Investigation of staged laser-plasma acceleration.

摘要

Laser-plasma accelerators (LPAs) have demonstrated high accelerating gradients on the order of tens of GV/m, two to three orders of magnitude greater than conventional accelerators. One fundamental issue of an LPA is that the driving laser loses energy to excite plasma waves and eventually, the laser energy will be too low to continue the wake excitation. LPAs could overcome this depletion by using staged acceleration, a sequence of modules where each module is driven by a fresh laser pulse. To demonstrate this concept, a new experimental setup (staging experiment) has been built at the LOASIS facility at LBNL. In this experiment, pulses from a 40 TW peak power laser system are split into a 25 TW pulse and a 15 TW pulse, where the first pulse is used for e-beam production in the first module and the second pulse is used for wake excitation in the second module to post-accelerate the e-beam.;The thesis consists of the design, installation and commissioning of the experimental setup and the investigation of three critical components: e-beam production, reflection of laser pulses with a plasma mirror, and large wake excitation below electron injection threshold. High quality, stable e-beam suitable for the first module were produced using 40 TW laser pulses. Various schemes of injection were explored at 25 TW but need further study to produce equally stable e-beam. Electron beam properties were characterized for slice energy spread and emittance to better understand e-beam propagation between the modules. A plasma mirror to reflect the 15 TW pulse near the focus and achieve compact coupling of the modules was developed and demonstrated sufficient reflective qualities for the staging experiment. A wakefield on the order of 30 GV/m was excited using 40 TW pulses, demonstrating a large accelerating field without electron injection. Wake excitation in the staging setup requires further study because the driving pulses were modulated during splitting, inhibiting pulses from reaching the necessary intensity for efficient wake excitation. These initial experiments have laid the foundation for a staging experiment by demonstrating key steps at the 40 TW peak power level.