A5003953667- Magnetic confinement fusion research
- Fusion materials and technologies
- Ionosphere and magnetosphere dynamics
- Plasma Diagnostics and Applications
- Superconducting Materials and Applications
- Laser-Plasma Interactions and Diagnostics
- Dust and Plasma Wave Phenomena
- Nuclear reactor physics and engineering
- Particle accelerators and beam dynamics
- Nuclear Materials and Properties
- Laser-induced spectroscopy and plasma
- Solar and Space Plasma Dynamics
- Metal and Thin Film Mechanics
- Advancements in Semiconductor Devices and Circuit Design
- Nuclear Physics and Applications
- Ion-surface interactions and analysis
- Particle Dynamics in Fluid Flows
- Electrostatic Discharge in Electronics
- Diamond and Carbon-based Materials Research
- Atomic and Molecular Physics
- Vacuum and Plasma Arcs
- High voltage insulation and dielectric phenomena
- Silicon Carbide Semiconductor Technologies
- Gas Dynamics and Kinetic Theory
- High-pressure geophysics and materials
National Institute for Fusion Science
2016-2025
National Institutes for Quantum Science and Technology
2024-2025
National Institutes of Natural Sciences
2014-2025
The Graduate University for Advanced Studies, SOKENDAI
2017-2025
Fusion Academy
2019
Fusion (United States)
2019
Kyoto University
2007-2008
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...
Abstract The EMC3‐Eirene code is improved in many aspects. Ad hoc boundary conditions for intrinsic impurities at the SOL‐core interface are removed by implicitly coupling to a 1D core model. Non‐uniform cross‐field transport coefficients allowed new version. A particle splitting technique implemented improving Monte Carlo statistic low‐temperature ranges of most interest. Domain splitting, which was possible toroidal direction only, now feasible all three directions, facilitating mesh...
Abstract In state-of-the-art stellarators, turbulence is a major cause of the degradation plasma confinement. To maximize confinement, which eventually determines amount nuclear fusion reactions, turbulent transport needs to be reduced. Here we report observation confinement regime in stellarator that characterized by increased and reduced fluctuations. The transition this driven injection submillimetric boron powder grains into plasma. With line-averaged electron density being kept...
Abstract An extended mesh system for EMC3‐EIRENE has been developed to simulate peripheral plasma including the ergodic and divertor leg regions of LHD. Both open closed configurations are available. A series simulations 8MW input power, five different electron densities at LCFS (last flux surface) open/closed were carried out. Approximately 10 times larger neutral pressure was observed under dome structure compared with configuration, which is in good agreement experimental measurements. In...
Modeling of impurity-seeded plasma in Large Helical Device (LHD) is presented for the first time by using three-dimensional transport code EMC3-EIRENE.High and low recycling coefficients impurity ions are assumed to include high absorption rates on wall surfaces due chemical activity neon nitrogen, respectively.Radiation power measured two bolometer systems particle flux divertor probes installed multiple toroidal sections utilized determine amount plasma.The uniformity non-uniformity a...
Abstract The transport properties and line emissions of carbon impurity in the stochastic layer Large Helical Device have been investigated with 3D edge code EMC3-EIRENE. A parameter study has performed to examine sensitivity simulation results on each term model source characteristics, i.e. amount location. modelling revealed that order reproduce experimental emission distribution, perpendicular coefficient ( D imp ) first wall play important roles, while changes ion thermal friction forces...
Abstract Recently, experiments on basic plasma physics issues for solving future problems in fusion energy have been performed a Large Helical Device. There are several to be solved devices energy. Emerging burning are: alpha-channeling (ion heating by alpha particles), turbulence and transport electron dominant helium ash exhaust, reduction of the divertor heat load. To solve these problems, understanding (1) wave–particle interaction through (inverse) Landau damping, (2) characteristics...
A three-dimensional (3-D) tomography technique is developed for the bolometry system in Large Helical Device using EMC3-EIRENE-defined mesh coordinates and relative gradient smoothing extended to 3-D space. We utilize two types of bolometers, resistive bolometers infra-red imaging video cover areas that are not visible with only one type bolometer, total channels which 1088. Although resolution reconstructed solution rises 59 400 voxels, we prove physically meaningful having little negative...
Abstract Controlled particulate injections from the PPPL impurity powder dropper (IPD) into Large Helical Device have demonstrated positive effects on wall conditions both an intra and inter-shot basis. Injections over a range of densities, input powers, pulse lengths, heating schemes, injection quantities main ion species show conclusive evidence improvement to plasma conditions. Successful are confirmed by spectroscopic measurements as well real-time visible camera signals. In 7 s long...
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...
