A5023485348- Magnetic confinement fusion research
- Ionosphere and magnetosphere dynamics
- Laser-Plasma Interactions and Diagnostics
- Solar and Space Plasma Dynamics
- Fusion materials and technologies
- Particle accelerators and beam dynamics
- Superconducting Materials and Applications
- Plasma Diagnostics and Applications
- Laser-induced spectroscopy and plasma
- Atomic and Subatomic Physics Research
- Nuclear Physics and Applications
- Atomic and Molecular Physics
- Astro and Planetary Science
- Nuclear reactor physics and engineering
- Geomagnetism and Paleomagnetism Studies
- Spacecraft and Cryogenic Technologies
- Spectroscopy and Laser Applications
- Geophysics and Gravity Measurements
- Fluid Dynamics and Turbulent Flows
- Physics of Superconductivity and Magnetism
- Advanced Chemical Physics Studies
- Particle Accelerators and Free-Electron Lasers
- X-ray Spectroscopy and Fluorescence Analysis
- Computational Physics and Python Applications
- Seismic Imaging and Inversion Techniques
University of Wisconsin–Madison
2013-2024
Princeton Plasma Physics Laboratory
1990-2013
University of California, San Diego
2001-2012
Oak Ridge National Laboratory
1997-2012
Massachusetts Institute of Technology
1997-2012
Office of Fusion Energy Sciences
2007
Office of Science
2007
General Atomics (United States)
1997-2005
Michigan State University
2002
Princeton University
1987-1998
Deuterium neutral beams with energies up to 110 keV were injected into TFTR (Tokamak Fusion Test Reactor) plasmas at low magnetic field such that the beam injection velocities comparable Alfv\'en velocity. Excitation of toroidal eigenmodes was observed by Mirnov coils and emission spectroscopy.
Intermittent plasma objects (IPOs) featuring higher pressure than the surrounding plasma, and responsible for ∼50% of E×BT radial transport, are observed in scrape off layer (SOL) edge DIII-D tokamak [J. Watkins et al., Rev. Sci. Instrum. 63, 4728 (1992)]. Conditional averaging reveals that IPOs, produced at a rate ∼3×103 s−1, positively charged also polarized, poloidal electric fields up to 4000 V/m. The IPOs move poloidally speeds 5000 m/s radially with E×BT/B2 velocities ∼2600 near last...
Intermittent plasma objects (IPOs), featuring higher pressure than the surrounding plasma, are responsible for ∼50% of E×BT radial transport in scrape off layer (SOL) Doublet III D (DIII-D) tokamak [J. L. Luxon, Nucl. Fusion 42, 614 (2002)] L- and H-mode discharges. Conditional averaging reveals that IPOs positively charged feature internal poloidal electric fields up to 4000 V/m. The move radially with E×BT/B2 velocities ∼2600 m/s near last closed flux surface (LCFS), ∼330 wall. slow down...
Neutral-beam heating of plasmas in the Tokamak Fusion Test Reactor at low preinjection densities [${n}_{e}$(0)\ensuremath{\simeq}${10}^{19}$ ${\mathrm{m}}^{\mathrm{\ensuremath{-}}3}$] were characterized by ${T}_{e}$(0)=6.5 keV, ${T}_{i}$(0)=20 ${n}_{e}$(0)=7\ifmmode\times\else\texttimes\fi{}${10}^{19}$ ${\mathrm{m}}^{\mathrm{\ensuremath{-}}3}$, ${\ensuremath{\tau}}_{E}$=170 msec, ${\ensuremath{\beta}}_{\mathrm{theta}}$=2, and a d(d,n${)}^{3}$He neutron emission rate ${10}^{16}$...
Simultaneous profile measurements of the toroidal rotation speed and ion temperature during unbalanced neutral beam injection in Tokamak Fusion Test Reactor show that momentum thermal diffusivities are comparable magnitude (${\mathrm{\ensuremath{\chi}}}_{\mathrm{\ensuremath{\varphi}}}$\ensuremath{\approxeq}1.5${\mathrm{\ensuremath{\chi}}}_{\mathrm{i}}$) vary similarly with plasma current minor radius. The correlation ${\mathrm{\ensuremath{\chi}}}_{\mathrm{\ensuremath{\varphi}}}$...
