S. FALABELLA, Y-J. CHEN, T. HOUCK, J. MCCARRICK, S. SAMPAYAN, J. WEIR (LLNL)
Using an induction linac, ETA-II, we are studying the interaction of a 2kA, 6MeV electron beam focused to a <2 mm diameter spot on high-Z foils. A focus shift was noticed when changing from 5 mil to 40 mil tantalum foil targets. This shift was subsequently attributed to the effect of a substantial fraction of the incident electron beam backscattering from the target, reducing the net beam current. This fraction varies with the thickness and density of the target. The presence and magnitude of the backscattered component was confirmed using Faraday cup collectors and beam-current monitors. Calculations confirm the magnitude of the focus shift is consistent with the observed backscattered fraction.
*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.
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