• 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.

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

A Mono-Energetic Gamma-Ray Compton scattering light source is being developed at LLNL. The electron beam for the interaction will be generated by a X-band RF gun and LINAC at the frequency of 11.424 GHz. High power RF in excess of 500 MW is needed to accelerate the electrons to energy of 250 MeV or greater. Two high power klystrons, each capable of generating 50 MW, 1.5 msec pulses, will be the main RF sources for the system. These klystrons will be powered by state of the art solid-state high voltage modulators. A RF pulse compressor, similar to the SLED II pulse compressor, will compress the klystron output pulse with a power gain factor of five. For compactness consideration, we are looking at a folded RF line. The goal is to obtain 500 MW at output of the compressor. The compressed pulse will then be distributed to the RF gun and to six traveling wave accelerator sections. Phase shifter and amplitude control are located at the RF gun input and additional control points along the LINAC to allow for parameter control during operation. This high power RF system is being designed and constructed. In this paper, we will present the design, layout, and status of this RF system.

• 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.

• K.M. Schirm, S. Curt, S. Döbert, G. McMonagle, G. Rossat, I. Syratchev, L. Timeo
  CERN, Geneva
• A.A. Haase, A. Jensen, E.N. Jongewaard, C.D. Nantista, D.W. Sprehn, A.E. Vlieks
  SLAC, Menlo Park, California
• A. Hamdi, F. Peauger
  CEA, Gif-sur-Yvette
• S.V. Kuzikov, A.A. Vikharev
  IAP/RAS, Nizhny Novgorod

The CLIC RF frequency has been changed in 2008 from the initial 30 GHz to the European X-band 11.9942 GHz permitting beam independent power production using klystrons for CLIC accelerating structure testing. A design and fabrication contract for five klystrons at that frequency has been signed by different parties with SLAC. France (CEA Saclay) is contributing a solid state modulator purchased in industry to the CLIC study. RF pulses over 120 MW peak at 230 ns length will be obtained by using a novel SLED I type pulse compression scheme designed and fabricated in Nizhny Novgorod, Russia. The X-band power test stand has been installed in the CLIC Test Facility CTF3 for independent structure and component testing in a bunker, but allowing, in a later stage, for powering RF components in the CTF3 beam lines. The design of the facility, results from commissioning of the RF power source and the performance of the Test Facility are reported.

• D.W. Sprehn, A.A. Haase, A. Jensen, E.N. Jongewaard, C.D. Nantista, A.E. Vlieks
  SLAC, Menlo Park, California

A 12 GHz 50MW X-band klystron is under development at the SLAC National Accelerator Laboratory Klystron Department. The klystron will be fabricated to support programs currently underway at three European Labs; CERN, PSI, and INFN Trieste. The choice of frequency selection was due to the CLIC RF frequency changing from 30 GHz to the European X-band frequency of 11.9942 GHz in 2008. Since the Klystron Department currently builds 50MW klystrons at 11.424 GHz known collectively as the XL4 klystrons, it was deemed cost-effective to utilize many XL4 components by leaving the gun, electron beam transport, solenoid magnet and collector unchanged. To realize the rf parameters required, the rf cavities and rf output hardware were necessarily altered. Some improvements to the rf design have been made to reduce operating gradients and increase reliability. Changes in the multi-cell output structure, waveguide components, and the window will be discussed along with testing of the devices. Five klystrons known as XL5 klystrons are scheduled for production over the next two years.

• D.W. Sprehn, A.A. Haase, A. Jensen, E.N. Jongewaard, D.W. Martin
  SLAC, Menlo Park, California

The SLAC National Accelerator Laboratory Klystron Department is developing a 10 MW, 5 Hz, 1.6 ms, 1.3 GHz plug-compatible Sheet-Beam Klystron as a less expensive and more compact alternative to the ILC baseline Multiple-Beam Klystron. Earlier this year a beam tester was constructed and began test. Device fabrication issues have complicated the analysis of the data collected from an intercepting cup for making beam quality measurements of the 130 A, 40-to-1 aspect ratio beam. Since the goal of the beam tester is to confirm 3d beam simulations it was necessary to rebuild the device in order to mitigate unwanted effects due to imperfect focusing construction. Measurements are underway to verify the results of this latest incarnation. Measurement will then be made of the beam after transporting through a drift tube and magnetic focusing system. In the klystron design, a TE oscillation was discovered during long simulation runs of the entire device which has since prompted two design changes to eliminate the beam disruption. The general theory of operation, the design choices made, and results of testing of these various devices will be discussed.