency chirping phase. This beam driven mode is excited when the beta value of helically trapped EPs exceeds a certain threshold. This instability is thought to be a new branch of resistive interchange mode destabilized by the trapped energetic ions. The radial transport, i.e. redistribution and losses, of helically trapped energetic ions induced by the mode transiently generates significant radial electric field near the plasma peripheral region. The large shear of thus generated radial electric field is thought to contribute to the observed suppression of micro-turbulence and transient increases of the temperature of fully ionized carbon impurity ions and electron density, suggesting improvement of bulk plasma confinement.

DOI： 10.1088/0029-5515/56/1/016002

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1038/srep30720

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/ctpp.201610042

記述言語：その他   掲載種別：研究論文（学術雑誌）  

Beam-driven Alfvén eigenmodes (AEs) have been studied in the TJ-II low-magnetic-shear flexible heliac (B 0 = 0.95 T, R = 1.5 m, a = 0.22 m), in L-mode hydrogen plasmas with hydrogen NBI and ECR heating (P NBI 1.0 MW, E NBI = 32 keV, P ECRH 0.6 MW). In low-density plasmas in the range = (0.3-1.5) ×1019 m-3, a large variety of AEs have been observed in the plasma core with the heavy ion beam probe diagnostic and Mirnov coils, in the frequency range 50 kHz < f AE < 380 kHz. In experiments in which the vacuum rotational transform is varied during the shot (dynamic configuration scan), some AEs exhibit changes in their nonlinear evolution from bursting-amplitude AEs with chirping frequency to steady-frequency AEs, and back. The range of intervals within which the AEs studied are chirping or steady-state is determined.

DOI： 10.1088/0029-5515/56/7/076001

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1134/S1063780X16050056

記述言語：その他   掲載種別：研究論文（学術雑誌）  

Nonlinear excitation of subcritical fast ion-driven modes
© 2016 IAEA, Vienna.In collisionless plasma, it is known that linearly stable modes can be destabilized (subcritically) by the presence of structures in phase-space. The growth of such structures is a nonlinear, kinetic mechanism, which provides a channel for free-energy extraction, different from conventional inverse Landau damping. However, such nonlinear growth requires the presence of a seed structure with a relatively large threshold in amplitude. We demonstrate that, in the presence of another, linearly unstable (supercritical) mode, wave-wave coupling can provide a seed, which can lead to subcritical instability by either one of two mechanisms. Both mechanisms hinge on a collaboration between fluid nonlinearity and kinetic nonlinearity. If collisional velocity diffusion is low enough, the seed provided by the supercritical mode overcomes the threshold for nonlinear growth of phase-space structure. Then, the supercritical mode triggers the conventional subcritical instability. If collisional velocity diffusion is too large, the seed is significantly below the threshold, but can still grow by a sustained collaboration between fluid and kinetic nonlinearities. Both of these subcritical instabilities can be triggered, even when the frequency of the supercritical mode is rapidly sweeping. These results were obtained by modeling the subcritical mode kinetically, and the impact of the supercritical mode by simple wave-wave coupling equations. This model is applied to bursty onset of geodesic acoustic modes in an LHD experiment. The model recovers several key features such as relative amplitude, timescales, and phase relations. It suggests that the strongest bursts are subcritical instabilities, with sustained collaboration between fluid and kinetic nonlinearities.

DOI： 10.1088/0029-5515/56/5/056009

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1103/PhysRevLett.116.015003

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/0741-3335/57/9/092001

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1063/1.4930130

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/0029-5515/55/11/113020

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/0029-5515/55/8/083024

その他リンク： https://iopscience.iop.org/article/10.1088/0029-5515/55/8/083024

記述言語：その他   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）  

DOI： 10.1088/0029-5515/55/6/063009

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/0029-5515/55/4/043008

記述言語：その他   掲載種別：研究論文（学術雑誌）  

Resistive interchange modes destabilized by helically trapped energetic ions in a helical plasma
© 2015 American Physical Society. A new bursting m=1/n=1 instability (m,n: poloidal and toroidal mode numbers) with rapid frequency chirping down has been observed for the first time in a helical plasma with intense perpendicular neutral beam injection. This is destabilized in the plasma peripheral region by resonant interaction between helically trapped energetic ions and the resistive interchange mode. A large radial electric field is induced near the edge due to enhanced radial transport of the trapped energetic ions by the mode, and leads to clear change in toroidal plasma flow, suppression of microturbulence, and triggering an improvement of bulk plasma confinement.

