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.

scholarly journals Enhancement of monoenergetic proton beamsviacone substrate in high intensity laser pulse-double layer target interactions

2010 ◽  
Vol 28 (4) ◽  
pp. 585-590 ◽  
Author(s):  
Weimin Zhou ◽  
Yuqiu Gu ◽  
Wei Hong ◽  
Leifeng Cao ◽  
Zongqing Zhao ◽  
...  
Keyword(s):  
Double Layer ◽  
High Intensity ◽  
Laser Light ◽  
Surface Current ◽  
Hot Electrons ◽  
Two Dimensional ◽  
Particle In Cell ◽  
Laser Plasma Interactions ◽  
High Intensity Laser ◽  
Intensity Laser

AbstractA scheme capable of enhancing the energy of monoenergetic protons in high intensity laser-plasma interactions is proposed and demonstrated by two dimensional particle-in-cell simulations. The focusing of laser light pulse and the guiding of surface currentviathe highZmaterial cone-shaped substrate increase the temperature of hot electrons, which are responsible for the electrostatic field accelerating protons. Moreover, the sub-micron proton layer coated on the cone-shaped substrate makes the total proton beam experience the same accelerating field, thus the monochromaticity is maintained. Compared to the normal film double layer target, the energy of monoenergetic proton beams can be improved about three times.

scholarly journals Shock waves in the magnetized cosmic web: the role of obliquity and cosmic ray acceleration

2020 ◽  
Vol 496 (3) ◽  
pp. 3648-3667 ◽  
Author(s):  
S Banfi ◽  
F Vazza ◽  
D Wittor
Keyword(s):  
Large Scale ◽  
Cosmic Ray ◽  
Adaptive Mesh ◽  
Relativistic Electrons ◽  
Particle In Cell ◽  
Large Scale Structures ◽  
Cosmic Ray Acceleration ◽  
Mesh Resolution ◽  
Local Shear

ABSTRACT Structure formation shocks are believed to be the largest accelerators of cosmic rays in the Universe. However, little is still known about their efficiency in accelerating relativistic electrons and protons as a function of their magnetization properties, i.e. of their magnetic field strength and topology. In this work, we analysed both uniform and adaptive mesh resolution simulations of large-scale structures with the magnetohydrodynamical grid code enzo, studying the dependence of shock obliquity with different realistic scenarios of cosmic magnetism. We found that shock obliquities are more often perpendicular than what would be expected from a random 3D distribution of vectors, and that this effect is particularly prominent in the proximity of filaments, due to the action of local shear motions. By coupling these results to recent works from particle-in-cell simulations, we estimated the flux of cosmic ray protons in galaxy clusters, and showed that in principle the riddle of the missed detection of hadronic γ-ray emission by the Fermi-LAT can be explained if only quasi-parallel shocks accelerate protons. On the other hand, for most of the cosmic web the acceleration of cosmic ray electrons is still allowed, due to the abundance of quasi-perpendicular shocks. We discuss quantitative differences between the analysed models of magnetization of cosmic structures, which become more significant at low cosmic overdensities.

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.

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>

The Role of Sense of Direction and Other Factors During Navigation in a Large-Scale, Unconstrained Environment

2013 ◽  
Author(s):  
Elisabeth J. Ploran ◽  
Ericka Rovira ◽  
James C. Thompson ◽  
Raja Parasuraman
Keyword(s):  
Large Scale ◽  
Sense Of Direction

Magnetic Properties of xCeO2•(50 − x) PbO•50B2O3 Glasses and Glass Ceramics

2017 ◽  
Vol 13 (1) ◽  
pp. 4486-4494 ◽  
Author(s):  
G.El Damrawi ◽  
F. Gharghar
Keyword(s):  
Magnetic Properties ◽  
Large Scale ◽  
Glass Ceramics ◽  
Magnetic Behavior ◽  
Crystal Formation ◽  
Dual Roles ◽  
Effective Agent ◽  
Ordered Structures ◽  
Essential Change

Cerium oxide in borate glasses of composition xCeO2·(50 − x)PbO·50B2O3 plays an important role in changing both microstructure and magnetic behaviors of the system. The structural role of CeO2 as an effective agent for cluster and crystal formation in borate network is clearly evidenced by XRD technique. Both structure and size of well-formed cerium separated clusters have an effective influence on the structural properties. The cluster aggregations are documented to be found in different range ordered structures, intermediate and long range orders are the most structures in which cerium phases are involved. The nano-sized crystallized cerium species in lead borate phase are evidenced to have magnetic behavior.  The criteria of building new specific borate phase enriched with cerium as ferrimagnetism has been found to keep the magnetization in large scale even at extremely high temperature. Treating the glass thermally or exposing it to an effective dose of ionized radiation is evidenced to have an essential change in magnetic properties. Thermal heat treatment for some of investigated materials is observed to play dual roles in the glass matrix. It can not only enhance alignment processes of the magnetic moment but also increases the capacity of the crystallite species in the magnetic phases. On the other hand, reverse processes are remarked under the effect of irradiation. The magnetization was found to be lowered, since several types of the trap centers which are regarded as defective states can be produced by effect of ionized radiation. 

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