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Two-stream (TS) and Bump-On-Tail (BOT) electron distributions can induce instabilities in collisionless plasmas, which is closely related to phenomena in space and fusion plasmas. Collisions can lead to unexpected plasma behavior, especially in dense and/or low temperature plasmas. In this work, the Vlasov-Poisson system with Krook collisions are used to study the effect of collisions. Normally, the collision can dissipate the system energy which causes the suppression of the instabilities. Against the traditional suppression effect of collision on the instability, it is found in our simulation that the collision can also excite the instability even in the forbidden beam velocity range predicted by the cold-beam theory. With collision, the beam velocity range can be divided into suppression area [vth/2, vc + vth], transition area [vc - vth, vc + vth], excitation area [vc + vth, 2vc] and forbidden area [2vc, +infinity] for TS instability. where vc is the critical velocity from cold-beam theory and vth is thermal velocity or the beam width in our simulation. The collision dissipation effect and the excitation of beam instability can compete with each other, which evoked the excitation of collision on TS instability. The collision can change the suppression and excitation condition from beam theory. However, for BOT instability, there is only suppression effect of collision on the instability. These results can expand the view of collision effect on instability of electrostatic plasmas.

A response to commenter Ke Lan's comment on our paper published in Nature Communications (2023)14:5782 by J. Yan et al

Propagation of high-current relativistic electron beam (REB) in plasma is relevant to many high-energy astrophysical phenomena as well as applications based on high-intensity lasers and charged-particle beams. Here we report a new regime of beam-plasma interaction arising from REB propagation in medium with fine structures. In this regime, the REB cascades into thin branches with local density hundred times the initial value and deposits its energy two orders of magnitude more efficiently than that in homogeneous plasma, where REB branching does not occur, of similar average density. Such beam branching can be attributed to successive weak scatterings of the beam electrons by the unevenly distributed magnetic fields induced by the local return currents in the skeletons of the porous medium. Results from a model for the excitation conditions and location of the first branching point with respect to the medium and beam parameters agree well with that from pore-resolved particle-in-cell simulations., Comment: 8 pages, 5 figures

We propose a new mechanism for generating coherent subcycle optical pulse by directing a relativistic electron beam (REB) into a plasma with a density up-ramp. The subcycle pulse is coherently emitted by bubble-sheath electrons in REB-induced superluminal plasma wake. Using three-dimensional particle-in-cell and far-field time-domain radiation simulations as well as analytical modeling, we show that an isolated subcycle optical shock can be produced at the Cherenkov angle. This radiation has ultra-short attosecond-scale duration and high intensity and exhibits excellent directionality with ultra-low angular divergence and stable carrier envelope phase. Its central frequency can be easily tuned over a wide range, from the far-infrared to the ultra-violet, by adjusting the plasma and driver-beam density., Comment: 7 pages, 3 figures

Branched flow is an interesting phenomenon that can occur in diverse systems. It is usually linear in the sense that the flow does not alter the medium properties. Branched flow of light on thin films was recently discovered. A question of interest is thus if nonlinear branched flow of light can also occur. Here we found using particle-in-cell simulations that with intense laser propagating in plasma with randomly uneven density distribution, photoionization by the laser can locally enhance the density variations along the laser paths and thus the branching of the laser. However, too-intense lasers can smooth the uneven electron density and suppress branching. The observed branching properties agree well with an analysis based on a Helmholtz equation for the laser electric field. Branched flow of intense laser in uneven plasma potentially opens up a new realm of intense laser-matter interaction., Comment: 6 pages, 5 figures

Imposing an external magnetic field in short-pulse intense laser-plasma interaction is of broad scientific interest in related plasma research areas. We propose a simple method using a virtual current layer by introducing an extra current density term to simulate the external magnetic field, and demonstrate it with three-dimensional particle-in-cell simulations. The field distribution and its evolution in sub-picosecond time scale are obtained. The magnetization process takes a much longer time than that of laser-plasma interaction due to plasma diamagnetism arising from collective response. The long-time evolution of magnetic diffusion and diamagnetic current can be predicted based on a simplified analytic model in combination with simulations., Comment: 5 pages, 5 figures

