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Development of a predictive capability of short-pulse laser-driven broadband x-ray radiography
摘要： High intensity, short-pulse laser interaction with a solid metal target produces broadband hard x rays potentially for various applications of x-ray radiography. Here experimental benchmarking of numerical modelling for short-pulse laser-driven broadband x-ray radiography is presented. Angular dependent x-ray spectra are first calculated with a hybrid particle-in-cell code, Large Scale Plasma (LSP), using fast electron parameters inferred from an analysis of measured bremsstrahlung signals. Subsequently, a calculated x-ray spectrum in the direction of radiography is used in photon transport calculations using a Monte Carlo code, Particle and Heavy Ion Transport code System (PHITS), to simulate a radiographic image including a modelled 3D test object, an x-ray attenuation filter and an image plate detector. Simulated radiographic images are compared with measurements obtained in an experiment using a 50-TW Leopard short-pulse laser at the University of Nevada Reno. Results show that simulations reproduce the experimental images well for three different attenuation filters (plastic, aluminium, and brass), while one-dimensional transmission profiles for the plastic and aluminium filters are quantitatively in good agreement. The modelling approach established in this work could be used as a predictive tool to simulate radiographic images of complex 3D solid objects at any arbitrary angular position or to optimize experimental components such as the source spectrum, x-ray attenuation filters and a detector type depending on a radiographic object without carrying out radiographic experiments.
关键词： Monte Carlo simulations,hybrid particle-in-cell,broadband x-ray radiography,short-pulse laser-produced x rays
更新于2025-09-23 15:21:01
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Radiation reaction in electrona??beam interactions with high-intensity lasers
摘要： Charged particles accelerated by electromagnetic fields emit radiation, which must, by the conservation of momentum, exert a recoil on the emitting particle. The force of this recoil, known as radiation reaction, strongly affects the dynamics of ultrarelativistic electrons in intense electromagnetic fields. Such environments are found astrophysically, e.g. in neutron star magnetospheres, and will be created in laser–matter experiments in the next generation of high-intensity laser facilities. In many of these scenarios, the energy of an individual photon of the radiation can be comparable to the energy of the emitting particle, which necessitates modelling not only of radiation reaction, but quantum radiation reaction. The worldwide development of multi-petawatt laser systems in large-scale facilities, and the expectation that they will create focussed electromagnetic fields with unprecedented intensities > 1023 Wcm?2, has motivated renewed interest in these effects. In this paper I review theoretical and experimental progress towards understanding radiation reaction, and quantum effects on the same, in high-intensity laser fields that are probed with ultrarelativistic electron beams. In particular, we will discuss how analytical and numerical methods give insight into new kinds of radiation–reaction-induced dynamics, as well as how the same physics can be explored in experiments at currently existing laser facilities.
关键词： Laser-wakefield acceleration,Radiation reaction,Synchrotron radiation,Particle-in-cell simulations,Strong-field QED,High-power lasers
更新于2025-09-23 15:21:01
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Electron dynamics in low pressure capacitively coupled radio frequency discharges
摘要： In low temperature plasmas, the interaction of the electrons with the electric field is an important current research topic that is relevant for many applications. Particularly, in the low pressure regime ((cid:1)10 Pa), electrons can traverse a distance that may be comparable to the reactor dimensions without any collisions. This causes “nonlocal,” dynamics which results in a complicated space- and time-dependence and a strong anisotropy of the distribution function. Capacitively coupled radio frequency (CCRF) discharges, which operate in this regime, exhibit extremely complex electron dynamics. This is because the electrons interact with the space- and time-dependent electric field, which arises in the plasma boundary sheaths and oscillates at the applied radio frequency. In this tutorial paper, the fundamental physics of electron dynamics in a low pressure electropositive argon discharge is investigated by means of particle-in-cell/Monte Carlo collisions simulations. The interplay between the fundamental plasma parameters (densities, fields, currents, and temperatures) is explained by analysis (aided by animations) with respect to the spatial and temporal dynamics. Finally, the rendered picture provides an overview of how electrons gain and lose their energy in CCRF discharges.
关键词： low pressure,particle-in-cell/Monte Carlo collisions simulations,electron dynamics,plasma parameters,capacitively coupled radio frequency discharges
更新于2025-09-23 15:21:01
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Parametric study of ultra-intense laser interaction with uniform and nano-porous near-critical plasmas
摘要： Responses of the uniform near-critical plasma (UNCP) and nano-porous near-critical plasma (NPNCP) upon interaction with a short-intense laser have been scrutinized using two-dimensional (2D) particle-in-cell simulations. Maximum proton energy variation by the deposition of uniform and nano-porous layers in front of a solid target for a wide range of laser intensities (normalized amplitude a0 = 5–25) and average densities of the front layer ne = 0.3 ? 3nc (where nc is the critical density) has been parametrically studied. It is found that the proton maximum energy for the front layers with sub-10 μm thicknesses is independent of the target porosity and density. However, in the relatively thick targets, the nano-porous structure decreases the laser energy absorption and, subsequently, the maximum proton energy compared to the uniform one. The results indicate that by employing UNCPs instead of NPNCPs, at the moderate laser intensity, the maximum proton energy reveals a 23% enhancement. This increment could be explained by rapid self-focusing of the laser pulse and dominant direct laser electron acceleration regime on the well-formed plasma channel in the UNCP layer. However, in the case of NPNCPs, the laser scattering from the plasma structure makes it less intense and more disordered, which influences the efficient laser energy coupling to the electrons.
