Tunable Laser Plasma Accelerator based on Longitudinal Density Tailoring*

Laser plasma accelerators (LPAs) have produced high-quality electron beams with GeV energies from centimeter scale devices and are being investigated as drivers of hyperspectral femtosecond light sources and high-energy colliders. Such applications require a high degree of stability, beam quality, and tunability. Here we report on a technique to inject electrons into the accelerating field of a laser-driven plasma wave and coupling of this injector to a lower-density, separately-adjustable plasma for further acceleration. The technique relies on a single laser pulse powering a plasma structure with a tailored longitudinal density profile, to produce beams that can be tuned in the range of 100 to 400MeV with percent level stability, using 40TW laser pulses.