Laser Plasma Electron Acceleration with kHz Lasers

激光等离子体加速已经成为一种很有前途的紧凑型电子束产生技术。在大多数情况下，使用具有相当低的重复频率(赫兹或更低)的100太瓦到拍瓦级别的激光系统来驱动这样的加速器并产生高达GeV级别的电子束。然而，许多应用要求更高的重复频率，最高可达千赫，甚至更高。最近，第一个原理验证实验证明了激光等离子体以千赫的重复频率加速了少数MeV电子。这些最初的结果是令人鼓舞的，但观测到的光束由于缺乏可靠性和稳定性，对应用还没有用处。目前的项目HighRep旨在将千赫激光-等离子体加速提高到更高的成熟度。为了做到这一点，我们将开发创新的目标，以更好地控制注入加速的等离子体波，这反过来应增加电子源的稳定性、可靠性和稳健性。靶标的开发将遵循两条主要研究路线：(1)用于产生微米级可控定制气体喷射分布的微喷嘴，例如允许在密度转变中触发电子注入；(2)单团簇具有微米定位的团簇靶标，用于控制注入并将电子能量增加到10 MeV或更高。激光等离子体加速器有可能通过电子在等离子体尾迹场中的电子辐射产生飞秒X射线爆发。在HighRep内部，我们将以千赫的重复频率对发射的X-UV光进行第一次测量。至关重要的是，该项目基于法国和德国集团在专业知识和设备方面的互补性。特别是，两个小组之间的合作将允许在两个不同的1TW最先进的激光系统上进行实验，这两个系统具有非常不同的参数。这将使我们能够研究不同情况下千赫激光-等离子体加速，并估计哪种激光技术最有前途。

Laser-plasma acceleration has emerged as a promising technique for producing electron beams in a compact manner. In the majority of cases, 100 TeraWatt to PetaWatt scale laser systems, with rather low repetition rates (Hz or less), are used to drive such accelerators and to produce electron beams up to the GeV scale. However, many applications require higher repetition rates up to the kHz level and beyond. Very recently, first proof-of-principle experiments have demonstrated laser-plasma acceleration of few-MeV electrons at kHz repetition rates. These first results are encouraging but the observed beams are not useful for applications yet as they lack reliability and stability. The current project, HighRep, aims to bring kHz laser-plasma acceleration to a higher level of maturity. To do so, we will develop innovative targets to better control the injection into the accelerating plasma waves, which should, in turn, increase the stability, reliability and robustness of the electron source. The target developments will follow two main research paths: (i) micro-nozzles for producing controlled tailored gas-jet distributions at the micrometer level, permitting for instance to trigger electron injection in density transitions, (ii) cluster targets with micrometer positioning of single clusters, for controlling injection and increasing the electron energy to 10 MeV and beyond. Laser-plasma accelerators have the potential of producing femtosecond X-ray bursts via betatron radiation of the electrons in the plasma wakefield. Within HighRep, we will carry out first measurements of the emitted X-UV light at kHz repetition rate. The project is crucially based on the complementarity of the French and German groups, both in terms of expertise and equipment. In particular, the collaboration between the two groups will permit to perform experiments on two different 1 TW state-of-the-art laser systems that have very different parameters. This will allow us to study kHz laser-plasma acceleration in different regimes and to estimate which laser technology is most promising.