DOI： 10.1103/PhysRevLett.114.155003

記述言語：その他   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： 10.1063/1.4891975

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/0029-5515/54/7/073017

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1063/1.4884365

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1063/1.4876619

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/0029-5515/53/11/113006

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/0029-5515/53/10/104015

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1103/PhysRevLett.111.035002

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/0029-5515/52/6/063023

記述言語：その他  

Long range temperature fluctuation in LHD
We report a detailed correlation technique to identify the long-range temperature fluctuation in the Large Helical Device. Correlation hunting has successfully realized the observation of electron temperature fluctuations, which are characterized by their correlation length comparable to the plasma minor radius, with low frequency of ~ 1-3kHz, ballistic radial propagation (at a speed of ~1km/s, of the order of diamagnetic drift velocity), spatial mode number of m/n = 1/1 (or 2/1), and amplitude of ~2% at the maximum. Bicoherence analysis confirmed their nonlinear coupling with local microscopic turbulent fluctuations. This long-range temperature fluctuation is a possible carrier of fast propagation in transport processes observed so far. We also comment on the theoretical interpretation. © 2011 The Japan Society of Plasma Science and Nuclear Fusion Research.

DOI： 10.1585/pfr.6.1402017

記述言語：その他  

DOI： 10.15669/pnst.2.72

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1103/PhysRevLett.107.115001

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/0029-5515/51/8/083022

記述言語：日本語  

DOI： 10.24546/81003310

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Geodesic acoustic modes (GAM) driven by energetic particles are observed in the Large Helical Device (LHD) by a heavy ion beam probe. The GAM localizes near the magnetic axis. It is confirmed that the energetic-particle-induced GAM is accompanied by an electrostatic potential fluctuation and radial electric field fluctuation. The amplitude of the potential fluctuation is several hundred volts, and it is much larger than the potential fluctuation associated with turbulence-induced GAMs observed in the edge region in tokamak plasmas. The energetic-particle-induced GAM modulates the amplitude of the density fluctuation in a high-frequency range. The observed GAM frequency is constant at the predicted GAM frequency in plasmas with reversed magnetic shear. On the other hand, it shifts upwards from the predicted GAM frequency in plasmas with monotonic magnetic shear.

DOI： 10.1088/0029-5515/51/7/073046

その他リンク： https://iopscience.iop.org/article/10.1088/0029-5515/51/7/073046

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/0029-5515/51/3/033005

記述言語：その他   掲載種別：研究論文（学術雑誌）  

Production of Sub-MeV Positive Gold Ion Beams with Various Gas Targets to Improve the Tandem Accelerator of the LHD-HIBP

DOI： 10.1585/pfr.5.S2087

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Reversed-shear Alfvén eigenmodes were observed for the first time in a helical plasma having negative q0′′ (the curvature of the safety factor q at the zero shear layer). The frequency is swept downward and upward sequentially via the time variation in the maximum of q. The eigenmodes calculated by ideal MHD theory are consistent with the experimental data. The frequency sweeping is mainly determined by the effects of energetic ions and the bulk pressure gradient. Coupling of reversed-shear Alfvén eigenmodes with energetic ion driven geodesic acoustic modes generates a multitude of frequency-sweeping modes. © 2010 The American Physical Society.

