A5043184063- Magnetic confinement fusion research
- Ionosphere and magnetosphere dynamics
- Solar and Space Plasma Dynamics
- Laser-Plasma Interactions and Diagnostics
- Plasma Diagnostics and Applications
- Particle accelerators and beam dynamics
- Fusion materials and technologies
- Superconducting Materials and Applications
- Ion-surface interactions and analysis
- X-ray Spectroscopy and Fluorescence Analysis
- Laser-induced spectroscopy and plasma
- Fluid Dynamics and Turbulent Flows
- Nuclear Physics and Applications
- Geomagnetism and Paleomagnetism Studies
- Integrated Circuits and Semiconductor Failure Analysis
- Atomic and Subatomic Physics Research
- Dust and Plasma Wave Phenomena
- Electron and X-Ray Spectroscopy Techniques
- Atomic and Molecular Physics
- Theoretical and Computational Physics
- Oceanographic and Atmospheric Processes
- Physics of Superconductivity and Magnetism
- Power Transformer Diagnostics and Insulation
- Cold Atom Physics and Bose-Einstein Condensates
- Quantum optics and atomic interactions
Kyushu University
2016-2025
National Institute for Fusion Science
2006-2024
Shimane University
2017-2018
Chubu University
2018
The University of Tokyo
1988-2017
Shizuoka University
2017
Kyoto University
1984-2017
Kyushu Tokai University
2017
Honda (Japan)
2017
Fusion Academy
2010-2012
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...
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.
The characteristics of geodesic–acoustic-mode (GAM) are investigated through direct and simultaneous measurement electrostatic density fluctuations with a heavy ion beam probe.
The present status of experiments on zonal flows in magnetic confinement is examined. innovative use traditional and modern diagnostics has revealed unambiguously the existence flows, their spatio-temporal characteristics, relationship to turbulence effects confinement. In particular, a number observations have been accumulated oscillatory branch named geodesic acoustic modes, suggesting necessity for theories give proper description. addition these basic properties several new methods...
The improvement of core electron heat confinement has been realized in a wide range helical devices such as CHS, LHD, TJ-II and W7-AS. Strongly peaked temperature profiles large positive radial electric field, E r , the region are common features for this improved confinement. Such observations consistent with transition to ‘electron-root’ solution ambipolarity condition context neoclassical transport, which is unique non-axisymmetric configurations. Based on background, collectively dubbed...
The variety of scalar and vector fields in laboratory nature plasmas is formed by plasma turbulence. Drift-wave fluctuations, driven density gradients magnetized plasmas, are known to relax the gradient while they can generate flows. On other hand, sheared flow direction magnetic causes Kelvin-Helmholtz type instabilities, which mix particle momentum. These different types fluctuations coexist nature, so that multiple mechanisms for structural formation exist extremely non-equilibrium...
We report observations of the dynamic response micro-fluctuations and turbulent flux to a low-frequency heating power modulation in Large Helical Device. The responses heat micro-fluctuation intensity differ from that change temperature gradient. This result violates local transport model, where turbulence is determined by A new relationship between flux, gradient found. In addition gradient, rate proposed as new, direct controlling parameter explain fast against periodic power.
This Letter presents the discovery of macroscale electron temperature fluctuations with a long radial correlation length comparable to plasma minor radius in toroidal plasma. Their spatiotemporal structure is characterized by low frequency $\ensuremath{\sim}1--3\text{ }\text{ }\mathrm{kHz}$, ballistic propagation, poloidal or mode number $m/n=1/1$ (or $2/1$), and an amplitude $\ensuremath{\sim}2%$ at maximum. Nonlinear coupling between long-range microscopic identified. A change fluctuation...
Fully non-inductive second (2nd) harmonic electron cyclotron (EC) plasma current ramp-up was demonstrated with a newlly developed 28 GHz system in the QUEST spherical tokamak. A high of 54 kA non-inductively ramped up and sustained stably for 0.9 s 270 kW wave. higher 66 also achieved slow vertical field. We have significantly than those previously 2nd EC waves. This fully method might be useful future burning devices fusion reactors, particular operations at half magnetic field same heating...
