A significant part of the laser wakefield acceleration (LWFA) research effort focuses on studying high-energy, quasi-monoenergetic electron beams. For other applications, such as the production and application of intense betatron x-ray radiation, Bremsstrahlung γ-rays and positron beams, the beam’s spectral quality is secondary to the number of electrons produced. This work discusses 3D particle-in-cell simulations of a highly efficient LWFA acceleration process, generating a broad spectrum of electrons, driven by a 12 TW few-cycle laser on high-density gas targets. In some cases, laser absorption in plasma exceeds 80%, and up to 27% of the driving laser energy is transferred to electrons over 20 MeV leaving the plasma. We also observe a deceleration of the accelerated beam at the plasma downramp and plasma exit, which arises from transitioning from laser-driven to beam-dominated wake, and also from the induced axial electric field. This effect is similar to magnetic vortex acceleration, where the induced axial electric field, instead of accelerating plasma ions, would slow down the opposite-charged electron beam and also a strong return current and backward electron beam.

激光尾波加速 (LWFA) 研究工作的一个重要部分集中在研究高能、准单能电子束。用于其他应用，如强电磁感应加速器 X 射线辐射、轫致辐射γ的生产和应用射线和正电子束，光束的光谱质量次要于产生的电子数量。这项工作讨论了高效 LWFA 加速过程的 3D 细胞内粒子模拟，在高密度气体目标上由 12 TW 少周期激光器驱动，产生广泛的电子。在某些情况下，等离子体中的激光吸收超过 80%，并且高达 27% 的驱动激光能量被转移到超过 20 MeV 的电子离开等离子体。我们还观察到在等离子体下降坡道和等离子体出口处加速光束的减速，这是由于从激光驱动到光束主导尾流的转变，以及感应轴向电场引起的。这种效应类似于磁涡流加速，其中感应轴向电场，而不是加速等离子体离子，