Advances in petascale kinetic plasma simulation with VPIC and Roadrunner

Bowers, K. J.; Albright, B. J.; Yin, L.; Daughton, W.; Roytershteyn, V.; Bergen, B.; Kwan, Thomas J. T.

doi:10.1088/1742-6596/180/1/012055

Cited by 179 publications

(112 citation statements)

References 31 publications

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“…In this paper, we use the particle-in-cell code VPIC [12][13][14] to model in two dimensions (2D) and three dimensions (3D) the nonlinear dynamics of SBS in solitary laser speckles, modeled in our simulations as diffraction-limited Gaussian beams. During SBS, ion acoustic waves may grow to finite amplitude, leading to amplitude-dependent nonlinearity, including ion trapping and subsequent trapping-induced IAW bowing (associated with a negative frequency shift dx < 0) and breakup, 15 as well as wave decay processes such as two-ion-wave decay.…”

Section: Introductionmentioning

confidence: 99%

Multi-dimensional dynamics of stimulated Brillouin scattering in a laser speckle: Ion acoustic wave bowing, breakup, and laser-seeded two-ion-wave decay

et al. 2016

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Two- and three-dimensional particle-in-cell simulations of stimulated Brillouin scattering (SBS) in laser speckle geometry have been analyzed to evaluate the relative importance of competing nonlinear processes in the evolution and saturation of SBS. It is found that ion-trapping-induced wavefront bowing and breakup of ion acoustic waves (IAW) and the associated side-loss of trapped ions dominate electron-trapping-induced IAW wavefront bowing and breakup, as well as the two-ion-wave decay instability over a range of ZTe/Ti conditions and incident laser intensities. In the simulations, the latter instability does not govern the nonlinear saturation of SBS; however, evidence of two-ion-wave decay is seen, appearing as a modulation of the ion acoustic wavefronts. This modulation is periodic in the laser polarization plane, anti-symmetric across the speckle axis, and of a wavenumber matching that of the incident laser pulse. A simple analytic model is provided for how spatial “imprinting” from a high frequency inhomogeneity (in this case, the density modulation from the laser) in an unstable system with continuum eigenmodes can selectively amplify modes with wavenumbers that match that of the inhomogeneity.

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Section: Introductionmentioning

confidence: 99%

Multi-dimensional dynamics of stimulated Brillouin scattering in a laser speckle: Ion acoustic wave bowing, breakup, and laser-seeded two-ion-wave decay

et al. 2016

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“…Though understanding of laser plasma interaction (LPI) has evolved over the nearly 50 years since the first linear theories 1,2 and measurements 3 of stimulated Raman scattering (SRS), recent laser-driven fusion experiments 4,5 together with advances in computation 6,7 and experimental measurement techniques 8,9 have led to renewed interest in this subject. [10][11][12] Laser coupling to plasma modes typically divides into coupling to low-frequency ion acoustic waves 13 and high frequency electron plasma wave (EPW) or Langmuir waves (LW), though with nonlinear modification of the particle distribution functions, electrostatic modes intermediate in frequency are possible as well, such as the electron acoustic mode, 14 observed in stimulated electron acoustic scattering (SEAS), 15 kinetic electrostatic electron nonlinear (KEEN) waves, 16 and the low frequency part of the beam acoustic modes (BAM).…”

Section: Introductionmentioning

confidence: 99%

Trapping induced nonlinear behavior of backward stimulated Raman scattering in multi-speckled laser beams

