The two-temperature relativistic electron spectrum from a low-density ($3\times {10}^{17}{\mathrm{cm}}^{-3}$) self-modulated laser wakefield accelerator (SM-LWFA) is observed to transition between temperatures of $19\pm 0.65$ and $46\pm 2.45\mathrm{MeV}$ at an electron energy of about 100 MeV. When the electrons are dispersed orthogonally to the laser polarization, their spectrum above 60 MeV shows a forking structure characteristic of direct laser acceleration (DLA). Both the two-temperature distribution and the forking structure are reproduced in a quasi-3D osiris simulation of the interaction of the 1-ps, moderate-amplitude ($a_0=2.7$) laser pulse with the low-density plasma. Particle tracking shows that while the SM-LWFA mechanism dominates below 40 MeV, the highest-energy ($>60\mathrm{MeV}$) electrons gain most of their energy through DLA. By separating the simulated electric fields into modes, the DLA-dominated electrons are shown to lose significant energy to the longitudinal laser field from the tight focusing geometry, resulting in a more accurate measure of net DLA energy gain than previously possible.

中文翻译：

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在低密度自调制激光尾波加速器中直接激光加速对高能电子光谱的主要贡献

低密度的两温相对论电子光谱$3\times {10}^{17}{\mathrm{厘米}}^{-3}$）观察到自调制激光尾波加速器（SM-LWFA）在 $19\pm 0.65$ 和 $46\pm 2.45\mathrm{病毒}$在大约100 MeV的电子能量下 当电子垂直于激光偏振散布时，其60 MeV以上的光谱显示出直接激光加速（DLA）的叉形结构特征。在1ps中等振幅（-ps）相互作用的准3D osiris仿真中，再现了两个温度分布和叉状结构。${\mathrm{一种}}_0=2.7$）激光脉冲与低密度等离子体。粒子跟踪显示，虽然SM-LWFA机制在40 MeV以下占主导地位，但最高能量（$>60\mathrm{病毒}$电子通过DLA获得大部分能量。通过将模拟电场分成多个模式，显示出DLA为主的电子从紧密聚焦的几何结构中向纵向激光场损失了大量能量，从而比以前可能的方式更精确地测量了净DLA能量增益。