High-frequency observations of light emitted from the interactions between plasma ions and injected neutral beam atoms allow measurement moderate-wavelength fluctuations in impurity ion densities. To detect turbulence local density, collisionally excited fluorescence a is measured either separately at several spatial points or with multichannel imaging detector. Similarly, role density using charge exchange recombination transitions by species interest. This technique can access relatively...
Comprehensive 2D turbulence and eddy flow velocity measurements on DIII-D demonstrate a rapidly increasing turbulence-driven shear that develops $\ensuremath{\sim}100\text{ }\text{ }\ensuremath{\mu}\mathrm{s}$ prior to the low-confinement ($L$ mode) high-confinement ($H$ transition appears trigger it. These changes are localized narrow layer 1--2 cm inside magnetic boundary. Increasing heating power increases Reynolds stress, energy transfer from poloidal flow, edge shearing rate then...
Long-wavelength (${\mathit{k}}_{\mathrm{\ensuremath{\perp}}}$${\mathrm{\ensuremath{\rho}}}_{\mathit{i}}$1) density turbulence has been measured with good spatial localization in the core region of a high temperature tokamak plasma auxiliary heating. Density fluctuations n\ifmmode \tilde{}\else \~{}\fi{}/n>0.5% exist for ${\mathit{k}}_{\mathrm{\ensuremath{\perp}}}$2 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ radial and poloidal correlation lengths typically 1--2.5 cm confinement region,...
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 authors compare the spectrum of regularly spaced photoabsorption resonances which appear in vicinity ionization threshold for atoms a strong magnetic field with predictions semiclassical strong-mixing models. Quasi-Landau resonance positions are shown to agree well two-dimensional WKB hydrogenic model depicts as bound states electron combined Coulomb and fields reduces Rydberg levels at low excitation. Simpler treatments based on modified Bohr atomic also discussed. data include...
Time-resolved measurements of the turbulent density flow field in a tokamak plasma reveal low-frequency ( approximately 15 KHz), coherent oscillations poloidal flow, v(theta). These have long wavelength (m<3) and narrow radial extent (k(r)rho(i) 0.2). The estimated flow-shearing rate is same order magnitude as turbulence decorrelation may thus regulate amplitude. features are consistent with theoretically predicted axisymmetric, self-regulating, sheared flows recognized geodesic acoustic modes.
Plasma turbulence characteristics, including radial correlation lengths, decorrelation times, amplitude profile and flow velocity, have been measured during a ρ* scan on DIII-D while all other transport relevant dimensionless quantities (e.g., β, ν*, κ, q, Te/Ti) are held nearly constant. The is by examining the properties of local long wavelength (k⊥ρi ≤ 1) density fluctuations, with beam emission spectroscopy. length Lc,r shown to scale ion gyroradius, ≈ 5ρi, times acoustic velocity as...
Characteristics and scaling properties of the geodesic acoustic mode (GAM), a coherent, radially-sheared high frequency (~15?kHz) zonal flow oscillation, are studied systematically using time-delay-estimation techniques applied to localized, multi-point density fluctuation measurements obtained by beam emission spectroscopy on DIII-D. The GAM amplitude is shown increase strongly with increasing safety factor, q95, likewise become undetectably small for q95 < 4.2, qualitatively consistent...
A low-frequency, spectrally broad (Deltaf approximately 10 kHz) poloidal flow structure that peaks near zero frequency is observed in time-resolved measurements of the turbulence velocity field core region (r/a 0.6-0.9) DIII-D tokamak plasmas. These flows exhibit a long wavelength (low m) and short radial coherence length comparable to ambient decorrelation length. Characteristics these are consistent with theoretically predicted residual or zero-mean-frequency zonal flows.
Research on the National Spherical Torus Experiment, NSTX, targets physics understanding needed for extrapolation to a steady-state ST Fusion Nuclear Science Facility, pilot plant, or DEMO. The unique operational space is leveraged test theories next-step tokamak operation, including ITER. Present research also examines implications coming device upgrade, NSTX-U. An energy confinement time, τE, scaling unified varied wall conditions exhibits strong improvement of BTτE with decreased electron...
The Tokamak Fusion Test Reactor (TFTR) (R. J. Hawryluk, to be published in Rev. Mod. Phys.) experiments on high-temperature plasmas, that culminated the study of deuterium–tritium D–T plasmas containing significant populations energetic alpha particles, spanned over two decades from conception completion. During design TFTR, key physics issues were magnetohydrodynamic (MHD) equilibrium and stability, plasma energy transport, impurity effects, reactivity. Energetic particle was given less...