A scheme for controlling the direction of energetic proton beam driven by intense laser pulse is proposed. Simulations show that a precisely directed and collimated proton bunch can be produced by a sub-picosecond laser pulse interacting with a target consisting of a thin solid-density disk foil with a solenoid coil attached to its back at the desired angle. It is found that two partially overlapping sheath fields are induced. As a result, the accelerated protons are directed parallel to the axis of the solenoid, and their spread angle is also reduced by the overlapping sheath fields. The proton properties can thus be controlled by manipulating the solenoid parameters. Such highly directional and collimated energetic protons are useful in the high-energy-density as well as medical sciences., Comment: 5 pages, 5 figures

Dimensional effects in particle-in-cell (PIC) simulation of target normal sheath acceleration (TNSA) of protons are considered. As the spatial divergence of the laser-accelerated hot sheath electrons and the resulting space-charge electric field on the target backside depend on the spatial dimension, the maximum energy of the accelerated protons obtained from three-dimensional (3D) simulations is usually much less that from two-dimensional (2D) simulations. By closely examining the TNSA of protons in 2D and 3D PIC simulations, we deduce an empirical ratio between the maximum proton energies obtained from the 2D and 3D simulations. This ratio may be useful for estimating the maximum proton energy in realistic (3D) TNSA from the results of the corresponding 2D simulation. It is also shown that the scaling law also applies to TNSA from structured targets., Comment: 20 pages, 7 figures, 3 tables, 45 references

It is shown by particle-in-cell simulation that intense circularly polarized (CP) laser light can be contained in the cavity of a solid-density circular Al-plasma shell for hundreds of light-wave periods before it is dissipated by laser-plasma interaction. A right-hand CP laser pulse can propagate almost without reflection into the cavity through a highly magnetized overdense H-plasma slab filling the entrance hole. The entrapped laser light is then multiply reflected at the inner surfaces of the slab and shell plasmas, gradually losing energy to the latter. Compared to that of the incident laser, the frequency is only slightly broadened and the wave vector slightly modified by appearance of weak nearly isotropic and homogeneous higher harmonics.

A new class of exact electrostatic solutions of the Vlasov-Maxwell equations based on the Jeans's theorem is proposed for studying the evolution and properties of two-dimensional anisotropic plasmas that are far from thermodynamic equilibrium. In particular, the free expansion of a slab of electron-ion plasma into vacuum is investigated., Comment: 13 pages, 1 figure

We have investigated the polarization of attosecond light bursts generated by nanobunches of electrons from relativistic few-cycle laser pulse interaction with the surface of overdense plasmas. Particle-in-cell simulation shows that the polarization state of the generated attosecond burst depends on the incident-pulse polarization, duration, carrier envelope phase, as well as the plasma scale length. Through laser and plasma parameter control, without compromise of generation efficiency, a linearly polarized laser pulse with azimuth $\theta^i=10^\circ$ can generate an elliptically polarized attosecond burst with azimuth $|\theta^r_{\rm atto}|\approx61^\circ$ and ellipticity $\sigma^r_{\rm atto}\approx0.27$; while an elliptically polarized laser pulse with $\sigma^i\approx0.36$ can generate an almost circularly polarized attosecond burst with $\sigma^r_{\rm atto}\approx0.95$. The results propose a new way to a table-top circularly polarized XUV source as a probe with attosecond scale time resolution for many advanced applications.

