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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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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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Electron Beam Brightness and Undulator Radiation Brilliance for a Laser Plasma Acceleration Based Free Electron Laser
摘要： We report here on spontaneous undulator radiation and free electron laser calculations after a 10-m long transport line (COXINEL) using a Laser Plasma acceleration (LPA) source. The line enables the manipulation of the properties of the produced electron beams (energy spread, divergence, dispersion) in view of light source applications. The electron beam brightness and undulator radiation brilliance are addressed by an analytical approach enabling us to point out the influence of chromatic effects in the COXINEL case.
关键词： undulator radiation,free electron laser,electron beam brightness,laser plasma acceleration
更新于2025-09-23 15:19:57
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Lasers for Novel Accelerators
摘要： Novel accelerator schemes are rapidly emerging in the wake of laser-plasma acceleration research and involve advanced high-power laser drivers for their operation. Significant progress has been made in laser performance during the past decade, including repetition rate, average and peak power, and footprint, making these systems attractive for many applications, including novel accelerators. Here we discuss laser driver requirements for the proposed novel accelerator schemes, examine emerging technologies and introduce a viable laser driver concept for a first generation of plasma accelerators.
关键词： novel accelerators,lasers,laser-plasma acceleration,high-power laser drivers
更新于2025-09-12 10:27:22
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Effect of the laser transverse profile in a capillary for laser-plasma acceleration with external injection
摘要： Guiding of a high intensity laser beam in a hollow dielectric capillary is investigated with application for a laser plasma wakefield accelerator stage. For such guiding, the transverse profile of the laser intensity at the capillary entrance has a strong influence on the fluctuations of the transverse plasma wakefield during the laser propagation. The effects of these fluctuations on the acceleration of an electron bunch injected at 100 MeV is analyzed in detail. Our results show that, in the best match conditions, the usually used Gaussian transverse profile leads to strong fluctuations generated by the diffraction of the edges of the laser at the capillary entrance. We demonstrate that by reducing this diffraction through the use of a flattened Gaussian laser profile, an efficient acceleration of the electron bunch can be obtained over several Rayleigh lengths.
关键词： hollow capillary,laser guiding,laser plasma acceleration,flattened Gaussian beam
更新于2025-09-11 14:15:04