AI 中文总结
本研究利用腔靶预热泡沫靶产生近临界密度等离子体，通过调节激光延迟，实现了高电荷相对论电子束的调谐，其性能优于固体箔靶和冷泡沫靶，为相关应用提供了可行方案。
AI 中文摘要
近临界密度（NCD）等离子体中的直接激光加速（DLA）可高效产生高电荷相对论电子束，但束参数高度依赖于对等离子体状态的精确操控。固体烧蚀产生的NCD等离子体演化迅速，带来了严重的可控性挑战。本研究通过纳秒激光驱动的腔靶（hohlraum）软X射线间接加热泡沫靶，制备了NCD等离子体；再用另一束皮秒激光辐照该等离子体以产生电子。通过调节激光脉冲延迟τ可控制等离子体轮廓和束参数。实验结果显示，当泡沫被加热时（τ=6 ns、9 ns），电子束表现出约13 MeV的有效温度、约80 MeV的截止能量，且对于动能大于7.5 MeV的电子，电荷达到数百nC/sr；这些数值显著高于固体箔靶相互作用的结果（温度约2.7 MeV、截止能量约20 MeV、电荷约9 nC/sr）以及冷泡沫靶相互作用的结果（温度约12 MeV、截止能量约50 MeV、电荷约5 nC/sr）。当延迟更长（τ=15 ns）时，电荷进一步增加而温度降低；当延迟更短（τ=3 ns）时，温度和电荷均更低。三维粒子模拟（3D PIC）将这些观测结果与冷泡沫的微观结构在不同延迟时间下与演化的等离子体密度轮廓之间的相互作用联系起来，该相互作用共同决定了电子束的电荷、有效温度和发散度。该研究成果为产生和定制相对论电子束提供了一种可行的方法，这对设计用于高能量密度物理和光核反应应用的激光驱动电子源至关重要。
英文摘要
Direct laser acceleration (DLA) in near-critical-density (NCD) plasmas can efficiently generate high-charge relativistic electron beams, yet beam parameters depend critically on precise plasma state manipulation. Solid-ablation NCD plasmas evolve rapidly, posing severe controllability challenges. We produce NCD plasma via indirectly heating foam targets with ns laser driven hohlraum soft X-ray. Electrons are generated through irradiating the plasma with another picosecond laser. Tuning the laser pulse delay $τ$ enables control of plasma profiles and beam parameters. Experiments show that when the foam is heated ($τ$ = 6 ns, 9 ns), the beam exhibits $T \sim 13$ MeV effective temperature, $E_k \sim 80$ MeV cutoff energy, and hundreds of nC/sr charge for $E_k > 7.5$ MeV. These values are significantly higher than those from solid-foil ($T$ $\sim$ 2.7 MeV, $E_k$ $\sim$ 20 MeV, $Q$ $\sim$ 9 nC/sr) and cold-foam ($T$ $\sim$ 12 MeV, $E_k$ $\sim$ 50 MeV, $Q$ $\sim$ 5 nC/sr) interactions. At a longer delay of $τ$ = 15 ns, the charge increases further while the temperature decreases, and at a shorter delay of $τ$ = 3 ns, both temperature and charge are lower. 3D PIC simulations link these observations to the interplay between the microstructure of the cold foam and the evolving plasma density profile at different delay times, which together determine the beam charge, effective temperature, and divergence. The finding provides a routine to generate and tailor the relativistic electron beams, which is essential for designing laser-driven electron sources for high energy density physics and photonuclear reaction applications.
