Velocity control and staging in laser wakefield accelerators using segmented capillary discharges

To achieve multi-GeV electron energies in the laser wakefield accelerator, it is necessary to propagate an intense laser pulse long distances in plasma channels while maintaining a proper phase with the accelerated electrons. We have demonstrated a method that allows control of the laser group velocity in long, multistage plasma channels. The control is achieved by modifying the index of refraction through a variation of the plasma density using a segmented capillary discharge.