arXiv subjects

C. T. Zhou

Publications and source records attributed to C. T. Zhou.

At least 19 recordsLinked to original sources

arXiv2025

Coherent attosecond pulses generated by a relativistic electron beam interacting with an intense laser at a grazing angle

The interaction between relativistic electron beams and intense laser fields has been extensively studied for generating high-energy radiation. However, achieving coherent radiation from such interactions needs to precisely control the phase matching of the radiationg electrons, which has proven to be exceptionally challenging. In this study, we demonstrate that coherent attosecond radiation can be produced when a laser pulse interacts at grazing angle with a relativistic electron beam. The electrons oscillate in the laser field and are modulated with a superluminal phase, coherent ultrashort pulse trains are produced in the far field at the Cherenkov angle. This is verified by theoretical modeling and numerical simulations, including three-dimensional particle-in-cell (PIC) simulations and far-field time-domain radiation simulations. Based on our proposed scheme, high-repetition-rate, compact, and high-energy attosecond pulse sources are feasible.

physics.plasm-ph↗

arXiv2023

Characteristics of Branched Flows of High-Current Relativistic Electron Beams in Porous Materials

Branched flow is a universal phenomenon in which treebranch-like filaments form through traveling waves or particle flows in irregular mediums. Branched flow of high-current relativistic electron beams (REBs) has been recently discovered [Phys. Rev. Lett. \textbf{130}, 185001 (2023)]. It exhibits unique features, including remarkably high beam density at predictable caustic locations, efficient energy coupling between the beam and background medium, etc. This paper presents investigations on REB branching, focusing on the influence of interaction parameters on branching patterns and providing detailed analyses of the dynamics of individual beam electrons. The insights gained contribute to a nuanced understanding of the intricate nature of REB branching and its potential applications in the future.

physics.plasm-ph↗

arXiv2023

Coherent subcycle optical shock from superluminal plasma wake

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.

physics.plasm-ph↗

arXiv2023

Branching of high-current relativistic electron beam in porous materials

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.

physics.plasm-ph↗

arXiv2022

Transport dynamics study of laser-accelerated proton beams and design of double achromatic beam translation system

Proton beams generated from laser acceleration show merit for their unique spatial (micron-size) and temporal (picosecond) properties, which make them desirable for many potential applications. However, the large energy spread and divergence angle make it difficult to maintain these beam properties after delivery. This hinders the wide application of laser acceleration. In this paper, we design a double achromatic beam translation system (DABTS), based on weak-focusing magnets, to realize achromatic transmission in both the horizontal and vertical directions, and compress the bunch length of the delivered proton beam at the same time. We make use of fringe angles and special steering magnets to effectively reduce the influence of chromatic aberrations and high-order nonlinear terms and realize close to ideal point-to-point optics. We believe this work contributes to the ongoing effort to apply laser accelerators to a variety of fields.

physics.acc-ph↗

arXiv2022

Branched flow of intense laser light in plasma with uneven density distribution

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.

physics.plasm-ph↗

arXiv2021

Where have all the interstellar silicon carbides gone?

The detection of the 11.3-micron emission feature characteristic of the Si--C stretch in carbon-rich evolved stars reveals that silicon carbide (SiC) dust grains are condensed in the outflows of carbon stars. SiC dust could be a significant constituent of interstellar dust since it is generally believed that carbon stars inject a considerable amount of dust into the interstellar medium (ISM). The presence of SiC dust in the ISM is also supported by the identification of presolar SiC grains of stellar origin in primitive meteorites. However, the 11.3-micron absorption feature of SiC has never been seen in the ISM and oxidative destruction of SiC is often invoked. In this work we quantitatively explore the destruction of interstellar SiC dust through oxidation based on molecular dynamics simulations and density functional theory calculations. We find that the reaction of an oxygen atom with SiC molecules and clusters is exothermic and could cause CO-loss. Nevertheless, even if this is extrapolable to bulk SiC dust, the destruction rate of SiC dust through oxidation could still be considerably smaller than the (currently believed) injection rate from carbon stars. Therefore, the lack of the 11.3-micron absorption feature of SiC dust in the ISM remains a mystery. A possible solution may lie in the currently believed stellar injection rate of SiC (which may have been overestimated) and/or the size of SiC dust (which may actually be considerably smaller than submicron in size).

astro-ph.GA↗

arXiv2020

Magnetic field amplification to the gigagauss scale via dynamos driven by femtosecond lasers

Reaching gigagauss magnetic fields opens new horizons both in atomic and plasma physics. At these magnetic field strengths, the electron cyclotron energy $\hbarω_{c}$ becomes comparable to the atomic binding energy (the Rydberg), and the cyclotron frequency $ω_{c}$ approaches the plasma frequency at solid state densities that significantly modifies optical properties of the target. The generation of such strong quasistatic magnetic fields in laboratory remains a challenge. Using supercomputer simulations, we demonstrate how it can be achieved all-optically by irradiating a micro-channel target by a circularly polarized relativistic femtosecond laser. The laser pulse drives a strong electron vortex along the channel wall, inducing a megagauss longitudinal magnetic field in the channel by the inverse Faraday effect. This seed field is then amplified up to a gigagauss level and maintained on a picosecond time scale via dynamos driven by plasma thermal expansion off the channel walls. Our scheme sets a possible platform for producing long living extreme magnetic fields in laboratories using readily available lasers. The concept might also be relevant for applications such as magneto-inertial fusion.

physics.plasm-ph↗

arXiv2019

Simulating the external magnetic field in short-pulse intense laser-plasma interaction

