A5027190422- Magnetic confinement fusion research
- Ionosphere and magnetosphere dynamics
- Superconducting Materials and Applications
- Fusion materials and technologies
- Laser-Plasma Interactions and Diagnostics
- Particle accelerators and beam dynamics
- Solar and Space Plasma Dynamics
- Nuclear reactor physics and engineering
- Physics of Superconductivity and Magnetism
- Nuclear Physics and Applications
- Dust and Plasma Wave Phenomena
- Plasma Diagnostics and Applications
- Nuclear Materials and Properties
- Thin-Film Transistor Technologies
- X-ray Spectroscopy and Fluorescence Analysis
- Ion-surface interactions and analysis
- Quantum, superfluid, helium dynamics
- NMR spectroscopy and applications
- Particle Detector Development and Performance
- Molten salt chemistry and electrochemical processes
- Particle Accelerators and Free-Electron Lasers
- Silicon and Solar Cell Technologies
- earthquake and tectonic studies
- Graphite, nuclear technology, radiation studies
- High-pressure geophysics and materials
National Institutes for Quantum Science and Technology
2016-2024
Royal Military Academy
2020
Japan Atomic Energy Agency
2007-2016
University of California, San Diego
2007
Advanced Science Research Center
2003-2004
The Graduate University for Advanced Studies, SOKENDAI
1999
In this Letter, we report analyses of spatiotemporal dynamics turbulence and structure in the limit-cycle oscillation (LCO) that precedes an L-to-H transition. Zonal flows are not observed during LCO, is periodic generations or decays barrier with edge-localized mean flow. Oscillatory Reynolds stress found to be too small accelerate LCO flow, by considering dielectric constant magnetized toroidal plasmas. Propagation changes density gradient amplitude into core also observed.
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...
In this paper, recent progress on experimental analysis and theoretical models for non-local transport (non-Fickian fluxes in real space) is reviewed. The non-locality the heat momentum observed plasma, departures from linear flux-gradient proportionality, externally triggered phenomena are described both L-mode improved-mode plasmas. Ongoing evaluation of 'fast front' 'intrinsically non-local' models, their success comparisons with data, discussed
The characteristics of geodesic–acoustic-mode (GAM) are investigated through direct and simultaneous measurement electrostatic density fluctuations with a heavy ion beam probe.
Several small/no ELM regimes such as EDA, grassy ELM, HRS, QH-mode, type II and V ELMs with good confinement properties have been obtained in Alcator C-Mod, ASDEX-Upgrade, DIII-D, JET, JFT-2M, JT-60U NSTX. All these show considerable reduction of instantaneous heat load onto divertor target plates contrast to conventional I energy losses are evaluated less than 5% the pedestal stored energy. These summarized widely categorized by their conditions terms operational space non-dimensional...
The electrostatic and density fluctuation are measured simultaneously with a heavy ion beam probe. the geodesic acoustic mode (GAM) frequency is observed in L-mode plasmas not H-mode plasmas. poloidal radial structure consistent GAM. So concluded to be GAM.The amplitude of GAM changes direction; it small near separatrix, has maximum at 3 cm inside separatrix decreases again 5 cm separatrix.The temporal behaviour ambient show significant coherence, phase modulation tends delay potential...
Edge localized mode (ELM) measurements in many tokamaks, including ASDEX-Upgrade, DIII-D, JET, JT-60U and MAST, are reviewed, which includes progress experimental observations at the plasma edge region by means of fast-time resolved diagnostics with high precision, such as scanning probe, radial interferometer chord, BES tangentially viewing fast-gated camera midplane. ELM dynamics data show that majority particle energy transport should be dominated ion convection physics associated...
The characteristics of momentum transport and plasma rotation in the toroidal direction are studied, using near-perpendicular neutral beam injection (PERP-NBI), co tangential counter (CTR) NBI JT-60U. Diffusive non-diffusive terms evaluated from transient analysis by source modulation. Fast ion losses due to field ripple, which locally induces edge CTR rotation, used as a novel source. Parameter dependence these coefficients i.e. diffusivity (χϕ) convection velocity (Vconv), relation between...
A peaked ion temperature profile is observed inside the magnetic island during mode locking after back transition from H to L in JT-60U. The thermal diffusivity evaluated 0.1 m(2)/s, which much smaller than that outside by an order of magnitude. present experiment gives clear evidence heat transport a can bifurcate and level be suppressed very low associated with strong flow shear at boundary.
The driving mechanism of toroidal rotation and the momentum transport are studied on JT-60U in relation to direction antiparallel plasma current, i.e. counter (CTR) direction, with near-perpendicular neutral beam (PERP-NB) injection. Fast ion losses due field ripple induce CTR peripheral region, magnitude PERP-NBs reduces by installing ferritic steel tiles as a consequence reduction losses. It is also found that velocity profiles core region can be explained considering diffusivity...
The fast potential change near the separatrix is measured directly at L-H transition by a heavy-ion-beam probe. changes with two different time scales triggered sawtooth crash: it drops first scale of 10--100 mus just after arrival heat pulse due to crash. Then, decreases again few 100 drop about 200 mus.
The effects of toroidal rotation and field (TF) ripple on the edge pedestal structure edge-localized-modes (ELMs) were examined in JT-60U. amplitude TF was changed by installation ferritic steel tiles (FSTs). profile VT became less counter with FSTs, particularly case where co-NBI used a large volume configuration. In this case, plasma pressure raised across whole plasma. At edge, higher temperature obtained growth width. However, effect FSTs significant small As at pedestal, ELM frequency...