Alfv\'{e}nic turbulent cascade perpendicular and parallel to the background magnetic field is studied accounting for anisotropic dispersive effects and turbulent intermittency. The perpendicular dispersion and intermittency make the perpendicular-wavenumber magnetic spectra steeper and speed up production of high ion-cyclotron frequencies by the turbulent cascade. On the contrary, the parallel dispersion makes the spectra flatter and decelerate the frequency cascade above the ion-cyclotron frequency. Competition of the above factors results in spectral indices distributed in the interval [-2,-3], where -2 is the index of high-frequency space-filling turbulence, and -3 is the index of low-frequency intermittent turbulence formed by tube-like fluctuations. Spectra of fully intermittent turbulence fill a narrower range of spectral indices [-7/3,-3], which almost coincides with the range of indexes measured in the solar wind. This suggests that the kinetic-scale turbulent spectra are shaped mainly by dispersion and intermittency. A small mismatch with measured indexes of about 0.1 can be associated with damping effects not studied here., Comment: 9 Pages, 3 Figures, and 2 Tables

Linear properties of kinetic Alfv\'{e}n waves (KAWs) and kinetic slow waves (KSWs) are studied in the framework of two-fluid magnetohydrodynamics. We obtain the wave dispersion relations that are valid in a wide range of the wave frequency $\omega $ and plasma-to-magnetic pressure ratio $\beta $. The KAW frequency can reach and exceed the ion cyclotron frequency at ion kinetic scales, whereas the KSW frequency remains sub-cyclotron. At $\beta \sim 1$, the plasma and magnetic pressure perturbations of both modes are in anti-phase, so that there is nearly no total pressure perturbations. However, these modes exhibit also several opposite properties. At high $% \beta $, the electric polarization ratios of KAWs and KSWs are opposite at the ion gyroradius scale, where KAWs are polarized in sense of electron gyration (right-hand polarized) and KSWs are left-hand polarized. The magnetic helicity $\sigma \sim 1$ for KAWs and $\sigma \sim -1$ for KSWs, and the ion Alfv\'{e}n ratio $R_{Ai}\ll 1$ for KAWs and $R_{Ai}\gg 1$ for KSWs. We also found transition wavenumbers where KAWs change their polarization from left- to right-hand. These new properties can be used to discriminate KAWs and KSWs when interpreting kinetic-scale electromagnetic fluctuations observed in various solar-terrestrial plasmas. This concerns, in particular, identification of modes responsible for kinetic-scale pressure-balanced fluctuations and turbulence in the solar wind., Comment: 13 pages, 13 figures. This version is accepted and published in the Astrophysical Journal

It is shown that the transverse Rayleigh-Taylor-like (RT) instability in the hole boring radiation pressure acceleration can be suppressed by using elliptically polarized (EP) laser. A moderate ${J}\times{B}$ heating of the EP laser will thermalize the local electrons, which leads to the transverse diffusion of ions, suppressing the short wavelength perturbations of RT instability. A proper condition of polarization ratio is obtained analytically for the given laser intensity and plasma density. The idea is confirmed by two dimensional Particle-in-Cell simulations, showing that the ion beam driven by the EP laser is more concentrated and intense compared with that of the circularly polarized laser., Comment: 5 pages, 4 figures. arXiv admin note: substantial text overlap with arXiv:1212.2435

Random excitation of intense periodic highly-localized single-cycle light pulses in a stochastic background by continuous-wave stimulated Brillouin scattering in long optical fibers with weak feedback is found experimentally. Events with low period numbers are dominant and the optical feedback is crucial for the phenomenon. A three-wave coupling model for the phenomenon is proposed. The results are in good qualitative agreement with the observed phenomenon. The latter should be relevant to the understanding of similar rogue wave events in other nonlinear dissipative systems., Comment: 9 pages, 3 figures

Early-time electron-positron correlation in vacuum pair-production in an external field is investigated. The entangled electron and positron wave functions are obtained analytically in the configuration and momentum spaces. It is shown that, relative to that of the one-dimensional theory, two- and three-dimensional calculations yield enhanced spatial correlation and broadened momentum spectrum. In fact, at early times the electron and positron almost coincide spatially. The correlation also depends on the direction of the applied field. For the spatial correlation, the transverse correlation is stronger than the longitudinal one., Comment: 9 pages 4 figures, Submitted to Chin. Phys. Lett

