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Ong, M. M.

Paper Title Page
WEPMS015 An Improved SF6 System for the FXR Induction Linac Blumlein Switches 2361
 
  • W. J. DeHope, K. L. Griffin, R. Kihara, M. M. Ong, O. Ross
    LLNL, Livermore, California
  
  Funding: This work was performed under the auspices of the US Department of Energy by the University of California, Lawrence Livermore National Laboratory, under Contract W-7405-Eng-48.

The now-mature FXR (Flash X-Ray) radiographic facility at Lawrence Livermore National Laboratory will be briefly described with emphasis on its pulsed power system. The heart of each accelerating cell's pulse-forming Blumlein is it's sulfur hexafluoride-based triggered closing switch. FXR's recent upgrade to a recirculating SF6 gas reclamation system will be described and the resulting accelerator performance and reliability improvements documented. This was accompanied by a detailed switch breakdown study on FXR's Test Stand* and the recent analysis of the resulting statistics will be shown.

* W. DeHope, D. Goerz, R. Kihara, M. Ong, G. Vogtlin, J. Zentler, "An Induction Linac Test Stand", 21st Particle Accelerator Conference, Knoxville, TN, May 20, 2005

 
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.