scholarly journals Dissipation of electron-beam-driven plasma wakes

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
Rafal Zgadzaj ◽  
T. Silva ◽  
V. K. Khudyakov ◽  
A. Sosedkin ◽  
J. Allen ◽  
...  
Keyword(s):  
Large Scale ◽  
Grazing Angle ◽  
Beam Current ◽  
Time Resolved ◽  
Particle In Cell ◽  
Electron Bunches ◽  
Plasma Wakefield Accelerators ◽  
Channel Boundary ◽  
Scale Particle ◽  
Plasma Measurements

Abstract Metre-scale plasma wakefield accelerators have imparted energy gain approaching 10 gigaelectronvolts to single nano-Coulomb electron bunches. To reach useful average currents, however, the enormous energy density that the driver deposits into the wake must be removed efficiently between shots. Yet mechanisms by which wakes dissipate their energy into surrounding plasma remain poorly understood. Here, we report picosecond-time-resolved, grazing-angle optical shadowgraphic measurements and large-scale particle-in-cell simulations of ion channels emerging from broken wakes that electron bunches from the SLAC linac generate in tenuous lithium plasma. Measurements show the channel boundary expands radially at 1 million metres-per-second for over a nanosecond. Simulations show that ions and electrons that the original wake propels outward, carrying 90 percent of its energy, drive this expansion by impact-ionizing surrounding neutral lithium. The results provide a basis for understanding global thermodynamics of multi-GeV plasma accelerators, which underlie their viability for applications demanding high average beam current.

scholarly journals Magnetic Field Amplification by a Plasma Cavitation Instability in Relativistic Shock Precursors

2022 ◽  
Vol 924 (1) ◽  
pp. L12
Author(s):  
J. R. Peterson ◽  
S. Glenzer ◽  
F. Fiuza
Keyword(s):  
Magnetic Field ◽  
Large Scale ◽  
Gamma Ray ◽  
Beam Current ◽  
Particle In Cell ◽  
Field Amplification ◽  
Relativistic Shocks ◽  
Wide Range ◽  
Cavitation Instability ◽  
Shock Precursor

Abstract Plasma streaming instabilities play an important role in magnetic field amplification and particle acceleration in relativistic shocks and their environments. However, in the far shock precursor region where accelerated particles constitute a highly relativistic and dilute beam, streaming instabilities typically become inefficient and operate at very small scales when compared to the gyroradii of the beam particles. We report on a plasma cavitation instability that is driven by dilute relativistic beams and can increase both the magnetic field strength and coherence scale by orders of magnitude to reach near-equipartition values with the beam energy density. This instability grows after the development of the Weibel instability and is associated with the asymmetric response of background leptons and ions to the beam current. The resulting net inductive electric field drives a strong energy asymmetry between positively and negatively charged beam species. Large-scale particle-in-cell simulations are used to verify analytical predictions for the growth and saturation level of the instability and indicate that it is robust over a wide range of conditions, including those associated with pair-loaded plasmas. These results can have important implications for the magnetization and structure of shocks in gamma-ray bursts, and more generally for magnetic field amplification and asymmetric scattering of relativistic charged particles in plasma astrophysical environments.

scholarly journals Enhancing Positron Production using Front Surface Target Structures

2020 ◽  
Author(s):  
Sheng Jiang ◽  
Anthony Link ◽  
Dave Canning ◽  
Julie Fooks ◽  
Paul Kempler ◽  
...  
Keyword(s):  
Large Scale ◽  
Front Surface ◽  
Substantial Effect ◽  
Positron Energy ◽  
Particle In Cell ◽  
Laser Plasma Interactions ◽  
High Intensity Laser ◽  
Scale Particle ◽  
Positron Production

Abstract We report the first experimental results and simulations that demonstrate a substantial effect of large-scale front-surface target structures on high-intensity laser-produced positrons. Specifically, as compared to a flat target under nominally the same laser conditions, an optimized Si microwire array target yielded a near 100% increase in the laser-to-positron conversion efficiency and produced a 10 MeV increase in positron energy. Full-scale particle-in-cell simulations that modeled the entire positron production and transport process starting from laser-plasma interactions provided additional insight into the beneficial role of target structuring. The agreement between experimental and simulated spectra suggests future target structure optimization for desired positron sources.

Particle Acceleration and Transport in the Magnetotail

2020 ◽  
Author(s):  
Mostafa El-ALaoui ◽  
Jean Berchem ◽  
Robert L. Richard ◽  
David Schriver ◽  
Giovanni Lapenta ◽  
...  
Keyword(s):  
Large Scale ◽  
Research Problem ◽  
Mhd Simulation ◽  
Particle Tracing ◽  
Particle In Cell ◽  
Simulation Techniques ◽  
Test Particles ◽  
Global Mhd Simulation ◽  
Magnetotail Reconnection ◽  
Scale Particle

<p>An outstanding problem of magnetospheric physics is to determine the energization of particles transported from the nightside to the dayside. To address this research problem, we leverage our simulation capabilities by combining three different simulation techniques: global magnetohydrodynamic (MHD) simulations, large-scale kinetic (LSK) particle tracing simulations, and large-scale particle in cell (PIC) simulations. First, we model a magnetotail reconnection event using an iPic3D simulation with initial and boundary conditions given by a global MHD simulation. The iPic3D simulation system includes the region of fast outflows emanating from the reconnection site that drives the formation of dipolarization fronts.Then, we follow millions of test particles that exit the iPic3D system using the electromagnetic fields from the MHD simulation as they convect to the dayside and quantify the different acceleration and transport mechanisms.</p>