Toroidal distributions of divertor particle flux during neon (Ne) and nitrogen (N2) seeded discharges were investigated in the Large Helical Device (LHD). By using 14 toroidally distributed probe arrays, which positioned at radially inner side where concentrates inward-shifted magnetic axis configuration, it is found that Ne puffing leads to quasi-uniform reduction fluxes; whereas localized reductions observed with N2 puffing. The asymmetric pattern strongly related field structure around...
Abstract The 3D ERO code, which simulates plasma–wall interaction and impurity transport in magnetically confined fusion‐relevant devices is described. As application, prompt deposition of eroded tungsten has been simulated at surfaces with shallow magnetic field 3 T. Dedicated PIC simulations have performed to calculate the characteristics sheath front plasma–exposed use as input for these simulations. Prompt reaches 100% highest electron temperature density. In comparison more simplified...
Abstract Recently an improved confinement regime, characterized by reduced turbulent fluctuations has been observed in the Large Helical Device upon injection of boron powder into plasma (Nespoli et al 2022 Nat. Phys. 18 350–56). In this article, we report more detail experimental observations increased temperature and decrease across cross section, on extended database. particular, compare powders different materials (B, C, BN), finding similar improvement turbulence response for three...
Three-dimensional trajectories of incandescent dust particles in plasmas were observed with stereoscopic fast framing cameras a large helical device. It proved that the is located peripheral plasma and most moves along magnetic field lines acceleration direction corresponds to flow. ICRF heated long pulse discharges terminated release amounts from closed divertor region. After experimental campaign, traces exfoliation carbon rich mixed-material deposition layers found Transport investigated...
Abstract The transport of impurities supplied by a multi‐species impurity powder dropper (IPD) in the large helical device (LHD) is investigated using three‐dimensional peripheral plasma fluid code (EMC3‐EIRENE) coupled with dust simulation (DUSTT). trajectories particles (Boron, Carbon, Iron, and Tungsten) dropped from IPD are studied full‐torus geometry. reveals an appropriate size optimum operational range drop rates for investigating without inducing radiation collapse. also predicts...
Abstract In the Large Helical Device (LHD) a low temperature mode (LTM) of helical divertor was discovered. It combines particle detachment and very large sub-divertor pressures up to 1.4 Pa. During LTM, electron in range from 0.25 0.42 eV so that volume recombination occurred. This result is remarkable because stellarators LHD Wendelstein 7-X only (0.03–0.3 Pa) were expected measured now due loss pressure conservation along flux tubes by an enhanced cross-field transport. demonstrates more...
The parallel flow of carbon impurity in a thick stochastic magnetic field layer called the 'ergodic layer' located at edge plasma Large Helical Device (LHD) is studied by space-resolved vacuum ultraviolet (VUV) spectroscopy, using 3 m normal incidence spectrometer. A full vertical profile C3+ evaluated from Doppler shift second order CIV line emission (2 × 1548.20 Å) horizontally-elongated position LHD. top and bottom edges ergodic has same direction toward outboard side along major radius...
A sheath layer in a magnetized collisionless plasma is analyzed by the one-dimensional kinetic equation. The bounded an absorbing wall and source with shifted Maxwellian velocity distribution function that characterized temperature, drifting parallel to magnetic field, cutoff velocity. field assumed be strong enough so ion Larmor radius comparable Debye length. In order include polarization effect of ions due electric equations describing potential profile are derived from gyrokinetic Vlasov...
In Large Helical Device (LHD), the detached plasma is obtained without external impurity gas feed by supplying an m/n = 1/1 resonant magnetic perturbation (RMP) field to a with outwardly shifted axis position of Rax 3.90 m where resonance exists in stochastic layer outside last closed flux surface. The detachment triggered appearance island when density, increased using hydrogen feed, exceeds threshold density. behavior intrinsically existing impurities, particular, carbon originating...
The heat flux deposition on the divertor targets with neon impurity injection EAST has been investigated using three-dimensional (3D) edge transport code EMC3-EIRENE. impact of different poloidal positions studied. It was found that impurities injected at in- and out-board divertors (i.e. strike points) lead to toroidally asymmetric distributions load targets, respectively. However, gas puffing upstream shows a symmetric distribution load. 3D effects radiation have help field line tracing...
Abstract An rovibrationally resolved collisional‐radiative model of molecular hydrogen (K. Sawada and M. Goto, Atoms 4: 29, 2016) is included in the authors' neutral transport code for large helical device (LHD) plasmas. The spatial distributions electron temperature density, including divertor leg regions, are given to code. molecules released from graphite target tracked. initial rotational vibrational states provided by simulation using a dynamics model. rovibrational population produced...
Abstract Toward real-time wall conditioning, impurity powder dropping experiments with boron were performed in the 22nd experimental campaign of Large Helical Device. To examine deposition and desorption process boron, we focus on hydride (BH) molecules which presumably populate near plasma-facing components. We spatially-resolved spectroscopic measurements emission by ions BH molecules. From measurement, found that B + concentrated divertor viewing chord, suggest region. By comparing H γ...