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The European X-ray Free Electron Laser (EuXFEL) is a light source of the 4th generation which provides spatially coherent ultrashort X-ray pulses at high rate. The facility enabled unprecedented advancement in fundamental research, but also needed new detectors to fit the EuXFEL requirements, such as single photon resolution, large dynamic range, and high repetition rate: three 2D megapixel detectors have been developed to cope with the demanding environment. The DEPleted Field Effect Transistors (DEPFET) Sensor with Signal Compression (DSSC) detector is one of them. The parallel readout from each pixel is performed employing a dedicated Application Specific Integrated Circuit (ASIC). The generated data flow is read through a 2-stage Field Programmable Gate Array (FPGA)-based Data AcQuisition (DAQ) chain: the Input Output Board (IOB) controls the primary readout from 16 ASICs and serializes data on high-speed links that are sent to the Patch Panel Transceiver (PPT). It is also responsible for the clock distribution and timing control of the front-end and switched power channels. The PPT reorders and forwards the received data toward the EuXFEL back-end, and allows remote control over the whole DAQ. A first DSSC camera, based on miniaturized silicon drift detectors (mini-SDD) has been available for users’ experiments since 2019, and a second DEPFET-based camera is under construction. The IOB firmware has been thoroughly reviewed and modified to cope with the new DEPFET sensors’ physics and to improve the performance of both the mini-SDD and DEPFET versions. We present an overview of the DSSC, focusing on the DAQ, highlighting the main properties of the environment where the detector operates. We assess the firmware improvements introduced, with a particular focus on the IOB, and present the results obtained in comparison to the original firmware.

The advent of X-ray free-electron lasers (XFELs) has revolutionized fundamental science, from atomic to condensed matter physics, from chemistry to biology, giving researchers access to X-rays with unprecedented brightness, coherence and pulse duration. All XFEL facilities built until recently provided X-ray pulses at a relatively low repetition rate, with limited data statistics. Here, results from the first megahertz-repetition-rate X-ray scattering experiments at the Spectroscopy and Coherent Scattering (SCS) instrument of the European XFEL are presented. The experimental capabilities that the SCS instrument offers, resulting from the operation at megahertz repetition rates and the availability of the novel DSSC 2D imaging detector, are illustrated. Time-resolved magnetic X-ray scattering and holographic imaging experiments in solid state samples were chosen as representative, providing an ideal test-bed for operation at megahertz rates. Our results are relevant and applicable to any other non-destructive XFEL experiments in the soft X-ray range.