Keith Cartwright

Sandia National Laboratories California

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T. D. Pointon

Royal Hobart Hospital

J.W. Luginsland

Michigan State University

M.D. Haworth

University of Notre Dame

Peter Mardahl

United States Air Force Research Laboratory

Matthew Tyler Bettencourt

Nvidia (United States)

Andrew Greenwood

Montanuniversität Leoben

C.K. Birdsall

University of California, Berkeley

John Verboncoeur

Michigan State University

Y. Y. Lau

University of Michigan–Ann Arbor

J. Gardelle

Commissariat à l'Énergie Atomique et aux Énergies Alternatives

Cooperative Institutions

Sandia National Laboratories

136

Sandia National Laboratories California

126

United States Air Force Research Laboratory

University of Michigan–Ann Arbor

Kirtland Air Force Base

U.S. Air Force Research Laboratory Directed Energy Directorate

Los Alamos National Laboratory

University of New Mexico

United States Naval Research Laboratory

National Technical Information Service

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Virtual prototyping of directed energy weapons

Keith Cartwright L.A. Bowers Andrew Greenwood C. Fichtl M.D. Haworth

We give an overview of how RF systems, from pulsed power to antennas, can be virtually prototyped with the ICEPIC (Improved Concurrent Electromagnetic Particle-in-Cell) code. ICEPIC simulates from first principles (Maxwell's equations and Lorenz's force law) the electrodynamics and charged particle dynamics of the RF-producing part of the system. Our simulations focus on gigawatt-class sources; the relativistic magnetron is shown as an example. Such simulations require enormous computational resources. These simulations successfully expose undesirable features of these sources and help us to suggest improvements.

Code (set theory)

Particle-in-cell

Electromagnetics

Virtual Prototyping

10.1109/dodugc.2003.1253378

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Citations (3)

On the elimination of numerical Cerenkov radiation in PIC simulations

Journal of Computational Physics (2004)

Andrew Greenwood Keith Cartwright J.W. Luginsland Ernest A. Baca

Stencil

10.1016/j.jcp.2004.06.021

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Citations (95)

Refraction and reflection of ion acoustic solitons by space charge sheath

Keith Cartwright C.K. Birdsall

Summary form only given. Experiments have shown that ion acoustic solitons tunnel through the space charge sheath in front of a grid without time delay. They are absorbed resonantly when the spatial width of the wave is close to the characteristic gradient scale length of the sheath. The reflection and transmission coefficients found in these experiments have compared well with theory in the long wavelength limit. However, to achieve this comparison, two parameters were added that were not in the original theory. These parameters allow for the absorption of wave energy by the space charge sheath. The goal of our numerical simulations, designed to reproduce the experimental results, is to uncover the mechanism of this energy loss and large speed of propagation through the sheath.

Reflection

10.1109/plasma.1996.550689

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Effects of Vacuum Impedance Changes on MITL Flow using 3D Electromagnetic PIC Simulations.

Troy Powell Keith Cartwright T. D. Pointon Andrew Biller C. Grabowski

Focused Impedance Measurement

10.2172/1881641

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PIC-DSMC numerical grid heating in collisional plasmas: Application to streamer discharge simulations.

OSTI OAI (U.S. Department of Energy Office of Scientific and Technical Information) (2019)

Christopher Moore Ashish Jindal Andrew Fierro Keith Cartwright Matthew Hopkins

Streamer discharge

Source

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Mutually magnetically insulated two-species Brillouin flow

Physics of Plasmas (2023)

Adam M. Darr Keith Cartwright

In this work, we use the Brillouin flow analytic framework to examine the physics of Magnetically Insulated Transmission Lines (MITL). We derive a model applicable to any particle species, including both positive and negative ions, in planar and cylindrical configurations. We then show how to self-consistently solve for two-species simultaneously, using magnetically insulated electrons and positive ions as an example. We require both layers to be spatially separated and magnetically insulated (mutually magnetically insulated); for a 7.5 cm gap with a 2 MV bias voltage, this condition requires magnetic fields in excess of 2.73 T. We see a close match between mutually insulated MITL performance and “superinsulated” (high degree of magnetic insulation) electron-only theory, as may be expected for these high magnetic fields. However, the presence of ions leads to several novel effects: (1) Opposite to electron-only theory, total electron currents increase rather than decrease as the degree of magnetic insulation becomes stronger. The common assumption of neglecting electrons for superinsulated MITL operation must be revisited when ions are present—we calculate up to 20× current enhancement. (2) The electron flow layer thickness increases up to double, due to ion space-charge enhancement. (3) The contributions from both ions and electrons to the MITL flow impedance are calculated. The flow impedance drops by over 50% when ions fill the gap, which can cause significant reflections at the load if not anticipated and degrade performance. Additional effects and results from the inclusion of the ion layer are discussed.

