Tunable Electron Multibunch Production in Plasma Wakefield Accelerators
  Synchronized, independently tunable and focused $\mu$J-class laser pulses are used to release multiple electron populations via photo-ionization inside an electron-beam driven plasma wave. By varying the laser foci in the laboratory frame and the position of the underdense photocathodes in the co-moving frame, the delays between the produced bunches and their energies are adjusted. The resulting multibunches have ultra-high quality and brightness, allowing for hitherto impossible bunch configurations such as spatially overlapping bunch populations with strictly separated energies, which opens up a new regime for light sources such as free-electron-lasers. 
B. Hidding, O. Karger, G. Wittig, C. Aniculaesei, D. Jaroszynski,   B.W.J. McNeil, L.T. Campbell, M.R. Islam, B. Ersfeld, Z....
physics.plasm-ph physics.acc-ph