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Figure 2
The chopper/shutter system. A high-heat-load chopper reduces power on downstream components to less than 1% of the original power in the X-ray beam. This chopper typically produces a 22 µs burst of X-rays at a repetition rate of 82.3 Hz. The Jülich chopper has a much shorter open time and is capable of isolating a single pulse from the initial synchrotron pulse train at a rate of 1 kHz. Since these choppers are continuously rotating, a shutter with a millisecond open-time acts like the shutter on a photographic camera, exposing the CCD detector on demand to the X-rays scattered by the sample. The millisecond shutter is shown in the open position in the figure. For third-generation synchrotron sources pulse widths are typically ∼100 ps and the inter-bunch spacing is normally 153.4 ns in 24-bunch mode at the APS.

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