A5089307482- Magnetic confinement fusion research
- Ionosphere and magnetosphere dynamics
- Solar and Space Plasma Dynamics
- Particle accelerators and beam dynamics
- Superconducting Materials and Applications
- Plasma Diagnostics and Applications
- Laser-Plasma Interactions and Diagnostics
- Fusion materials and technologies
- Laser-induced spectroscopy and plasma
- Meteorological Phenomena and Simulations
- Fluid Dynamics and Turbulent Flows
- Magnetic Field Sensors Techniques
- Geomagnetism and Paleomagnetism Studies
- Dust and Plasma Wave Phenomena
- Geophysics and Gravity Measurements
- Particle Accelerators and Free-Electron Lasers
- Acoustic Wave Resonator Technologies
- Gyrotron and Vacuum Electronics Research
- Ocean Waves and Remote Sensing
- Spacecraft and Cryogenic Technologies
- Tropical and Extratropical Cyclones Research
- Characterization and Applications of Magnetic Nanoparticles
- Diamond and Carbon-based Materials Research
- Nuclear reactor physics and engineering
- Particle Dynamics in Fluid Flows
University of California, Los Angeles
2015-2025
General Atomics (United States)
2006-2022
Princeton Plasma Physics Laboratory
2006-2017
University of California, Berkeley
2015
University of California, Irvine
2006-2012
Nova Photonics (United States)
2006-2010
University of California, San Diego
2003-2009
Fusion (United States)
2006-2009
Angelo State University
2006
Higashihiroshima Medical Center
2006
Experimental results from a magnetized argon plasma column demonstrate controlled transition to turbulent state as the magnetic field (B) strength is increased. At lower B there an onset of fluctuations in density and potential. These are shown be due drift waves that have been modified by flow shear. As increased character undergoes several changes. changes include general decrease coherence, increase phase lag (between potential), straightening observed dispersion relation. Concomitantly,...
A wide variety of fast ion driven instabilities are excited during neutral beam injection (NBI) in the National Spherical Torus Experiment (NSTX) [Nucl. Fusion 40, 557 (2000)] due to large ratio velocity Alfvén velocity, Vfast∕VAlfvén, and high beta. The Vfast∕VAlfvén ITER 39, 2137 (1999)] NSTX is comparable. modes can be divided into three categories: chirping energetic particle (EPM) frequency range 0 120kHz, toroidal eigenmodes (TAE) with a 50kHz 200kHz, compressional global (CAE GAE,...
Kinetic theory and experimental observations of a special class energetic particle driven instabilities called here beta-induced Alfvén-acoustic eigenmodes (BAAEs) are reported confirming, previous results [N. N. Gorelenkov et al., Plasma Phys. Controlled Fusion 49, B371 (2007)]. The kinetic is based on the ballooning dispersion relation where drift frequency effects retained. BAAE gaps recovered in theory. It shown that observed certain low-frequency DIII-D [J. L. Luxon, Nucl. 42, 614...
Extremely low density operation free of error field penetration supports the excitation trace-level quiescent runaway electron (RE) populations during flat-top DIII-D Ohmic discharges. Operation in regime allows accurate measurement all key parameters important to RE excitation, including internal broadband magnetic fluctuation level. onset is characterized and found be consistent with primary (Dreicer) generation rates. Impurity-free collisional suppression population investigated by...
Thermal energy confinement times in National Spherical Torus Experiment (NSTX) dimensionless parameter scans increase with decreasing collisionality. While ion thermal transport is neoclassical, the source of anomalous electron these discharges remains unclear, leading to considerable uncertainty when extrapolating future spherical tokamak (ST) devices at much lower Linear gyrokinetic simulations find microtearing modes be unstable high collisionality discharges. First non-linear turbulence...
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 National Spherical Torus Experiment (NSTX) has undergone a major upgrade, and the NSTX Upgrade (NSTX-U) Project was completed in summer of 2015.NSTX-U first plasma subsequently achieved, diagnostic control systems have been commissioned, H-mode accessed, magnetic error fields identified mitigated, physics research campaign carried out.During ten run weeks operation, NSTX-U surpassed record pulse-durations toroidal (TF), high-performance ~1 MA plasmas comparable to best sustained near...