Zonal flows, thought crucial to the saturation and self-regulation of turbulence turbulent transport in magnetically confined plasmas, have been observed characterized edge region DIII-D plasmas. These flows exhibit temperature scaling characteristics spatial features predicted for geodesic acoustic modes (GAMs), a class higher-frequency zonal seen nonlinear simulations plasma turbulence. The (GAMs) flow-field radial 0.85 ⩽ r/a 1.0 via application time-delay-estimation techniques...
Discharges exhibiting the highest plasma energy and fusion reactivity yet realized in DIII-D tokamak [Plasma Physics Controlled Nuclear Fusion Research, 1986 (International Atomic Energy Agency, Vienna, 1987), Vol. I, p. 159] have been produced by combining benefits of a hollow or weakly sheared central current profile [Phys. Plasmas 3, 1983 (1996)] with high confinement (H mode) edge. In these discharges, low-power neutral beam injection heats electrons during initial ramp, “freezes in”...
Unique measurements of the basic plasma-flow characteristics in a low pressure (⩽53 mPa H2) spherically convergent ion focus are obtained using high-voltage (⩽5 kV) emissive and double probes. The radial plasma potential distribution agrees with collisionless, recirculating, space-charge-limited current model. Flow convergence increases voltage neutral decreases cathode grid wire spacing current. Core radii within 4–5 times ideal geometric limit measured, observed core sizes consistent...
Previous studies of plasma microturbulence have indicated that the fluctuation power scales with radial wave number, k⊥ , like k⊥−2→k⊥−3.5 for ≥2 cm−1. This implies low k fluctuations may dominate spectrum. Beam emission spectroscopy (BES) has been developed to provide spatially localized measurements density in this region spectrum (k⊥ ≤2 cm−1). A 20-channel system installed on TFTR which images one heating neutral beams (via fiber optics) onto a set photoconductive photodiode detectors....
Beam Emission Spectroscopy (BES), a high-sensitivity, good spatial resolution imaging diagnostic system, has been deployed and recently upgraded expanded at the DIII-D tokamak to better understand density fluctuations arising from plasma turbulence. The currently system images over an approximately 5 × 7 cm region mid-plane (radially scannable 0.2 < r/a ≤ 1) with 6 (radial poloidal) grid of rectangular detection channels, one microsecond time resolution. BES observes collisionally-induced,...
Two-dimensional measurements of density fluctuations are obtained in the radial and poloidal plane DIII-D tokamak with Beam Emission Spectroscopy (BES) diagnostic system. The goals to visualize spatial structure time evolution turbulent eddies, as well obtain 2D statistical properties turbulence. an array localized BES channels configured image a midplane region plasma. 32 have been deployed, each resolution about 1 cm directions, thus providing turbulence wave number range 0&lt;k⊥⩽3...
High temporal and spatial resolution measurements in the boundary of DIII-D tokamak show that edge-localized modes (ELMs) are produced low field side, poloidally localized composed fast bursts (∼20 to 40μs long) hot, dense plasma on a background less dense, colder (∼5×1018m−3, 50 eV) possibly created by themselves. The ELMs travel radially scrape-off layer (SOL), starting at separatrix ∼450m∕s, slow down ∼150m∕s near wall, convecting particles energy SOL walls. temperature density ELM...
Turbulence is significantly reduced in a tokamak plasma as result of neon seeding an L-mode discharge. Correspondingly, confinement improved and cross-field ion thermal transport reduced. Fully saturated turbulence the range 0.1</=k( perpendicular)rho(s)</=0. 6 measured at rho = 0.7 exhibits factor 5 reduction total power after injection, with almost complete suppression for k( perpendicular)rho(s)>0.35. These observations are consistent calculated linear growth rate perpendicular)rho(s)>0.5...
The highly indented plasmas of the PBX-M tokamak experiment [Plasma Physics and Controlled Nuclear Fusion Research (IAEA, Vienna, 1989), Vol. 1, p. 97] have reached plasma regimes both high volume-averaged beta (βt), high-beta poloidal (βp), show evidence suppression external surface modes by passive stabilizing system. Values βt up to 4.0 I/aB (% MA/m T) with Ti(0)≊4 keV been obtained. A magnetohydrodynamic analysis βp=2.0 indicates that these are near threshold second stability regime....