Plasma gradient controlled injection and postacceleration of high quality electron bunches

Plasma density gradient control of wake phase velocity and trapping threshold in a laser wakefield accelerator produced electron bunches with absolute longitudinal and transverse momentum spreads more than ten times lower than in previous experiments (0.17 and 0.02 MeV/c FWHM, respectively) and with central momenta of 0.76+/-0.02 MeV/c, stable over a week of operation. Simulations validated against diagnostics show that use of such bunches as a wakefield accelerator injector can produce stable beams with 0.2 MeV/c-class momentum spread at high energies. Preservation of bunch momentum spread requires high simulation momentum accuracy, and related self-trapped simulations showed that high order particle weight effectively suppresses simulation momentum errors allowing design of low emittance stages.