A5023466921- Magnetic confinement fusion research
- Fusion materials and technologies
- Laser-Plasma Interactions and Diagnostics
- Nuclear Physics and Applications
- Laser-induced spectroscopy and plasma
- Superconducting Materials and Applications
- Nuclear reactor physics and engineering
- Ionosphere and magnetosphere dynamics
- Plasma Diagnostics and Applications
- Particle accelerators and beam dynamics
- Atomic and Molecular Physics
- Semiconductor materials and devices
- Atomic and Subatomic Physics Research
- Nuclear Materials and Properties
- Radiation Detection and Scintillator Technologies
- Advanced Data Storage Technologies
- High-pressure geophysics and materials
- Gyrotron and Vacuum Electronics Research
- Advancements in Semiconductor Devices and Circuit Design
- Ion-surface interactions and analysis
- Cold Fusion and Nuclear Reactions
- Nuclear and radioactivity studies
- Electrostatic Discharge in Electronics
- Radioactive contamination and transfer
- Solar and Space Plasma Dynamics
General Atomics (United States)
2013-2023
Oak Ridge National Laboratory
2005-2022
Stony Brook University
2022
University of California, San Diego
2022
Japan External Trade Organization
2014
Purdue University West Lafayette
2011
Princeton University
1995
Princeton Plasma Physics Laboratory
1995
Max Planck Society
1991
DuPont (United States)
1971-1978
A knowledge of solid hydrogen pellet lifetimes in a plasma is critical to the design devices refuel tokamak fusion reactors. When injected into plasma, ablated material from undergoes transonic flow since it heated while expands. Calculations are done on behavior for various conditions and sizes. From these calculations, ablation rate determined. scaling law given which allows be easily calculated any conditions. The results calculations give good agreement when compared with experiments.
High repetition rate injection of deuterium pellets from the low-field side (LFS) DIII-D tokamak is shown to trigger high-frequency edge-localized modes (ELMs) at up $12\ifmmode\times\else\texttimes\fi{}$ low natural ELM frequency in $H$-mode plasmas designed match ITER baseline configuration shape, normalized beta, and input power just above threshold. The pellet size, velocity, location were chosen limit penetration outer 10% plasma. resulting perturbations plasma density energy...
The evolution of laser-generated MeV, MA electron beams propagating through conductors and insulators has been studied by comparing measurement modeling the distribution MeV protons that are sheath accelerated propagated electrons. We find flow metals is uniform can be laser imprinted, whereas propagation induces spatial disruption fast Agreement found with material dependent modeling.
High-pressure gas-jet injection of neon and argon is shown to be a simple robust method mitigate the deleterious effects disruptions on DIII-D tokamak. The gas jet penetrates central plasma at its sonic velocity. deposited species dissipates >95% by radiation substantially reduces mechanical stresses vessel caused poloidal halo currents. species-charge distribution can include >50% fraction neutral which inhibits runaway electrons. favorable scaling this technique burning fusion plasmas discussed.
The capability to inject deuterium pellets from the magnetic high field side (HFS) has been added DIII-D tokamak [J. L. Luxon and G. Davis, Fusion Technol. 8, 441 (1985)]. It is observed that injected HFS lead deeper mass deposition than identical outside midplane, in spite of a factor 4 lower pellet speed. have used generate peaked density profile plasmas [peaking (ne(0)/〈ne〉) excess 3] develop internal transport barriers when centrally heated with neutral beam injection. are formed...
It is shown that the ablation of a solid hydrogen pellet subject to plasma likely produce quasi-steady dense neutral gas cloud. The total integrated density cloud such electrons lose essentially all their energy in electron flux degraded by inelastic collisions and elastic backscattering with molecules, providing local heating acceleration gas. Only small fraction reaches surface pellet, raising pellet's temperature point where at balance lost through vaporization. vaporization rate, turn,...
Pellet injection from the inner wall is planned for use in ITER as primary core fuelling system since gas expected to be highly inefficient burning plasmas. Tests of guide tube have shown that 5 mm pellets with up 300 m s−1 speeds can survive intact and provide necessary rate. Modelling extrapolation pellet experiments present day's smaller tokamaks leads prediction this method will efficient beyond pedestal region. Using triggering frequent small edge localized modes an attractive...
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 first results of edge-localized mode (ELM) pacing using small spherical lithium granules injected mechanically into H-mode discharges are reported. Triggering ELMs was accomplished a simple rotating impeller to inject sub-millimetre size at speeds few tens meters per second the outer midplane EAST fusion device. During injection phase, were triggered with near 100% efficiency and amplitude induced as measured by Dα clearly reduced compared contemporaneous naturally occurring ELMs. In...