DOI： 10.1103/PhysRevLett.105.145003

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1063/1.3491317

記述言語：英語   掲載種別：研究論文（学術雑誌）  

A heavy ion beam probe was installed on the Large Helical Device (LHD) to investigate the roles of radial electric fields (Er ) in magnetically confined high-temperature plasmas. Two new observations are presented. One is the observation of electrostatic potential profiles during the formation of extremely hollow density profiles of impurities, called the impurity hole (Ida K et al 2009 Phys. Plasmas 16 056111), in the LHD plasmas. The measured Er is negative, and the Er determined by the ambipolarity condition of neoclassical particle fluxes is consistent with this observation. However, the transport analysis indicates that the formation of the extremely hollow profile is not attributable to the impurity fluxes driven by Er and the density and temperature gradients of the impurity. The other new observation is on the geodesic acoustic mode (GAM). The electrostatic potential fluctuation associated with the GAM, which is probably induced by energetic particles, in plasmas with the reversed or weak magnetic shear is identified. The GAM is localized in the core region of the plasma.

DOI： 10.1088/0741-3335/52/12/124025

その他リンク： https://iopscience.iop.org/article/10.1088/0741-3335/52/12/124025

記述言語：日本語  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/0029-5515/50/2/025001

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/1009-0630/11/4/19

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.13182/FST10-A10829

その他リンク： https://www.tandfonline.com/doi/abs/10.13182/FST10-A10829

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Extension of Improved Particle and Energy Confinement Regime in the Core of LHD Plasma
Recent two major topics of Large Helical Device (LHD) towards fusion relevant conditions, high-density operation and high-ion-temperature operation, are reported. Super dense core plasma was obtained by the combination of repetitive hydrogen ice pellet injection and high power neutral beam injection (NBI) heating. A very peaked density profile with the highest central density of 1.1 &times; 10²¹ m^-3 was produced showing that the particle transport was suppressed very well in the plasma core. The spatial density profile varies as the position of magnetic axis (R_ax), and the steepest profile is obtained at R_ax = 3.95 m. The highest central ion temperature of 5.6 keV was obtained in hydrogen plasma at electron density of 1.6 &times; 10¹⁹ m^-3 by NBI, where a peaked ion-temperature profile with internal ion energy transport barrier was observed. The profile of electron temperature did not change much and was broad even when the ion temperature had a peaked profile. The central ion temperature is higher than the electron temperature, which is a new operation regime of LHD. High central ion temperature accompanied strong toroidal rotation and an extreme hollow profile of carbon ions (impurity hole). These steep temperature profiles were obtained so far at around R_ax = 3.6 m. The compatibility between particle and energy confinement is a new issue of LHD to explore a new operation regime for attractive fusion reactor.

DOI： 10.1585/pfr.4.027

記述言語：英語  

Measurements of spatial structure of plasma potential and density fluctuations by multichannel heavy ion beam probe on large helical device

DOI： 10.1063/1.2981177

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1063/1.2971207

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1063/1.2889012

記述言語：その他  

Status of the heavy ion beam probe system in the Large Helical Device
A heavy ion beam probe (HIBP) system has been installed into the Large Helical Device (LHD) to measure the spatial profile of the plasma potential and density fluctuations. The optimization of the HIBP system, especially the beam injector, is described. The negative ion beam is required for the MeV beam production in a tandem accelerator. A sputter-type heavy negative ion source has been developed as an intense Au- beam source to produce Au+ beams with energy in the MeV range. The extraction electrodes and the Einzel lens system of the ion source have been designed taking into account the beam optics, and installed into the real machine. Throughout the plasma diagnostics on LHD experiments, the consumptions of vaporized caesium and gold target are being characterized for practical operations. In addition, the experimental charge fractions are compared with the theoretical fractions for understanding the charge-changing behavior of Au- ions and optimizing the fraction of Au+ ions at the exit of the tandem accelerator of the HIBP system. © 2008 American Institute of Physics.

