A5078432805- Magnetic confinement fusion research
- Fusion materials and technologies
- Superconducting Materials and Applications
- Ionosphere and magnetosphere dynamics
- Nuclear reactor physics and engineering
- Laser-Plasma Interactions and Diagnostics
- Plasma Diagnostics and Applications
- Laser-induced spectroscopy and plasma
- Particle accelerators and beam dynamics
- Nuclear Materials and Properties
- Semiconductor materials and devices
- Pulsars and Gravitational Waves Research
- Atomic and Molecular Physics
- Advanced X-ray Imaging Techniques
- Advanced Data Storage Technologies
- Advanced MRI Techniques and Applications
- High-pressure geophysics and materials
- Advanced Thermodynamic Systems and Engines
- Atomic and Subatomic Physics Research
- Nuclear Physics and Applications
- Ion-surface interactions and analysis
- Tribology and Lubrication Engineering
- Physics of Superconductivity and Magnetism
- Electron and X-Ray Spectroscopy Techniques
- Thin-Film Transistor Technologies
Oak Ridge National Laboratory
2018-2024
University of California, San Diego
2022
General Atomics (United States)
2022
Stony Brook University
2022
Auburn University
2009-2019
University of Wisconsin–Madison
2016
University of Vermont
2008
The technology to form and shoot high-Z cryogenic solid pellets mixed with deuterium using a gas gun that are shattered upon injection into plasma has been developed at Oak Ridge National Laboratory for mitigating disruptions. This selected as the basis baseline disruption mitigation system on ITER. development of pellet systems progressed be able accelerate large pure argon neon or without including deuterium. Impact studies have carried out shallow angles determine funnel performance in...
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...
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...
Numerous studies of the brightest Cambridge pulsar, B1133+16, have revealed little order in its individual pulses, apart from a weak 30-odd-rotation-period fluctuation feature and that some 15 per cent star's pulsars are ‘nulls’. New Arecibo observations confirm this it modulates all emission, not simply ‘saddle’ region. By replacing each pulse with scaled version average profile, we were able to quench subpulse modulation thereby demonstrate ‘null’ pulses exhibit similar periodicity. A...
Sensitive Arecibo observations provide an unprecedented ability to detect nulls for accurate pulse-modulation quelling (PMQ) analysis. We demonstrate that a number of conal pulsars show "periodic nulling" similar the phenomenon found earlier in pulsar B1133+16.
Kinetic instabilities in the MHz range driven by runaway electrons (REs) have been observed for first time during current quench (CQ) disruptions triggered massive injection of argon DIII-D. These are well-correlated with intermittent RE losses beginning formation. The phase is not when power exceeds a threshold. Novel measurements distribution function CQ indicate that appear energy (ERE) 2.5–3 MeV, number modes grows linearly ERE, and their frequencies lie 0.1–3 MHz, below ion cyclotron...
Abstract Experimental trends in thermal plasma partial recombination resulting from massive <?CDATA ${{\text{D}}_2}$?> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mtext>D</mml:mtext> </mml:mrow> <mml:mn>2</mml:mn> </mml:msub> </mml:math> injection into high-Z (Ar) containing runaway electron (RE) plateaus DIII-D and JET are studied for the purpose of achieving sufficiently low density ( ${n_{\text{e}}} \approx {10^{18}}{{\text{m}}^{...
Plasma shutdown experiments in DIII-D have injected multiple shattered pellets at different toroidal locations for the first time, as is planned ITER disruption mitigation system. Systematically varying relative timing of two suggests that simultaneously may influence assimilation each other, altering resulting characteristics compared to a single pellet injecting similar neon quantities. Thermal quench (TQ) radiation measured near injection location reduced with dual pellets, contrary TQ...
A 1D radial diffusion model is developed to study the observed rapid expulsion of argon from runaway electron plateau in DIII-D tokamak following secondary massive low-Z (D2 or He) gas injection. The found be caused by further cooling background plasma due added neutrals, accompanied recombination ions and greatly increased outward transport rate (now dominantly neutral form) out beam. After expulsion, power loss dominated wall (rather than radiation); this result resolves balance...
The filterscope diagnostic on DIII-D utilizes photomultiplier tubes to measure visible light emission from the plasma. system has undergone a substantial upgrade since previous attempts cross-calibrate with other spectroscopic diagnostics were unsuccessful. optics now utilize dichroic mirror initially split at nearly 99% transmission or reflectance for below above 550 nm. This allows Dα without degrading plasma wavelengths nm (to Dβ, Dγ, W–I, C-III, etc.). Additional optimization of optical...
Shattered pellet injection (SPI) has been adopted as the baseline disruption mitigation system for ITER, radiative payload penetration into DIII-D plasmas from SPI is superior to those using massive gas (MGI) method. Because of substantial differences in energy content ITER plasma and present experiments, reliable 3D MHD modeling, benchmarked against experiments needed project plasmas. In support these needs, depth fragment was investigated by injecting two discharges with vastly different...
