Nicholas Roberds
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View article: RAMSES impact on Sandia's pulsed power program
RAMSES impact on Sandia's pulsed power program Open
View article: Characterizing the effect of hypersonic boundary layer turbulence on antenna performance: A computational approach
Characterizing the effect of hypersonic boundary layer turbulence on antenna performance: A computational approach Open
The degradation of antenna performance during hypersonic re-entry is a well known phenomenon that can lead to complete radio blackout. Recent additions to the Empire code establish it as a tool for the study and analysis of the problem. Co…
View article: Parasitic Modulation of Microwave Signals by a Hypersonic Plasma Layer
Parasitic Modulation of Microwave Signals by a Hypersonic Plasma Layer Open
During hypersonic flight, compressional and viscous heating of the air can form a plasma layer which encases the aircraft. If the boundary layer becomes turbulent, then the electron density fluctuations can effect a parasitic modulation in…
View article: Microwave pulse transmission through a hypersonic plasma layer
Microwave pulse transmission through a hypersonic plasma layer Open
View article: EMPIRE User Manual
EMPIRE User Manual Open
code calculates concentrations of As, B, Cd, Cu, Fe, Mg, Na, Ni, Se, and Zn using empirical relationships derived from experimental observations of aqueous concentrations as a function of pH for fossil-fuel combustion residues. The leachin…
View article: Numerical simulation of a relativistic magnetron using a fluid electron model
Numerical simulation of a relativistic magnetron using a fluid electron model Open
An approach to numerically modeling relativistic magnetrons, in which the electrons are represented with a relativistic fluid, is described. A principal effect in the operation of a magnetron is space-charge-limited (SCL) emission of elect…
View article: Electrostatic Relativistic Fluid Models of Electron Emission in a Warm Diode
Electrostatic Relativistic Fluid Models of Electron Emission in a Warm Diode Open
A semi-analytic fluid model has been developed for characterizing relativistic electron emission across a warm diode gap. Here we demonstrate the use of this model in (i) verifying multi-fluid codes in modeling compressible relativistic el…
View article: A Robust, Performance-Portable Discontinuous Galerkin Method for Relativistic Hydrodynamics
A Robust, Performance-Portable Discontinuous Galerkin Method for Relativistic Hydrodynamics Open
In this work, we present a discontinuous-Galerkin method for evolving relativistic hydrodynamics. We include an exploration of analytical and iterative methods to recover the primitive variables from the conserved variables for the ideal e…
View article: Electrostatic Relativistic Fluid Models of Electron Emission in a Warm Diode.
Electrostatic Relativistic Fluid Models of Electron Emission in a Warm Diode. Open
View article: The influence of surface impurities on photoelectric currents driven by intense soft x rays
The influence of surface impurities on photoelectric currents driven by intense soft x rays Open
In an x-ray driven cavity experiment, an intense flux of soft x rays on the emitting surface produces significant emission of photoelectrons having several kiloelectronvolts of kinetic energy. At the same time, rapid heating of the emittin…
View article: A Robust, Performance-Portable Discontinuous Galerkin Method for Relativistic Hydrodynamics
A Robust, Performance-Portable Discontinuous Galerkin Method for Relativistic Hydrodynamics Open
View article: Surface heating and plasma desorption models in EMPIRE.
Surface heating and plasma desorption models in EMPIRE. Open
View article: Simulation of a relativistic magnetron using a fluid electron model.
Simulation of a relativistic magnetron using a fluid electron model. Open
Simulation results for a two-dimensional A6 magnetron are then presented. Computed bunching of the electron cloud occurs and coincides with significant microwave power generation. Numerical convergence of the solution is considered. Sharp …
View article: New inflow boundary conditions for relativistic and Newtonian fluids.
New inflow boundary conditions for relativistic and Newtonian fluids. Open
View article: Verification of EMPIRE Plasma Physics Codes.
Verification of EMPIRE Plasma Physics Codes. Open
View article: High-fidelity modeling of breakdown in helium: initiation processes and secondary electron emission
High-fidelity modeling of breakdown in helium: initiation processes and secondary electron emission Open
Understanding the role of physical processes contributing to breakdown is critical for many applications in which breakdown is undesirable, such as capacitors, and applications in which controlled breakdown is intended, such as plasma medi…
View article: Developing Field Emission Models Employing Nanoscale Surface Characterization.
Developing Field Emission Models Employing Nanoscale Surface Characterization. Open
View article: Micron-scale Field Emission Model for PIC-DSMC Simulations Based on Nanoscale Surface Characterization.
Micron-scale Field Emission Model for PIC-DSMC Simulations Based on Nanoscale Surface Characterization. Open
View article: Towards Predictive Plasma Science and Engineering through Revolutionary Multi-Scale Algorithms and Models (Final Report)
Towards Predictive Plasma Science and Engineering through Revolutionary Multi-Scale Algorithms and Models (Final Report) Open
This report describes the high-level accomplishments from the Plasma Science and Engineering Grand Challenge LDRD at Sandia National Laboratories. The Laboratory has a need to demonstrate predictive capabilities to model plasma phenomena i…
View article: Power flow simulations of the Z accelerator using EMPIRE.
Power flow simulations of the Z accelerator using EMPIRE. Open
View article: AMPPED LDRD: Advanced Models of the Physics & Phenomena of Electrical Discharge.
AMPPED LDRD: Advanced Models of the Physics & Phenomena of Electrical Discharge. Open
This Laboratory Directed Research and Development (LDRD) project aimed at addressing an unmet need for physics-based models that enable prediction of electrical breakdown in the presence of high voltage gradients and real-world environment…
View article: Collecting Evidence from Experiments and Simulations for Credible Predictions of Gas Breakdown by High Energy Photons.
Collecting Evidence from Experiments and Simulations for Credible Predictions of Gas Breakdown by High Energy Photons. Open
View article: Initial Comparison of EMPIRE Simulations with Diodes Driven by the Photoelectric Effect.
Initial Comparison of EMPIRE Simulations with Diodes Driven by the Photoelectric Effect. Open
View article: Modeling DC electrical breakdown using a truncated emission spectrum for trapped radiation
Modeling DC electrical breakdown using a truncated emission spectrum for trapped radiation Open
Spontaneously emitted radiation from excited atoms can be of principle importance in certain modes of electrical breakdown, especially positive streamers and some regimes of Townsend breakdown. The electrostatic particle-in-cell code Aleph…
View article: Sawtooth oscillation behavior with varying amounts of applied stellarator rotational transform
Sawtooth oscillation behavior with varying amounts of applied stellarator rotational transform Open
Tokamak-like sawtooth oscillations are observed in the Compact Toroidal Hybrid (CTH), a current-carrying stellarator. CTH has the unique ability to change the amount of the applied vacuum rotational transform from external stellarator coil…
View article: Surface photon flux dynamics during breakdown initiation
Surface photon flux dynamics during breakdown initiation Open
View article: Non-axisymmetric equilibrium reconstruction of a current-carrying stellarator using external magnetic and soft x-ray inversion radius measurements
Non-axisymmetric equilibrium reconstruction of a current-carrying stellarator using external magnetic and soft x-ray inversion radius measurements Open
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 performed on the…
View article: Low edge safety factor operation and passive disruption avoidance in current carrying plasmas by the addition of stellarator rotational transform
Low edge safety factor operation and passive disruption avoidance in current carrying plasmas by the addition of stellarator rotational transform Open
Low edge safety factor operation at a value less than two (q(a)=1/ι̷tot(a)<2) is routine on the Compact Toroidal Hybrid device with the addition of sufficient external rotational transform. Presently, the operational space of this curren…