Stable electron beams with low absolute energy spread from A laser wakefield accelerator with plasma density ramp controlled injection

Laser wakefield accelerators produce accelerating gradients up to hundreds of GeV/m, and recently demonstrated 1-10 MeV energy spread at energies up to 1 GeV using electrons self-trapped from the plasma. Controlled injection and staging may further improve beam quality by circumventing tradeoffs between energy, stability, and energy spread/emittance. We present experiments demonstrating production of a stable electron beam near 1 MeV with hundred-keV level energy spread and central energy stability by using the plasma density profile to control self- injection, and supporting simulations. Simulations indicate that such beams can be post accelerated to high energies, potentially reducing momentum spread in laser accelerators by 100-fold or more.