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X-Ray Attenuation Cell [electronic resource].

Published
Washington, D.C : United States. Dept. of Energy. Office of the Assistant Secretary for Defense Programs, 2000.
Oak Ridge, Tenn. : Distributed by the Office of Scientific and Technical Information, U.S. Dept. of Energy.
Physical Description
100 Kilobytes pages : digital, PDF file
Additional Creators
Lawrence Livermore National Laboratory, United States. Department of Energy. Office of the Assistant Secretary for Defense Programs, and United States. Department of Energy. Office of Scientific and Technical Information
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Summary
To minimize the pulse-to-pulse variation, the LCLS FEL must operate at saturation, i.e. 10 orders of magnitude brighter spectral brilliance than 3rd-generation light sources. At this intensity, ultra-high vacuums and windowless transport are required. Many of the experiments, however, will need to be conducted at a much lower intensity thereby requiring a reliable means to reduce the x-ray intensity by many orders of magnitude without increasing the pulse-to-pulse variation. In this report we consider a possible solution for controlled attenuation of the LCLS x-ray radiation. We suggest using for this purpose a windowless gas-filled cell with the differential pumping. Although this scheme is easily realizable in principle, it has to be demonstrated that the attenuator can be made short enough to be practical and that the gas loads delivered to the vacuum line of sight (LOS) are acceptable. We are not going to present a final, optimized design. Instead, we will provide a preliminary analysis showing that the whole concept is robust and is worth further study. The spatial structure of the LCLS x-ray pulse at the location of the attenuator is shown in Fig. 1. The central high-intensity component, due to the FEL, has a FWHM of ≈100 {micro}m. A second component, due to the undulator's broad band spontaneous radiation is seen as a much lower intensity ''halo'' with a FWHM of 1 mm. We discuss two versions of the attenuation cell. The first is directed towards a controlled attenuation of the FEL up to the 4 orders of magnitude in the intensity, with the spontaneous radiation halo being eliminated by collimators. In the second version, the spontaneous radiation is not sacrificed but the FEL component (as well as the first harmonic of the spontaneous radiation) gets attenuated by a more modest factor up to 100. We will make all the estimates assuming that the gas used in the attenuator is Xenon and that the energy of the FEL is 8.25 keV. At lower FEL energies the problems associated with the attenuator become much easier and reformulation of our results for the case of other gases is straightforward.
Report Numbers
E 1.99:ucrl-id-138125
ucrl-id-138125
Subject(s)
Other Subject(s)
Note
Published through SciTech Connect.
03/03/2000.
"ucrl-id-138125"
Toor, A.; Ryutov, D.
Type of Report and Period Covered Note
Topical;
Funding Information
W-7405-Eng-48
View MARC record | catkey: 13824802