A5077333630- Magnetic confinement fusion research
- Fusion materials and technologies
- Ionosphere and magnetosphere dynamics
- Laser-Plasma Interactions and Diagnostics
- Superconducting Materials and Applications
- Plasma Diagnostics and Applications
- Nuclear Materials and Properties
- Solar and Space Plasma Dynamics
- Laser-induced spectroscopy and plasma
- Ion-surface interactions and analysis
- Particle accelerators and beam dynamics
- Dust and Plasma Wave Phenomena
- Atomic and Molecular Physics
- Semiconductor materials and devices
- Metal and Thin Film Mechanics
- Nuclear reactor physics and engineering
- Fluid Dynamics and Turbulent Flows
- Atomic and Subatomic Physics Research
- Mathematics, Computing, and Information Processing
- Advancements in Semiconductor Devices and Circuit Design
- High-pressure geophysics and materials
- Atmospheric Ozone and Climate
- Nuclear Physics and Applications
- 3D Modeling in Geospatial Applications
- Vacuum and Plasma Arcs
University of California, San Diego
2013-2024
General Atomics (United States)
2006-2024
Princeton University
2018
University of California, Los Angeles
2011-2012
Kent State University
2010-2011
University of Wisconsin–Madison
2010
San Jose State University
2006-2010
University of Toronto
2009
Oak Ridge National Laboratory
2009
University of California, Berkeley
2008
We report the results of direct measurements, using video microscopy in combination with optical tweezers, constrained diffusion an isolated uncharged PMMA sphere a density-matched fluid confined between two parallel flat walls. Our experimental methodology allows us to study hindered as explicit function its distance from walls, without interference sedimentation or electrostatic interaction particle and The measured coefficients are used test predictions wall drag effect predicted by...
Dust production and accumulation present potential safety operational issues for the ITER. diagnostics can be divided into two groups: of dust on surfaces in plasma. Diagnostics from both groups are employed contemporary tokamaks; new suitable ITER also being developed tested. is likely to occur hidden areas, e.g., between tiles under divertor baffles. A novel electrostatic detector monitoring these regions has been tested at PPPL. In DIII-D tokamak include Mie scattering Nd:YAG lasers,...
Abstract. Ternary homogeneous nucleation (THN) of H2SO4, NH3 and H2O has been used to explain new particle formation in various atmospheric regions, yet laboratory measurements THN have failed reproduce observations. Here, we report first observations made under conditions relevant the lower troposphere ([H2SO4] 106–107 cm−3, [NH3] 0.08–20 ppbv, a temperature 288 K). Our show that can enhance H2SO4 aerosol enhancement factor (EF) rate (J) due (the ratio J measured with vs. without NH3)...
DIII-D experiments on rapid shutdown runaway electron (RE) beams have improved the understanding of processes involved in RE beam control and dissipation. Improvements feedback enabled stable confinement out to volt-second limit ohmic coil, as well enabling a ramp down zero current. Spectroscopic studies shown that neutrals tend be excluded from centre. Measurements energy distribution function indicate broad with mean order several MeV peak energies 30–40 MeV. The appears more skewed...
An azimuthally symmetric radially sheared plasma fluid flow is observed to spontaneously form in a cylindrical magnetized helicon device with no external sources of momentum input. A turbulent conservation analysis shows that this shear sustained by the Reynolds stress generated collisional drift turbulence device. The results provide direct experimental support for basic theoretical picture drift-wave-shear-flow interactions.
A severe consequence of a disruption on large tokamaks such as ITER could be the generation multi-megaelectronvolt electron beams that damage vacuum vessel and structures machine if they hit wall unmitigated. The mitigation runaway is thus key requirement for reliable operation ITER. In order to achieve mitigation, new fast shutdown technique has been developed: injection shattered cryogenic pellet in plasma, which expected increase density up levels where beam processes are mitigated by...
The absolute rate of nonlinear energy transfer among broadband turbulence, low-frequency zonal flows (ZFs) and geodesic acoustic modes (GAMs) was measured for the first time in fusion-grade plasmas using two independent methods across a range heating powers. results show that turbulent kinetic from intermediate frequencies (20--80 kHz) transferred into ZFs GAMs, as well fluctuations at higher ($>80\text{ }\text{ }\mathrm{kHz}$). As power increased, turbulence GAMs GAM amplitudes peaked then...
MHD simulations of rapid shutdown scenarios by massive particle injection in DIII-D, Alcator C-Mod and ITER are performed order to study runaway electron (RE) transport during mitigated disruptions. The include a RE confinement model using drift-orbit calculations for test particles. A comparison limited diverted plasma shapes is studied DIII-D simulations, improved the shape found due both spatial localization reduced toroidal spectrum nonlinear activity. compare which impurity (Ar)...
Impurities (H 2 , D He, Ne or Ar) injected into steady (non-disrupting) discharges with massive gas injection (MGI) are shown to mix the plasma core dominantly via magnetohydrodynamic activity during thermal quench (TQ). Mixing efficiencies of impurities measured be order 0.05–0.4. 0D modelling experiments is found reproduce observed TQ and current durations reasonably well (typically within ±25% so), although shutdown onset times underestimated (by around 2×). Preliminary ITER based on...
