A5080557780- Magnetic confinement fusion research
- Ionosphere and magnetosphere dynamics
- Particle accelerators and beam dynamics
- Fusion materials and technologies
- Superconducting Materials and Applications
- Plasma Diagnostics and Applications
- Laser-Plasma Interactions and Diagnostics
- Solar and Space Plasma Dynamics
- Nuclear Physics and Applications
- Laser-induced spectroscopy and plasma
- Spacecraft and Cryogenic Technologies
- Atomic and Molecular Physics
- Atomic and Subatomic Physics Research
- Astronomical Observations and Instrumentation
- Vacuum and Plasma Arcs
- Electromagnetic Compatibility and Measurements
- Dust and Plasma Wave Phenomena
- Physics of Superconductivity and Magnetism
- Nuclear reactor physics and engineering
- Stellar, planetary, and galactic studies
- Astro and Planetary Science
- Particle Accelerators and Free-Electron Lasers
- Advanced Sensor Technologies Research
- Surface Roughness and Optical Measurements
- Electrical Fault Detection and Protection
Oak Ridge National Laboratory
2015-2024
Max Planck Institute for Plasma Physics - Greifswald
2016-2018
Australian National University
2002-2016
CEA Cadarache
1997-2016
Max Planck Society
2007-2016
Physikalisch-Technische Bundesanstalt
2016
University of Opole
2016
National Institute for Fusion Science
2008-2016
Culham Science Centre
2016
Princeton Plasma Physics Laboratory
1994-2016
A stochastic magnetic boundary, produced by an applied edge resonant perturbation, is used to suppress most large edge-localized modes (ELMs) in high confinement ($H$-mode) plasmas. The resulting $H$ mode displays rapid, small oscillations with a bursty character modulated coherent 130 Hz envelope. transport barrier and core are unaffected the despite threefold drop toroidal rotation. These results demonstrate that boundaries compatible may be attractive for ELM control next-step fusion tokamaks.
International collaboration on development of a stellarator confinement database has progressed. More than 3000 data points from nine major experiments have been compiled. Robust dependences the energy time density and heating power confirmed. Dependences other operational parameters, i.e. minor radii, magnetic field rotational transform , evaluated using inter-machine analyses. In order to express in unified scaling law, systematic differences each subgroup are quantified. An posteriori...
Large sub-millisecond heat pulses due to Type-I edge localized modes (ELMs) have been eliminated reproducibly in DIII-D for periods approaching nine energy confinement times (τE) with small dc currents driven a simple magnetic perturbation coil. The current required eliminate all but few isolated ELM impulses during coil pulse is less than 0.4% of plasma current. Based on field line modelling, the fields resonate flux surfaces across most pedestal region (0.9 ⩽ ψN 1.0) when q95 = 3.7 ± 0.2,...
Abstract Fusion energy research has in the past 40 years focused primarily on tokamak concept, but recent advances plasma theory and computational power have led to renewed interest stellarators. The largest most sophisticated stellarator world, Wendelstein 7-X (W7-X), just started operation, with aim show that earlier weaknesses of this concept been addressed successfully, intrinsic advantages persist, also at parameters approaching those a future fusion plant. Here we first physics...
Plasma offers a promising alternative to metal for wide variety of radiofrequency antenna applications. In this letter we report measurements efficiencies up 50% and radiation patterns plasma column elements. It is demonstrated that the current distribution along can be controlled by density. columns used instead elements in communications antennas.
The Advanced Toroidal Facility (ATF), now under construction at Oak Ridge National Laboratory, will be the world’s largest stellarator experiment when it begins operation in early 1987. It have a 2.1-m major radius and 0.3-m average plasma radius, magnetic field capability of up to 2 T for 5-s pulse 1 steady state, 5 MW heating. ATF is designed study wide range toroidal confinement issues, including stability high-beta plasmas, low-collisionality transport, impurity behavior, configuration...
In certain applications, the surface wave driven plasma column can replace metal as guiding medium in radio frequency antennas. Such antennas offer possibility of low radar detectability and negligible mutual coupling when de-energized. Experimental results are presented confirming that two most important physical issues, namely antenna efficiency noise, not compromised by use a plasma. It is also shown relatively high be predicted simple calculation.
A low amplitude (δbr∕BT=1 part in 5000) edge resonant magnetic field perturbation with toroidal mode number n=3 and poloidal numbers between 8 15 has been used to suppress most large type I localized modes (ELMs) without degrading core plasma confinement. ELMs have suppressed for periods of up 8.6 energy confinement times when the safety factor q95 is 3.5 4. The are replaced by packets events (possibly II ELMs) small amplitude, narrow radial extent, a higher level density fluctuations,...
Substantial progress was made during the period 1981-1986 in plasma parameters, physics understanding, and improvement of stellarator/heliotron concept. Recent advances include (1) substantial achievements higher parameters currentless operation, (2) new theoretical results with respect to beta limits, second stability region, effect a helical axis, electric fields on transport, reduction secondary currents; (3) improvements reactor The key issues have been further refined, short-term...
The Wendelstein 7-X (W7-X) optimized stellarator fusion experiment, which went into operation in 2015, has been operating since 2017 with an un-cooled modular graphite divertor. This allowed first divertor physics studies to be performed at pulse energies up 80 MJ, as opposed 4 MJ the phase, where five inboard limiters were installed instead of a This, and number other upgrades device capabilities, extension regimes higher plasma density, heating power, performance overall, e.g. setting new...
