A5053398030- Magnetic confinement fusion research
- Fusion materials and technologies
- Superconducting Materials and Applications
- Ionosphere and magnetosphere dynamics
- Laser-Plasma Interactions and Diagnostics
- Plasma Diagnostics and Applications
- Particle accelerators and beam dynamics
- Laser-induced spectroscopy and plasma
- Atomic and Molecular Physics
- Laser Design and Applications
- Atomic and Subatomic Physics Research
- Solar and Space Plasma Dynamics
- Semiconductor materials and devices
- Semiconductor Quantum Structures and Devices
- Spectroscopy and Laser Applications
- Solid State Laser Technologies
- Physics of Superconductivity and Magnetism
- Fluid Dynamics and Turbulent Flows
- Nuclear reactor physics and engineering
- Photorefractive and Nonlinear Optics
- Advanced Fiber Laser Technologies
- Nuclear Physics and Applications
- Advanced Data Storage Technologies
- Silicon Carbide Semiconductor Technologies
- Astronomical Observations and Instrumentation
General Atomics (United States)
2013-2023
University of California, Los Angeles
2003-2018
California State University, San Marcos
2018
Palomar College
2018
National Institute for Fusion Science
2018
Lawrence Livermore National Laboratory
1995-2015
DIII-D National Fusion Facility
1998-1999
Fusion (United States)
1998
Max Planck Institute for Plasma Physics
1996
Massachusetts Institute of Technology
1995
This paper describes the design and operation of a 40 spatial channel Thomson scattering system that uses multiple 20-Hz Nd:YAG lasers to measure electron temperature density profiles periodically throughout an entire plasma discharge. As many as eight may be fired alternately for average measurement frequency 160 Hz, or they in rapid succession (<10 kHz), producing burst pulses measuring transient events. The high resolution (1.3 cm) wide dynamic range (10 eV–20 keV) enable this...
The paradigm of shear suppression turbulence as the mechanism for low to high confinement mode (L H) transition is examined by quantitative comparison predictions with experimental results from DIII-D tokamak [Plasma Physics and Controlled Fusion Research (International Atomic Energy Agency, Vienna, 1986), p. 159]. L H trigger V×B rotation, not main ion pressure gradient. radial electric field Er increases before fluctuation suppression, consistent increasing cause suppression. spatial...
Combined theoretical and experimental work has resulted in the creation of a paradigm which allowed semi-quantitative understanding edge confinement improvement that occurs H-mode. Shear E*B flow fluctuations plasma can lead to decorrelation fluctuations, decreased radial correlation lengths reduced turbulent transport. Changes electric field, density transport consistent with shear stabilization turbulence have been seen several tokamaks. The purpose this paper is discuss most recent data...
Edge conditions in DIII-D are being quantified order to provide insight into the physics of H mode regime. Several studies show that electron temperature is not key parameter controls L-H transition. Gradients edge and pressure much more promising candidates for elements such parameters. They systematically increase during L phases discharges which make a transition mode, these increases typically larger than underlying quantities. The quality confinement strongly correlated with height...
A Thomson scattering system is being developed for Joint European Torus with 15 mm spatial resolution and a foreseen accuracy temperature better than 15% at density of 1019 m−3. This required the internal transport barrier edge pedestal it can not be fully achieved present light detection ranging systems. The laser this Nd:YAG, 5 Joule, 20 Hz. Scattering volumes from R=2.9 m to R=3.9 are imaged onto 1 diameter fibers, F/25 collection aperture. Two fibers used per volume. Using optical delay...
The authors' data indicate that the L-mode to H-mode transition in DIII-D tokamak is associated with sudden reduction anomalous, fluctuation-connected transport across outer midplane of plasma. In addition edge density and magnetic fluctuations observed at transition, radial electric field becomes more negative after transition. They have determined scaling power threshold various plasma parameters; roughly linear increase toroidal are particularly significant. Control ELM frequency duration...
The ITER Threshold Database, which at present comprises data from nine divertor tokamaks, is described. main results are presented and discussed. properties dependences of the power threshold in individual devices reviewed. In particular, analysis shows a rather general linear dependence on magnetic field, but non-monotonic density that varies device to device. Investigation combined database suggests P thres approximately=0.3n e B T 2.5 reasonable agreement with data. This expression yields...
The L to H transition in the DIII-D tokamak [Plasma Physics and Controlled Nuclear Fusion Research 1986 (IAEA, Vienna, 1987), Vol. I, p. 159] is associated with a decrease edge density magnetic fluctuations. In addition, single-null divertor plasmas, reduction heat flux asymmetry between inner outer hit spots occurs. These observations indicate that anomalous, fluctuation-connected transport across midplane of plasma. Magnetic fluctuations are measured poloidally distributed set Mirnov loops...
A multichannel, two-color, quadrature heterodyne interferometer is used to measure the line density in DIII-D tokamak. The unique feature of this real-time vibration-compensated combination high speed (1 MHz), resolution (2π/256), and wide range (±8193 fringes). Quadrature phase information from a CO2 laser (10.6 μm) He–Ne (0.63 are digitized with high-speed (6 MHz) flash digitizers. Zero crossings signals counted digital circuitry yielding quarter fringe 4-MHz bandwidth. Further 1/256...
Tokamak discharges using the expanded boundary divertor in DIII-D device exhibit H-mode confinement. With neutral-beam power up to 6 MW, energy confinement remains comparable Ohmic value at a plasma current of 1 MA. Confinement is also independent density and toroidal field. increases with current, but exact functional dependence is, as yet, uncertain. These results show that H mode can be achieved reactor-compatible open configuration.
