A5085471231- Magnetic confinement fusion research
- Fusion materials and technologies
- Superconducting Materials and Applications
- Ionosphere and magnetosphere dynamics
- Laser-Plasma Interactions and Diagnostics
- Particle accelerators and beam dynamics
- Plasma Diagnostics and Applications
- Nuclear reactor physics and engineering
- Nuclear Physics and Applications
- Laser-induced spectroscopy and plasma
- Semiconductor materials and devices
- Advanced Data Storage Technologies
- Atomic and Subatomic Physics Research
- Plasma and Flow Control in Aerodynamics
- Atomic and Molecular Physics
- Physics of Superconductivity and Magnetism
- Nuclear Materials and Properties
- Magnetic Field Sensors Techniques
- Electrostatic Discharge in Electronics
- Mechanical Failure Analysis and Simulation
- Semiconductor Quantum Structures and Devices
- Electron and X-Ray Spectroscopy Techniques
- Solar and Space Plasma Dynamics
- Advancements in Semiconductor Devices and Circuit Design
- Particle Detector Development and Performance
Oak Ridge National Laboratory
2015-2024
General Atomics (United States)
2015-2022
Stony Brook University
2022
University of California, San Diego
2018-2022
Princeton University
2015-2018
Max Planck Institute for Plasma Physics - Greifswald
2018
Oak Ridge Associated Universities
2018
Columbia University
2008-2016
Culham Centre for Fusion Energy
2015
Culham Science Centre
2015
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...
Abstract Negative triangularity (NT) is a potentially transformative configuration for tokamak-based fusion energy with its high-performance core, edge localized mode (ELM)-free edge, and low-field-side divertors that could readily scale to an integrated reactor solution. Previous NT work on the TCV DIII-D tokamaks motivated installation of graphite-tile armor lower outer wall DIII-D. A dedicated multiple-week experimental campaign was conducted qualify scenario future reactors. During...
The DIII-D tokamak magnetic diagnostic system [E. J. Strait, Rev. Sci. Instrum. 77, 023502 (2006)] has been upgraded to significantly expand the measurement of plasma response intrinsic and applied non-axisymmetric “3D” fields. placement design 101 additional sensors allow resolution toroidal mode numbers 1 ≤ n 3, poloidal wavelengths smaller than MARS-F, IPEC, VMEC magnetohydrodynamic model predictions. Small 3D perturbations, relative equilibrium field (10−5 < δB/B0 10−4), require...
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...
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...
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...
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...
Novel spatial, temporal, and energetically resolved measurements of bremsstrahlung hard-x-ray (HXR) emission from runaway electron (RE) populations in tokamaks reveal nonmonotonic RE distribution functions whose properties depend on the interplay electric field acceleration with collisional synchrotron damping. Measurements are consistent theoretical predictions momentum-space attractors that accumulate electrons. measured to shift a higher energy when force is reduced by decreasing toroidal...
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,...
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 Precise values for radiated energy in tokamak disruption experiments are needed to validate mitigation techniques burning plasma tokamaks like ITER and SPARC. Control room analysis of power ( P rad ) on JET assumes axisymmetry, since fitting 3D radiation structures with limited bolometry coverage is an under-determined problem. In mitigated disruptions, toroidally asymmetric 3D, due fast-growing MHD modes localized impurity sources. To address this problem, Emis3D adopts a physics...
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...
DIII-D experiments using new detailed magnetic diagnostics show that linear, ideal magnetohydrodynamics (MHD) theory quantitatively describes the structure (as measured externally) of three-dimensional (3D) equilibria resulting from applied fields with toroidal mode number n = 1, while a nonlinear solution to MHD force balance, VMEC code, requires inclusion ≥ 1 achieve similar agreement. These tests are carried out near ITER baseline parameters, providing validated basis on which exploit 3D...
Optimal error field correction (EFC) is thought to be achieved when coupling the least-stable “dominant” mode of plasma nulled at each toroidal number (n). The limit this picture tested in DIII-D tokamak by applying superpositions in- and ex-vessel coil set n = 1 fields calculated fully orthogonal dominant mode. In co-rotating H-mode low-density Ohmic scenarios, found be, respectively, 7× 20× less sensitive as compared in-vessel field. For scenarios investigated, any geometry EFC can thus...
The first rapid tokamak discharge shutdown using dispersive core payload deposition with shell pellets has been achieved in the DIII-D tokamak. Shell are being investigated as a possible new path toward achieving disruption mitigation both low conducted wall heat loads and slow current quench. Conventional injects radiating impurities into outer edge of plasma, which tends to result poor impurity assimilation creates strong cooling outward flow, thus requiring undesirable high-Z achieve...
Abstract Runaway electrons (REs) created during tokamak disruptions pose a threat to the reliable operation of future larger machines. Experiments using shattered pellet injection (SPI) have been carried out at JET investigate ways prevent their generation or suppress them if avoidance is not sufficient. Avoidance possible SPI contains sufficiently low fraction high-Z material, it fired early in advance disruption prone runaway generation. These results are consistent with previous similar...
Simulations of massive gas injection for disruption mitigation in DIII-D are carried out to compare the toroidal peaking radiated power cases one and two jets. The radiation factor (TPF) results from a combination distribution impurities heat flux associated with mode. When ignoring effects strong uni-directional neutral beam rotation present experiment, injected found spread helically along field lines preferentially toward high-field-side, which is explained terms nozzle equation....
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...
Areas of agreement and disagreement with present-day models runaway electron (RE) evolution are revealed by measuring MeV-level bremsstrahlung radiation from electrons (REs) a pinhole camera. Spatially resolved measurements localize the RE beam, reveal energy-dependent transport, can be used to perform full two-dimensional (energy pitch-angle) inversions phase-space distribution. Energy-resolved find qualitative modeling on role collisional synchrotron damping in modifying distribution...
Shattered pellet injection (SPI) systems that form cryogenic pellets in a pipe-gun for of material to mitigate disruptions have been fabricated and installed use thermal mitigation runaway electron (RE) dissipation experiments on JET KSTAR. These are support disruption research ITER based an ORNL three-barrel design flexibility size selection variable composition studies. The SPI KSTAR common feature the barrels being collimated into single line enters vacuum vessel. shattered bent stainless...
Abstract Disruption mitigation remains a critical, unresolved challenge for ITER. To aid in addressing this challenge, shattered pellet injection (SPI) system was installed on JET and experiments conducted at range of thermal energy fractions stored energies excess 7 MJ. The primary goals these were to investigate the efficacy SPI ability plasma assimilate multiple pellets. Single injections produced saturation total radiated ( W rad ) with increasing injected neon content, suggesting...
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}}^{...