Stable laser-pulse propagation in plasma channels for GeV electron acceleration

To achieve multi-GeV electron energies in the laser wakefield accelerator ( LWFA) it is necessary to propagate an intense laser pulse long distances in plasma without disruption. A 3D envelope equation for a laser pulse in a t apered plasma channel is derived, which includes wakefields and relativisti c and nonparaxial effects, such as finite pulse length and group velocity d ispersion. It is shown that electron energies of similar to GeV in a plasma -channel LWFA can be achieved by using short pulses where the forward Raman and modulation nonlinearities tend to cancel. Further energy gain can be a chieved by tapering the plasma density to reduce electron dephasing.