Robustness of Time-Resolved Measurement to Unknown and Variable Beam Current in Particle Beam Microscopy

2021 ◽  
Author(s):  
Luisa Watkins ◽  
Sheila W. Seidel ◽  
Minxu Peng ◽  
Akshay Agarwal ◽  
Christopher C. Yu ◽  
...  
Keyword(s):  
Particle Beam ◽  
Beam Current ◽  
Time Resolved

scholarly journals Elucidating the Onset of Plasticity in Sliding Contacts Using Differential Computational Orientation Tomography

2021 ◽  
Vol 69 (3) ◽  
Author(s):  
S. J. Eder ◽  
P. G. Grützmacher ◽  
M. Rodríguez Ripoll ◽  
J. F. Belak
Keyword(s):  
Grain Boundary ◽  
Large Scale ◽  
Surface Deformation ◽  
Boundary Migration ◽  
Material Design ◽  
Lattice Rotation ◽  
Time Resolved ◽  
Near Surface ◽  
Color Saturation ◽  
Dynamics Simulations

Abstract Depending on the mechanical and thermal energy introduced to a dry sliding interface, the near-surface regions of the mated bodies may undergo plastic deformation. In this work, we use large-scale molecular dynamics simulations to generate “differential computational orientation tomographs” (dCOT) and thus highlight changes to the microstructure near tribological FCC alloy surfaces, allowing us to detect subtle differences in lattice orientation and small distances in grain boundary migration. The analysis approach compares computationally generated orientation tomographs with their undeformed counterparts via a simple image analysis filter. We use our visualization method to discuss the acting microstructural mechanisms in a load- and time-resolved fashion, focusing on sliding conditions that lead to twinning, partial lattice rotation, and grain boundary-dominated processes. Extracting and laterally averaging the color saturation value of the generated tomographs allows us to produce quantitative time- and depth-resolved maps that give a good overview of the progress and severity of near-surface deformation. Corresponding maps of the lateral standard deviation in the color saturation show evidence of homogenization processes occurring in the tribologically loaded microstructure, frequently leading to the formation of a well-defined separation between deformed and undeformed regions. When integrated into a computational materials engineering framework, our approach could help optimize material design for tribological and other deformation problems. Graphic Abstract .

scholarly journals Time-resolved PIV measurements of a deflected submerged jet interacting with liquid-gas and liquid-liquid interfaces

2021 ◽  
Author(s):  
Stefan Puttinger ◽  
Mahdi Saeedipour
Keyword(s):  
Liquid Layer ◽  
Large Scale ◽  
Free Surface Flow ◽  
Industrial Applications ◽  
Liquid Pool ◽  
Surface Flow ◽  
Two Phase ◽  
Time Resolved ◽  
Submerged Jet ◽  
Major Interest

AbstractThis paper presents an experimental investigation on the interactions of a deflected submerged jet into a liquid pool with its above interface in the absence and presence of an additional lighter liquid. Whereas the former is a free surface flow, the latter mimics a situation of two stratified liquids where the liquid-liquid interface is disturbed by large-scale motions in the liquid pool. Such configurations are encountered in various industrial applications and, in most cases, it is of major interest to avoid the entrainment of droplets from the lighter liquid into the main flow. Therefore, it is important to understand the fluid dynamics in such configurations and to analyze the differences between the cases with and without the additional liquid layer. To study this problem, we applied time-resolved particle image velocimetry experiments with high spatial resolution. A detailed data analysis of a small layer beneath the interface shows that although the presence of an additional liquid layer stabilizes the oscillations of the submerged jet significantly, the amount of kinetic energy, enstrophy, and velocity fluctuations concentrated in the proximity of the interface is higher when the oil layer is present. In addition, we analyze the energy distribution across the eigenmodes of a proper orthogonal distribution and the distribution of strain and vortex dominated regions. As the main objective of this study, these high-resolution time-resolved experimental data provide a validation platform for the development of new models in the context of the volume of fluid-based large eddy simulation of turbulent two-phase flows.

scholarly journals Reconfiguration of human evolving large-scale epileptic brain networks prior to seizures: an evaluation with node centralities

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Rieke Fruengel ◽  
Timo Bröhl ◽  
Thorsten Rings ◽  
Klaus Lehnertz
Keyword(s):  
Large Scale ◽  
Brain Networks ◽  
Brain Regions ◽  
Brain Network ◽  
Theoretical Concept ◽  
Global Network ◽  
Time Resolved ◽  
Functional Connections ◽  
Node Centrality ◽  
Network Mechanism

AbstractPrevious research has indicated that temporal changes of centrality of specific nodes in human evolving large-scale epileptic brain networks carry information predictive of impending seizures. Centrality is a fundamental network-theoretical concept that allows one to assess the role a node plays in a network. This concept allows for various interpretations, which is reflected in a number of centrality indices. Here we aim to achieve a more general understanding of local and global network reconfigurations during the pre-seizure period as indicated by changes of different node centrality indices. To this end, we investigate—in a time-resolved manner—evolving large-scale epileptic brain networks that we derived from multi-day, multi-electrode intracranial electroencephalograpic recordings from a large but inhomogeneous group of subjects with pharmacoresistant epilepsies with different anatomical origins. We estimate multiple centrality indices to assess the various roles the nodes play while the networks transit from the seizure-free to the pre-seizure period. Our findings allow us to formulate several major scenarios for the reconfiguration of an evolving epileptic brain network prior to seizures, which indicate that there is likely not a single network mechanism underlying seizure generation. Rather, local and global aspects of the pre-seizure network reconfiguration affect virtually all network constituents, from the various brain regions to the functional connections between them.

Sign in / Sign up

Export Citation Format

Share Document