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The European X-ray Free Electron Laser (EuXFEL) began its user operation five years ago, opening and offering new research possibilities. The facility delivers high brilliance, ultra-short, spatially coherent x-ray pulses with a high repetition rate to six instruments (FXE, SPB/SFX, MID, HED, SCS and SQS) by means of three different beamlines (SASE 1, SASE 2 and SASE 3). One of the first detectors used for early-stage experiments was the Adaptive Gain Integrating Pixel Detector (AGIPD), custom designed to meet the challenging needs of scientific instruments. The AGIPD is a megahertz-rate integrating hybrid megapixel camera with a per-pixel adaptive gain amplification, allowing the integration of up to 104 of 12 keV photons per pixel in its low gain stage. Currently, three scientific instruments, namely SPB/SFX, MID and HED employ the AGIPD systems, the latter mentioned using a prototype, half-megapixel camera with an upgraded version of readout ASICs. The AGIPDs at EuXFEL are successfully used for experimental techniques like serial femtosecond crystallography, MHz single particle imaging, MHz x-ray photon correlation spectroscopy or MHz diffraction of materials under high pressures in a diamond anvil cell. Since September 2017, the AGIPD is continuously used and has become an established detector technology, with further advancements and developments planned. Delivering quality experimental data requires reliable and reproducible detector characterisation and calibration that have to be performed regularly with a continuous improvement of correction methods in close collaboration with scientific instruments. This work summarises five years of experience operating the AGIPD detectors at the EuXFEL scientific instruments. It gives an overview of scientific capabilities and examples of successful studies performed with AGIPD detectors. Moreover, challenges concerning detector calibration and characterisation are presented.
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