Direct laser acceleration (DLA) of electrons in a plasma of near-critical electron density (NCD) and the associated synchrotron-like radiation are discussed for moderate relativistic laser intensity (normalized laser amplitude a₀ ≤ 4.3) and ps length pulse. This regime is typical of kJ PW-class laser facilities designed for high-energy-density (HED) research. In experiments at the PHELIX facility, it has been demonstrated that interaction of a 10¹⁹ W/cm² sub-ps laser pulse with a sub-mm length NCD plasma results in the generation of high-current well-directed super-ponderomotive electrons with an effective temperature ten times higher than the ponderomotive potential [Rosmej et al., Plasma Phys. Controlled Fusion 62, 115024 (2020)]. Three-dimensional particle-in-cell simulations provide good agreement with the measured electron energy distribution and are used in the current work to study synchrotron radiation from the DLA-accelerated electrons. The resulting x-ray spectrum with a critical energy of 5 keV reveals an ultrahigh photon number of 7 × 10¹¹ in the 1–30 keV photon energy range at the focused laser energy of 20 J. Numerical simulations of betatron x-ray phase contrast imaging based on the DLA process for the parameters of a PHELIX laser are presented. The results are of interest for applications in HED experiments, which require a ps x-ray pulse and a high photon flux.

中文翻译：

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在中等相对论激光强度下，来自直接激光加速电子的明亮电子加速器辐射

讨论了中等相对论激光强度（归一化激光振幅a ₀ ≤ 4.3）和 ps 长度脉冲的近临界电子密度 (NCD) 等离子体中电子的直接激光加速 (DLA) 和相关的类似同步加速器的辐射。这种机制是专为高能量密度 (HED) 研究而设计的 kJ PW 级激光设备的典型特征。在 PHELIX 设施的实验中，已经证明 10 ¹⁹ W/cm ²亚 ps 激光脉冲与亚毫米长 NCD 等离子体的相互作用导致产生高电流、定向良好的超功率电子与有效温度比有质动力电位高十倍 [Rosmej et al. ，等离子体物理。受控融合62 , 115024 (2020)]。三维粒子胞内模拟与测量的电子能量分布具有良好的一致性，并用于当前研究来自 DLA 加速电子的同步辐射。得到的具有 5 keV 临界能量的 X 射线光谱揭示了在 20 J 聚焦激光能量下在 1-30 keV 光子能量范围内的 7 × 10 ¹¹超高光子数。电子加速器 X 射线相衬的数值模拟提出了基于 DLA 过程的 PHELIX 激光器参数成像。结果对于 HED 实验中的应用很有意义，这需要 ps x 射线脉冲和高光子通量。