Hard xrays produced by intense laserproduced fast electrons interacting with solids are a vital source for producing radiographs of highdensity objects and implosion cores for inertial confinement fusion. Accurate calculation of hard xray sources requires a threedimensional (3D) simulation geometry that fully models the electron transport dynamics, including electron recirculation and the generation of absolute photon yields. To date, 3D simulations of laserproduced bremsstrahlung photons over tens of picoseconds and code benchmarking have not been performed definitively. In this study, we characterize subpicosecond laserproduced fast electrons by modeling angularly resolved bremsstrahlung measurements for refluxing and nonrefluxing targets using the 3D hybrid particleincell (PIC), Large Scale Plasma code. Bremsstrahlung radiation and escaped electron data were obtained by focusing a 50TW Leopard laser (15 J, 0.35 ps, 2 × 10 19 W/cm 2 ) on a 100 μmthick Cu foil and a Cu with a large plastic backing (Cu–CH target). Data for both the Cu and Cu–CH targets were reproduced for simulations with a given set of electron parameters. Comparison of the simulations revealed that the hard xray emission from the Cu target was significantly longer in duration than that from the Cu–CH target. The benchmarked hybrid PIC code could prove to be a powerfulmore »
Fast electron transport dynamics and energy deposition in magnetized, imploded cylindrical plasma
Inertial confinement fusion approaches involve the creation of highenergydensity states through compression. High gain scenarios may be enabled by the beneficial heating from fast electrons produced with an intense laser and by energy containment with a highstrength magnetic field. Here, we report experimental measurements from a configuration integrating a magnetized, imploded cylindrical plasma and intense laserdriven electrons as well as multistage simulations that show fast electrons transport pathways at different times during the implosion and quantify their energy deposition contribution. The experiment consisted of a CH foam cylinder, inside an external coaxial magnetic field of 5 T, that was imploded using 36 OMEGA laser beams. Twodimensional (2D) hydrodynamic modelling predicts the CH density reaches 9.0 g cm − 3 , the temperature reaches 920 eV and the external Bfield is amplified at maximum compression to 580 T. At predetermined times during the compression, the intense OMEGA EP laser irradiated one end of the cylinder to accelerate relativistic electrons into the dense imploded plasma providing additional heating. The relativistic electron beam generation was simulated using a 2D particleincell (PIC) code. Finally, threedimensional hybridPIC simulations calculated the electron propagation and energy deposition inside the target and revealed the roles the compressed and selfgenerated Bfields more »
 Authors:
 ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; more »
 Award ID(s):
 1725178
 Publication Date:
 NSFPAR ID:
 10300809
 Journal Name:
 Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences
 Volume:
 379
 Issue:
 2189
 Page Range or eLocationID:
 20200052
 ISSN:
 1364503X
 Sponsoring Org:
 National Science Foundation
More Like this


Abstract Recently, particle in cell (PIC) simulations have shown that relativistic turbulence in collisionless plasmas can result in an equilibrium particle distribution function where turbulent heating is balanced by radiative cooling of electrons. Strongly magnetized plasmas are characterized by higher energy peaks and broader particle distributions. In relativistically moving astrophysical jets, it is believed that the flow is launched Poynting flux dominated and that the resulting magnetic instabilities may create a turbulent environment inside the jet, i.e., the regime of relativistic turbulence. In this paper, we extend previous PIC simulation results to larger values of plasma magnetization by linearly extrapolating the diffusion and advection coefficients relevant for the turbulent plasmas under consideration. We use these results to build a single zone turbulent jet model that is based on the global parameters of the blazar emission region, and consistently calculate the particle distribution and the resulting emission spectra. We then test our model by comparing its predictions with the broadband quiescent emission spectra of a dozen blazars. Our results show good agreement with observations of lowsynchrotron peaked (LSP) sources and find that LSPs are moderately Poynting flux dominated with magnetization 1 ≲ σ ≲ 5, have bulk Lorentz factor Γj ∼more »

Abstract Magnetic reconnection is invoked as one of the primary mechanisms to produce energetic particles. We employ largescale 3D particleincell simulations of reconnection in magnetically dominated ( σ = 10) pair plasmas to study the energization physics of highenergy particles. We identify an acceleration mechanism that only operates in 3D. For weak guide fields, 3D plasmoids/flux ropes extend along the z direction of the electric current for a length comparable to their crosssectional radius. Unlike in 2D simulations, where particles are buried in plasmoids, in 3D we find that a fraction of particles with γ ≳ 3 σ can escape from plasmoids by moving along z , and so they can experience the largescale fields in the upstream region. These “free” particles preferentially move in z along Speiserlike orbits sampling both sides of the layer and are accelerated linearly in time—their Lorentz factor scales as γ ∝ t , in contrast to γ ∝ t in 2D. The energy gain rate approaches ∼ eE rec c , where E rec ≃ 0.1 B 0 is the reconnection electric field and B 0 the upstream magnetic field. The spectrum of free particles is hard, dN free / d γ ∝ γmore »

Attosecond pulses formed by high order harmonics (HHs) of an infrared (IR) laser field is a powerful tool for studying and controlling ultrafast dynamics of electrons in atoms, molecules and solids at its intrinsic timescale. However, in the Xray range the energy of attosecond pulses is rather limited. Their amplification is an important but very challenging problem since none of the existing amplifiers can support the corresponding PHz bandwidth. In our previous work [1] we proposed a method for the attosecond pulse amplification in hydrogenlike active medium of a recombination plasmabased Xray laser dressed by a replica of the fundamental frequency IR field used for the HH generation. Due to the IRfieldinduced sublasercycle Stark shift and splitting of the lasing energy levels the gain of the active medium is redistributed over the combination frequencies, separated from the resonance by even multiples of the frequency of the IR field. If the incident HHs forming an attosecond pulse train are tuned in resonance with the induced gain lines and the active plasma medium is strongly dispersive for the modulating IR field, then during the amplification the relative phases of harmonics and (under the optimal choice of the IR field strength) the shapemore »

We describe a systematic development of kinetic entropy as a diagnostic in fully kinetic particleincell (PIC) simulations and use it to interpret plasma physics processes in heliospheric, planetary, and astrophysical systems. First, we calculate kinetic entropy in two forms – the “combinatorial” form related to the logarithm of the number of microstates per macrostate and the “continuous” form related to f ln f, where f is the particle distribution function. We discuss the advantages and disadvantages of each and discuss subtleties about implementing them in PIC codes. Using collisionless PIC simulations that are twodimensional in position space and threedimensional in velocity space, we verify the implementation of the kinetic entropy diagnostics and discuss how to optimize numerical parameters to ensure accurate results. We show the total kinetic entropy is conserved to three percent in an optimized simulation of antiparallel magnetic reconnection. Kinetic entropy can be decomposed into a sum of a position space entropy and a velocity space entropy, and we use this to investigate the nature of kinetic entropy transport during collisionless reconnection. We find the velocity space entropy of both electrons and ions increases in time due to plasma heating during magnetic reconnection, while the position space entropymore »