Brillouin zone

Electron flow

10.1063/5.0145768

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Citations (4)

Relativistic Electron Beam Transport Through a Background Gas at SPHINX: Drift Cell Redesign and Initial EMPIRE Simulations

2020 IEEE International Conference on Plasma Science (ICOPS) (2023)

Elaine Louise Rhoades Christopher Moore Benjamin Elbrecht Nicolas Szalek Israel Owens

Validation of plasma physics codes like EMPIRE requires performing uncertainty quantification comparing experimental data and simulation results. The Short Pulse, High Intensity Nanosecond X-radiator (SPHINX) is a high-voltage, high-shot rate bremsstrahlung accelerator at Sandia National Laboratories. SPHINX can additionally be operated in electron-beam mode by changing from the standard tantalum converter to a 1-mil titanium converter connected to a drift cell that is filled with low-pressure gas. The primary beam diagnostic for the drift cell is currently calorimetry, with an option for photon doppler velocimetry (PDV) when testing samples. Recently, design work has occurred for a new drift cell for SPHINX that will significantly expand diagnostic capabilities to allow for additional information to be gathered during validation experiments. We will present an overview of the design changes for the new drift cell and present initial results of EMPIRE simulations investigating beam behavior across a range of parameters in the new drift cell.

Sphinx

Relativistic electron beam

10.1109/icops45740.2023.10481244

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Hybrid PIC acceleration schemes for discharges

Keith Cartwright John Verboncouer C.K. Birdsall

Summary for only given, as follows. Kinetic simulation of plasmas in which equilibrium occurs over ion timescales poses a computational challenge due to the disparate timescales of the electron plasma frequency (/spl sim/10/sup 9/), the ion plasma frequency (/spl sim/10/sup 7/), and the ionization frequency (/spl sim/10/sup 7/). Hybrid electrostatic PIC algorithms are presented in which the electrons reach thermodynamic equilibrium with the ions each time step. There are three different approximations for the electrons. First, the nonlinear Boltzmann relationship for the electrons can be applied to the bulk of a plasma. Second there is a truncated Maxwellian which is used in undriven sheaths; this approximation truncates the electron distribution at the wall potential. The last method used the steady-state electron distribution function in a DC electric field, with elastic collisions between electrons and neutral gas atoms. The collision frequency, /spl nu//sub m/(/spl upsi/), can be a tabulated or fitted function; the method is implemented using argon cross-sections. These approximations neglect effects faster than the ion time-scales, decreasing the computer time used by over an order of magnitude; however, they increase the complexity of the boundary conditions, and the simulation is no longer self-consistent. Theoretical ramifications of these approximations are examined, and results are compared with full PIC simulations of undriven sheaths, ion acoustic waves and DC discharges (PDP).

Collision frequency

10.1109/plasma.1997.605185

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November 2016 HERMES Outdoor Shot Series 10268-313: Free Space Fields and Current Coupling.

Benjamin Yee Keith Cartwright T. D. Pointon

During the trials during November 2016 at the HERMES III facility, a number of sensors were fielded to measure the free fields and currents coupled to aerial and buried cables. Here, we report on the work done to compensate, correct, and analyze these signals. Average results are presented for selected sets of sensors and prelimi- nary analyses are provided of the time and frequency domain signals. Electric fields were typically on the order of 10 kV/m, magnetic fields were approximately 10 AT, and currents were around 10 A. Several opportunities for improvement are identified including quantification of radiation effects on sensors, higher accuracy compensation techniques, increased sensitivity in differential sensor measurements, and exploration of the use of I-dots in conductivity calculations.

Free space

10.2172/1481505

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Review of Cold Cathode Research at the Air Force Research Laboratory

IEEE Transactions on Plasma Science (2008)

Don Shiffler M.D. Haworth Keith Cartwright R. Umstattd M. Ruebush

Over the last decade, the Air Force Research Laboratory, Directed Energy Directorate (AFRL/DE) has engaged in a high current density field emission cathode research program. This program explored the aspects of cathode materials as well as the details of cathode geometries and emission physics. This paper summarizes the results of this ongoing research effort to date. We review the history and motivation for the program, which provide insight into the physics issues of concern for various vacuum electronic sources. One important aspect of the program consists of the investigation of new cathode materials. For many high power microwave (HPM) sources, neutral out-gassing, which ties critically with cathode materials, plays a key role in the effective operation of the source. These material properties influence plasma formation, which in turn dictates the operation of an HPM device. For a cathode material, AFRL chose to focus on cesium-iodide-coated carbon fiber cathodes, which we discuss in detail here. A second important aspect of the program consists of understanding emission physics and the optimum geometries for a cathode. This aspect couples closely with electron beam quality, which in turns effects the electron beam interaction with microwaves in the HPM structure. This paper concludes with a discussion of the implementation of the cathode material on both a Magnetically Insulated transmission Line Oscillator and a relativistic magnetron.

Cold cathode

Hot cathode

10.1109/tps.2008.926227

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Citations (91)