Both external and internal magnetic probes have been used in low-current discharges high-current to study the field configuration its fluctuations OHTE toroidal pinch with reversal. The equilibrium is close that of Taylor state central half plasma (μ≡μ0bJ/B constant) but differs outer (μ gradually goes zero at edge). Measurements indicate dominant fluctuation mode observed resistive kink m=1, n≂18. measured relative level scales as B̃/B∼S−1/2, where S Reynolds number.
Measurements in DIII-D of edge ion and electron temperatures ( ) just prior to the transition H-mode are presented. A fitting model based on a hyperbolic tangent function is used analysis. The observed increase during L-phase with application auxiliary heating. temperature rise small if power threshold close ohmic level absence heating large well above level. approximately proportional toroidal magnetic field , for either reversed or forward direction. However, field, at least factor two higher than
Accurate equilibrium reconstruction and detailed stability analysis of a strongly shaped, double-null, βT=11% discharge shows that the plasma core is in second stable regime to ideal ballooning modes. The using all available data (coil currents, poloidal magnetic loops, motional Stark effect data, kinetic pressure profile, axis location, location two q=1 surfaces) region negative shear near axis, an outer positive region, low connecting two. inner allows large boundary, even at q (q95=2.6),...
Thomson scattering measurements of ne and Te in the divertor region a Tokamak are reported. These data used as input to boundary physics codes such UEDGE DEGAS benchmark predictive capabilities these codes. have also contributed characterization tokamak disruptions. A Nd:YAG laser (20 Hz, 1 J, 15 ns, 1064 nm) is directed vertically through lower DIII–D Tokamak. custom, aspherical collection lens (f/6.8) images beam from 21 cm above target plates into eight spatial channels with 1.5 vertical...
A seven channel polychromator, utilizing high performance interference filters (transmission ≳80%, rejection at laser wavelength>105), has been tested for use in the multi-Nd:YAG Thomson scattering system DIII-D tokamak. Unique features of this polychromator are combination throughput, easy alignment, flexibility, compact size, and low cost when compared with other alternatives. Light is introduced to (f/1.75) via a fiber optic bundle which permits small (3.0 cm diam) optics leads...
The transition from the low to high mode of plasma confinement ( $L\ensuremath{-}H$ transition) is studied in DIII-D by an experimental technique which allows arbitrarily slow transition. During initial transition, periodic turbulent instability bursts are observed near separatrix inhibit full These damped self-generated shear flows, and a predator-prey-type relationship shown give good description data. As neutral-beam power raised, oscillations change type III edge localized modes. Another...
A fiber optic, heterodyne, two-color interferometer utilizing wavelength division multiplexing technology has been developed for measuring electron density in plasmas. Vibration compensation is accomplished via common path 1.31 and 1.55μm distributed feedback laser interferometers. All beam combining, splitting, frequency modulation, collimation are by shared single-mode optic components. Measurements of an argon radio-frequency generated plasma with densities 1020m−3 show effective...
One of the systems planned for measurement electron density in ITER is a multi-channel tangentially viewing combined interferometer-polarimeter (TIP). This work discusses current status design, including preliminary optical table layout, calibration options, error sources, and performance projections based on CO2/CO laser system. In two-color interferometry carried out at 10.59 μm 5.42 separate polarimetry plasma induced Faraday effect, utilizing rotating wave technique, made μm. The...
New experiments on DIII-D have demonstrated the steady-state potential of hybrid scenario, with 1 MA plasma current driven fully non-inductively and βN up to 3.7 sustained for ∼3 s (∼1.5 diffusion time, τR, in DIII-D), providing basis an attractive option operation ITER FNSF. Excellent confinement is achieved (H98y2 ∼ 1.6) without performance limiting tearing modes. The regime overcomes need off-axis drive efficiency, taking advantage poloidal magnetic flux pumping that believed be result a...
A design to extend the unique divertor Thomson scattering system on DIII-D allow measurements of electron temperature and density in high triangularity plasmas is presented. Access this region selectable a shot-by-shot basis by redirecting laser beam existing inboard - beneath lower floor using moveable, high-damage threshold, in-vacuum mirror then again vertically. The currently measured remains available with retracted. Scattered light collected from viewchords near in-vacuum, optical...
A full-scale 120 m path length ITER toroidal interferometer and polarimeter (TIP) prototype, including an active feedback alignment system, has been constructed undergone initial testing at General Atomics. In the TIP two-color interferometry is carried out 10.59 μm 5.22 using a CO2 quantum cascade laser (QCL) respectively while separate polarimetry measurement of plasma induced Faraday effect made μm. The system uses co-linear right left-hand circularly polarized beams upshifted by 40 44...
The transition from low-confinement (L-mode) to high-confinement (H-mode) plasmas has been directly produced by injecting frozen deuterium pellets in the DIII-D tokamak. H-mode transitions were at edge electron and ion temperatures below L-mode values. This implies that a critical temperature is not necessary for transitions. experimentally determined plasma parameters well those predicted several theories of trigger H-mode, indicating need revision these theories.
Recent measurements of the two-dimensional (2-D) spatial profiles divertor plasma density, temperature, and emissivity in DIII-D tokamak [J. Luxon et al., Proceedings 11th International Conference on Plasma Physics Controlled Nuclear Fusion (International Atomic Energy Agency, Vienna, 1987), p. 159] under highly radiating conditions are presented. Data obtained using a Thomson scattering system other diagnostics optimized for measuring high electron densities low temperatures these detached...
Measurements are presented of toroidicity-induced (TAEs) and reverse shear (RSAEs) Alfven eigenmodes made using the standard two-colour CO2 interferometer on DIII-D modified for increased bandwidth. Typical values effective line-integrated density perturbation in found to be d(nL)/nL ~ 10−3, comparisons with NOVA calculations as well magnetic measurements. There is a strong difference measured power spectrum between vertical radial chords through plasma. On average, views characterized by...