• I. Jovanovic, Y. Yin
  Purdue University, West Lafayette, Indiana
• S. Boucher, R. Tikhoplav
  RadiaBeam, Marina del Rey
• G. Travish
  UCLA, Los Angeles, California

One approach for detecting special nuclear material (SNM) at a distance is to use highly penetrating gamma-rays (>6 MeV) to produce photofission. We are investigating inverse gamma-ray sources (IGS), based on inverse Compton scattering (ICS) of a laser pulse on a relativistic electron bunch. Nearly monochromatic gamma rays with high brightness, very small source size and divergence can be produced in IGS. For the interaction drive laser recirculation it is necessary to meet the repetition rate requirements. Three implementations of laser recirculation are proposed for the interaction drive laser, which can significantly reduce the requirements on the interaction drive laser average power. It is found that the recently demonstrated recirculation injection by nonlinear gating (RING) technique offers unique advantages for beam recirculation in IGS.

• 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.

• I. Syratchev, A. Cappelletti
  CERN, Geneva

One crucial development for CLIC is an adjustable high-power rf device which controls the output power level of individual Power Extraction and Transfer Structures (PETS) even while fed with a constant drive beam current. The CLIC two-beam rf system is designed to have a low, approximately 10^-7, breakdown rate during normal operation and breakdowns will occur in both accelerating structures and the PETS themselves. In order to recover from the breakdowns and reestablish stable operation, it is necessary to have the capability to switch off a single PETS/accelerating structure unit and then gradually ramp generated power up again. The baseline strategy and implementation of such a variable high-power mechanism is described.

• F. Hug, A. Araz, R. Eichhorn, N. Pietralla
  TU Darmstadt, Darmstadt

The Superconducting Linear Accelerator S-DALINAC at the University of Darmstadt/ Germany is a recirculating Linac with two recirculations. Currently acceleration in the Linac is done on crest of the acceleration field using the maximum of the field in every turn. The recirculation of the beam is done isochronous without any longitudinal dispersion. In this recirculation scheme the energy spread of the resulting beam is determined by the stability of the used RF system. In this work we will present a new non-isochronous recirculation scheme, which uses longitudinal dispersion in the recirculations and an acceleration on edge of the accelerating field as it is done in microtrons. We will present beam dynamic calculations which show the usability of this system even in a Linac with only two recirculations and first measurements of longitudinal dispersion using RF monitors.