We present the development of the DSSC instrument: an ultra-high speed detector system for the new European XFEL in Hamburg. The DSSC will be able to record X-ray images with a maximum frame rate of 4.5 MHz. The system is based on a silicon pixel sensor with a DEPFET as a central amplifier structure and has detection efficiency close to 100% for X-rays from 0.5 keV up to 10 keV. The sensor will have a size of approximately 210 210 mm composed of 1024 1024 pixels with hexagonal shape. Two hundred fifty six mixed signal readout ASICs are bump-bonded to the detector. They are designed in 130 nm CMOS technology and provide full parallel readout. The signals coming from the sensor are processed by an analog filter, immediately digitized by 8-bit ADCs and locally stored in an SRAM, which is able to record at least 640 frames. In order to fit the dynamic range of about photons of 1 keV per pixel into a reasonable output signal range, achieving at the same time single 1 keV photon resolution, a non-linear characteristic is required. The proposed DEPFET provides the needed dynamic range compression at the sensor level. The most exciting and challenging property is that the single 1 keV photon resolution and the high dynamic range are accomplished within the 220 ns frame rate of the system. The key properties and the main design concepts of the different building blocks of the system are discussed. Measurements with the analog front-end of the readout ASIC and a standard DEPFET have already shown a very low noise which makes it possible to achieve the targeted single photon resolution for 1 keV photons at 4.5 MHz and also for 0.5 keV photons at half of the speed. In the paper the new experimental results obtained coupling a single pixel to an 8 8 ASIC prototype are shown. This 8 8 ASIC comprises the complete readout chain from the analog front-end to the ADC and the memory. The characterization of a newly fabricated non-linear DEPFET is presented for the first time.Index Terms-DEPFET, DSSC, silicon radiation detectors, X-ray detectors, X-ray free electron lasers.

The first DSSC 1-megapixel camera became available at the European XFEL in the Hamburg area in February 2019. It was successfully tested, installed and commissioned at the Spectroscopy and Coherent Scattering Instrument. DSSC is a high-speed, large-area, 2-D imaging detector system optimized for photon science applications in the energy range between 0.25 keV and 6 keV. The camera is based on direct conversion Si-sensors and is composed of 1024×1024 pixels of hexagonal shape with a side length of 136 µm. 256 ASICs provide full parallel readout, comprising analog filtering, digitization and in-pixel data storage. In order to cope with the demanding X-ray pulse time structure of the European XFEL, the DSSC provides a peak frame rate of 4.5 MHz. The first megapixel camera is equipped with Miniaturized Silicon Drift Detector pixel arrays. The intrinsic response of the pixels and the linear readout limit the dynamic range but allow one to achieve noise values of about 60 electrons r.m.s. at the highest frame rate. The challenge of providing high-dynamic range (~10 4 photons/pixel/pulse) and single photon detection simultaneously requires a non-linear system front-end, which will be obtained with the DEPFET active pixel technology foreseen for the advanced version of the camera. This technology will provide lower noise and a nonlinear response at the sensor level. The paper describes the The manuscript was submitted on 28.02.2021. The development described in this work was initiated, funded and coordinated by the European XFEL GmbH in the framework of the DSSC project.

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Ten detector modules based on monolithic 7-cell Si-drift detectors with integrated is about 300 eV and below 1 % between 4.5 keV and 18 keV, respectively. After irradiation with a total dose of ∼2 Mrad the resolution decreases by ∼40 %. By shielding the cell borders and JFETs from direct irradiation with usage of a Zr mask, a spectral peak-to-valley ratio of ∼1000 was achieved.

A silicon drift detector (SDD) was used for ex situ and time-resolved in situ¯uorescence X-ray absorption ®ne structure (XAFS) on lowconcentrated catalyst samples. For a single-element and a sevenelement SDD the energy resolution and the peak-to-background ratio were veri®ed at high count rates, suf®cient for¯uorescence XAFS. An experimental set-up including the seven-element SDD without any cooling and an in situ cell with gas supply and on-line gas analysis was developed. With this set-up the reduction and oxidation of a zeolite supported catalyst containing 0.3 wt% platinum was followed by¯uorescence near-edge scans with a time resolution of 10 min each. From ex situ experiments on low-concentrated platinumand gold-based catalysts¯uorescence XAFS scans could be obtained with suf®cient statistical quality for a quantitative analysis. Structural information on the gold and platinum particles could be extracted by both the Fourier transforms and the near-edge region of the XAFS spectra. Moreover, it was found that with the seven-element SDD concentrations of the element of interest as low as 100 ppm can be examined by¯uorescence XAFS.