Low edge safety factor operation at a value less than two (q(a)=1/ι̷tot(a)&lt;2) is routine on the Compact Toroidal Hybrid device with addition of sufficient external rotational transform. Presently, operational space this current carrying stellarator extends down to q(a)=1.2 without significant n = 1 kink mode activity after initial plasma rise phase discharge. The disruption dynamics these low plasmas depend upon fraction helical field transform from coils that generated by current. We...
© 2019 IAEA, Vienna. Novel measurements and modeling of runaway electron (RE) dynamics in DIII-D have resolved experimental discrepancies validated predictions for ITER, improving confidence that RE avoidance mitigation can be predictably achieved. Considering formation, first assessments the seed current demonstrates present hot-tail theories are not yet accurate require improved treatment pellet dynamics. kinetic instabilities MHz-range been made formation phase, with intensity these modes...
Abstract New experiments have been conducted at DIII-D to improve the physics understanding of plasma initiation assisted by electron cyclotron (EC) wave injection, allowing better extrapolation ITER. This has achieved applying an EC pulse prior start inductive (i.e. generation a loop voltage). A pre-plasma was formed during that characterized in terms maximum density and temperature. Parametric scans were performed study influence injected power, injection angle, pre-fill gas pressure on...
The passive stability of vertically elongated current-carrying toroidal plasmas has been investigated in the Compact Toroidal Hybrid, a stellarator/tokamak hybrid device. In this experiment, fractional transform f, defined as ratio imposed external rotational from stellarator coils to total transform, was varied 0.04 0.50, and elongation κ 1.4 2.2. Plasmas that were unstable evidenced by motion plasma vertical direction. Vertical drifts are measured with set poloidal field pickup coils. A...
The assimilation of argon injected into post-disruption runaway electron (RE) plateaus is studied and compared to the vertical loss rate for vertically unstable RE plateaus. A 1D diffusion model developed include neutral ionization used help in data interpretation. It found that radial mixing time scale ions (~0.05 s) comparable timescale. Neutral becomes dominant Ar species plateau large numbers (); at same diffusivity decreases due plasma cooling, causing a saturation on scale. Injection...
Shattered pellet injection (SPI) experiments on Joint European Torus (JET) are an important element in determining the physics basis for mitigating disruptions ITER. The initial design of JET SPI system included three barrels to produce pellets with diameters 4.5, 8.1, and 12.5 mm. variability speed by operating without a mechanical punch was limited led poor integrity, so removed. Fragment size distribution is function desire change resulting fragment not originally requirement. After first...
Abstract Current profile reconstructions are obtained for high current ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>I</mml:mi> <mml:mi>p</mml:mi> </mml:msub> <mml:mo>≃</mml:mo> <mml:mn>550</mml:mn> </mml:mrow> </mml:math> kA) post-disruption runaway electron (RE) plateau plasmas in DIII-D. Two novel methods of measuring the RE high-current plateaus introduced and compared: localization q = 2 rational surface using visible...
Abstract Experiments in DIII-D demonstrate that the upstream plasma density to detach an un-pumped slot divertor is similar for a V-shaped and flat-end slot, despite significantly higher neutral pressure contrast SOLPS-ITER predictions. The detachment threshold can be reduced by using in-slot instead of main-chamber gas fuelling or placing strike point on inner slanted baffle end, as described simulations with full drift physics. When increasing line-averaged (without extrinsic impurities),...
Abstract Six nominally repeat neon shattered pellet injection (SPI) shutdowns of stable DIII-D Super H-modes are studied to understand the 3D properties radiation and impurity transport. The efficiency peaking determine whether first wall melting is expected following disruption mitigation in ITER. Previous studies make use axisymmetric approximations infer efficiencies, but validating high required by ITER necessitates improved accuracy, this work contributes exploring density structures...
Abstract Formation of non-thermal (hot) electrons is studied during the thermal quench shattered pellet injection (SPI) discharge shutdowns in DIII-D tokamak. Both pure neon and mixed neon/deuterium are studied. High-energy radiation (SXR EUV) brightness levels show indications electron formation TQ. The densities order 10 18 m −3 temperatures estimated to be keV. appear mostly lost subsequent current quench, as no signal relativistic runaway typically seen at end quench. non-thermals have...
Non-axisymmetric free-boundary equilibrium reconstructions of stellarator plasmas are performed for discharges in which the magnetic configuration is strongly modified by ohmically driven plasma current. These studies were on compact toroidal hybrid device using V3FIT reconstruction code with a set 50 diagnostics external to plasma. With assumption closed flux surfaces, measurements allow accurate estimates net within last surface, edge safety factor, and shape these highly non-axisymmetric...