et al. 2012

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In inertial confinement fusion experiments, stimulated Raman scattering (SRS) occurs when electron density fluctuations are amplified resonantly by the incident laser beams and scattered light. These beams comprise several thousands of individual laser speckles. We have found in single-speckle studies that electron trapping lowers the threshold intensity for SRS onset to a value below that from linear theory and enhances scattering. The trapping-induced plasma-wave frequency shift leads to wave-front bowing and filamentation processes that saturate SRS and limit scattering within a speckle. With large-scale simulations, we have now examined how laser speckles interact with one another through three-dimensional (3D) particle-in-cell (PIC) simulations of two interacting speckles and 2D PIC simulations of ensembles of laser speckles (hundreds of speckles). Our work shows that kinetic trapping physics also governs the onset and saturation of SRS in ensembles of speckles. Speckles interact in a manner that is nonlinear and nonlocal: An intense speckle can destabilize its neighbors through transport of hot electrons and SRS waves, resulting in enhanced emission of particles and waves that, in turn, act upon the original speckle. In this manner, speckles below threshold when in isolation can be above the threshold in multi-speckled beams under conditions for laser-driven fusion experiments at the National Ignition Facility (NIF) and ensembles of speckles are thus found to collectively lower the SRS onset threshold. Simulations of the hohlraum interior where laser beams overlap show that multi-speckled laser beams at low average intensity (a few times 10 14 W/cm 2 ) have correspondingly lower thresholds for enhanced SRS and that the sub-ps bursts of SRS saturate through trapping induced nonlinearities. Because of electron trapping effects, SRS reflectivity grows slowly with average laser intensity. While SRS reflectivity saturates under NIF conditions, SRS hot electron energy increases with increasing laser intensity and may contribute to capsule preheat. V C 2012 American Institute of Physics. [http://dx.

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“…Particles in the sheet have a net drift U i = −U e to give a current density J = en 0 (U i − U e ) consistent with ∇ × B = 4πJ/c. The simulations are performed using the VPIC [20] and NPIC codes [21,22], both of which solve the relativistic VlasovMaxwell system of equations.…”

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confidence: 99%

Formation of Hard Power Laws in the Energetic Particle Spectra Resulting from Relativistic Magnetic Reconnection

et al. 2014

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Using fully kinetic simulations, we demonstrate that magnetic reconnection in relativistic plasmas is highly efficient at accelerating particles through a first-order Fermi process resulting from the curvature drift of particles in the direction of the electric field induced by the relativistic flows. This mechanism gives rise to the formation of hard power-law spectra in parameter regimes where the energy density in the reconnecting field exceeds the rest mass energy density σ ≡ B 2 /(4πnmec 2 ) > 1 and when the system size is sufficiently large. In the limit σ 1, the spectral index approaches p = 1 and most of the available energy is converted into non-thermal particles. A simple analytic model is proposed which explains these key features and predicts a general condition under which hard power-law spectra will be generated from magnetic reconnection.PACS numbers: 52.27. Ny, 52.35.Vd, 98.54.Cm, 98.70.Rz Introduction -Magnetic reconnection is a fundamental plasma process that allows rapid changes of magnetic field topology and the conversion of magnetic energy into plasma kinetic energy. It has been extensively discussed in solar flares, Earth's magnetosphere, and laboratory applications. However, magnetic reconnection remains poorly understood in high-energy astrophysical systems [1]. Magnetic reconnection has been suggested as a mechanism for producing high-energy emissions from pulsar wind nebula, gamma-ray bursts, and jets from active galactic nuclei [2][3][4][5][6]. In those systems, it is often expected that the magnetization parameter σ ≡ B 2 /(4πnmc 2 ) exceeds unity. Most previous kinetic studies focused on the non-relativistic regime σ < 1 and reported several acceleration mechanisms such as acceleration at X-line regions [7][8][9] and Fermi-type acceleration within magnetic islands [8][9][10][11]. More recently, the regime σ = 1-100 has been explored using pressure-balanced current sheets and strong particle acceleration has been found in both diffusion regions [12][13][14][15] and island regions [16,17]. However, this initial condition requires a hot plasma component inside the current sheet to maintain force balance, which may not be justified for high-σ plasmas.

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Advances in petascale kinetic plasma simulation with VPIC and Roadrunner

Cited by 179 publications

References 31 publications

Multi-dimensional dynamics of stimulated Brillouin scattering in a laser speckle: Ion acoustic wave bowing, breakup, and laser-seeded two-ion-wave decay

Multi-dimensional dynamics of stimulated Brillouin scattering in a laser speckle: Ion acoustic wave bowing, breakup, and laser-seeded two-ion-wave decay

Trapping induced nonlinear behavior of backward stimulated Raman scattering in multi-speckled laser beams

Formation of Hard Power Laws in the Energetic Particle Spectra Resulting from Relativistic Magnetic Reconnection

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