Bruce Langdon - Academia.edu (original) (raw)

Papers by Bruce Langdon

3D and r,z particle simulations of heavy ion fusion beams

The space-charge-dominated beams in a heavy ion beam driven inertial fusion (HIF) accelerator mus... more The space-charge-dominated beams in a heavy ion beam driven inertial fusion (HIF) accelerator must be focused onto small (few mm) spots at the fusion target, and so preservation of a small emittance is crucial. The nonlinear beam self-fields can lead to emittance growth; thus, a self-consistent field description is necessary. We have developed a multi-dimensional time-dependent discrete particle simulation code, WARP, and are using it to study the behavior of HIF beams. The code's 3d package combines features of an accelerator code and a particle-in-cell (PIC) plasma simulation. Novel techniques allow it to follow beams through many accelerator elements over long distances and around bends. We have used the code to understand the emittance growth observed in the MBE4 experiment at Lawrence Berkeley Laboratory (LBL) under conditions of aggressive drift-compression. We are currently applying it to LBL's planned ILSE experiments, and (most recently) to an ESQ injector option ...

Single speckle SRS threshold as determined by electron trapping, collisions and speckle duration

Speckle SRS intensity threshold has been shown to increase with spatial dimension, D, because bot... more Speckle SRS intensity threshold has been shown to increase with spatial dimension, D, because both diffraction and trapped electron escape rate increase with D, though the net effect is to substantially decrease the threshold compared to 1D linear gain calculations. On the other hand, the apparent threshold appears to decrease with integration time in PIC simulations. We present an optimum nonlinearly resonant calculation of the SRS threshold, taking into account large fluctuations of the SRS seed reflectivity, R0. Such fluctuations, absent in 1D, are caused by a gap in the linear reflectivity gain spectrum which leads to an exponential probability distribution for R0. While the SRS threshold intensity is of course finite, these fluctuations lead to a decrease of apparent threshold with increasing speckle lifetime. L. Yin et al., Physics of Plasmas 15, 013109 (2008). D. S. Montgomery et al., 9, 2311(2002). Bruce Langdon et al., 38^th Anomalous Absorption Conference (2008). Harvey A....

Single speckle SRS threshold as determined by electron trapping, collisions and speckle duration

Plasma physics via computer simulation

INSTITUTE OF PHYSIC SERIES IN PLASMA PHYSICS SIMULATION CK BlRDSALL AB LANGDON ... Series in Plas... more INSTITUTE OF PHYSIC SERIES IN PLASMA PHYSICS SIMULATION CK BlRDSALL AB LANGDON ... Series in Plasma Physics Series Editors: Steve Cowley, Imperial College, UK Peter Stott, CEA Cadarache, France Hans Wilhelmsson, Chalmers University of Technology, Sweden ...

Modeling the longitudinal wall impedance instability in heavy ion beams using an R-Z PIC code

The effects of the longitudinal wall impedance instability in a heavy ion beam are of great inter... more The effects of the longitudinal wall impedance instability in a heavy ion beam are of great interest for heavy ion fusion drivers. We are studying this instability using the R-Z thread of the WARP PIC code. We describe the code and our model of the impedance due to the accelerating modules of the induction LINAC as a resistive wall. We

Kinetic theory for fluctuations and noise in computer simulation of plasma

Physics of Fluids, 1979

The Crab nebula's wisps as shocked pulsar wind

The Crab synchrotron nebula has been successfully modelled as the post-shock region of a relativi... more The Crab synchrotron nebula has been successfully modelled as the post-shock region of a relativistic, magnetized wind carrying most of the spindown luminosity from the central pulsar. While the Crab is the best-studied example, most of the highest spindown luminosity pulsars are also surrounded by extended synchrotron nebulae, and several additional supernova remnants with 'plerionic' morphologies similar to the Crab are known where the central object is not seen. All these objects have nonthermal, power-law spectra attributable to accelerated high-energy particles thought to originate in a Crab-like relativistic pulsar wind. However, proposed models have so far treated the wind shock as an infinitesimally thin discontinuity, with an arbitrarily ascribed particle acceleration efficiency. To make further progress, investigations resolving the shock structure seemed in order. Motivated by these considerations, we have performed particle-in-cell (PIC) simulations of perpendicularly magnetized shocks in electron-positron and electron-positron-ion plasmas. The shocks in pure electron-positron plasmas were found to produce only thermal distributions downstream, and are thus poor candidates as particle acceleration sites. When the upstream plasma flow also contained a smaller population of positive ions, however, efficient acceleration of positrons, and to a lesser extent of electrons, was observed in the simulations.

