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Brown, C. G.

Paper Title Page
TUPMS031 High-energy Picosecond Laser Pulse Recirculation for Compton Scattering 1251
 
  • I. Jovanovic, S. G. Anderson, C. P.J. Barty, C. G. Brown, D. J. Gibson, F. V. Hartemann, J. Hernandez, M. Johnson, D. P. McNabb, M. J. Messerly, J. A. Pruet, M. Shverdin, C. Siders, A. M. Tremaine
    LLNL, Livermore, California
  
  Funding: This work was performed under the auspices of the U. S Department of Energy by the University of California, Lawrence Livermore National Laboratory under Contract No. W-7405-Eng-48.

Frequency upconversion of laser-generated photons by inverse Compton scattering for applications such as nuclear spectroscopy and gamma-gamma collider concepts on the future ILC would benefit from an increase of average source brightness. The primary obstacle to higher average brightness is the relatively small Thomson scattering cross section. It has been proposed that this limitation can be partially overcome by use of laser pulse recirculation. The traditional approach to laser recirculation entails resonant coupling of low-energy pulse train to a cavity through a partially reflective mirror.* Here we present an alternative, passive approach that is akin to "burst-mode" operation and does not require interferometeric alignment accuracy. Injection of a short and energetic laser pulse is achieved by placing a thin frequency converter, such as a nonlinear optical crystal, into the cavity in the path of the incident laser pulse. This method leads to the increase of x-ray/gamma-ray energy proportional to the increase in photon energy in frequency conversion. Furthermore, frequency tunability can be achieved by utilizing parametric amplifier in place of the frequency converter.

* G. Klemz, K. Monig, and I. Will, "Design study of an optical cavity for a future photon-collider at ILC", Nucl. Instrum. Meth. A 564, 212-224 (2006).

 
THPMS014 Design of a High Field Stress, Velvet Cathode for the Flash X-Ray (FXR) Induction Accelerator 3023
 
  • T. L. Houck, C. G. Brown, D. E. Fleming, B. R. Kreitzer, K. E. Lewis, M. M. Ong, J. M. Zentler
    LLNL, Livermore, California
  
  Funding: This work was performed under the auspices of the U. S. Department of Energy by University of California, Lawrence Livermore National Laboratory under Contract W-7405-Eng-48.

A new cathode design has been proposed for the Flash X-Ray (FXR) induction linear accelerator with the goal of lowering the beam emittance. The present design uses a conventional Pierce geometry and applies a peak field of 134 kV/cm (no beam) to the velvet emission surface. Voltage/current measurements indicate that the velvet begins emitting near this peak field value and images of the cathode show a very non-uniform distribution of plasma light. The new design has a flat cathode/shroud profile that allows for a peak field stress of 230 kV/cm on the velvet. The emission area is reduced by about a factor of four to generate the same total current due to the greater field stress. The relatively fast acceleration of the beam, approximately 2.5 MeV in 10 cm, reduces space charge forces that tend to hollow the beam for a flat, non-Pierce geometry. The higher field stress achieved with the same rise time is expected to lead to an earlier and more uniform plasma formation over the velvet surface. Simulations of the proposed design are presented.

 
FRPMS048 Characterization of a High Current Induction Accelerator Electron Beam via Optical Transition Radiation from Dielectric Foils 4087
 
  • V. Tang, C. G. Brown, T. L. Houck
    LLNL, Livermore, California
  
  Funding: This work was performed under the auspices of the U. S. Department of Energy by University of California, Lawrence Livermore National Laboratory under Contract W-7405-Eng-48.

Traditionally, thin metal foils are employed for optical transition radiation (OTR) beam diagnostics but the possibility of plating or shorting accelerator insulating surfaces precludes their routine use on high-demand machines. The successful utilization of dielectric foils in place of metal ones would alleviate this issue but necessitates more modeling and understanding of the OTR data for inferring desired beam parameters because of the dielectric's finite permittivity. Additionally, the temperature dependence of the relevant foil parameters must be accounted for due to instantaneous beam heating. Here, we analyze quartz and kapton foil OTR data from the Flash X-Ray (FXR) induction linear accelerator using a model that includes these effects and discuss the resultant FXR beam profiles.