  A new scheme for injection and acceleration of electrons in wakefield
accelerators is suggested based on the co-action of a laser pulse and an
electron beam. This synergy leads to stronger wakefield generation and higher
energy gain in the bubble regime. The strong deformation of the whole bubble
leads to electron self-injection at lower laser powers and lower plasma
densities. To predict the practical ranges of electron beam and laser pulse
parameters an interpretive model is proposed. The effects of altering the
initial electron beam position on self-trapping of plasma electrons are
studied. It is observed, a high quality (25 fs), high charge (340 pC ), 1 GeV
electron bunch is produced by injection of a 280 pC electron beam in the
decelerating phase of the 48 TW laser driven wakefield.
