• X.J. Wang, D.A. Harder, J.B. Murphy, H.J. Qian, Y. Shen, X. Yang
  BNL, Upton, Long Island, New York
• H. Freund, W.H. Miner
  SAIC, McLean

We report the first experimental characterization of efficiency and spectrum enhancement in a laser-seeded free-electron laser (FEL) using a tapered undulator. Output and spectra in the fundamental and 3rd harmonic were measured versus distance for uniform and tapered undulators. With a 4% field taper over 3 m, a 300% (50%) increase in the fundamental (3rd harmonic) output was observed. A significant improvement in the spectra with the elimination of side-bands was observed using a tapered undulator. The experiment is in good agreement with predictions using the MEDUSA simulation code.

Slides

• X. Yang, M. Li, W. Li
  CAEP/IAE, Mianyang, Sichuan
• X.J. Shu
  IAP, Beijing

After the first lasing in March 2005 in CAEP, the FEL-THz facility is updated ,the former thermionic cathode injector was replaced using a high brightness photo-cathode injector. The facility mainly consists of a 4.5cells photo-cathode RF-GUN injector ,a hybrid undulator and the optical oscillator cavity. Number of undulator periods is 44, the peak value of the undulator is 4900Gs ,the good aperture is 6mm .The cathode material is Cs2Te and the quadruple light is used , the width of the driving laser is 12ps， the quantum efficiency is about 1%. The commissioning of the injector is finished, the electron energy of the injector was measured and it is about 8MeV ,the energy spread is about 1% and the electron beam normalized emittance is about 9πmm.mrad. The charge is about 100pC and up to 1nC per micro-pulse , the repetition rate is 54.167MHz .The calculated wavelength of the light is about 125micron. At present ,the spontaneous emission experiment is undertaking .

Slides

• D.A. Jaroszynski, M.P. Anania, E. Brunetti, S. Chen, S. Cipiccia, B. Ersfeld, J.P. Farmer, M.R. Islam, R.C. Issac, G. Raj, A. J. W. Reitsma, R.P. Shanks, G. Vieux, G.H. Welsh, S.M. Wiggins, X. Yang
  USTRAT/SUPA, Glasgow
• R.A. Bendoyro, F. Fiuza, M. Marti, J.L. Martins
  Instituto Superior Tecnico, Lisbon
• N. Bourgeois
  University of Oxford, Oxford
• J.M. Dias, N. Lemos, L.O. Silva
  GoLP, Lisbon
• P.S. Foster, R. Pattathil
  STFC/RAL, Chilton, Didcot, Oxon
• W.A. Gillespie
  University of Dundee, Nethergate, Dundee, Scotland
• S.M. Hooker
  OXFORDphysics, Oxford, Oxon
• T. Ibbotson
  University of Oxford, Clarendon Laboratory, Oxford
• A. MacLeod
  UAD, Dundee
• D. Maneuski, V. O'Shea
  University of Glasgow, Glasgow
• M.W. Poole
  STFC/DL/ASTeC, Daresbury, Warrington, Cheshire

We describe the latest results to develop brilliant incoherent and coherent radiation sources based on laser-plasma wakefield accelerators. We demonstrate both experimentally and theoretically a brilliant gamma ray sub 10 femtosecond source based on betatron radiation in the plasma density wake trailing behind an intense laser pulse. Furthermore, experimental and theoretical progress towards a compact free-electron laser based on a laser-plasma wakefield accelerator will be discussed.