Progress toward a Free Electron Laser Driven by a Laser Plasma Accelerator
Abstract: Laser plasma accelerators (LPAs) rely on the nonlinear interaction between ultra-intense laser pulses (intensity >1018 W/cm2) and underdense gas targets. Following ionization, the laser generates a strong co-propagating plasma wave in which background electrons can be self-injected in accelerating field gradients in excess of 100 GV/m. In recent years, efforts have focused both on extending the beam energy well past the multi-GeV range and on characterizing and optimizing the beam quality (i.e., beam brightness). At few-femtosecond duration, multi-kA current, and submicron emittance, the LPA beam quality supports several high-profile applications, including driving a compact free electron laser (FEL).
At Lawrence Berkeley National Laboratory's BELLA Center, we are currently pursuing an LPA FEL at soft X-ray energies (100- to 300-MeV electrons, producing 45- to 400-nm photons), capitalizing on the LPA system compactness and laser synchronization. In my talk, recent experiments on high-quality LPA performance will be discussed, including a tunable shock-injected LPA configuration, and single-shot emittance measurements for two LPA injection schemes. The proposed layout for the LPA FEL transport and beam-manipulation line will be presented, including critical e-beam focusing optics such as the active plasma lens, the strong-focusing VISA undulator, and a chicane to mitigate the percent-level LPA energy spread. Extensive front-to-end modeling was performed to optimize the LPA FEL line, validating the possibility of coherent FEL gain of several orders of magnitude for realistic LPA parameters. The presentation will finish with the current status of our new LPA FEL facility, including the new FEL-dedicated 100-TW laser system, the transport line assembly, and undulator characterization.