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.

physics.plasm-ph↗

arXiv2018

Direction and divergence control of laser-driven energetic proton beam using a disk-solenoid target

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.

physics.plasm-ph↗

arXiv2018

The baryon loading effect on relativistic astrophysical jet transport in the interstellar medium

The composition of the astrophysical relativistic jets remains uncertain. By kinetic particle-in-cell simulations, we show that the baryon component in the jet, or the so-called baryon loading effect (BLE), heavily affects relativistic jets transport dynamics in the interstellar medium. On the one hand, with the BLE, relativistic jets can transport in a much longer distance, because jet electrons draw a significant amount of energy from jet baryons via the Buneman-induced electrostatic waves and the Weibel-mediated collisionless shock; on the other hand, the jet electron phase space distribution may transform from a bottom-wide-single-peak structure to a center-wide-multiple-peak one by increasing the BLE, which largely influences the observed jet morphology. Implications for related astrophysical studies are also discussed.

physics.plasm-ph↗

arXiv2018

Transport of relativistic jet in the magnetized intergalactic medium

The kinetic effects of magnetic fields on the transport of relativistic jet in the intergalactic medium remain uncertain, especially for their perpendicular component. By particle-in-cell simulations, we find that when only jet electrons are fully magnetized, they are directly deflected by the magnetic field, but jet protons are mainly dragged by collective charge-separation electric field. However, when both electrons and protons are fully magnetized, the contrary is the case. Their balance tremendously distorts the jet density and electromagnetic fields, leading to enormous energy exchange between different species and fields. As a result, the electron spectrum energy distribution (SED) gets reshaped and the power law slope of the SED decreases as the magnetic field strength increases. In other words, we may infer that magnetic fields around the relativistic jet play a crucial role in shaping the observed SED.

physics.plasm-ph↗

arXiv2018

Scaling Laws of Ion Acceleration in Ultrathin Foils Driven by Laser Radiation Pressure

Scaling laws of ion acceleration in ultrathin foils driven by radiation pressure of intense laser pulses are investigated by theoretical analysis and two-dimensional particle-in-cell simulations. Considering the instabilities are inevitable during laser plasma interaction, the maximum energy of ions should have two contributions: the bulk acceleration driven by radiation pressure and the sheath acceleration in the moving foil reference induced by hot electrons. A theoretical model is proposed to quantitatively explain the results that the cutoff energy and energy spread are larger than the predictions of "light sail" model, observed in simulations and experiments for a large range of laser and target parameters. Scaling laws derived from this model and supported by the simulation results are verified by the previous experiments.

physics.plasm-ph↗

arXiv2018

Generation of ten kilotesla longitudinal magnetic fields in ultraintense laser-solenoid target interactions

Production of the huge longitudinal magnetic fields by using an ultraintense laser pulse irradiating a solenoid target is considered. Through three-dimensional particle-in-cell simulations, it is shown that the longitudinal magnetic field up to ten kilotesla can be observed in the ultraintense laser-solenoid target interactions. The finding is associated with both fast and return electron currents in the solenoid target. The huge longitudinal magnetic field is of interest for a number of important applications, which include controlling the divergence of laser-driven energetic particles for medical treatment, fast-ignition in inertial fusion, etc., as an example, the well focused and confined directional electron beams are realized by using the solenoid target.

physics.plasm-ph↗

arXiv2018

Multidimensional effects on proton acceleration using high-power intense laser pulses

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.

physics.plasm-ph↗

arXiv2017

Injection dynamics of direct-laser accelerated electrons in a relativistic transparency regime

The dynamics of electron injection in the direct laser acceleration (DLA) regime was investigated by means of three-dimensional particle-in-cell simulations and theoretical analysis. It is shown that when an ultra-intense laser pulse propagates into a near-critical density or relativistically transparent plasma, the longitudinal charge-separation electric field excites an ion wave. The ion wave modulates the local electric field and acts as a set of potential wells to guide the electrons, located on the edge of the plasma channel, to the central region, where the DLA takes place later on. In addition, it is pointed out that the self-generated azimuthal magnetic fields tend to suppress the injection process of electrons by deflecting them away from the laser field region. Understanding these physical processes paves the way for further optimizing the properties of direct-laser accelerated electron beams and the associated X/gamma-ray sources.

physics.plasm-ph↗

arXiv2016

Single 100-terawatt attosecond X-ray light pulse generation

The birth of attosecond light sources is expected to inspire a breakthrough in ultrafast optics, which may extend human real-time measurement and control techniques into atomic-scale electronic dynamics. For applications, it is essential to obtain a single attosecond pulse of high intensity, large photon energy and short duration. Here we show that single 100-terawatt attosecond X-ray light pulse with intensity ${1\times10^{21}}\textrm{W}/\textrm{cm}^{ 2}$ and duration ${7.9} \textrm{as}$ can be produced by intense laser irradiation on a capacitor-nanofoil target composed of two separate nanofoils. In the interaction, a strong electrostatic potential develops between two nanofoils, which drags electrons out of the second foil and piles them up in vacuum, forming an ultradense relativistic electron nanobunch. This nanobunch exists in only half a laser cycle and smears out in others, resulting in coherent synchrotron emission of a single pulse. Such an unprecedentedly giant attosecond X-ray pulse may bring us to view a real attoworld.

physics.plasm-ph↗

arXiv2014

Suppression of transverse ablative Rayleigh-Taylor-like instability in the hole-boring radiation pressure acceleration by using elliptically polarized laser pulses

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.

physics.plasm-ph↗