基于激光尾波场加速的桌面伽玛射线辐射源

Table-top gamma ray source based on the laser-plasma accelerator at SJTU is proposed. The generation mechanism is firstly based on the generation of ultra-relativistic electron beam from laser-driven plasma (laser wakefield acceleration). In this process we will improve the electron beam quality by optimization both of electron injection and wake structure. Then secondly the generation of Bremsstrahlung gamma rays by stopping the electron beam in a heavy metal convertor such as tantalum. Additional radiation generation mechanisms including the Compton backscattering between the electron beam and the laser beam itself will be explored as well. The research is experimental in nature and will be supported by theory and simulations. The experimental part will be based on the 200 TW laser system and interaction chamber facilities already available at the Key Laboratory for Laser-Plasmas of the Ministry of Education and the Department of Physics at SJTU. The proposed gamma ray source will have dramatic advantages and uniqueness compared with conventional techniques: first of all it is compact; the gamma rays are having a beam-like spatial profile with mrad. divergence, ultrashort pulse duration and will have an ultra-small source size allowing the possibility of various applications in modern science technology.

本课题将针对上海交通大学已建成的200太瓦激光装置，研究以激光等离子体加速为基础的台面型伽玛辐射源。通过对电子注入机制和尾场控制两方面的优化来提升尾波加速的电子束质量。在伽玛射线产生机制方面，方案一是利用尾波加速的高质电子束与重金属转换靶（如钽靶）相互作用的轫致辐射过程产生伽玛射线；方案二是利用该电子束与激光束的背向康普顿散射产生高频伽玛射线。我们将从理论和实验两方面对这两种机制加以研究，理论上扩展和开发相应的尾波加速和辐射计算数值模拟程序，完成对实验过程的总体模拟和设计；实验上将在上海交大激光等离子体实验室的激光器及靶场平台上开展上述实验。预期通过该项目的研究，产生具有小体积、低发散角、超短脉冲、可用于多学科实验的伽玛射线源。

在过去四年的项目执行期内，项目组成员根据项目研究计划，从高品质激光尾波电子加速和伽玛射线源产生两方面开展了理论和实验研究。理论上提出了改进的离化注入和对撞光场注入方案，大大降低了加速电子束的能散和发射度，提高了电子束品质；提出了基于等离子体通道的波荡辐射概念，并用粒子模拟加以验证，增强了辐射谱和偏振的可调谐性；开展了激光尾波电子加速和被加速电子束与固体靶相互作用的韧致辐射实验，获得了1.2GeV的准单能电子束，观察到高能伽玛射线辐射；开展了激光与电子束的逆康普顿散射实验，获得了20MeV的伽玛光子辐射，并通过数值模拟成功解释了远场辐射的菱形分布特征。共发表学术论文28篇，其中3篇发表在Nature Photonics, Light: Science & Applications, Physical Review Letters上。这些研究提升了激光尾波加速电子束的品质和对全光逆康普顿散射的认识，初步实现了桌面型伽玛辐射源，为其将来进一步应用奠定了基础。