Kinetic-Ion Simulations of Stimulated Brillouin Backscattering in Ignition Target Plasmas and Reduced Models for Nonlinear Saturation

1D and 2D simulations with the BZOHAR^2,3 hybrid code (kinetic PIC ions and Boltzmann fluid elect... more 1D and 2D simulations with the BZOHAR^2,3 hybrid code (kinetic PIC ions and Boltzmann fluid electrons) are being used to investigate the saturation of stimulated Brillouin backscatter (SBBS) instability for plasma conditions in ignition campaign experiments in the National Ignition Facility. Ignition targets must be designed so that backscatter is not severe. BZOHAR can simulate ion kinetic and fluid nonlinearities

2. 5D EM direct implicit PIC simulation using AVANTI

Eulerian-Lagrangian Kinetic Simulations of Laser-Plasma Interactions

ABSTRACT

Nonlinear Inverse Bremsstrahlung and Heated Electron Distributions

Le Journal de Physique Colloques, 1979

When Zv 0 2 / v e 2 ≳1, inverse bremsstrahlung results in a non-Maxwellian velocity distribution ... more When Zv 0 2 / v e 2 ≳1, inverse bremsstrahlung results in a non-Maxwellian velocity distribution for which the absorption is reduced by up to a factor of 2 compared with the Maxwellian distribution usually assumed. Transport and atomic processes are also altered. Especially in ...

Magnetic field transport in laser-fusion targets

Physics of Fluids, 1978

IEEE Transactions on Plasma Science, 1994

Highlights are presented from among the many contributions made by Oscar Buneman to the science, ... more Highlights are presented from among the many contributions made by Oscar Buneman to the science, engineering, and mathematics communities. Emphasis is placed not only on “what” this pioneer of computational plasma physics contributed but, of equal importance, on “how” he made his contributions. Therein lies the difference between technical competence and scientific greatness. The picture which emerges illustrates the open-mindedness,

Journal of Computational Physics, 1974

The electromagnetic field grids in fine-resolution two-dimensional or mediumresolution three-dime... more The electromagnetic field grids in fine-resolution two-dimensional or mediumresolution three-dimensional plasma simulation are very large. We propose a method whereby only a fraction of the grid need be in fast core at any given time. The basic idea is to do several consecutive field solutions with coarse grids displaced relative to one another. The separate solutions may pertain to different time steps ("jiggling") or the same time step ("interlacing"). The combination of these separate solutions can provide some aspects of the accuracy improvement obtainable with the fine grid which is the superposition of the separate grids. These techniques may be useful when one is strongly limited by the size of random-access memory but can afford to place greater demands on serial-access memory and processor speed. Their effect is to reduce "aliasing" errors, in which plasma perturbations are unphysically coupled when their wave numbers differ by wave vectors characteristic of the grid. Resolution may then be improved by methods described elsewhere. In order to evaluate these methods quantitatively, dispersion relations for plasma oscillations are examined. Aliasing effects, such as gridinduced instability, can be greatly reduced. However, depending on the smoothness of the velocity distribution, "jiggling" can introduce new troublesome modes with frequencies -At-l; "interlacing" has no known ill side effects. Simulation results are in agreement with theory. In two and three dimensions, there is also a decrease in computation time compared to using a finer gride with similar reduction in grid effects.

