We discuss the first experimental demonstration of electron acceleration by a laser wakefield over distances greater than a Rayleigh range (or the distance a laser normally propagates in vacuum). A self-modulated laser wakefield plasma wave is shown to have a field gradient that exceeds that of an RF Iinac by four orders of magnitude (E ≥ 200 GV/m) and accelerates electrons with over l-nC of charge per bunch in a beam with space-charge-limited emittance (1 mm-mrad). Above a laser power threshold, a plasma channel, created by the intense ultrashort laser pulse (I~ 4 x 1018 W/cm2, λ = 1 μm, τ = 400 fs), was found to increase the laser propagation distante, decrease the electron beam divergence, and increase the electron energy. The plasma wave, directly measured with coherent Thomson scattering is shown to damp—due to beam loading-in a duration of 1.5 ps or ~ 100 plasma periods. These results may have important implications for the proposed fast ignitor concept.
Available at: http://works.bepress.com/donald_umstadter/76/