## 2 Overview European XFEL
### The Experiment Hall and Ancillary Instrumentation
#### 2.4.1 Large Area Detectors for European XFEL  
Already in 2006 European XFEL launched a significant program for the development of large area detectors for FEL experiments, since it was clear that the requirements to detectors for FEL experiments in general and European XFEL specifically could not be fulfilled by existing devices [28]. General requirements include an integrating operation mode, enabling the detection of several X-ray photons per pixel and per pulse, very low noise, enabling to detect single X-ray photons, and a high dynamic range, enabling to count 10\({}^{4}\) or more X-ray photons in a single pixel. Specific requirements for European XFEL include the need for frame rates of up to 4.5 MHz, in order to be compatible with X-ray pulse delivery within the pulse train structure (compare Figure 2), high throughput, to collect as many images as possible per unit time, and radiation hardness. More recently, the possibility of vetoing specific events was added as a requirement. Three large projects were selected and are pursued together with external partners. Laboratory infrastructure, in particular for detector calibration and characterization, has been designed and is operated by the European XFEL detector group [29]. In addition, a few smaller projects consisted in modifying existing cameras, mostly designed for 10 Hz operation, and in upgrading the Gotthard one-dimensional strip detector [30] to 4.5 MHz repetition rate. In the following the three large area detector projects are described briefly.  
The Adaptive Gain Integrated Pixel Detector (AGIPD) is developed by a consortium led by DESY [31]. The main features of this detector are 200 \(\times\) 200 \(\upmu\)m\({}^{2}\) pixels, dynamic gain switching with 3 stages, a dynamic range of \(\sim\)10\({}^{4}\) at 12 keV, single photon detection (6\(\sigma\)) above 7 keV, in-vacuum operation, the capability of storing up to 352 images within the 600 \(\upmu\)s pulse train, and to read out these data in-between pulse trains. As sensor material 500 \(\upmu\)m thick Si is used. Two 1 Mpixel AGIPD devices constitute the primary 2D detectors at the SPB/SFX and MID instruments. A 4 Mpixel device is under development as part of the SFX User Consortium, as is a 1 Mpixel device with GaAs sensor for the HIBEF User Consortium.  
The Large Pixel Detector (LPD) is developed by a consortium led by STFC [32]. The main features of this detector are 500 \(\times\) 500 \(\upmu\)m\({}^{2}\) pixels, three amplifiers with different gain per pixel, a dynamic range of up to \(\sim\)10\({}^{5}\) at 12 keV, single photon detection (3\(\sigma\)) above \(\sim\)12 keV, the capability of storing up to 512 images within the 600 \(\upmu\)s pulse train, and to read out these data in-between pulse trains. As sensor material, 500 \(\upmu\)m thick Si is used. A 1 Mpixel LPD device will be employed at the FXE instrument, primarily for liquid scattering experiments.  
The DepFET Sensor with Signal Compression (DSSC) detector is developed by a consortium initially led by the Max-Planck-Society (MPG) [33]. The main features of this detector are hexagonal 236 \(\upmu\)m diameter pixels, a non-linear gain, a dynamic range of \(\sim\)6 \(\times\) 10\({}^{3}\) at 1 keV, single photon detection (5\(\sigma\)) above 0.7 keV, in-vacuum operation, the capability of storing up to 800 images withinthe 600 \(\upmu\)s pulse train, and to transfer up to 640 frames in-between pulse trains. The highest frame rate of the DSSC detector therefore is 6.4 kHz. As sensor material 300 \(\upmu\)m thick Si is used. One 1 Mpixel DSSC device is considered as the primary 2D detector for the SCS and SQS instruments. In a first phase, a simplified detector with 1 Mpixel Si drift diodes with reduced performance will be available for experiments.