The progress of physical understanding as well parameter improvement net-current-free helical plasma is reported for the Large Helical Device since last Fusion Energy Conference in Daejeon 2010. second low-energy neutral beam line was installed, and central ion temperature has exceeded 7 keV, which obtained by carbon pellet injection. Transport analysis high-Ti plasmas shows that ion-thermal conductivity viscosity decreased after injection although does not long. effort been focused on...
Abstract The driving and damping mechanism of plasma flow is an important issue because shear has a significant impact on turbulence in plasma, which determines the transport magnetized plasma. Here we report clear evidence due to stochastization magnetic field. Abrupt toroidal associated with transition from nested flux surface stochastic field observed when at rational decreases 0.5 large helical device. This resulting profile flattening are much stronger than expected Rechester–Rosenbluth...
In the JFT-2M tokamak (JFT standing for JAERI Fusion Torus), limit cycle oscillation (LCO), together with several variables, i.e., electrostatic potential, radial electric field, electron density, turbulence intensity, and Dα emission from divertor region, is observed before L-to-H transition. The spatiotemporal dynamics of LCO analysed in detail. Zonal flows are not seen, while modulation edge-localized poloidal flow density gradient. Modulation also seen Reynolds stress, caused by that...
In JFT-2M, ferritic steel plates (FPs) were installed on almost the whole inner surface of vacuum vessel. This arrangement is called inside wall (FIW), and third step advanced material tokamak experiment programme. The toroidal field (TF) ripple was reduced by optimizing thickness FPs but total structure has become more complex, with a non-periodic feature in direction, because existence ports other components that limit periodic installation FPs. We investigated effect this complex heat...
A complex multistage transition of the edge radial electric field is observed in JT-60U H-mode phase without localized mode. An interesting feature that poloidal rotation velocity carbon impurity ions changes later H-phase a comparable change main ion pressure gradient, indicating parallel momentum (and particle) balance channel.
Abstract Spatiotemporal evolutions of radial electric field and turbulence are measured simultaneously in the H-mode transition, which is a prototypical example structure formation high-temperature plasmas. In dynamical phase where transport barrier established abruptly, time-space-frequency-resolved turbulent particle flux obtained. Here we report validation mechanism quantitatively. It found that suppressed predominantly by reducing density fluctuation amplitude cross between potential...
Abstract The turbulent structure formation, where strongly-inhomogeneous turbulence and global electromagnetic fields are self-organized, is a fundamental mechanism that governs the evolution of high-temperature plasmas in universe laboratory (e.g., generation edge transport barrier (ETB) H-mode toroidal plasmas). roles inhomogeneities radial electric field ( E r ) known inevitable. In this mechanism, whether first derivative (shear) or second (curvature) works most decisive determining...
Compatibility between the plasma and low activation ferritic steel, which is a candidate material for fusion demonstration reactors, has been investigated step by in JFT-2M tokamak. We have entered third stage of Advanced Material Tokamak EXperiment (AMTEX), where inside vacuum vessel wall completely covered with steel plates (FIW). The effects FIW on production, impurity release, operation region, H-mode characteristics investigated. No negative effect observed up to now. A high normalized...
Effects of the edge collisionality on ELM characteristics have been investigated in grassy regime JT-60U. Both high and low q regions ( 95 > 6 ∼ 4.3), amplitude becomes higher at (density). This dependence is opposite to observed type I regime, where decreases with increasing collisionality. The stability analysis suggests that 4.3 can be triggered by infinite- n ballooning mode localized inside pedestal, when peeling–ballooning modes are stable. In case collisionality, also unstable, as...
We investigate spatial structures of turbulence and turbulent transport modulated by the geodesic acoustic mode (GAM), from which excitation mechanism GAM is discussed. The found to be predominantly excited through a localized Reynolds stress force, rather than dynamic shearing force. evaluated growth rate larger linear damping coefficients on same order magnitude as effective time evolution in kinetic energy.
A new operational regime has been discovered on JFT-2M under the boronized first wall condition to produce High Recycling Steady (HRS) H-mode, which is characterized by good energy confinement (H89P ∼ 1.6) at a high density of around 70% Greenwald (ne/nGW), low radiated power fraction, and complete disappearance large ELMs. Accompanying HRS H-mode transition, coherent magnetic fluctuation seen probes vessel wall. These fluctuations have frequency order 10–100 kHz with significant variation....
In order to understand the physics of ELM trigger and determine size, fast dynamics type I grassy ELMs have been studied in JT-60U, using new diagnostics with high spatial temporal resolutions such as a lithium beam probe (Δ t ∼ 0.5 ms) charge exchange recombination spectroscopy 2.5 ms), which can measure electron density ion temperature, respectively. The evolution pressure profile pedestal region has evaluated for first time by detailed edge measurements. Then, density, temperature cycle...
The solitary radial electric field in the edge of toroidal plasma is studied based on bifurcation model. Results are applied to tokamak and helical plasmas, dependence structure parameters geometrical factors analyzed. order magnitude estimate for not far from experimental observations. It shown that, height reduced substantially owing ripple particle transport, while width influenced less. implications results limit achievable gradient H-mode pedestal also discussed.