Implicit time integration for plasma simulation

Journal of Computational Physics, 1982

... d, = 2, d, = 1).24 COHEN, LANGDON,ANDFRIEDMAN that control the degree of implicitness and tha... more ... d, = 2, d, = 1).24 COHEN, LANGDON,ANDFRIEDMAN that control the degree of implicitness and that ... 1. For midt2 b 1, implicit schemes may be stable, but the highfrequency oscillations are ... for the least damped simpleharmonic oscillator normal mode is plotted as a function of 41 ...

Smoothing and spatial grid effects in implicit particle simulation

Journal of Computational Physics, 1984

ABSTRACT

Analysis of the time integration in plasma simulation

Journal of Computational Physics, 1979

This paper treats the collective behavior of hot plasma as modified by the numerical time integra... more This paper treats the collective behavior of hot plasma as modified by the numerical time integration methods used to integrate the particle equations of motion in computer simulation of plasmas. No approximation, other than ignoring roundoff errors, is made in analyzing the finite-difference algorithms. Our results reduce simply and exactly to the corresponding results of plasma theory in the limit ..delta..t..-->..0. The possibility of nonphysical instability is considered. The results of this and of previous papers are combined to describe both the spatial and temporal difference algorithms. The theory is generalized to a class of integration schemes, some algorithms are analyzed, and a new example is synthesized. The difficulty of developing algorithms stable at very large time steps is examined. The present analysis may be combined with an earlier rigorous analysis of the spatial grid used for field equations, to develop a kinetic theory of simulation plasmas paralleling that for real plasmas. This theory may be of use in the design and interpretation of computer simulation experiments.

On enforcing Gauss' law in electromagnetic particle-in-cell codes

Computer Physics Communications, 1992

Computer Physics Communications, 1988

An overview of the electromagnetic Direct Implicit PLC plasma simulation algorithm is presented i... more An overview of the electromagnetic Direct Implicit PLC plasma simulation algorithm is presented in the form it is now implemented in the 2.5D code AVANTI. A test case that has ideal properties for testing the algorithm is presented. Recently the relativistic extension of the algorithm has been investigated and preliminary consideration is given to the changes required in the algorithm for this capability. " '~/ x is the position vector, E and B are the electro-* This work was performed under the auspices of the US magnetic fields, and n represents the time level Department of Energy by Lawrence Livermore National t,, = n Lit. Note that the explicit relativistic scheme Laboratory under contract No. W-7405-Eng-48.

Investigations of a Sheet Model for a Bounded Plasma with Magnetic Field and Radiation

Computer Simulation of Plasma and Many Body Problems, 1967

3D and r,z particle simulations of heavy ion fusion beams

Single speckle SRS threshold as determined by electron trapping, collisions and speckle duration

Plasma physics via computer simulation

Modeling the longitudinal wall impedance instability in heavy ion beams using an R-Z PIC code

Kinetic theory for fluctuations and noise in computer simulation of plasma

Physics of Fluids, 1979

The Crab nebula's wisps as shocked pulsar wind

Kinetic-Ion Simulations of Stimulated Brillouin Backscattering in Ignition Target Plasmas and Reduced Models for Nonlinear Saturation

2. 5D EM direct implicit PIC simulation using AVANTI

Eulerian-Lagrangian Kinetic Simulations of Laser-Plasma Interactions

ABSTRACT

Nonlinear Inverse Bremsstrahlung and Heated Electron Distributions

Le Journal de Physique Colloques, 1979

Magnetic field transport in laser-fusion targets

Physics of Fluids, 1978

IEEE Transactions on Plasma Science, 1994

Journal of Computational Physics, 1974

Implicit time integration for plasma simulation

Journal of Computational Physics, 1982

Smoothing and spatial grid effects in implicit particle simulation

Journal of Computational Physics, 1984

ABSTRACT

Analysis of the time integration in plasma simulation

Journal of Computational Physics, 1979

On enforcing Gauss' law in electromagnetic particle-in-cell codes

Computer Physics Communications, 1992

Computer Physics Communications, 1988

Investigations of a Sheet Model for a Bounded Plasma with Magnetic Field and Radiation

Computer Simulation of Plasma and Many Body Problems, 1967