Yu-Jiuan Chen and Arthur C. Paul (LLNL)
The accelerator for the second-axis of the Dual Axis Radiographic Hydrodynamic Test (DARHT) facility will deliver a 18 20 MeV, 2 kA, 2 ?s long electron current pulse with the Lapostolle emittance not greater than 1000 ? mm-mrad. The Diagnostic X (D-X) beamline will extract the beam from the DARHT-II downstream transport line and transport this beam from the accelerator exit to the D-X firing point to provide four lines of sight for x-ray radiography. The design goal is to deliver four x-ray pulses with the DARHT-II x-ray dose format and time-integrated spot size on each line of sight. Several processes can degrade beam quality by increasing the beam emittance, increasing the time-varying transverse beam motion, creating a halo, or creating a time-varying beam envelope. In this paper, we consider those processes in the passive magnet lattice beamline and indicate how they constrain the D-X beamline design. We discuss how beam emittance affects the x-ray forward dose and establish a design goal for the final emittance to be less than 1875 ? mm-mrad. The D-X beamline will be made out 8-cm radius aluminum pipe to minimize the resistive wall effects on the beam. We discuss the background gas focusing effects and establish the vacuum requirements to be less than 10-8 torrs. Finally a beamline configuration will be presented.
* This work was performed under the auspices of the U.S. Department of Energy by University of California Lawrence Livermore National Laboratory under contract No. W-7405-Eng-48.
Comments or Questions to
linac2000@slac.stanford.edu