A5072458922- Magnetic confinement fusion research
- Ionosphere and magnetosphere dynamics
- Particle accelerators and beam dynamics
- Fusion materials and technologies
- Plasma Diagnostics and Applications
- Laser-Plasma Interactions and Diagnostics
- Solar and Space Plasma Dynamics
- Superconducting Materials and Applications
- Generative Adversarial Networks and Image Synthesis
- Atomic and Molecular Physics
- Model Reduction and Neural Networks
- Astro and Planetary Science
- Nuclear Physics and Applications
- Atomic and Subatomic Physics Research
- Laser-induced spectroscopy and plasma
- Statistical Mechanics and Entropy
- Adversarial Robustness in Machine Learning
- High-pressure geophysics and materials
- Theoretical and Computational Physics
- Gaussian Processes and Bayesian Inference
- Stochastic Gradient Optimization Techniques
- Domain Adaptation and Few-Shot Learning
- Quantum Computing Algorithms and Architecture
- Power Transformer Diagnostics and Insulation
- Machine Learning in Materials Science
Yamagata University
2016-2025
Yamagata University Hospital
2024
Toyohashi University of Technology
2021
Kyoto University
2014-2020
Tohoku University
2018-2020
Max Planck Institute for Plasma Physics
2018
Max Planck Society
2018
National Institute for Fusion Science
2000-2009
National Institutes of Natural Sciences
1998-2008
Fujitsu (Japan)
2005
This Letter presents experimental confirmation of the presence zonal flows in magnetically confined toroidal plasma using an advanced diagnostic system--dual heavy ion beam probes. The simultaneous observation electric field at two distant locations (approximately 1.5 m apart) high temperature 1 keV) provides a fluctuation spectrum (or flow), spatiotemporal structure (characteristic radial length approximately cm and lifetime ms), their long-range correlation with symmetry (n=0), difference...
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...
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.
We compare a number of radiative transfer models for atmospheric sounding in the millimeter and submillimeter wavelength range, check their consistency, investigate deviations from each other. This intercomparison deals with three different aspects models: (1) inherent physics gaseous absorption lines how they are modeled, (2) calculation coefficients, (3) full geometries, i.e., up‐looking, down‐looking, limb‐looking. The correctness consistency implementations tested by comparing...
The bifurcation nature of the electrostatic structure is studied in toroidal helical plasma Compact Helical System (CHS) [K. Matsuoka et al., Proceedings 12th International Conference on Plasma Physics and Controlled Nuclear Fusion Research, Nice, 1988 (International Atomic Energy Agency, Vienna, 1989), Vol. 2, p. 411]. Observation bifurcation-related phenomena introduced, such as characteristic patterns discrete potential profiles, various self-sustained oscillations termed electric...
A pulsating behavior of the electrostatic potential has been discovered in a low-density, high-electron-temperature plasma CHS heliotron/torsatron. The profiles were observed to swing repeatedly between two distinctive states constant external magnetic field under continuous supply particles and energy. change profile, which occurs on much faster time scale (microseconds) than diffusive (milliseconds), is accompanied by changes density temperature. This discovery clearly demonstrates that...
During combined electron cyclotron and neutral beam heating, an abrupt drop rise in potential by about one half of the central temperature ( $\ensuremath{\sim}400$ V) was observed core compact helical system heliotron/torsatron plasma. Drastic changes radial electric field between positive negative states occur over periods as short 60 $\ensuremath{\mu}$s, which is much shorter than energy confinement time scale a few milliseconds. A nonlinear relation current obtained. This first...
The transition of a radial electric field from negative to positive value is observed in the compact helical system when electron loss sufficiently enhanced by superposition off-axis second harmonic cyclotron heating on neutral beam heated plasmas. Existence threshold for particle flux required cause experimentally certified. compared with theoretical prediction.
A zonal magnetic field is found in a toroidal plasma. The has symmetric bandlike structure, which uniform the and poloidal directions varies radially with finite wavelength of mesoscale, analogous to flows. time-dependent bicoherence analysis reveals that should be generated by background plasma turbulence. discovery classified as new kind phenomenon structured generation, giving insight into phenomena such dipole generation rotational planets.
Escaping energetic ions have been measured with a scintillator-based probe which can provide both information of pitch angle and gyroradius detected in compact helical system. The measurement was started February 1997. It confirmed that output signals are due to neutral beam-injected fast ions. A Lorentz orbit code developed ion orbits reaching the were computed understand loss process Birthplace initial calculated by Monte Carlo beam deposition HFREYA. From comparison between variation...
Achieving steady-state plasma operation at high temperatures is one of the important goals worldwide magnetic fusion research. High approximately 1–2 keV, and sustainment operations have been reported. Recently regime was greatly extended in Large Helical Device (LHD). A high-temperature created maintained for 54 min with 1.6 GJ 2005FY experimental programme. The three-dimensional heat-deposition profile LHD helical divertor modified, during long-pulse discharges it effectively dispersed...