It is shown that the transverse Rayleigh Taylor like instability can be well stabilized by using elliptically polarized laser in the hole boring radiation pressure acceleration regime. The $\bm{J}\times\bm{B}$ effect of the laser will thermalize the local electrons and support a transverse diffusion mechanism of the ions, resulting in the stabilization of the short wavelength perturbations, which is quite similar to the ablative Rayleigh Taylor instability in the initial confinement fusion research. The proper range of polarization ratio is obtained from a theoretical model for the given laser intensity and plasma density. The stabilization mechanism is well confirmed by two dimensional Particle-in-Cell simulations, and the ion beam driven by the elliptically polarized laser is more concentrated and intense compared with that of the circularly polarized laser., Comment: 6 pages, 5 figures

It is shown that well collimated mono-energetic ion beams with a large particle number can be generated in the hole-boring radiation pressure acceleration regime by using an elliptically polarized laser pulse with appropriate theoretically determined laser polarization ratio. Due to the $\bm{J}\times\bm{B}$ effect, the double-layer charge separation region is imbued with hot electrons that prevent ion pileup, thus suppressing the double-layer oscillations. The proposed mechanism is well confirmed by Particle-in-Cell simulations, and after suppressing the longitudinal double-layer oscillations, the ion beams driven by the elliptically polarized lasers own much better energy spectrum than those by circularly polarized lasers., Comment: 6 pages, 5 figures, Phys. Plasmas (2013) accepted

Reconnection of the self-generated magnetic fields in laser-plasma interaction was first investigated experimentally by Nilson {\it et al.} [Phys. Rev. Lett. 97, 255001 (2006)] by shining two laser pulses a distance apart on a solid target layer. An elongated current sheet (CS) was observed in the plasma between the two laser spots. In order to more closely model magnetotail reconnection, here two side-by-side thin target layers, instead of a single one, are used. It is found that at one end of the elongated CS a fan-like electron outflow region including three well-collimated electron jets appears. The ($>1$ MeV) tail of the jet energy distribution exhibits a power-law scaling. The enhanced electron acceleration is attributed to the intense inductive electric field in the narrow electron dominated reconnection region, as well as additional acceleration as they are trapped inside the rapidly moving plasmoid formed in and ejected from the CS. The ejection also induces a secondary CS.

Proton acceleration by ultra-intense laser pulse irradiating a target with cross-section smaller than the laser spot size and connected to a parabolic density channel is investigated. The target splits the laser into two parallel propagating parts, which snowplow the back-side plasma electrons along their paths, creating two adjacent parallel wakes and an intense return current in the gap between them. The radiation-pressure pre-accelerated target protons trapped in the wake fields now undergo acceleration as well as collimation by the quasistatic wake electrostatic and magnetic fields. Particle-in-cell (PIC) simulation shows that stable long-distance acceleration can be realized, and a 30 fs monoenergetic ion beam of > 10 GeV peak energy and < 2degree divergence can be produced by a 9.8 *10^21 W/cm2 circularly polarized laser pulse., Comment: 9page,4figures

A two-dimensional generalized cubic nonlinear Schr\"odinger equation with complex coefficients for the group dispersion and nonlinear terms is used to investigate the evolution of a finite-amplitude localized initial perturbation. It is found that modulation of the latter can lead to side-band formation, wave condensation, collapse, turbulence, and inverse cascade, although not all together nor in that order., Comment: 12 pages, 5 figures

Evolution of the single-mode ablative Rayleigh-Taylor instability in the presence of preheating is investigated numerically. It is found that the instability evolution depends strongly on the preheating length $L$ in front of the ablation-front interface. For weak preheating ($L/L_{\rm SH}\leq f_0$, where $L_{\rm SH}$ is the Spitzer-Harm length and $f_0\sim 20$ is a critical value), the linear growth rate has a sharp maximum and a secondary spike-bubble structure is generated. Interaction of this growing structure with the master spike-bubble leads to rupture of the latter. However, for strong preheating ($L/L_{\rm SH}>20$), the linear growth rate has no sharp maximum and no secondary spike-bubble is generated. Instead, the master spike-bubble evolves into an elongated jet. These results are interpreted in terms of the evolution and interaction of the instability-generated harmonic modes., Comment: 5 pages, 4 figures