• M. Shverdin, F. Albert, S.G. Anderson, C.P.J. Barty, A.J. Bayramian, M. Betts, T.S. Chu, C.A. Ebbers, D.J. Gibson, F.V. Hartemann, R.A. Marsh, D.P. McNabb, M. J. Messerly, H.H. Phan, M.A. Prantil, C. Siders, S.S.Q. Wu
  LLNL, Livermore, California

Generation of mono-energetic, high brightness gamma-rays requires state of the art lasers to both produce a low emittance electron beam in the linac and high intensity, narrow linewidth laser photons for scattering with the relativistic electrons. Here, we overview the laser systems for the 3rd generation Monoenergetic Gamma-ray Source (MEGa-ray) currently under construction at Lawrence Livermore National Lab. We also describe a method for increasing the efficiency of laser Compton scattering through laser pulse recirculation. The fiber-based photoinjector laser will produce 50 uJ temporally and spatially shaped UV pulses at 120 Hz to generate a low emmittance electron beam in the X-band RF photoinjector. The interaction laser generates high intensity photons that focus into the interaction region and scatter off the accelerated electrons. This system utilizes chirped pulse amplification and commercial diode pumped solid state Nd:YAG amplifiers to produce 0.5 J, 10 ps, 120 Hz pulses at 10⁶⁴ nm and up to 0.2 J after frequency doubling. A single passively mode-locked Ytterbium fiber oscillator seeds both laser systems and provides a timing synch with the linac.

• F.V. Hartemann, F. Albert, S.G. Anderson, C.P.J. Barty, A.J. Bayramian, T.S. Chu, R.R. Cross, C.A. Ebbers, D.J. Gibson, R.A. Marsh, D.P. McNabb, M. J. Messerly, M. Shverdin, C. Siders
  LLNL, Livermore, California
• E.N. Jongewaard, T.O. Raubenheimer, S.G. Tantawi, A.E. Vlieks
  SLAC, Menlo Park, California
• V. A. Semenov
  UCB, Berkeley, California

Recent progress in accelerator physics and laser technology have enabled the development of a new class of tunable 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 Mono-Energetic Gamma-ray (MEGa-ray) source driven by a compact, high-gradient X-band linac is currently under development and construction at LLNL. High-brightness, relativistic electron bunches produced by an X-band linac designed in collaboration with SLAC 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 via Compton scattering. This MEGa-ray source will be used to excite nuclear resonance fluorescence in various isotopes. Applications include homeland security, stockpile science and surveillance, nuclear fuel assay, and waste imaging and assay. The source design, key parameters, and current status are presented, along with important applications, including nuclear resonance fluorescence, photo-fission, and medical imaging.

• R.A. Marsh, S.G. Anderson, C.P.J. Barty, T.S. Chu, C.A. Ebbers, D.J. Gibson, F.V. Hartemann
  LLNL, Livermore, California
• C. Adolphsen, E.N. Jongewaard, T.O. Raubenheimer, S.G. Tantawi, A.E. Vlieks, J.W. Wang
  SLAC, Menlo Park, California

In support of Compton scattering gamma-ray source efforts at LLNL, a multi-bunch test stand is being developed to investigate accelerator optimization for future upgrades. This test stand will enable work to explore the science and technology paths required to boost the current 10 Hz mono-energetic gamma-ray (MEGa-Ray) technology to an effective repetition rate exceeding 1 kHz, potentially increasing the average gamma-ray brightness by two orders of magnitude. Multiple bunches must be of exceedingly high quality to produce narrow-bandwidth gamma-rays. Modeling efforts will be presented, along with plans for a multi-bunch test stand at LLNL. The test stand will consist of a 5.5 cell X-band rf photoinjector, single accelerator section, and beam diagnostics. The photoinjector will be a high gradient standing wave structure, featuring a dual feed racetrack coupler. The accelerator will increase the electron energy so that the emittance can be measured using quadrupole scanning techniques. Multi-bunch diagnostics will be developed so that the beam quality can be measured and compared with theory. Design will be presented with modeling simulations, and layout plans.