A5001485553- Magnetic confinement fusion research
- Particle accelerators and beam dynamics
- Plasma Diagnostics and Applications
- Fusion materials and technologies
- Superconducting Materials and Applications
- Ionosphere and magnetosphere dynamics
- Laser-Plasma Interactions and Diagnostics
- Particle Accelerators and Free-Electron Lasers
- Solar and Space Plasma Dynamics
- Atomic and Molecular Physics
- Gyrotron and Vacuum Electronics Research
- Mass Spectrometry Techniques and Applications
- Metal and Thin Film Mechanics
- X-ray Spectroscopy and Fluorescence Analysis
- Engineering Applied Research
- Mechanical Failure Analysis and Simulation
- Ion-surface interactions and analysis
- Nuclear Physics and Applications
- Dust and Plasma Wave Phenomena
- Physics of Superconductivity and Magnetism
- Laser-induced spectroscopy and plasma
- Nuclear reactor physics and engineering
- Advanced Radiotherapy Techniques
- Gamma-ray bursts and supernovae
- Particle Detector Development and Performance
National Institute for Fusion Science
2014-2024
National Institutes of Natural Sciences
2009-2022
The Graduate University for Advanced Studies, SOKENDAI
2000-2020
Nagoya University
2004-2020
Max Planck Institute for Plasma Physics
2011
University of Tsukuba
1997-2001
Japan Atomic Energy Agency
1989
As the finalization of a hydrogen experiment towards deuterium phase, exploration best performance plasma was intensively performed in large helical device. High ion and electron temperatures, Ti Te, more than 6 keV were simultaneously achieved by superimposing high-power cyclotron resonance heating onneutral beam injection (NBI) heated plasma. Although flattening temperature profile core region observed during discharges, one could avoid degradation increasing density. Another key parameter...
This paper reports results on the progress in steady-state high-βp ELMy H-mode discharges JT-60U. A fusion triple product, nD(0)τETi(0), of 3.1 × 1020 m−3 s keV under full non-inductive current drive has been achieved at Ip = 1.8 MA, which extends record value product by 50%. high-beta plasma with βN ∼ 2.7 sustained for 7.4 (∼60τE), duration determined only facility limits, such as capability poloidal field coils and upper limit injection neutral beams. Destabilization neoclassical tearing...
A negative-ion-based neutral beam injection (NBI) system, in which large caesium-seeded negative-ion sources are utilized, has operated reliably the Large Helical Device (LHD) since it was operational 1998. The power of hydrogen been increased up to 13.1 MW with three injectors. In one injector modified ion utilizing a multi-slotted grounded grid, reached 5.7 an energy 184 keV, exceeds designed value 180 keV and 5 MW. Individual control local arc-discharge independently divided arc filament...
Extremely hollow profiles of impurities (denoted as “impurity hole”) are observed in the plasma with a steep gradient ion temperature after formation an internal transport barrier (ITB) Large Helical Device [A. Iiyoshi et al., Nucl. Fusion 39, 1245 (1999)]. The radial profile carbon becomes during ITB phase and central density keeps dropping reaches 0.1%–0.3% at end phase. diffusion coefficient convective velocity evaluated from time evolution assuming convection constant ITB. analysis gives...
In the first four years of LHD experiment, several encouraging results have emerged, most significant which is that MHD stability and good transport are compatible in inward shifted axis configuration. The observed energy confinement at this optimal configuration consistent with ISS95 scaling an enhancement factor 1.5. over smaller heliotron devices attributed to high edge temperature. We find plasma average beta 3% stable configuration, even though theoretical conditions Mercier modes...
Recent experimental results in the Large Helical Device have indicated that a large pressure gradient can be formed beyond stability criterion for Mercier (high-n) mode. While against an interchange mode is violated inward-shifted configuration due to enhancement of magnetic hill, neoclassical transport and confinement high-energy particle are, contrast, improved by this inward shift. Mitigation unfavourable effects MHD instability has led significant extension operational regime....
High-power negative and positive ion-based neutral beam injectors (NBIs) are operated with high reliability in the Large Helical Device (LHD). The total injection power is >20 MW, such high-power beams available every 3 min. performance of LHD NBI system has extended parameter regime to levels equivalent those obtained large tokamaks. Three NBIs inject a 16 MW an energy 180 keV, which world's highest from (H−), one (H+) injects 7 at 40 keV. duration can be beyond 1 min reduced NBIs,...
Abstract In recent deuterium experiments on the large helical device (LHD), we succeeded in expanding temperature domain to higher regions for both electron and ion temperatures. Suppression of energetic particle driven resistive interchange mode (EIC) by a moderate increase is key technique extend high LHD plasmas. We found clear isotope effect formation internal transport barrier A new measure hydrogen fraction was developed order investigate behavior mixing state. The revealed that...
An extremely hollow profile of carbon impurity (denoted as an ‘impurity hole’) is observed associated with increase in the ion temperature gradient after injection Large Helical Device. The central density drops to 0.3% plasma due a strong outward convection driven by gradient, while inward predicted neoclassical theory. Transport analysis gives low diffusion coefficient 0.4 m 2 s −1 and velocity 3 at half minor radius.
A spontaneous rotation in the co-direction is observed plasmas with an ion internal transport barrier (ITB), where temperature gradient relatively large (∂ T i /∂ r ∼ 5 keV m −1 and ) LHD. Because of gradients, magnitude toroidal flow, , becomes enough to cancel flows driven by tangential injected neutral beams net velocity almost zero at outer half plasma minor radius even counter-dominant NB injections. The effect pinch excluded if it exits because velocity. flow appears direction...
