• S. Döbert, A. Grudiev, G. Riddone, W. Wuensch, R. Zennaro
  CERN, Geneva
• C. Adolphsen, F. Wang, J.W. Wang
  SLAC, Menlo Park, California
• T. Higo, S. Matsumoto, K. Yokoyama
  KEK, Ibaraki

Prototype accelerating structures for the Compact Linear Collider (CLIC) are being developed and high-power tested in a collaboration between SLAC, KEK and CERN. Several undamped, low group-velocity and strongly tapered prototypes (of the so-called T18 design) have been operated above 100 MV/m average gradient at a very low breakdown rates. Recently two new structures with the same iris apertures but now including higher order mode damping waveguides in each cell (TD18 design) have been tested at SLAC and KEK. The damped versions could be processed to similar gradients but an increased breakdown rate was observed. The damping waveguides lead to a magnetic field enhancement in the outer diameter of the cells which results in increased pulsed surface heating. The maximum pulsed temperature rise is 80 deg at the design gradient of 100 MV/m compared to only 20 deg for the undamped version. The high-power tests of the two TD18 structures are analyzed with special emphasis on the influence on breakdown rate of the enhanced magnetic field and consequent increased pulsed surface temperature rise.

• F.V. Hartemann, F. Albert, S.G. Anderson, C.P.J. Barty, A.J. Bayramian, R.E. Bonnanno, T.S. Chu, R.R. Cross, C.A. Ebbers, D.J. Gibson, T.L. Houck, R.A. Marsh, D.P. McNabb, M. J. Messerly, R.D. Scarpetti, M. Shverdin, C. Siders, S.S.Q. Wu
  LLNL, Livermore, California
• C. Adolphsen, A.E. Candel, E.N. Jongewaard, Z. Li, C. Limborg-Deprey, T.O. Raubenheimer, S.G. Tantawi, A.E. Vlieks, F. Wang, J.W. Wang, F. Zhou
  SLAC, Menlo Park, California
• V.A. Semenov
  UCB, Berkeley, California

Continued progress in accelerator physics and laser technology have enabled the development of a new class of tunable x-ray and gamma-ray light sources based on Compton scattering between a high-brightness, relativistic electron beam and a high intensity laser pulse produced via chirped-pulse amplification (CPA). A precision, tunable, monochromatic (< 0.4% rms spectral width) source driven by a compact, high-gradient X-band linac designed in collaboration with SLAC is under construction at LLNL. High-brightness (250 pC, 3.5 ps, 0.4 mm.mrad), relativistic electron bunches will interact with a Joule-class, 10 ps, diode-pumped CPA laser pulse to generate tunable γ-rays in the 0.5-2.5 MeV photon energy range. This gamma-ray source will be used to excite nuclear resonance fluorescence in various isotopes. Fields of endeavor include homeland security, stockpile science and surveillance, nuclear fuel assay, and waste imaging and assay. The source design, key parameters, and current status will be discussed, along with important applications, including nuclear resonance fluorescence and high precision medical imaging.