CEA, DAM, DIF, 91297 Arpajon, France.
LOA, ENSTA ParisTech, CNRS, Ecole Polytechnique, Université Paris-Saclay, 91762 Palaiseau, France.
Phys Rev Lett. 2018 Jun 22;120(25):254802. doi: 10.1103/PhysRevLett.120.254802.
Recent progress in laser-driven plasma acceleration now enables the acceleration of electrons to several gigaelectronvolts. Taking advantage of these novel accelerators, ultrashort, compact, and spatially coherent x-ray sources called betatron radiation have been developed and applied to high-resolution imaging. However, the scope of the betatron sources is limited by a low energy efficiency and a photon energy in the 10 s of kiloelectronvolt range, which for example prohibits the use of these sources for probing dense matter. Here, based on three-dimensional particle-in-cell simulations, we propose an original hybrid scheme that combines a low-density laser-driven plasma accelerator with a high-density beam-driven plasma radiator, thereby considerably increasing the photon energy and the radiated energy of the betatron source. The energy efficiency is also greatly improved, with about 1% of the laser energy transferred to the radiation, and the γ-ray photon energy exceeds the megaelectronvolt range when using a 15 J laser pulse. This high-brilliance hybrid betatron source opens the way to a wide range of applications requiring MeV photons, such as the production of medical isotopes with photonuclear reactions, radiography of dense objects in the defense or industrial domains, and imaging in nuclear physics.
近年来，激光驱动等离子体加速的发展使得电子能够被加速到数百千兆电子伏特。利用这些新型加速器，已经开发出了称为同步加速器辐射的超短、紧凑且空间相干的 X 射线源，并将其应用于高分辨率成像。然而，同步加速器源的应用范围受到低能量效率和 10 千电子伏特量级的光子能量的限制，例如，这限制了这些源在探测高密度物质方面的应用。在这里，我们基于三维粒子模拟，提出了一种原始的混合方案，将低密度激光驱动等离子体加速器与高密度束流驱动等离子体辐射器相结合，从而显著提高了光子能量和同步加速器源的辐射能量。能量效率也得到了极大的提高，约有 1%的激光能量被转化为辐射，当使用 15J 激光脉冲时，γ 射线光子能量超过兆电子伏特范围。这种高亮度混合同步加速器源为需要兆电子伏特光子的各种应用开辟了道路，例如利用光子核反应生产医用同位素、国防或工业领域中高密度物体的射线照相以及核物理成像。