We report on the characteristics of electronegative plasma in a large-scale hydrogen negative ion (H−) source. The measurement has been made with time-resolved Langmuir probe installed beam extraction region. H− density is monitored cavity ring-down system to identify electrons charges. electron-saturation current decreases rapidly after starting seed Cs, and ion-ion observed steps down during electron jumps up correspondingly. time integral decreasing charge agrees well collected probe....
It was observed that the vacuum magnetic island produced by an external error field in large helical device shrank presence of plasma. This evidenced disappearance flat regions electron temperature profile obtained Thomson scattering. behavior depended on configuration which plasmas were produced.
Internal transport barriers with respect to electron thermal (eITB) were observed in the large helical device, when cyclotron resonance heating (ECH) power was highly localized on centre of a plasma sustained by neutral beam injection. The eITB is characterized high central temperature 6–8 keV an extremely steep gradient, as 55 m−1 and low diffusivity within normalized average radius ρ≈0.3 well existence clear thresholds for ECH collisionality.
Characteristics of MHD instabilities and their impacts on plasma confinement are studied in current free plasmas the Large Helical Device. Spontaneous L–H transition is often observed high beta close to 2% at low toroidal fields (Bt ⩽ 0.75 T). The stored energy starts rise rapidly just after accompanying clear electron density but quickly saturates due growth m = 2/n 3 mode (m n: poloidal numbers), rational surface which located edge barrier region, localized (ELM) like activities having...
Remarkable progress in the physical parameters of net-current free plasmas has been made Large Helical Device (LHD) since last Fusion Energy Conference Chengdu, 2006 (Motojima et al 2007 Nucl. 47 S668 ). The beta value reached 5% and a high-beta state beyond 4.5% from diamagnetic measurement maintained for longer than 100 times energy confinement time. density temperature regimes have also extended. central exceeded 1 × 10 21 m −3 due to formation an internal diffusion barrier . ion 5.2 keV...
Reversed-shear Alfvén eigenmodes were observed for the first time in a helical plasma having negative q₀'' (the curvature of safety factor q at zero shear layer). The frequency is swept downward and upward sequentially via variation maximum q. calculated by ideal MHD theory are consistent with experimental data. sweeping mainly determined effects energetic ions bulk pressure gradient. Coupling reversed-shear ion driven geodesic acoustic modes generates multitude frequency-sweeping modes.
The peaked ion-temperature profile with steep gradient, the so-called ion internal transport barrier (ion ITB), was formed in neutral beam heated plasmas on Large Helical Device and high-ion-temperature regime of helical has been significantly extended. thermal diffusivity ITB plasma decreases down to neoclassical level. heavy probe observed smooth potential negative radial electric field root) core region where significantly. large toroidal rotation also momentum analysed qualitatively....
The discharge scenario of high temperature plasma with a helical configuration has significantly progressed. increase central ion due to the reduction wall recycling was clearly observed. peaking heating profile and charge exchange loss energetic ions play an important role for further improvement heat transport in internal barrier (ITB) core. ITB electron have been successfully integrated superposition centrally focused cyclotron plasma, regime comparable (Ti ~ Te) extended. width formed is...
Recent research results on negative-ion-rich plasmas in a large negative ion source have been reviewed. Spatial density and flow distributions of hydrogen ions (H−) positive together with those electrons are investigated 4-pin probe photodetachment (PD) signal Langmuir probe. The PD is converted to local H− from calibration scanning cavity ring down measurement. Introduction Cs changes the slope plasma potential distribution depending upon grid bias. A higher electron H2 locally shields bias...
Pellet injection has been used as a primary fuelling scheme in the Large Helical Device. With pellet injection, operational region of NBI plasmas extended to higher densities while maintaining favourable dependence energy confinement on density, and several important values, such plasma stored 0.88 MJ, time 0.3 s, β 2.4% at 1.3 T density 1.1 × 1020 m -3, have achieved. These parameters cannot be attained by gas puffing. Ablation subsequent behaviour investigated. The measured penetration...
Recent large helical device experiments revealed that the transition from ion root to electron occurred for first time in neutral-beam-heated discharges, where no nonthermal electrons exist. The measured values of radial electric field were found be qualitative agreement with those estimated by neoclassical theory. A clear reduction thermal diffusivity was observed after mode as predicted theory when loss is more dominant than anomalous loss.
An internal transport barrier (ITB) was observed in the electron temperature profile Large Helical Device [O. Motojima et al., Phys. Plasmas 6, 1843 (1999)] with a centrally focused intense cyclotron resonance microwave heating. Inside ITB core improved, and high temperature, exceeding 10 keV low density, achieved collisionless regime. The formation of electron-ITB is correlated neoclassical root strong radial electric field determined by ambipolar flux. direction tangentially injected...
During the first two years of LHD experiment following results have been achieved: (i) higher Te (Te(0) = 4.4 keV at ⟨ne⟩ 5.3 × 1018 m-3 and Pabs 1.8 MW); (ii) confinement (τE 0.3 s, Te(0) 1.1 6.5 1019 2.0 (iii) stored energy, Wpdia 880 kJ B 2.75 T. High performance plasmas realized in inward shifted magnetic axis configuration (R 3.6 m) where helical symmetry is recovered particle orbit properties are improved by a trade-off MHD stability due to appearance hill. Energy was systematically...
The performance of net-current free heliotron plasmas has been developed by findings innovative operational scenarios in conjunction with an upgrade the heating power and pumping/fuelling capability Large Helical Device (LHD). Consequently, regime extended, particular, regard to high density, long pulse length beta. Diversified studies LHD have elucidated advantages plasmas. In internal diffusion barrier (IDB) a combination efficient pumping local island divertor function core fuelling...