关键词： proton acceleration,near-critical plasmas,particle-in-cell simulations,ultra-intense laser,laser-plasma interaction
更新于2025-09-23 15:21:01
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Influence of target curvature on the characteristics of particle beams generated by laser ion acceleration with microstructured enhanced targets at ultra high intensity
摘要： Following the advances in laser science that have been performed recently, the push to improve the quality of the laser generated particle beams has seen a lot of interest in the past decade. The work presented in this paper aims to study the role of target curvature using 2D PIC simulations to ascertain its influence on the angular spread and peak energy for the accelerated proton beam, and the characteristics of the gamma photons produced for potential usage as secondary sources. For the scope of this work we parametrically probed different curvature radii of a microstructured enhanced target impacted by a laser pulse with predetermined parameters. This paper continues past studies (Tatomirescu et al 2017 AIP Conf. Proc. 1796 020013; Tatomirescu et al 2017 AIP Conf. Proc. 1916 030002) and concentrates on determining the target curvature effect when using conical structures for pulse focusing. The results show promising enhanced focus of the accelerated particles and an enhancement of the peak energy of the accelerated particles.
关键词： variable target curvature,particle-in-cell,ultra high intensity laser pulse,microstructured target
更新于2025-09-23 15:19:57
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Ion acceleration with an ultra-intense two-frequency laser tweezer
摘要： Ultra-intense lasers produce and manipulate plasmas, allowing to locally generate extremely high static and electromagnetic fields. This study presents a concept of an ultra-intense optical tweezer, where two counter-propagating circularly polarized intense lasers of different frequencies collide on a nano-foil. Interfering inside the foil, lasers produce a beat wave, which traps and moves plasma electrons as a thin sheet with an optically controlled velocity. The electron displacement creates a plasma micro-capacitor with an extremely strong electrostatic field, that efficiently generates narrow-energy-spread ion beams from the multi-species targets, e.g. protons from the hydrocarbon foils. The proposed ion accelerator concept is explored theoretically and demonstrated numerically with the multi-dimensional particle-in-cell simulations.
关键词： optical tweezer,particle-in-cell simulations,plasma,ion acceleration,ultra-intense lasers
更新于2025-09-23 15:19:57
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Recoil effects on reflection from relativistic mirrors in laser plasmas
摘要： Relativistic mirrors can be realized with strongly nonlinear Langmuir waves excited by intense laser pulses in underdense plasma. On reflection from the relativistic mirror, the incident light affects the mirror motion. The corresponding recoil effects are investigated analytically and using particle-in-cell simulations. It is found that if the fluence of the incident electromagnetic wave exceeds a certain threshold, the relativistic mirror undergoes a significant back reaction and splits into multiple electron layers. The reflection coefficient of the relativistic mirror and the factors of electric field amplification and frequency upshift of the electromagnetic wave are obtained.
关键词： particle-in-cell simulations,relativistic mirrors,Langmuir waves,laser plasmas,recoil effects
更新于2025-09-23 15:19:57
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Investigation of Light-sail and Hole-boring Radiation Pressure Accelerations upon the Interaction of Ultra-intense Laser Pulses with Thin Targets
摘要： The radiation pressure acceleration (RPA) scheme with a circularly polarized laser pulse is well-known to provide an efficient generation of intense, energetic quasi-monochromatic ion beams. Depending on the thickness of targets, the RPA appears in two distinct modes: the light-sail (LS) RPA, which develops in ultrathin targets, and the hole-boring (HB) RPA, which develops in relatively thick targets. In this work, we investigated the ion acceleration dynamics of the LS-RPA and the HB-RPA through a fully relativistic particle-in-cell (PIC) simulation. The transition and competition between LS- and HB-RPA modes are investigated with suitable explanations of a one-dimensional (1D) theoretical model. To check the validity of the 1D results and investigate the multi-dimensional effects, two-dimensional simulations are also carried out. The present work may provide a deeper understanding of RPA and useful guidelines for generating high-quality and high-fluence ion beams.
关键词： Ion acceleration,Radiation pressure acceleration,Laser-plasma interaction,Particle-in-cell simulation
更新于2025-09-23 15:19:57
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Laser reflection as a catalyst for direct laser acceleration in multipicosecond laser-plasma interaction
摘要： We demonstrate that laser reflection acts as a catalyst for superponderomotive electron production in the preplasma formed by relativistic multipicosecond lasers incident on solid density targets. In 1D particle-in-cell simulations, high energy electron production proceeds via two stages of direct laser acceleration: an initial stochastic backward stage and a final nonstochastic forward stage. The initial stochastic stage, driven by the reflected laser pulse, provides the preacceleration needed to enable the final stage to be nonstochastic. Energy gain in the electrostatic potential, which has been frequently considered to enhance stochastic heating, is only of secondary importance. The mechanism underlying the production of high energy electrons by laser pulses incident on solid density targets is of direct relevance to applications involving multipicosecond laser-plasma interactions.
关键词： particle-in-cell simulations,superponderomotive electron production,direct laser acceleration,laser reflection,multipicosecond laser-plasma interaction
更新于2025-09-19 17:13:59
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Interaction features of two ultra-intense laser pulses self-trapped in underdense plasmas
摘要： The interaction of two parallel relativistic laser beams in underdense plasmas is investigated by considering the evolution of their wave envelopes. The energy transfer between the two lasers is given by an expression based on the evolution of the total laser power in a regime without beam mixing. It is shown that how the energy is transferred depends nonlinearly on the initial phase difference of the lasers, and the result of the interaction depends on the laser intensity, spot radius, and their separation distance. The results are verified by direct numerical solution of the relativistic nonlinear Schr?dinger equations for the laser envelopes as well as particle-in-cell simulation. The study and results should be helpful for understanding the energy transfer behavior of multiple co-propagating laser beams in underdense plasmas.
关键词： nonlinear Schr?dinger equations,underdense plasmas,energy transfer,laser beams,particle-in-cell simulation
更新于2025-09-19 17:13:59