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....
Plasma fuelling with pellet injection, pacing of edge localized modes (ELMs) by small frequent pellets and disruption mitigation gas jets or injected solid material are some the most important technological capabilities needed for successful operation ITER. Tools being developed at Oak Ridge National Laboratory that can be employed on ITER to provide necessary core ELMs disruptions. Here we present progress development technology reliable high throughput inner wall fuelling, ELM frequency...
The evolution of the runaway electron (RE) energy distribution function fε during massive gas injection into centered post-disruption plateaus has been reconstructed. Overall, is found to be much more skewed toward low than predicted by avalanche theory. reconstructions also indicate that RE pitch angle θ not uniform, but tends large at energies and small ∼ 0.1–0.2 high energies. Overall power loss from plateau appears dominated collisions with background free bound electrons, leading line...
Abstract A newly installed Lithium Granule Injector (LGI) was used to pace edge localized modes (ELM) in DIII-D. ELM pacing efficiency studied injecting lithium granules of nominal diameter 0.3–0.9 mm, speed 50–120 m s −1 and average injection rates up 100 Hz for 0.9 mm 700 0.3 granules. The triggering found depend strongly on size the injected granules, with close 100% obtained lower smaller sizes, weakly depending granule velocity. Robust demonstrated ITER-like plasmas entire shot length,...
During pellet injection in tokamaks, a rapid movement of ablation substance towards the low-field or outward major radius R direction is observed, favoring from high-field side order to promote deeper fuel penetration. The motion has been attributed vertical curvature and ∇B drift current induced inside ionized ablated material by 1/R toroidal field variation. uncompensated weakly diamagnetic (β<0.1) cloud will cause charge separation at boundary. resulting electrostatic induces E×B...
Data on the discharge behavior, thermal loads, halo currents, and runaway electrons have been obtained in disruptions DIII-D tokamak [J. L. Luxon G. Davis, Fusion Technol. 8, 2A 441 (1985)]. These experiments also evaluated techniques to mitigate while minimizing electron production. Experiments injecting cryogenic impurity “killer” pellets of neon argon massive amounts helium gas successfully reduced these disruption effects. The current generation, scaling, mitigation are understood good...
Solid deuterium clusters provide a new type of target for laser-matter interactions. We present theory the generation laser driven Coulomb explosions that create hot fusion-producing ion tail. derive an initial distribution function exploded ions, arbitrary cluster-size distribution, and solve D-D neutron-production rate during free expansion these ions into vacuum. find good agreement between experiment: suggests explanation observed saturation drop in neutron yield beyond definite cluster...
Impurity deposition and mixing during gas jet-initiated plasma shutdown is studied using a rapid ({approx}2 ms), massive ({approx}10{sup 22} particles) injection of neon or argon into stationary DIII-D H-mode discharges. Fast-gated camera images indicate that the bulk jet neutrals do not penetrate far pedestal. Nevertheless, high ({approx}90%) thermal quench radiated power fractions are achieved; this appears to be facilitated through combination fast ion heat transport, both driven by...
A model is developed to describe the evolution of a solid armature point where metallic contact with rails lost. The idea that current/melt wave begins at rear armature, current concentrated by velocity skin effect, and propagates forward along rail/armature interface as molten material When melt reaches front transition plasma brush occurs. calculation simulating an earlier experiment General Atomics shows close agreement measured velocity, inferred from increase in muzzle voltage observed...
It is shown that transverse injection of a hypervelocity high-density spheromak plasmoid into tokamak plasma may be viable fueling scheme. Three important processes occur and are discussed individually: establishment equilibrium, slowing down, disassembly the compact toroid.
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...
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...
Optimal strategies for disruption mitigation benefit from the understanding of details both spatially and temporally. Beyond assessment efficacy a particular proposed Disruption Mitigation System (DMS), ITER's longevity will require accounting mitigated unmitigated disruptions. Accurate models validated simulations that detail multiple ITER scenarios with disruptions are essential accurate estimates load damage. The primary candidate DMS is Shattered Pellet Injection (SPI); its must be...
This Letter reports the first measurements of fast confined $\ensuremath{\alpha}$-particle energy distribution in a fusion plasma. The pellet charge exchange technique shows generated $\ensuremath{\alpha}$'s core Tokamak Fusion Test Reactor plasma slow down classically, and appear to be well confined. Preliminary indications are that stochastic ripple effects responsible for steepening outside $(r/a\ensuremath{\gtrsim}0.35)$. Sawteeth mixing is suggested data during post-beam-heating decay.