M. Osakabe
A5068064548- Magnetic confinement fusion research
- Particle accelerators and beam dynamics
- Plasma Diagnostics and Applications
- Fusion materials and technologies
- Ionosphere and magnetosphere dynamics
- Superconducting Materials and Applications
- Laser-Plasma Interactions and Diagnostics
- Nuclear Physics and Applications
- Solar and Space Plasma Dynamics
- Atomic and Subatomic Physics Research
- Atomic and Molecular Physics
- Nuclear reactor physics and engineering
- Gyrotron and Vacuum Electronics Research
- Ion-surface interactions and analysis
- Particle Accelerators and Free-Electron Lasers
- Laser-induced spectroscopy and plasma
- Mass Spectrometry Techniques and Applications
- Radiation Detection and Scintillator Technologies
- Metal and Thin Film Mechanics
- Nuclear Materials and Properties
- Dust and Plasma Wave Phenomena
- High-pressure geophysics and materials
- Electrostatic Discharge in Electronics
- Engineering Applied Research
- Diamond and Carbon-based Materials Research
National Institute for Fusion Science
2016-2025
National Institutes of Natural Sciences
2015-2024
The Graduate University for Advanced Studies, SOKENDAI
2015-2024
Surugadai University
2024
Fusion Academy
1994-2024
Mahasarakham University
2023
Institute of Natural Science
2021
Nagoya University
2000-2020
Max Planck Institute for Plasma Physics
2011-2019
Max Planck Society
2019
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...
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...
Wendelstein 7-X is the first comprehensively optimized stellarator aiming at good confinement with plasma parameters relevant to a future power plant. Plasma operation started in 2015 using limiter configuration. After installing an uncooled magnetic island divertor, extending energy limit from 4 80 MJ, continued 2017. For this phase, electron cyclotron resonance heating (ECRH) capability was extended 7 MW, and hydrogen pellet injection implemented. The enhancements resulted highest triple...
Proton-boron (p11B) fusion is an attractive potential energy source but technically challenging to implement. Developing techniques realize its requires first developing the experimental capability produce p11B in magnetically-confined, thermonuclear plasma environment. Here we report clear measurements supported by simulation of with high-energy neutral beams and boron powder injection a high-temperature (the Large Helical Device) that have resulted diagnostically significant levels alpha...
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 thermal transport barrier resulting in a high central electron temperature of $\ensuremath{\sim}2\mathrm{keV}$ is established the core electron-cyclotron-resonance heated plasmas Compact Helical System Heliotron/Torsatron. The formation correlated with reduction density fluctuations and structural change radial electric field profile at location. results suggest that decrease fluctuation should contribute to anomalous drastic increase barrier.
Peak fusion power production of 6.2\ifmmode\pm\else\textpm\fi{}0.4 MW has been achieved in TFTR plasmas heated by deuterium and tritium neutral beams at a total 29.5 MW. These have an inferred central alpha particle density 1.2\ifmmode\times\else\texttimes\fi{}${10}^{17}$ ${\mathrm{m}}^{\mathrm{\ensuremath{-}}3}$ without the appearance either disruptive magnetohydrodynamics events or detectable changes Alfv\'en wave activity. The measured loss rate energetic particles agreed with...
Divertor plasma characteristics in the Large Helical Device (LHD) have been investigated mainly by using Langmuir probes. The three-dimensional structure of helical divertor, which is naturally produced heliotron-type magnetic configuration, clearly seen measured particle and power deposition profiles on divertor plates. These observations are consistent with numerical results field line tracing. flux to plates increases almost linearly averaged density. high-recycling regime detachment,...
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...
The systems of charge-exchange spectroscopy (CXS) have been improved on the Large Helical Device (LHD). Pitch-controlled fiber bundles give faster readout time, and double-slit increase number channels that can be obtained with a single charge-coupled device detector. evolutions ion temperature sampling time 10 ms are obtained, profiles temperature, toroidal rotation velocity, density carbon impurity data at 51 spatial points measured CXS systems.
Remarkable progress has been made in diagnosing energetic particle instabilities on presentday machines and establishing a theoretical framework for describing them.This overview describes the much improved diagnostics of Alfvén modelling tools developed world-wide, discusses interpreting observed phenomena.A multi-machine comparison is presented giving information performance both different plasma conditions outlining expectations ITER based our present knowledge.
The deuterium operation of the large helical device (LHD) began in March 7, 2017, after long-term preparation and commissioning apparatuses necessary for execution experiment. A comprehensive set neutron diagnostics was developed installed onto LHD through numerous efforts preparation. Neutron play an essential role both yield management radiation safety extension energetic-particle physics study LHD. flux monitor (NFM) characterized by fast-response wide dynamic range capabilities is...
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,...
Comprehensive understanding of energetic-ion-driven global instabilities such as Alfvén eigenmodes (AEs) and their impact on energetic ions bulk plasma is crucially important for tokamak stellarator/helical plasmas in the future deuterium–tritium (DT) burning experiments. Various types modes associated enhanced ion transport are commonly observed toroidal plasmas. Toroidicity-induced AEs ellipticity-induced AEs, whose gaps generated through poloidal mode coupling, both Global reversed shear...
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...
Achievement of reactor relevant plasma condition in Helical type magnetic devices and exploration its related physics fusion engineering are the aim Large Device (LHD) project. In recent experiments on LHD, we have achieved ion-temperature 8.1 keV at 1 × 1019 m−3 by optimization wall conditioning using long pulse discharge Ion Cyclotron Heating (ICH). The electron temperature 10 1.6 was also Electron (ECH). For further improvement performance, upgrade (LHD), including deuterium experiment,...
Two pairs of high-frequency magnetic probes were installed in the Large Helical Device (LHD). During injection a perpendicular neutral beam, ion cyclotron emissions (ICEs) with fundamental frequency corresponding to at plasma edge detected, which are same type ICE as measured former spare range frequencies (ICRF) heating antennas. This was further investigated regard phase and intensity signals. Another found LHD, these ICEs synchronized bursts toroidicity induced Alfvén eigenmodes (TAE)...
Understanding of energetic particle (EP) confinement is one the critical issues in realizing fusion reactor.In stellarator/helical devices, research on EP key topics to obtain better by utilizing flexibility three-dimensional magnetic field.Study transport Large Helical Device (LHD) has been performed means escaping diagnostics hydrogen plasma operation.By starting deuterium operation LHD, study EPs progressed remarkably using newly developed comprehensive neutron providing information...
The deuterium operation of the Large Helical Device (LHD) heliotron started in March 7, 2017, after longterm preparation and commissioning works necessary to execute experiment.A comprehensive set neutron diagnostics was implemented accelerate energetic-particle physics research LHD.The calibrated ex-vessel flux monitor indicated that total emission rate first campaign reached 3.3×10 15 n/s inward shifted magnetic field configuration where confinement helically trapped energetic ions is...
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...
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.