Neoclassical tearing modes (NTMs) often lead to the decrease of plasma performance and can disruptions, which makes them a major impediment in development operating scenarios present toroidal fusion devices. Recent gyrokinetic simulations predict turbulence cross-field transport at O-point islands, turn affects NTM dynamics. In this paper, heat model magnetic islands employing spatially non-uniform thermal diffusivity (χ⊥) is presented. This used derive χ⊥ from electron temperature data...
A new frequency-stepped Doppler backscattering (DBS) system has been integrated into a real-time steerable electron cyclotron heating launcher to simultaneously probe local background turbulence (f < 10 MHz) and high-frequency (20–550 density fluctuations in the DIII-D tokamak. The allows for 2D steering (horizontally vertically) over wide angular ranges optimize location wavenumber response. vertical can be optimized during discharge real time. DBS employs programmable frequency...
Experiments in L- and H-mode plasmas performed on the DIII-D tokamak explored ion cyclotron emission (ICE) propagation via recently upgraded ICE diagnostic. The distance between plasma outer wall was scanned to alter evanescent region, which seen impact detection of runaway electron-driven whistler modes a comparable frequency range typical harmonics (f≳10fci) [Heidbrink et al., Plasma Phys. Controlled Fusion 61, 014007 (2018)]. In L-mode plasmas, core did not exhibit clear trends as...
Results obtained on the Madison Symmetric Torus (MST) reversed-field pinch [Fusion Technol. 19, 131 (1991)] after installation of design poloidal field winding are presented. Values βθe0≡2μ0ne0Te0/B2θ(a)∼12% achieved in low-current (I=220 kA) operation; here, ne0 and Te0 central electron density temperature, Bθ(a) is magnetic at plasma edge. An observed decrease βθe0 with increasing current may be due to inadequate fueling, enhanced wall interaction, growth a radial error vertical cut shell...
Experiments on the National Spherical Torus Experiment [M. Ono et al., Nucl. Fusion 40, 557 (2000)] found strong bursts of toroidal Alfvén eigenmode (TAE) activity correlated with abrupt drops in neutron rate. A fairly complete data set offers opportunity to benchmark NOVA [C. Z. Cheng, Phys. Rep. 211, 1 (1992)] and ORBIT [R. B. White M. S. Chance, Fluids 27, 2455 (1984)] codes low aspect ratio tokamak (ST) geometry. The internal structure TAE was modeled good agreement is measurements made...
Fast-ion transport induced by Alfvén eigenmodes (AEs) is studied in beam-heated plasmas on the National Spherical Torus Experiment [Ono et al., Nucl. Fusion 40, 557 (2000)] through space, time, and energy resolved measurements of fast-ion population. losses associated with multiple toroidicity-induced AEs (TAEs), which interact nonlinearly terminate avalanches, are characterized. A depletion range >20 keV, leading to sudden drops up 40% neutron rate over 1 ms, observed a broad spatial...
Global modes?including kinks and tearing modes (f ~ 400?kHz)?play critical roles in many aspects of plasma performance. Their investigation on NSTX is aided by an array fixed-frequency quadrature reflectometers used to determine their radial density perturbation structure. The has been recently upgraded 16 channels spanning 30?75?GHz (ncutoff = (1.1?6.9) ? 1019?m?3 O-mode), improving spatial sampling access the core H-mode plasmas. upgrade yielded significant new results that advance...
Transport and turbulence profiles were directly evaluated using probes for the first time in edge scrape-off layer (SOL) of NSTX [Ono et al., Nucl. Fusion 40, 557 (2000)] low (L) high (H) confinement, power (Pin∼ 1.3 MW), beam-heated, lower single-null discharges. Radial turbulent particle fluxes peak near last closed flux surface (LCFS) at ≈4×1021 s−1 L-mode are suppressed to ≈0.2×1021 H mode (80%–90% lower) mostly due a reduction density fluctuation amplitude phase between radial velocity...
The high-k () wavenumber spectrum of density fluctuations has been measured for the first time in MAST (Lloyd et al 2003 Nucl. Fusion 43 1665). This was accomplished with implementation Doppler backscattering (DBS) core measurements a spherical tokamak. DBS become well-established and versatile diagnostic technique measurement intermediate- k (, higher) flows magnetically confined fusion experiments. Previous implementations have standard, large aspect ratio tokamaks. A novel two-dimensional...
