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. 2015 Mar;22(2):461-4.
doi: 10.1107/S160057751402829X. Epub 2015 Feb 4.

A small and robust active beamstop for scattering experiments on high-brilliance undulator beamlines

Clement E Blanchet  1 , Christoph Hermes  1 , Dmitri I Svergun  1 , Stefan Fiedler  1
Affiliations

A small and robust active beamstop for scattering experiments on high-brilliance undulator beamlines

Clement E Blanchet et al. J Synchrotron Radiat. 2015 Mar.

Abstract

A small active in-vacuum beamstop has been developed to monitor the flux of intense third-generation synchrotron X-ray beams protecting the downstream detector from the direct beam. Standard active beamstops, where a built-in diode directly absorbs the beam, have limitations in size and lifetime. In the present design, a silicon PIN diode detects the photons back-scattered from a cavity in the beamstop. This approach drastically reduces the radiation dose on the diode and thus increases its lifetime. The beamstop with a diameter of 2 mm has been fabricated to meet the requirements for the P12 bioSAXS beamline of EMBL Hamburg at PETRA III (DESY). The beamstop is in regular user operation at the beamline and displays a good response over the range of energies tested (6-20 keV). Further miniaturization of the diode is easily possible as its size is not limited by the PIN diode used.

Keywords: SAXS; back-scattering; radiation resistance; silicon PIN diode; small footprint.

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Figures

Figure 1
Figure 1
(a) Schematics of a SAXS experiment: the X-ray beam (red) hits the sample, photons are scattered by the sample and are collected on the detector. The transmitted direct beam is intercepted by the beamstop. (b) Cross-sectional drawing of the beamstop illustrating its principle. The incident beam, represented by the red arrow, enters the tungsten chamber (in orange) and hits the back of the chamber. Part of the beam is scattered on the diode (in blue). The signal produced by the photons counted on the photosensitive area (in yellow) is proportional to the incident beam intensity. (c) Photograph of the beamstop elements: the diode (in the center), is mounted on the profiled aluminium bar (on the left) and covered by the tungsten chamber (on the right).
Figure 2
Figure 2
(a) Photocurrent I produced by the diode as a function of the incident photon flux. (b) Response of the active beamstop monitor for different energies (the errors are within the size of the symbol except for 6 keV, measured with a lower photon flux). (c) Time series of the beamstop photocurrent (red) and the ring current (black). In the magnified insert the ‘topping up’ operation of PETRA III is reflected in the measured photocurrent.
Figure 3
Figure 3
Spatial sensitivity of the beamstop: photocurrent produced by the beamstop for different positions of the beam along the horizontal and the vertical directions.
See this image and copyright information in PMC

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