A5024677936- Magnetic confinement fusion research
- Fusion materials and technologies
- Plasma Diagnostics and Applications
- Laser-Plasma Interactions and Diagnostics
- Superconducting Materials and Applications
- Ionosphere and magnetosphere dynamics
- Particle accelerators and beam dynamics
- Laser-induced spectroscopy and plasma
- Nuclear reactor physics and engineering
- Nuclear Physics and Applications
- Semiconductor materials and devices
- Nuclear Materials and Properties
- Advanced Data Storage Technologies
- Atomic and Molecular Physics
- Ion-surface interactions and analysis
- Advancements in Semiconductor Devices and Circuit Design
- Electrostatic Discharge in Electronics
- Electron and X-Ray Spectroscopy Techniques
- Silicon and Solar Cell Technologies
- Diamond and Carbon-based Materials Research
- Physics of Superconductivity and Magnetism
- Atomic and Subatomic Physics Research
- Semiconductor Quantum Structures and Devices
- Radiation Effects in Electronics
- Mass Spectrometry Techniques and Applications
University of California, San Diego
2015-2024
Universidad Católica Santo Domingo
2022-2023
General Atomics (United States)
2005-2022
Oak Ridge National Laboratory
2009-2022
Stony Brook University
2022
Max Planck Institute for Plasma Physics - Greifswald
2018
Princeton University
2018
Oak Ridge Associated Universities
2018
Princeton Plasma Physics Laboratory
2016
Sandia National Laboratories
2016
An overview of the present status research toward final design ITER disruption mitigation system (DMS) is given. The DMS based on massive injection impurities, in order to radiate plasma stored energy and mitigate potentially damaging effects disruptions. this will be extremely challenging due many physics engineering constraints such as limitations port access amount species injected impurities. Additionally, questions relevant remain unsolved mechanisms for mixing assimilation impurities...
Of all electrons, runaway electrons have long been recognized in the fusion community as a distinctive population. They now attract special attention part of ITER mission considerations. This review covers basic physics ingredients phenomenon and ongoing efforts (experimental theoretical) aimed at electron (RE) taming next generation tokamaks. We emphasize prevailing themes last 20 years: hot-tail mechanism production, RE interaction with impurity ions, role synchrotron radiation kinetics,...
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...
Probe measurements in the PISCES linear device indicate presence of plasma radially far from where it is produced. We show that this mainly caused by large-scale structures with high radial velocity. Data Tore Supra tokamak striking similarities shape these intermittent events as well fluctuation density probability distribution and frequency spectrum. The fact intermittent, are so similar devices tokamaks indicates universality convective transport magnetically confined plasmas.
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,...
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...
Abstract Shattered pellet injection (SPI) is one of the prime candidates for ITER disruption mitigation system because its deeper penetration and larger particle flux than massive gas (MGI) (Taylor et al 1999 Phys. Plasmas 6 1872) using deuterium (Commaux 2010 Nucl. Fusion 50 112001, Combs IEEE Trans. Plasma Sci . 38 400, Baylor 2009 49 085013). The will likely use mostly high Z species such as neon more effective thermal pumping constraints on maximum amount or helium that could be...
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.
Far Scrape-Off Layer (SOL) and near-wall plasma parameters in DIII-D depend strongly on the discharge confinement regime. In L-mode discharges cross-field transport increases with average density flattens far SOL profiles, thus increasing contact low field side (LFS) main chamber wall. H-mode between edge localized modes (ELMs) plasma–wall is weaker than L-mode. During ELM fluxes of particles heat to LFS wall increase transiently above values. Depending conditions, ELMs are responsible for...
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...
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)...
Injection of large shattered pellets composed variable quantities the main ion species (deuterium) and high-Z impurities (neon) in DIII-D tokamak demonstrates control thermal quench (TQ) current (CQ) properties mitigated disruptions. As pellet composition is varied, TQ radiation fractions increase continuously with quantity radiating impurity pellet, a corresponding decrease divertor heating. Post-TQ plasma resistivities as result higher fraction, allowing decay timescales based on...
Realization of a high-current (approaching 1 MA) post-disruption runaway electron (RE) beam in DIII-D yields controlled access to very low edge safety factor (qa) conditions. This enables unique observation and study low-order kink instabilities plasmas where the current is carried entirely by relativistic REs. The conventional external stability boundary (in terms qa internal inductance, ℓi) found accurately predict operational space RE beam, with limited ≈2. Kink appear characteristic...
Abstract A series of experiments have been executed at JET to assess the efficacy newly installed shattered pellet injection (SPI) system in mitigating effects disruptions. Issues, important for ITER disruption mitigation system, such as thermal load mitigation, avoidance runaway electron (RE) formation, radiation asymmetries during quench electromagnetic control and RE energy dissipation addressed over a large parameter range. The efficiency has examined various SPI strategies. paper...
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....
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...
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...
We report on the first demonstration of dissipation fully avalanched post-disruption runaway electron (RE) beams by shattered pellet injection in DIII-D tokamak. Variation injected species shows that depends strongly mixture, while comparisons with massive gas do not show a significant difference between pellets or gas, suggesting is rapidly ablated relativistic electrons before radial penetration into beam can occur. Pure dominantly neon increases RE current through pitch-angle scattering...
Relativistic electron (RE) beams at high current density (low safety factor, qa) yet very low free-electron accessed with D2 secondary injection in the DIII-D and JET tokamak are found to exhibit large-scale MHD instabilities that benignly terminate RE beam. In JET, this technique has enabled termination of MA-level currents without measurable first-wall heating. This scenario thus offers an unexpected alternate pathway achieve mitigation collisional dissipation. Benign is explained by two...
Abstract The thermo-mechanical response of an ATJ graphite sample to controlled runaway electron (RE) dissipation, realized in DIII-D, is modelled with a novel work-flow that features the RE orbit code KORC, Monte Carlo particle transport Geant4 and finite element multiphysics software COMSOL. KORC provides striking positions momenta, calculates volumetric energy deposition COMSOL simulates thermoelastic response. Brittle failure predicted according maximum normal stress criterion, which...
Abstract Post-disruption runaway electron (RE) kinetic energy K and pitch angle sin are critical parameters for determining resulting first wall material damage during strikes, but very challenging to measure experimentally. During the final loss instability, confined RE reconstructed center-post strikes both high impurity (high-Z) low (low-Z) plasmas by combining soft x-ray, hard synchrotron emission, total radiated power measurements. Deconfined (wall impacting) sinθ is then these shots...
A particle balance analysis was conducted during a deuterium (D2) shattered pellet injection-induced plasma shutdown on the DIII-D tokamak to determine why less than 20% of material is assimilated into core by mid-current quench (CQ). Initially, most D2 injected as frozen shards and ionized upon entering vessel. During thermal quench, particles move divertors subsequently center post (CP) walls, where they rapidly recycle partially accumulate neutrals without assimilating plasma. In...