Bailly-Grandvaux M, Kawahito D, McGuffey C, Strehlow J, Edghill B, Wei M S, Alexander N, Haid A, Brabetz C, Bagnoud V, Hollinger R, Capeluto M G, Rocca J J, Beg F N
Center for Energy Research, University of California San Diego, La Jolla, California 92093, USA.
Department of Mechanical and Aerospace Engineering, University of California San Diego, La Jolla, California 92093, USA.
Phys Rev E. 2020 Aug;102(2-1):021201. doi: 10.1103/PhysRevE.102.021201.
Structures on the front surface of thin foil targets for laser-driven ion acceleration have been proposed to increase the ion source maximum energy and conversion efficiency. While structures have been shown to significantly boost the proton acceleration from pulses of moderate-energy fluence, their performance on tightly focused and high-energy lasers remains unclear. Here, we report the results of laser-driven three-dimensional (3D)-printed microtube targets, focusing on their efficacy for ion acceleration. Using the high-contrast (∼10^{12}) PHELIX laser (150J, 10^{21}W/cm^{2}), we studied the acceleration of ions from 1-μm-thick foils covered with micropillars or microtubes, which we compared with flat foils. The front-surface structures significantly increased the conversion efficiency from laser to light ions, with up to a factor of 5 higher proton number with respect to a flat target, albeit without an increase of the cutoff energy. An optimum diameter was found for the microtube targets. Our findings are supported by a systematic particle-in-cell modeling investigation of ion acceleration using 2D simulations with various structure dimensions. Simulations reproduce the experimental data with good agreement, including the observation of the optimum tube diameter, and reveal that the laser is shuttered by the plasma filling the tubes, explaining why the ion cutoff energy was not increased in this regime.
为了提高离子源的最大能量和转换效率，人们提出了在用于激光驱动离子加速的薄箔靶前表面构建结构。虽然已证明这些结构能显著提高中等能量通量脉冲产生的质子加速效果，但它们在紧聚焦高能激光作用下的性能仍不明确。在此，我们报告激光驱动的三维（3D）打印微管靶的实验结果，重点关注其离子加速效能。使用高对比度（约10¹²）的PHELIX激光（150J，10²¹W/cm²），我们研究了覆盖有微柱或微管的1μm厚箔片中离子的加速情况，并与平面箔片进行了比较。前表面结构显著提高了从激光到轻离子的转换效率，相对于平面靶，质子数量增加了高达5倍，尽管截止能量没有增加。我们发现微管靶存在一个最佳直径。我们的研究结果得到了使用具有各种结构尺寸的二维模拟对离子加速进行的系统粒子模拟研究的支持。模拟结果与实验数据吻合良好，包括对最佳管直径的观测，并揭示激光被填充在管内的等离子体遮蔽，这解释了在此情况下离子截止能量为何没有增加。