The major objective of the National Spherical Torus Experiment (NSTX) is to understand basic toroidal confinement physics at low aspect ratio and high βT in order advance spherical torus (ST) concept. In do this, NSTX utilizes up 7.5 MW neutral beam injection, 6 harmonic fast waves (HHFWs), it operates with plasma currents 1.5 MA elongations 2.6 a field 0.45 T. New facility, diagnostic modelling capabilities developed over past two years have enabled research team make significant progress...
In this paper we report on observations and interpretations of a new class global MHD eigenmode solutions arising in gaps the low frequency Alfvén–acoustic continuum below geodesic acoustic mode frequency. These modes have been just reported (Gorelenkov et al 2007 Phys. Lett. 370 70–7) where preliminary comparisons indicate qualitative agreement between theory experiment. Here show more quantitative comparison emphasizing recent NSTX experiments eigenmodes, referred to as beta-induced...
The mission of the National Spherical Torus Experiment (NSTX) is demonstration physics basis required to extrapolate next steps for spherical torus (ST), such as a plasma facing component test facility (NHTX) or an ST based (ST-CTF), and support ITER. Key issues are transport, steady state high β operation. To better understand electron new high- k scattering diagnostic was used extensively investigate gyro-scale fluctuations with varying temperature gradient scale length. Results from n = 3...
Abstract Chirping toroidicity-induced Alfvén eigenmodes (TAEs) are destabilized during neutral beam injection on the National Spherical Torus Experiment (NSTX (Ono M. et al 2000 Nucl. Fusion 40 557)) by super-Alfvénic ions with velocities up to five times larger than velocity. TAEs exhibit repeated bursts in amplitude and down-chirps frequency. Larger bursts, so-called TAE avalanches , eventually observed correlate a loss of fast 30% over ∼1 ms. Frequency, radial structure characterized via...
Abstract Strong toroidal Alfvén eigenmode (TAE) avalanches on NSTX, the National Spherical Torus Experiment (Ono et al 2000 Nucl. Fusion 40 557 ) are typically correlated with drops in neutron rate range 5–15%. In previous studies of L-mode plasmas, these were found to be consistent modelled losses fast ions. Here we expand study TAE NSTX H-mode plasmas improved analysis techniques. At measured mode amplitudes, simulations ORBIT code predict that ion negligible. However, scatter ions energy,...
The National Spherical Torus Experiment (NSTX, (Ono et al 2000 Nucl. Fusion 40 557 )) routinely operates with neutral beam injection as the primary system for heating and current drive. resulting fast ion population is super-Alfvénic, velocities 1 < v / Alfven 5. This provides a strong drive toroidicity-induced Alfvén eigenmodes (TAEs). As discharge evolves, builds up TAEs exhibit increasing bursts in amplitude down-chirps frequency, which eventually lead to so-called TAE avalanche....
An energy-channeling mechanism is proposed to explain flattening of the electron temperature profiles at a high beam power in beam-heated National Spherical Torus Experiment (NSTX). Results self-consistent simulations neutral-beam-driven compressional Alfv\'en eigenmodes (CAEs) NSTX are presented that demonstrate strong coupling CAEs kinetic waves resonance location. It suggested can channel energy from ions location resonant mode conversion edge density profile, modifying deposition profile.
In this Letter we present data from experiments on the National Spherical Torus Experiment Upgrade, where it is shown for first time that small amounts of high pitch-angle beam ions can strongly suppress counterpropagating global Alfv\'en eigenmodes (GAE). GAE have been implicated in redistribution fast and modification electron power balance previous NSTX. The ability to predict stability modes, developing methods control them, important fusion reactors like International Tokamak...
Measurements of local density and magnetic field fluctuations near the pedestal top, conditionally averaged over edge localized mode (ELM) cycle, have been made in Mega Amp Spherical Tokamak (MAST). A Doppler backscattering (DBS) system installed at MAST was used to measure intermediate-k top pedestal. novel diagnostic technique combining DBS with cross-polarization scattering (CP-DBS) enabled also be locally measured similar wave numbers. Polarization isolation other effects for CP-DBS are...