This review presents experimental studies on improved confinement (IC) modes observed mainly in stellarator plasmas. The IC result from structural bifurcation, often accompanied with discrete and sudden changes electromagnetic thermodynamic structures. phenomenology of the bifurcated states occurring various configurations is described fundamental observations associated mechanisms bifurcation improvements. Particular emphasis placed physics radial electric field, which a key quantity that...
Observation of the parametric-modulational interaction between drift-wave fluctuation (7–8 kHz) and azimuthally symmetric sheared radial electric field structure (∼0.4 in a cylindrical laboratory plasma is presented. Oscillation synchronized at modulations wave number Reynolds stress per mass density spectrum. Bispectral analysis location where has finite numbers shows that nonlinear energy transfers from drift to occur. Nonlocal fluctuations via “channel field” spectral space as well real...
Fully non-inductive plasma maintenance was achieved by a microwave of 8.2 GHz and 40 kW for more than 1 h 55 min with well-controlled plasma-facing wall (PFW) temperature 393 K, using hot in the middle-sized spherical tokamak QUEST, until discharge finally terminated uncontrollability density. The PFW composed atmospheric plasma-sprayed tungsten stainless steel. plays an essential role reducing amount wall-stored hydrogen facilitates recycling. behaviour fuel investigated monitoring...
Reliable estimation of equilibrium flow shear from reciprocating probe measurements is challenging since the quantity interest corresponds to second derivative observable plasma potential. In addition, a time series potential obtained by plunging affected both head position and fluctuations, complicating components their errors. We tackle this problem employing Gaussian process regression that able infer even derivatives spatial or temporal profile in form probability distribution function....
The long-term development of the transitional regime drift-wave turbulence is studied in a magnetized plasma column by means conditional-average technique. In regime, small changes magnetic-field strength as control parameter lead to large correlation times, indicating existence critical point an underlying nonequilibrium continuous phase transition. This and spatiotemporal dynamics shows similarities puff splitting, slug-gap jamming. Published American Physical Society 2025
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...
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...
The present paper extends the theory of geodesic acoustic mode (GAM) oscillation, which so far has been applied to tokamaks, helical systems. By using drift kinetic equations for three-dimensional equilibriums, a generalized dispersion relation is obtained including Landau damping. oscillation frequency in terms squared sum Fourier components magnetic field intensity expressed by means flux coordinates. An analytic form collisionless damping rate GAM solving perturbatively. It found that...
The eigenmode of a geodesic acoustic mode in the presence temperature gradient is discussed. Eigenmodes are obtained and characteristic wavelength scales as ρi2/3LT1/3 (ρi: ion gyroradius, LT: scale length). direction propagation
A method for zonal flow study by using direct density fluctuation measurements is proposed. When ambient drift-wave turbulence modulated flows (i.e. in the drift-wave-zonal systems), an envelope of fluctuations has spectral peaks around frequencies. peak at geodesic acoustic mode (GAM) frequency observed measured edge plasma JFT-2M tokamak. The significant cross-bicoherence also found between and its GAM frequency. This result demonstrates that we can measure only data. provides a...
After intensive discharge cleaning of the chamber wall, non-inductive current start-up experiments have been successfully performed in QUEST moderate vertical fields about 1.0–1.5 mT with positive n-index. Simultaneously, increasing plasma current, an asymmetric toroidal flow energetic electrons was observed and direct measurements driven by this were taken a newly developed Langmuir probe technique. A numerical study electron orbits indicates that total is enough to play dominant role...
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...
Fluctuations are experimentally studied using Langmuir probes and magnetic in the a/2\ensuremath{\lesssim}r\ensuremath{\le}a region of REPUTE-1 reversed-field-pinch plasma. An electron-heat flux ${\mathit{q}}_{\mathit{E}}^{\mathit{e}}$ due to electrostatic fluctuations is too small account for total ${\mathit{q}}_{\mathrm{total}}^{\mathit{e}}$. It implied that mainly determine electron energy confinement interior region.