D. P. Brennan
A5060790671- Magnetic confinement fusion research
- Ionosphere and magnetosphere dynamics
- Fusion materials and technologies
- Superconducting Materials and Applications
- Solar and Space Plasma Dynamics
- Particle accelerators and beam dynamics
- Plasma Diagnostics and Applications
- Laser-Plasma Interactions and Diagnostics
- Fluid Dynamics and Turbulent Flows
- Nuclear reactor physics and engineering
- Physics of Superconductivity and Magnetism
- Plasma and Flow Control in Aerodynamics
- Nuclear Physics and Applications
- Gas Dynamics and Kinetic Theory
- Dust and Plasma Wave Phenomena
- Nuclear Materials and Properties
- Advanced Data Storage Technologies
- Ocean Waves and Remote Sensing
- Laser-induced spectroscopy and plasma
- Atomic and Molecular Physics
- Atomic and Subatomic Physics Research
- Computational Fluid Dynamics and Aerodynamics
- Tropical and Extratropical Cyclones Research
- Nuclear physics research studies
- Meteorological Phenomena and Simulations
Princeton University
2015-2024
Film Independent
2022
Culham Science Centre
2001-2021
General Atomics (United States)
2001-2021
Princeton Plasma Physics Laboratory
2015-2021
United Kingdom Atomic Energy Authority
2005-2021
Tibbar Plasma Technologies (United States)
2018-2021
Fermi Research Alliance
2021
Fermi National Accelerator Laboratory
2021
Los Alamos National Laboratory
2014-2021
This paper provides analyses of three types diversity combining systems in practical use. These are: selection diversity, maximal-ratio and equal-gain systems. Quantitative measures the relative performance (under realistic conditions) are provided. The effects various departures from ideal conditions, such as non-Rayleigh fading partially coherent signal or noise voltages, considered. Some discussion is also included merits predetection postdetection problems determining using long-term...
High-confinement (H-mode) operation is the choice for next-step tokamak devices based either on conventional or advanced physics. This choice, however, comes at a significant cost both and tokamaks because of effects edge localized modes (ELMs). ELMs can produce erosion in divertor affect beta limit reduced core transport regions needed operation. Experimental results from DIII-D [J. L. Luxon et al., Plasma Physics Controlled Nuclear Fusion Research 1986 (International Atomic Energy Agency,...
DIII-D experiments at low density (n_{e}∼10^{19} m^{-3}) have directly measured whistler waves in the 100-200 MHz range excited by multi-MeV runaway electrons. Whistler activity is correlated with intensity (hard x-ray emission level), occurs novel discrete frequency bands, and exhibits nonlinear limit-cycle-like behavior. The frequencies scale magnetic field strength electron as expected from dispersion relation. modes are stabilized increasing field, which consistent wave-particle...
H-mode operation is the choice for next-step tokamak devices based either on conventional or advanced physics. This choice, however, comes at a significant cost both and tokamaks because of effects edge-localized modes (ELMs). ELMs can produce erosion in divertor affect β limit reduced core transport regions needed operation. Recent experimental results from DIII-D have demonstrated new operating regime, quiescent which solves these problems. We achieved ELM-free yet has good density...
Reducing plasma flow clearly decreases the stability of tearing modes in multiple regimes (sawtooth, hybrid) both high- and low-aspect-ratio tokamaks (DIII-D [J. L. Luxon, Nucl. Fusion 42, 614 (2002)], Joint European Torus [M. Keilhacker JET Team, Plasma Phys. Controlled 41, 301 (1999)], National Spherical Experiment Ono, S. M. Kaye, Y.-K. Peng, 40, 557 (2000)], each with distinct means lessening rotation). Further, reducing makes pre-existing “saturated” islands larger at same beta (β)....
Research on the National Spherical Torus Experiment, NSTX, targets physics understanding needed for extrapolation to a steady-state ST Fusion Nuclear Science Facility, pilot plant, or DEMO. The unique operational space is leveraged test theories next-step tokamak operation, including ITER. Present research also examines implications coming device upgrade, NSTX-U. An energy confinement time, τE, scaling unified varied wall conditions exhibits strong improvement of BTτE with decreased electron...
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...
The effects of kinetic whistler-wave instabilities on the runaway-electron (RE) avalanche is investigated. With parameters from DIII-D experiments, we show that RE scattering excited whistler waves can explain several poorly understood experimental results seen in a variety tokamaks. We find an increase growth rate and threshold electric field, bringing present model much closer to observations than previous results. excitation resonant electrons are calculated self-consistently using...
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...
The onset conditions for the m / n = 2/1 neoclassical tearing mode are studied in terms of drive, triggering instabilities, and toroidal rotation or shear, spherical torus NSTX (Ono M. et al 2000 Nucl. Fusion 40 557 ). There three typical these modes, given order increasing drive required onset: by energetic particle edge localized modes cases where appear to grow without a trigger. In all cases, increases with implying stabilizing effect from shear.
