• W. Leemans, E. Esarey, G. Fubiani, C.G.R. Geddes, P. Michel, B. Nagler, K. Nakamura, C.B. Schroeder, B. Shadwick, C. Toth, J. Van Tilborg
  LBNL, Berkeley, California
• D.L. Bruhwiler
  Tech-X, Boulder, Colorado
• J.R. Cary
  CIPS, Boulder, Colorado
• C. Filip, E. Michel
  University of Nevada, Reno, Reno, Nevada
• A.J. Gonsalves, S.M. Hooker
  OXFORDphysics, Oxford, Oxon

Laser driven accelerators are capable of producing energetic electron beams using ultra-high gradients on the order of 10^-100 GV/m. Prior to 2004, experiments had demonstrated high energy acceleration but with 100 % energy spread. Recent experiments have shown that 100 MeV class intense electron beams with narrow energy spread [1-3] can be generated in mm-scale structures. At the multi-beam L’OASIS facility at LBNL we have produced beams with narrow energy spread using a channel guided laser accelerator [1]. As opposed to single beam experiments, two additional laser beams are used to first produce a plasma channel which then guides an intense drive laser beam over greater distances than in single beam experiments. By properly controlling the channel, 100 MeV-class beams were produced with few percent energy spread, containing 0.3 nC of charge and with a normalized emittance around 1-2 π mm-mrad. Characterization of the bunch length and shape is underway using an electro-optic technique operating in the THz regime that has been implemented and tested using single-beam experiments. Experiments have started to increase the energy to the GeV-level. Hydrogen filled capillary discharges are used to guide beams from the 100 TW-class LOASIS laser and, to date, guiding of 5x1017 W/cm2 over 33 mm has already been shown. Such structures are expected to produce GeV electron beams when laser intensities exceeding 2x1018 W/cm2 are realized. If the normalized emittance from the 100 MeV beams remains preserved and the relative energy spread is reduced during acceleration, such a beam could be used for development of a laser wakefield driven FEL.

[1] C.G.R. Geddes et al., Nature 431, 538- 541(2004). [2] S.P.D. Mangles et al., Nature 431, 535 –538 (2004). [3] J. Faure et al., Nature 431, 541-544 (2004).