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Control of electron beam energy-spread by beam loading effects in a laser-plasma accelerator
摘要： We present experimental results from a laser wakefield electron accelerator driven by 70 TW ultrashort laser pulses in Helium and Helium–Nitrogen gaseous plasmas with two different Nitrogen concentrations, showing distinct electron-beam qualities. In order to get a clear view of the involved phenomenon, two-dimensional particle-in-cell simulations are performed which not only agreed with the experimental results but also provided an investigation on the evolution of accelerating structures. The experimental and simulation results depict that the beam loading effect can strongly modify the longitudinal accelerating electric field of the wake wave, imposing diametrically opposite effects on the final electron-beam qualities, especially the energy-spread, in the Helium–Nitrogen gas mixtures with different Nitrogen concentrations. In the Helium–Nitrogen-mixed plasma with a lower Nitrogen concentration (0.5%), if appropriately controlled, the beam loading effect can be employed to flatten the accelerating electric field for reducing the electron-beam energy spread. In contrast, in the Helium–Nitrogen-mixed plasmas with a higher Nitrogen concentration (5%), the accelerating electric field of the wake is locally reversed by the self-fields of the overloaded electron bunch, and the correspondingly generated negative-slope region of electric field increases the electron-beam energy-spread.
关键词： experimental laser plasma acceleration,ionization injection,laser wakefield acceleration
更新于2025-09-23 15:21:01
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Zemax ray tracing model for plasma waveguides
摘要： Plasma-based waveguides are currently employed for laser wakefield acceleration to extend the focal region of laser beams. A parabolic transverse plasma density profile, suitable for laser guiding, can be established in a dielectric capillary as a consequence of a discharge in gas. In this work, we report on a new ray tracing model, based on the Zemax software, able to simulate the envelope of a laser beam propagating through a plasma waveguide. The potentialities offered by Zemax in terms of geometries and materials and the possibility to create custom objects do allow the simulation of complex and various scenarios, as for example curved plasma waveguides.
关键词： plasma,laser,waveguide,laser-wakefield acceleration (LWFA)
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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Direct laser acceleration of electrons in high-Z gas target and effect of threshold plasma density on electron beam generation
摘要： An experimental study of laser driven electron acceleration in N2 and N2-He mixed gas-jet target using laser pulses of duration ~60-70 fs is presented. Generation of relativistic electron beam with quasi-thermal spectra was observed at a threshold density of ~1.6×1018 cm-3 in case of the pure N2. At an optimum fraction of 50% of He in N2, generation of quasi-monoenergetic electron beams was observed at a comparatively higher threshold density of ~2×1018 cm-3, with an average peak energy of ~168 MeV, average energy spread of ~21%, and average total beam charge of ~220 pC. Electron acceleration could be attributed to the direct laser acceleration as well as the hybrid mechanism. Observation of an optimum fraction of He in N2 (in turn threshold plasma density) for comparatively better quality electron beam generation could be understood in terms of the plasma density dependent variation in the dephasing rate of electrons with respect to the transverse oscillating laser field. Results are also supported by the 2D PIC simulations performed using the code EPOCH.
关键词： Laser Wakefield Acceleration,Laser Plasma Acceleration,Direct Laser Acceleration,Ionization Induced Injection
更新于2025-09-23 15:19:57
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Tomographic reconstruction algorithms for structured gas density profiles of the targets for laser wakefield acceleration
摘要： The output of a laser wakefield accelerator strongly depends on the gas target density profile. In this work we focus on the reconstruction of the 3D density profiles from tomographic measurements. We compare analytical and iterative methods, and we propose a new one, FARM, which is tailored for the reconstruction of gas targets for laser wakefield acceleration. Several methods are tested on both simplified and realistic geometries. The algorithms are evaluated in terms of the quality of the density profile reconstruction, the number of projections needed, and the computation time required.
关键词： interferometry,tomography,laser wakefield acceleration,density profile,gas target,laser plasma acceleration,tomographic reconstruction,laser electron acceleration
更新于2025-09-23 15:19:57
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Charge coupling in multi-stage laser wakefield acceleration
摘要： The multi-stage technique in the laser driven acceleration of electrons has become a critical part for full-optical jitter-free accelerators. Several independent laser drivers and shorter plasma targets allow the stable and reproducible acceleration of electron bunches (or beam) at the GeV energies with narrower energy spreads. Moreover, the charge coupling, necessary for ef?cient acceleration in the consecutive acceler-ation stages, depends collectively on the parameters of the injected electron beam, the booster stage, and the nonlinear transverse dynamics of the electron beam in the laser pulse wake. An unmatched electron beam injected in the booster stage and its nonlinear transverse evolution may result in perturbations and even a reduction of the ?eld strength in the acceleration phase of the wake?eld. Thus, the analysis and characterization of charge coupling in multi-stage laser wake?eld acceleration (LWFA) are important. Here, we investigate acceleration of an externally injected electron beam in the laser wake?eld, emulating two-stage LWFA, using fully relativistic multi-dimensional particle-in-cell simulations. We also study the underlying critical parameters that affect the ef?cient coupling and acceleration of the injected electron beam in the booster stage.