Variation of the plasma position relative to centre helical coil winding is a very effective means controlling MHD stability and trapped particle confinement in heliotron/torsatron systems, but improving one these two characteristics with this parameter simultaneously has detrimental effect on other. The inward shifted configuration favourable for drift orbit optimization predicted be unstable according Mercier criterion. Various physics problems, such as electric field structure, rotation...
A toroidal flow antiparallel to the <E(r) x B(straight theta)> drift direction is observed in hot electron mode plasmas when a large positive electric field and sharp temperature gradient are sustained inside internal transport barrier Compact Helical System. This reaches up 5x10(4) m/s at plasma center, it enough reverse driven by tangentially injected neutral beam. These observations clearly show favors minimum nablaB barrier.
High beta plasmas with a volume averaged equilibrium value of 2.1% were produced in CHS using tangential neutral beam injection. This was achieved the confinement improvement (reheat mode) observed after turning off strong gas puffing. Wall conditioning titanium gettering used to make high density operation (ne ⩽ 8 × 1019 m-3) possible for low magnetic fields (Bt = 0.6 T). The discharges start hill configuration (in vacuum) and finally achieve Mercier stable owing self-stabilization effect...
The MHD equilibrium properties of neutral beam heated plasmas have been experimentally investigated in the Compact Helical System (CHS)-a low aspect ratio (Ap ~ 5) heliotron/torsatron. This configuration is characterized by a strong breaking helical symmetry. radial profiles measured various diagnostics shown significant Shafranov shift due to plasma pressure. deviation magnetic axis from vacuum position has become as large 50% minor radius. When three-dimensional code VMEC used reconstruct...
An extended application of Gabour's wavelet to bicoherence analysis succeeds in resolving the instantaneous structure three wave couplings between disparate scale electric field fluctuations high temperature core a toroidal plasma device named compact helical system. The obtained results quantify an intermittent linkage turbulence and zonal flows—a highlighted issue present research. This is first demonstration that nature coupling should underlie power modulation due flows.
We report recent progress in the study of neoclassical internal transport barriers (N-ITBs) compact helical system (CHS) experiment. N-ITBs have been observed electron cyclotron (EC) heated NBI plasmas. The improved confinement region for electrons is expanded compared with that previous N-ITB plasmas by only EC heating. Moreover, ion temperature found to be increased simultaneously two three times (Ti(0) ∼ 400–500 eV), a steep gradient at ρ 0.6. From measurement averaged peak energy...
Turbulence and zonal flow at a transport barrier are studied with twin heavy ion beam probes in toroidal helical plasma. A wavelet analysis is used to extract turbulence properties, e.g. spectra of both density potential fluctuations, the coherence phase between them dispersion relation. Particle estimated from fundamental characteristics found clearly rise their intermittent activities after broken down. Time-dependent reveals that intermittency correlated evolution stationary flow.
The experimental studies on zonal flows and turbulence have been carried out in Compact Helical System [K. Matsuoka, S. Kubo, M. Hosokawa et al., Plasma Physics Controlled Nuclear Fusion Research, Proc. 12th Int. Conf., Nice, 1988 (International Atomic Energy Agency, Vienna, 1989, Vol. 2, p. 411] using twin heavy ion beam probes. paper presents the observations of stationary flow, nonlinear couplings between flow turbulence, role improved confinement, together with recent discovery magnetic...
The H-mode initiated by the control of rotational transform profile in CHS exhibits a very rapid transition (in 100 s or less) NBI heated plasmas. There is no obvious difference behaviour between hydrogen and deuterium. Langmuir probe measurement has revealed that change floating potential occurs at transition, but follows formation an edge transport barrier. presence surface just inside last closed flux sawtooth crash triggered internal modes play important role CHS.
Toroidal Alfvén eigenmodes (TAEs) of low toroidal mode number, n=1 and 2, are observed in neutral-beam-heated plasmas the compact helical system heliotron/torsatron. The frequency is proportional to computed TAE lies near lower bound innermost gap. modes excited only when beam velocity exceeds about half central net plasma current induced by coinjected neutral beams required range. localized core region, between 0.2 0.6 minor radius.Received 15 October...
The edge transport barrier (ETB) for particle is formed in the neutral beam (NB) heated hydrogen discharges compact helical system (CHS). transition to ETB formation and back are controlled by heating power. existence of power threshold confirmed it roughly proportional density. Hα emission signal shows a clear drop at (the timescale decrease ∼1 ms high case). continues full duration NB injection (100 ms) with moderate level radiation loss. Local density profile measurement increase movement...