The transport of heavy impurities has been investigated at the Wendelstein 7-X stellarator during core electron root confinement (CERC) experiments. Iron atoms were injected via laser blow-off technique and analyzed by VUV x-ray spectrometers. amount iron does not change global plasma parameters but yields strong enough line radiation for detailed studies based on impurity code STRAHL. latter is supplied with neo-classical diffusion convection profiles from drift kinetic equation solver...
Wendelstein 7-X, a superconducting optimized stellarator built in Greifswald/Germany, started its first plasmas with the last closed flux surface (LCFS) defined by 5 uncooled graphite limiters December 2015. At end of 10 weeks long experimental campaign (OP1.1) more than 20 independent diagnostic systems were operation, allowing detailed studies many interesting plasma phenomena. For example, fast neutral gas manometers supported video cameras (including one fast-frame camera frame rates...
Access to the MHD second stability regime has been achieved in ATF torsatron. Experimental \ensuremath{\beta} values (${\ensuremath{\beta}}_{0}$\ensuremath{\le}3%, with fast ions contributing \ensuremath{\approxeq}(1/3 of pressure at high \ensuremath{\beta}) are well above theoretical transition value (${\ensuremath{\beta}}_{c}$\ensuremath{\approxeq}1.3% for ideal modes) required reach this regime. The relatively low ${\ensuremath{\beta}}_{c}$ results from operation peaked profiles. measured...
Electron-cyclotron and neutral-beam heating have been used to produce currentless plasma with $〈\ensuremath{\beta}〉\ensuremath{\approx}(1\ensuremath{-}2)%$ in the Heliotron-$E$ device. For moderately peaked profiles, magnetohydrodynamic activity that peaks at $t=1$ surface has observed. The characteristics of fluctuations are consistent theoretical expectations for an $m=1$ pressure-driven instability. is associated particle energy losses but not yet directly linked global confinement.
As a result of experimental observations localized heat flux on components magnetically connected to radiating waveguides in Tore Supra and TdeV, the acceleration electrons near lower hybrid (LH) antennas has been investigated. A simple analytical model developed compute dynamics particles field approximation. Landau damping very high N|| (20 < 100) component launched spectrum thermal scrape-off layer (SOL) is found occur. Simulation typical LH pulse indicates that can be accelerated up 2-3...
Key physics issues in the design of a high- quasi-axisymmetric stellarator configuration are discussed. The goal study is compact with aspect ratio comparable to that tokamaks and good transport stability properties. Quasi-axisymmetry has been used provide drift trajectories. Ballooning stabilization accomplished by strong axisymmetric shaping, yielding whose core second regime for ballooning modes. A combination externally generated shear non-axisymmetric corrugation plasma boundary...
Electrostatic turbulence has been investigated in the edge region of Advanced Toroidal Facility (ATF). A reversal poloidal phase velocity fluctuations observed (velocity shear) which determines a characteristic plasma radius. The location this shear layer depends on magnetic configuration, limiter radius and conditions. Using position as reference point, density fluctuation levels ATF (currentless stellarator) are very similar to those previously reported TEXT (ohmically heated tokamak),...
The physics of enhanced confinement regimes in tokamaks is reviewed and some directions for further enhancements are assessed. H-mode regime examined. A number other observations confinement, having common peaked density profiles, compared to the theory ion temperature gradient modes. Two schemes promise enhancing second stability control electric fields, discussed. contributions alternate concepts understanding tokamak transport described.
The addition of an ℓ = 1 helical winding to the heliac central conductor adds a significant degree flexibility configuration by making it possible control rotational transform and shear. Such is essential for experiment because presence low-order resonances in profile can cause breakup equilibrium magnetic surfaces. use additional also permits reduction total current deepen well.
CO2 laser interferometry was used to determine electron density profiles in copper vacuum arcs just before and after the transition from low-voltage quiescent mode high-voltage associated with anode-spot formation. Just transition, electron-density are peaked on axis, maxima of 9×1014 cm−3 6×1014 cathode anode regions, respectively. At about 0.1 ms profile region remains unchanged, while central near drops be a factor 2. No constriction observed at any axial position. Previously reported...
During the first operational phase (referred to as OP1.1) of new Wendelstein 7-X (W7-X) stellarator, five poloidal graphite limiters were mounted on inboard side vacuum vessel, one in each toroidal modules which form W7-X vessel. Each limiter consisted nine specially shaped tiles, designed conform last closed field line geometry bean-shaped section standard OP1.1 magnetic configuration (Sunn Pedersen et al 2015 Nucl. Fusion 55 126001). We observed with multiple infrared and visible camera...
A set of new water-cooled divertor components is being designed for the Wendelstein 7-X stellarator to protect edges primary plasma facing during bootstrap current evolution (~ 40 s). These components, referred as scraper elements (SEs), will intercept field lines and associated heat flux that would otherwise overload main target in certain operational scenarios. The SEs are calculated experience peak fluxes ~15-16 MW/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML"...
Abstract In the Wendelstein 7-X stellarator, main locations of particle sources are expected to be carbon divertors, baffles and graphite heat shield first wall. this paper, is implemented in EMC3-EIRENE understand areas magnitudes recycling flux component. It found that simulation not a significant source neutrals. The simulated shown correlate well with footprints plasma-wetting seen post-experimental campaign in-vessel inspection photos. reconstruction line-integrated H-alpha measurements...
Experimental results on the Texas Tokamak (TEXT) [Nucl. Technol./Fusion 1, 479 (1982)] and Advanced Toroidal Facility (ATF) torsatron [Fusion Technol. 10, 179 (1986)] indicate that electrostatic fluctuations can explain edge transport of particles perhaps energy. Certain mechanisms for drive (radiation ionization, as well density temperature gradients) stabilization (velocity shear) are suggested by these results. The experimental fluctuation levels turbulence characteristics be reproduced...