Yu-Jiuan Chen, Darwin D.-M. Ho, James F. McCarrick, Arthur C. Paul, Brian R. Poole, Stephen Sampayan, Li-Fang Wang, John T. Weir (LLNL)
The second-axis of the Dual Axis Radiographic Hydrodynamic Test (DARHT) facility will provide four 2.1 mm spot size, x-ray pulses within 2 ?s with their x-doses in the range of several hundred rads at a meter for x-ray imaging. To achieve its performance specifications, there should be a sufficient amount of the DARHT-II x-ray converter material remaining while it turns into plasma and expands rapidly due to the heating of previous beam pulses. Furthermore, the beam-target interactions, such as the unwanted focusing by the backstreaming ions from the desorbed gas from the target surface for the first pulse and by those from the target plasma for the subsequent pulses, and the instabilities of the beam propagating in dense plasma, should be mitigated. We have modified the single pulse target experimental facility on the Experimental Test Accelerator II (ETA-II) to perform the double pulse target experiments to validate the DARHT-II multi-pulse target concept. The 1.15 MeV, 2 kA Snowtron injector will be used to provide the first electron pulse. The 6 MeV, 2 kA ETA-II beam will be used as the probe beam, i.e., the second pulse. The ETA-II target is located inside a focusing magnet (near the center). To use the same ETA-II final focus lens, an iron sleeve will be inserted from the downstream side of the magnet to reduce the downstream sides magnetic field, and the Snowtron beam will strike the x-ray converter from the back. The physics design of the final focus area will be presented. We have modeled the hydrodynamics of the target expansion for the Snowtron beam. Comparison against the DARHT-II target 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