关键词： charge coupling,multi-stage,electron beam,plasma wave,laser wakefield acceleration
更新于2025-09-23 15:19:57
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Polarization-Dependent Self-Injection by Above Threshold Ionization Heating in a Laser Wakefield Accelerator
摘要： We report on the experimental observation of a decreased self-injection threshold by using laser pulses with circular polarization in laser wakefield acceleration experiments in a nonpreformed plasma, compared to the usually employed linear polarization. A significantly higher electron beam charge was also observed for circular polarization compared to linear polarization over a wide range of parameters. Theoretical analysis and quasi-3D particle-in-cell simulations reveal that the self-injection and hence the laser wakefield acceleration is polarization dependent and indicate a different injection mechanism for circularly polarized laser pulses, originating from larger momentum gain by electrons during above threshold ionization. This enables electrons to meet the trapping condition more easily, and the resulting higher plasma temperature was confirmed via spectroscopy of the XUV plasma emission.
关键词： self-injection,Laser wakefield acceleration,XUV spectroscopy,above threshold ionization,polarization
更新于2025-09-23 15:19:57
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Proof-of-Principle Experiment for Nanoparticle-Assisted Laser Wakefield Electron Acceleration
摘要： Laser electron accelerators have paved the way to build compact electron accelerators, but the quality of the electron beam should be improved to enable efficient use in various specialized applications. We demonstrate a proof-of-principle experiment for nanoparticle-assisted laser wakefield acceleration (NA LWFA) to improve the quality of the electron beam. Nanoparticles are generated through laser ablation of an aluminum target and introduced into a helium plasma to trigger the injection of electrons into the nonlinear plasma wake excited by 70 TW femtosecond laser pulses. We observe a significant enhancement of the electron beam energy, energy spread, and divergence compared with the case of self-injection. For instance, the best quality electron bunches present a maximum energy of up to 340 MeV, with a relative energy spread of 4.7% and a vertical divergence of 5.9 mrad. The initial results on NA LWFA are very promising and motivate further theoretical and experimental research into developing nanoparticle-assisted laser wakefield acceleration.
关键词： femtosecond laser pulses,electron beam quality,plasma wake,nanoparticle-assisted,laser wakefield acceleration
更新于2025-09-19 17:13:59
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All-optical acceleration in the laser wakefield
摘要： Muons produced by the Bethe–Heitler process from laser wakefield accelerated electrons interacting with high Z materials have velocities close to the laser wakefield. It is possible to accelerate those muons with laser wakefield directly. Therefore for the first time we propose an all-optical ‘Generator and Booster’ scheme to accelerate the produced muons by another laser wakefield to supply a prompt, compact, low cost and controllable muon source in laser laboratories. The trapping and acceleration of muons are analyzed by one-dimensional analytic model and verified by two-dimensional particle-in-cell (PIC) simulation. It is shown that muons can be trapped in a broad energy range and accelerated to higher energy than that of electrons for longer dephasing length. We further extrapolate the dependence of the maximum acceleration energy of muons with the laser wakefield relativistic factor γ and the relevant initial energy E0. It is shown that a maximum energy up to 15.2 GeV is promising with γ = 46 and E0 = 1.45 GeV on the existing short pulse laser facilities.
关键词： laser wakefield acceleration,muon source
更新于2025-09-19 17:13:59
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Plasma eyepieces for petawatt class lasers
摘要： Focusing petawatt class laser beams to a variety of spot sizes for different applications is expensive in cost, labor, and space. In this paper, we propose a plasma lens to flexibly resize the laser beam by utilizing the self-focusing effect of laser in plasmas. Using a fixed conventional focusing system to focus the laser a short distance in front of the plasma, we can adjust the effective laser beam waist within a certain range, with the plasma lens acting as an adjustable eyepiece in a telescope. Such a setup is a powerful tool for laser wakefield accelerator experiments in state-of-the-art petawatt laser projects and allows for scanning focal spot parameters.
关键词： self-focusing effect,plasma lens,laser wakefield acceleration,petawatt lasers,adjustable eyepiece
更新于2025-09-19 17:13:59