临界密度等离子体透镜的探测方法和实验研究

Laser ion acceleration has made great progress in recent 30 years. Such Compact accelerator has a broad range of potential applications in cancer therapy, proton radiagraphy, and plasma diagnostics. However, limited to nowaday laser system, the accelerated beam quality is still a distance behind the practical application reqirment. In order to conqure the rigorous requirement for the laser system，we porpose to use "near-critical-density plasma lens" to spontaneously improve the laser pulse quality, as well as the accelerated ion beam energy. This project is focused on the theretical and experimental study of the near critical density plasma lens diagnostic method. The plasma lens will be created either by the pre-pulse ionized plasma expansion or the coated nearcrtical density layer.The density evolution of the plasma lens will be simulated and measured, and the best generation window for ion acceleration will be given. The magnetic field inside the plasma lens will also be measured to understand the mechanism of the laser self-focusing and the electron resonance acceleration. The plasma lens technology will be applied into the Peking Uniersity 200TW laser plasma accelerator system， which will achieve stable proton beams with central energy higher than 15MeV for the future application experiment.

激光离子加速器在近三十年中取得了很大的进展。这种超小型激光离子加速器在癌症治疗，质子成像，等离子体诊断方面有着广泛的应用前景。为了克服激光加速对现阶段激光器的苛刻要求，我们在前期研究中提出利用"临界密度等离子体透镜"对激光进行自发整形优化的方法，理论上可以大幅提高加速质子的能量和品质。本项目专注于等离子体透镜的探测方法理论和实验研究，分别从预脉冲驱动和临界密度复合靶体的两种等离子体透镜产生方法出发,利用多种探测方法，分别对等离子体透镜的密度、磁场等参数进行测量，得到其时空分布和演化规律；同时对激光在透镜中的自聚焦效应和高能共振电子的产生物理机制进行验证；最终将等离子体透镜技术实际运用到北京大学200TW激光加速器中，争取获得能量在15MeV以上的质子束，并初步开展质子照相，生物细胞辐照等应用性实验。

激光质子加速器在近三十年中取得了很大的进展。这种小型的加速器，在癌症治疗，质子成像，等离子体诊断方面具有广泛的应用前景。为了克服激光加速对现阶段激光器的苛刻要求，本项目主要针对激光烧蚀的临界密度等离子体透镜开展理论和实验研究。当激光在密度指数上升的等离子体透镜中传输时，将自发的实现自聚焦，提高有效作用光强和能量转换效率，改善加速质子的能量和品质。项目利用PIC程序进行了模拟计算，在理论上推导出烧蚀激光和主激光的对应关系，获得优化的等离子体密度分布。项目团队还北京大学CLAPA实验平台上搭建了激光烧蚀系统，利用mJ能量的烧蚀激光实现了所需微米尺度的临界密度预等离子体。在加速实验中，利用烧蚀等离子体透镜,有效的提高了加速质子束的电量和能量。同时，利用改善后的质子束，项目还在激光质子束照相等方面开展了一系列的研究工作，获得最佳7微米的空间分辨率。