DOI： 10.1063/1.2819323

記述言語：その他  

Experimental progress on zonal flow physics in toroidal plasmas
The present status of experiments on zonal flows in magnetic confinement experiments is examined. The innovative use of traditional and modern diagnostics has revealed unambiguously the existence of zonal flows, their spatio-temporal characteristics, their relationship to turbulence and their effects on confinement. In particular, a number of observations have been accumulated on the oscillatory branch of zonal flows, named geodesic acoustic modes, suggesting the necessity for theories to give their proper description. In addition to these basic properties of zonal flows, several new methods have elucidated the processes of zonal flow generation from turbulence. Further investigation of the relationship between zonal flows and confinement is strongly encouraged as cross-device activity including low temperature, toroidal and linear devices. © 2007 IAEA.

DOI： 10.1088/0029-5515/47/10/S19

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/0741-3335/49/10/002

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1585/pfr.2.S1100

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/0741-3335/49/3/002

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1063/1.2338311

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/0741-3335/48/4/S15

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/0741-3335/48/4/S13

記述言語：その他  

Optimization of negative ion sources for a heavy-ion-beam probe
The development of plasma-sputter-type negative ion sources is underway for the heavy-ion-beam probe system as plasma diagnostic beams of the large helical device (LHD) for potential and fluctuation field measurements. Our purpose is to increase the doubly charged exchanged Au+ beam intensity to enhance the detection signal after passing through the plasmas of the LHD. For this purpose, the characterization of the Au- ion source and the beam optics has been carried out both experimentally and numerically. Based on these results, a new plasma-sputter-type negative ion source is designed and tested. © 2006 American Institute of Physics.

DOI： 10.1063/1.2170094

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.13182/FST06-A1095

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： 10.1088/0029-5515/46/2/010

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： 10.1088/0029-5515/45/2/002

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/0741-3335/45/12A/027

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1063/1.1599057

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/0741-3335/45/7/307

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1103/PhysRevLett.88.055006

その他リンク： https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.88.055006

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/0029-5515/41/8/301

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： 10.1088/0741-3335/41/8/307

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1063/1.1149474

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/0029-5515/37/1/I12

開催年月日： 2020年12月

記述言語：日本語   会議種別：口頭発表（一般）  

開催地：オンライン   国名：日本国  

開催年月日： 2019年11月 - 2019年12月

記述言語：日本語   会議種別：口頭発表（招待・特別）  

開催地：中部大学   国名：日本国  

LHDにおいてNBI時に高速イオン励起測地線音波(EGAM)がバースト的に発生する。この時、GAMの周期より十分長く、バースト継続時間より短い時間で平均した平均電位の変動が観測された。電位はプラズマ中心領域で負に、規格化小半径0.2より外では正に変動しており、中心近傍で負電場が形成されている。この電場形成は高速イオンの損失を示唆している。中心近傍においてはEGAM発生時に電位揺動及び密度揺動も減少しており、負電場形成との関連が考えられる。

開催年月日： 2019年11月

記述言語：英語   会議種別：口頭発表（一般）  

国名：中華人民共和国  

開催年月日： 2019年9月

記述言語：日本語   会議種別：口頭発表（一般）  

開催地：岐阜大学   国名：日本国  

記述言語：日本語  

国名：日本国  

記述言語：日本語  

国名：日本国  

記述言語：日本語  

国名：日本国  

記述言語：日本語  

国名：日本国  

記述言語：日本語  

国名：日本国  

記述言語：日本語  

国名：日本国  

記述言語：日本語   会議種別：口頭発表（一般）  

開催地：岩手   国名：日本国  

記述言語：日本語   会議種別：口頭発表（一般）  

開催地：岩手   国名：日本国  

記述言語：英語   会議種別：口頭発表（一般）  

国名：日本国  

種別：大会・シンポジウム等 

参加者数：550

種別：査読等 

外国語雑誌　査読論文数：5

日本語雑誌　査読論文数：0

国際会議録　査読論文数：0

国内会議録　査読論文数：0

種別：査読等 

外国語雑誌　査読論文数：3

日本語雑誌　査読論文数：0

国際会議録　査読論文数：0

国内会議録　査読論文数：0

種別：学会・研究会等