New rapid shutdown strategies have been recently tested in the DIII-D tokamak to mitigate runaway electrons (REs). Disruptions ITER are predicted generate multi-MeV REs that could damage machine. The RE population large tokamaks is expected be dominated by avalanche amplification which can mitigated at high density levels collisional drag. Particle injection schemes for suppression of developed and ITER-relevant scenarios: massive gas injection, shattered pellet (SPI) shell injection....
High-pressure noble gas jet injection is a mitigation technique which potentially satisfies the requirements of fast response time and reliability, without degrading subsequent discharges. Previously reported experiments on DIII-D showed good success at reducing deleterious disruption effects. In this paper, results recent Alcator C-Mod are reported. Jointly, these have greatly improved understanding dynamics processes involved in mitigating both machines, sequence events following observed...
A fast imaging camera is used to unveil the spatio-temporal properties of radially convective events in CSDX linear plasma device [M. J. Burin et al., Phys. Plasmas, 12, 052320 (2005)]. The exposure time set 1μs and between frames 10μs. series from a Langmuir probe pixel 50000-frame movie are compared cross-correlated. Excellent agreement two diagnostics found for spatial scales greater than 2.5mm. fluctuations inside main column change different poloidal mode numbers as function time....
It has been known for a long time that microscopic dust appears in plasmas fusion devices. Recently it was shown can be responsible the termination of long- discharges. Also, ITER-scale experiments pose safety problems related to its chemical activity, tritium retention and radioactive content. In particular, presence vacuum chamber ITER is one main concerns licensing process. Here we review recent progress understanding different experimental theoretical aspects physics dynamics transport...
Studies of naturally occurring and artificially introduced carbon dust are conducted in DIII-D TEXTOR. In DIII-D, does not present operational concerns except immediately after entry vents. Submicrometre sized is routinely observed using Mie scattering from a Nd : Yag laser. The source strongly correlated with the presence type I edge localized modes (ELMs). Larger size (0.005–1 mm diameter) by optical imaging, showing elevated levels Inverse dependence velocity on inferred found imaging...
Experiments have been performed in the DIII-D tokamak [J. L. Luxon, Nucl. Fusion 42, 614 (2002)] toward understanding runaway electron formation and amplification during rapid discharge shutdown, as well achieving complete collisional suppression of these electrons via massive delivery impurities. Runaway acceleration appear to be explained using zero-dimensional (0D) current quench toroidal electric field. 0D or even one-dimensional modeling a Dreicer seed term, however, appears too small...
Recent experiments in the DIII-D tokamak have demonstrated real-time control and dissipation of post-disruption runaway electron (RE) beams. In event that disruption avoidance, control, mitigation schemes fail to avoid or suppress RE generation, active beam may be an important line defense prevent rapid, localized deposition energy onto vulnerable vessel sections. During immediately after current quench, excessive radial compression beams is avoided by a combination techniques, improving...
PISCES-B was used for a series of high-fluence plasma exposures to investigate the deuterium fuel retention properties tungsten, when exposed continuous irradiation. The goal determine whether in tungsten saturates at sufficiently high fluence, or continues increase as function fluence. During pure exposure, up maximum fluence 2 × 1028 m−2, results indicate that saturation is not reached and scales square root time, indicative diffusion dominating uptake tungsten. However, measurements...
Modification of the two existing DIII-D neutral beamlines is planned to allow vertical steering provide off-axis beam current drive (NBCD) peaked as far half plasma minor radius. New calculations for a downward-steered indicate strong with good localization so long toroidal magnetic field, B T , and current, I p point in same direction. This due alignment injection (NBI) local pitch field lines. model has been tested experimentally on by injecting equatorially mounted NBs into reduced size...
A method for measuring nonlinear energy transfer in the frequency domain using a two-field model of drift turbulence is proposed, and theoretical motivation experimental results are presented. The approach based on cross-bispectral analysis quadratic nonlinearities turbulent internal kinetic balance equations directly derived from fluid plasma continuity momentum equations. Application technique to data laboratory experiment reveals weak collisional turbulence; show density fluctuation...
The findings of previous blob studies in the interchange-dominated regime TORPEX helium (Muller et al 2007 Phys. Plasmas 14 110704) and hydrogen plasmas (Furno 2008 Rev. Lett. 100 055004) are summarized compared. onset blobs is studied as a function vertical magnetic field Bz, proving existence also drift-interchange-dominated characterized by Bz < 1 mT. These blobs, despite being inherently three-dimensional sheath-disconnected, exhibit statistical properties similar to interchange regime....
Collisional electron drift wave turbulence generates packet structures with density and vorticity fluctuations in the central plasma pressure gradient region of a linear device. Tracking these packets reveals that they follow an outward directed spiral-shaped trajectory (r,θ) plane, are azimuthally stretched, develop anisotropy as approach axisymmetric, radially sheared azimuthal flow located at boundary. Nonlinear energy transfer measurements time-delay analysis confirm structure absorption...
The first visible light images of synchrotron emission from disruption runaway electrons are presented. forward-detected continuum radiation runaways is identified as by comparing two survey spectrometers and fast cameras viewing in opposite toroidal directions. Analysis the elongation 2D oval-shaped beams indicates that velocity pitch angle v⊥/v|| ranges 0.1 to 0.2 for detected electrons, with energies above 25 MeV. intensity a camera tail energy distribution reaches up 60 MeV, which agrees...