The high-energy petawatt PETAL laser system was commissioned at CEA’s Laser Mégajoule facility during the 2017–2018 period. This paper reports in detail on the first experimental results obtained at PETAL on energetic particle and photon generation from solid foil targets, with special emphasis on proton acceleration. Despite a moderately relativistic (<10¹⁹ W/cm²) laser intensity, proton energies as high as 51 MeV have been measured significantly above those expected from preliminary numerical simulations using idealized interaction conditions. Multidimensional hydrodynamic and kinetic simulations, taking into account the actual laser parameters, show the importance of the energetic electron production in the extended low-density preplasma created by the laser pedestal. This hot-electron generation occurs through two main pathways: (i) stimulated backscattering of the incoming laser light, triggering stochastic electron heating in the resulting counterpropagating laser beams; (ii) laser filamentation, leading to local intensifications of the laser field and plasma channeling, both of which tend to boost the electron acceleration. Moreover, owing to the large (∼100 μm) waist and picosecond duration of the PETAL beam, the hot electrons can sustain a high electrostatic field at the target rear side for an extended period, thus enabling efficient target normal sheath acceleration of the rear-side protons. The particle distributions predicted by our numerical simulations are consistent with the measurements.

中文翻译：

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使用高能拍瓦 PETAL 激光器增强离子加速

2017 年至 2018 年期间，CEA 的 Laser Mégajoule 设施调试了高能拍瓦 PETAL 激光系统。本文详细报告了在 PETAL 获得的关于从固体箔目标产生高能粒子和光子的第一个实验结果，特别强调质子加速。尽管中等相对论（<10 ¹⁹ W/cm ²) 激光强度，测量到的质子能量高达 51 MeV，明显高于使用理想化相互作用条件进行初步数值模拟的预期值。考虑到实际激光参数的多维流体动力学和动力学模拟显示了由激光基座产生的扩展低密度前等离子体中高能电子产生的重要性。这种热电子的产生通过两个主要途径发生：(i) 入射激光的受激反向散射，在由此产生的反向传播激光束中触发随机电子加热；(ii) 激光成丝，导致激光场和等离子体通道的局部增强，这两者都倾向于提高电子加速度。此外，由于大 (~100 μm) PETAL 束的腰部和皮秒持续时间，热电子可以在目标背面长时间维持高静电场，从而实现背面质子的有效目标法向鞘加速。我们的数值模拟预测的粒子分布与测量结果一致。