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The acceleration of electron beams with multiple transverse structures in wakefields driven by Laguerre-Gaussian pulses has been studied through three-dimensional (3D) particle-in-cell simulations. Under different laser-plasma conditions, the wakefield shows different transverse structures. In general cases, the wakefield shows a donut-like structure and it accelerates the ring-shaped hollow electron beam. When a lower plasma density or a smaller laser spot size is used, besides the donut-like wakefield, a central bell-like wakefield can also be excited. The wake sets in the center of the donut-like wake. In this case, both a central on-axis electron beam and a ring-shaped electron beam are simultaneously accelerated. Further, reducing the plasma density or laser spot size leads to an on-axis electron beam acceleration only. The research is beneficial for some potential applications requiring special pulse beam structures, such as positron acceleration and collimation. [ABSTRACT FROM AUTHOR]

With two-dimensional quantum electrodynamics (QED) particle-in-cell simulations, a dense electron–positron (e−e+) pair generation from laser-solid interactions is demonstrated. When the interaction of two linearly polarized laser pulses with a thin target enters into the relativistic transparency regime, a stable standing wave (SW) field can be formed by the overlap of the two counter-propagating laser pulses directly. The present study aims to clarify the effects of the SW field on the dynamics of e−e+ pair plasmas. Our results indicate that under the combined effect of the SW field and radiation reaction (RR) effect, the created e−e+ pairs can be trapped into the electric field nodes when the field strength is strong. The trapping effect contributes to the generation of γAV ≥ 400 and ultra-dense pair plasmas in the two-side irradiation scheme. Despite different laser intensities, these pair plasmas have a Maxwellian spectral distribution with a peak energy of 150 MeV. Besides, the periodical modulation of the average energy, spatial, phase-space, and angular patterns of the e−e+ pair plasmas can be triggered. In the angular patterns, as long as the SW field exists, pair plasmas can be pinched along the laser polarization direction. These results may offer a better understanding of the laser–solid interactions in the experiments when 10-PW laser facilities come into operation in the future. [ABSTRACT FROM AUTHOR]

Enhanced electron-positron (e−e+) pair production using two obliquely incident lasers interacting with a solid target is investigated through multi-dimensional particle-in-cell (PIC) simulations. Two obliquely incident lasers can strengthen the laser-hole boring effect, which enhances the reflected focusing laser field and the consequent quantum electrodynamics effects. PIC simulations show that by using two 10 PW-scale lasers, a high-yield (3 × 1010) overdense (∼1022 cm−3) positron beam can be generated and laser to pair energy conversion efficiency can be increased up to one percent. Such positron yield is fifty times higher than that produced from a single laser with the same peak power. The robustness of such a scheme is confirmed by numerically studying parametric influences of the oblique incident angle, temporal asynchrony and phase difference between the two lasers. It is found that the temporal asynchrony and the phase difference have minor effects on the pair production. The proposed scheme may provide great potential for high dense pair plasma generation in experiments with coming approachable high power laser facilities. [ABSTRACT FROM AUTHOR]