Significant progress in obtaining high performance discharges lasting many energy confinement times the DIII-D tokamak has been realized recent experimental campaigns. Normalized ~10 sustained for more than 5τE with qmin>1.5. (The normalized is measured by product βN H89, indicating proximity to conventional β limits and quality, respectively.) These H mode have an ELMing edge 1. The global parameters were chosen optimize potential fully non-inductive current sustainment at performance,...
The prevention of neoclassical tearing modes (NTMs) in tokamak plasmas is a major challenge for fusion. Ideal can seed NTMs through forced reconnection, yet sawtoothing discharges it not well understood why particular sawtooth crash seeds NTM after several preceding sawteeth did not. Also, sometimes appear and grow without an obvious ideal mode causing island. Based on theoretical experimental results new mechanism onset proposed tested which explains these puzzling observations. Tearing...
Strongly magnetized plasmas are rich in spatial and temporal scales, making a computational approach useful for studying these systems. The most accurate model of plasma is based on kinetic equation that describes the evolution distribution function each species six-dimensional phase space. High dimensionality renders this impractical computations long time scales. Fluid models an approximation to model. reduced allows wider range and∕or scales be explored. Computational modeling requires...
The mission of the National Spherical Torus Experiment (NSTX) is demonstration physics basis required to extrapolate next steps for spherical torus (ST), such as a plasma facing component test facility (NHTX) or an ST based (ST-CTF), and support ITER. Key issues are transport, steady state high β operation. To better understand electron new high- k scattering diagnostic was used extensively investigate gyro-scale fluctuations with varying temperature gradient scale length. Results from n = 3...
Magnetic reconnection is ubiquitous in the magnetosphere, solar corona, and toroidal fusion research discharges. In a device, magnetic island saturates at width which produces minimum energy of configuration. At saturation, modified current density profile, function flux island, essentially flat, growth rate proportional to difference O-point X-point. Further modification profile interior causes change stability additional or contraction saturated island. Because field lines an are isolated...
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...
For high β, highly shaped plasmas in the DIII-D tokamak [J. L. Luxon and G. Davis, Fusion Technol. 8, 441 (1985)], value of tearing stability index Δ′ calculated at a rational surface can be especially sensitive to pressure current profiles. Near marginal for global ideal mode, pole exists equilibrium parameter space, as predicted by analytic theory. The proximity an reconstruction this space strongly decreases accuracy calculations. Tearing calculations on kinetic reconstructions series...
We have initiated an experimental programme to address some of the questions associated with operation a tokamak high bootstrap current fraction under performance conditions, without assistance from transformer. In these discharges, stationary (or slowly improving) conditions are maintained for up 3.7 s at βN ≈ βp approaching 3.3. The achievable and pressure limited by relaxation oscillation, involving growth collapse internal transport barrier ρ ≥ 0.6. gradually increases profile broadens...
We show that the kinetic effects of energetic particles can play a crucial role in stability m/n=2/1 tearing mode tokamaks (e.g., JET, JT-60U, and DIII-D), where fraction particle beta(frac) is high. Using model equilibria based on DIII-D experimental reconstructions, nonideal MHD linear cases unstable to 2/1 investigated including deltaf particle-in-cell for coupled nonlinear 3D resistive code NIMROD [C. C. Kim et al., Phys. Plasmas 15, 072507 (2008)10.1063/1.2949704]. It observed have...
Abstract DIII-D physics research addresses critical challenges for the operation of ITER and next generation fusion energy devices. This is done through a focus on innovations to provide solutions high performance long pulse operation, coupled with fundamental plasma understanding model validation, drive scenario development by integrating core boundary plasmas. Substantial increases in off-axis current efficiency from an innovative top launch system EC power, pressure broadening Alfven...
The National Spherical Torus Experiment (NSTX) is currently being upgraded to operate at twice the toroidal field and plasma current (up 1 T 2 MA), with a second, more tangentially aimed neutral beam (NB) for rotation control, allowing pulse lengths up 5 s. Recent NSTX physics analyses have addressed topics that will allow NSTX-Upgrade achieve research goals critical Fusion Nuclear Science Facility. These include producing stable, 100% non-inductive operation in high-performance plasmas,...
The adjoint Fokker-Planck equation method is applied to study the runaway probability function and expected slowing-down time for highly relativistic electrons, including loss of energy due synchrotron radiation. In direct correspondence Monte Carlo simulation methods, has a smooth transition across separatrix, which can be attributed effect pitch angle scattering term in kinetic equation. However, same numerical accuracy, more efficient than method. gives novel estimate current decay...
Abstract JET, the world’s largest operating tokamak with unique Be/W wall and tritium handling capability, completed a Deuterium-Tritium (D-T) campaign in 2021 (Maggi et al 29th Fusion Energy Conf. ) following decade of preparatory experiments, dedicated enhancements, technical rehearsals training (Horton 2016 Eng. Des. 109–111 925). Operation raises significant technical, safety scientific challenges not encountered standard protium or deuterium operation. This contribution describes...