K. Tsumori
A5039965709- Particle accelerators and beam dynamics
- Magnetic confinement fusion research
- Plasma Diagnostics and Applications
- Superconducting Materials and Applications
- Fusion materials and technologies
- Ionosphere and magnetosphere dynamics
- Atomic and Molecular Physics
- Gyrotron and Vacuum Electronics Research
- Ion-surface interactions and analysis
- Particle Accelerators and Free-Electron Lasers
- Laser-Plasma Interactions and Diagnostics
- Mass Spectrometry Techniques and Applications
- Solar and Space Plasma Dynamics
- Metal and Thin Film Mechanics
- Nuclear Physics and Applications
- Electrostatic Discharge in Electronics
- Atomic and Subatomic Physics Research
- Physics of Superconductivity and Magnetism
- Dust and Plasma Wave Phenomena
- Semiconductor materials and devices
- Spacecraft and Cryogenic Technologies
- Electromagnetic Launch and Propulsion Technology
- Diamond and Carbon-based Materials Research
- Electron and X-Ray Spectroscopy Techniques
- Radiation Effects in Electronics
National Institute for Fusion Science
2016-2025
The Graduate University for Advanced Studies, SOKENDAI
2015-2024
National Institutes of Natural Sciences
2011-2023
Nagoya University
2000-2022
Doshisha University
2011-2022
Max Planck Institute for Plasma Physics
2011-2019
National Institutes for Quantum Science and Technology
2019
ITER
2019
Fusion for Energy
2019
The University of Tokyo
2015
The Large Helical Device (LHD) has successfully started running plasma confinement experiments after a long construction period of eight years. During the and machine commissioning phases, variety milestones were attained in fusion engineering which led to first operation, was ignited on 31 March 1998. Two experimental campaigns carried out In campaign, magnetic flux mapping clearly demonstrated nested structure surfaces. conducted with second harmonic 84 82.6 GHz ECH at heating power input...
The Large Helical Device (LHD) experiments [O. Motojima, et al., Proceedings, 16th Conference on Fusion Energy, Montreal, 1996 (International Atomic Energy Agency, Vienna, 1997), Vol. 3, p. 437] have started this year after a successful eight-year construction and test period of the fully superconducting facility. LHD investigates variety physics issues large scale heliotron plasmas (R=3.9 m, a=0.6 m), which stimulates efforts to explore currentless disruption-free steady under an optimized...
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,...
The deuterium experiment started from March 2017 on the large helical device (LHD) as a part of LHD high-performance upgrade project. objectives are: 1) to realize operation; 2) explore physics isotope effect; 3) demonstrate confinement capability energetic particles in devices; and 4) research plasma-material interactions using benefit stable steady-state operation ability LHD. As preparations for experiment, positive-ion-based neutral beam injectors (NBIs) are upgraded increase their...
Beam-divergence characteristics of single negative ion beamlet have been experimentally investigated with a superimposition controlled perturbation radio frequency wave (RF) field in filament-arc discharge source. Oscillations negative-ion width and axis responding to the RF were observed, which may be cause larger beam divergence angle source for ITER. It is pointed out that oscillation depends on perveance an such suppressed at perveance-matched conditions low frequency.
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....
Recent results of energetic ion driven MHD instabilities observed in the heliotron/torsatron devices Compact Helical System (CHS) and Large Device (LHD) are presented. Alfvén eigenmodes (AEs) fishbone-like burst modes (FBs) destabilized by ions were NBI heated plasmas CHS. The AEs toroidicity induced (TAEs) global (GAEs), where identified toroidal mode numbers n = 1 2 for TAEs 0 GAEs. frequencies FBs less than, at most, half minimum TAE gap frequency do not exhibit obvious density dependence...
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...
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...