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The European X-ray Free Electron Laser (Altarelli, 2006) is a high-intensity X-ray light source currently being constructed in Hamburg, Germany, that will provide spatially coherent X-rays in the energy range between 0.25 keV and 25 keV. The machine will deliver a unique time structure, consisting of up to 2700 pulses, with a 4.5 MHz repetition rate, 10 times per second at very high photon fluxes up to 1017 photons/s (Tschentscher, 2012). The LPD (Hart, 2012; Koch, 2013), DSSC (Porro, 2010, 2012; Lutz, 2010) and AGIPD (Graafsma, 2009) detectors are being developed to provide Mpixel imaging capabilities at the aforementioned repetition rates for a dynamic range spanning from single photon sensitivity to 104 –105 photons per pixel. The detectors are optimized for specific energy ranges. A direct consequence of the aforementioned detectors’ characteristics is that they generate raw data volumes unprecedented in photon science, ranging up to 1Mpixel x 640 memory cells x 10 pulse/s x 16 bit, i.e. 12.8 Gbyte/s. On-detector vetoing may not necessarily lower these rates much - a memory cell freed by a vetoed pulse may be used by data from one of the remaining 2700 pulses a train consists of. The PC-layer may reduce this data amount by additional software triggering, but this is not guaranteed. Figure 1 gives an overview of the different data products at European XFEL, as well as their flows and involved user roles, under the assumption that processing takes place within XFEL’s Karabo framework (Heisen, 2013). In addition to the high data rates, the Mpixel detectors’ on-sensor memory-cell and multi-gain-stage architectures necessary for the high dynamic range, pose unique challenges in detector-specific data corrections and calibration (Weidenspointner, 2012; Sztuk-Dambietz, 2013a). These challenges are addressed by providing a dedicated and thoroughly characterized set of test stands, which utilize continuous sources (Fe-55, X-ray tubes) as well as a pulsed setup: PulXar (Sztuk-Dambietz, 2013b), which is designed to produce X-ray pulses of 50-150 ns duration, within a 0.6 ms burst followed by a 99.4 ms gap. The radiation it produces thus closely matches the XFEL pulse structure. Additionally, simulation tools are being developed to assist in detector characterization (Bohlen and Joy, 2013). |
