## 4 Experimental Stations
### Experimental Station Alvra
#### 4.1.2 ESA Prime and Flex  
The techniques introduced in Section 4.1 will be applied at two instruments, which are located in line with the X-ray beam: ESA Prime and ESA Flex (see Figure 15). Due to the bendable KB mirrors the X-rays can be focussed at either instrument, with the minimum focus of 1.5 \(\upmu\)m achieved at ESA Prime. Both instruments can be used with the optical laser for pump-probe experiments, with an anticipated time resolution of better than 50 fs [108]. ESA Prime is chamber that can be operated under vacuum, He, or neutral atmosphere and combines a large 2D 16 M JUNGFRAU scattering detector [159, 160, 161] and a dual-crystal [PERSON] X-ray emission spectrometer [162, 150, 163]. This allows experiments to be performed using both scattering and emission techniques simultaneously, which has proven to be a powerful combination for molecular [156, 157] and protein [158, 155] samples. The chamber has the possibility of using different types of sample injectors, including several specifically for SFX sample delivery [135, 164]. The expected achievable resolution of the crystallography measurements at 12.4 keV is better than 1.5 A (\(Q_{\mathrm{max}}=7\) A\({}^{-1}\)) and the X-ray spectrometer will be capable of measuring the full photon energy  
Figure 14: Schematic layout of the X-ray optics at the Aramis-1 beamline. Note the compound refractive lenses (CRLs) are a possible future upgrade. range of SwissFEL resonantly, with non-resonant measurements from 1-2 keV. This energy range is shown in Figure 16 with the elements labelled and the available analyzer crystals shown (see Table 3). The Bragg angle range covered by the spectrometer is from 40\({}^{\circ}\) to 80\({}^{\circ}\). Thanks to the dual-crystal design this spectrometer is capable of measuring multiple signals simultaneously, for example the K\(\alpha\) and K\(\beta\) X-ray emission from a 3\(d\) transition metal. The detector used for these measurements is a 4.5 M JUNGFRAU, which consists of 9 \(\times\) 0.5 M modules in a linear geometry with an area of 4 \(\times\) 72 cm. This allows the detector to cover all possible Bragg angles without requiring motion of the detector. The regions of interest containing the X-ray signals can be read out without reading out the entire 4.5 M detector. Due to the excellent noise characteristics of the detector, this spectrometer will be capable of single-photon sensitivity below 2 keV when operated in a high gain mode [159; 165]. The scattering or serial femtosecond crystallography experiments benefit greatly from the per-pixel dynamic gain switching of the JUNGFRAU detector, which has 3 levels of gain, resulting in a dynamic range of 10\({}^{4}\) photons at 12 keV. This gain switching occurs automatically, allowing the detector to handle transparently the broad range of incident intensities expected at SwissFEL. Further details on the JUNGFRAU detector can be found in Section 4.3. The detector is mounted on the back flange of the ESA Prime chamber, and has two holes to allow the beam to pass through the detector. This will allow the detector to be positioned in two scattering geometries: one where the beam is centered on the detector, to allow for fully symmetric scattering measurements, and one where the beam is close to one edge of the detector, which increases the scattering range of the detector, while simultaneously increasing the maximum accessible Bragg angle of the von Hamos spectrometer. The minimum sample-to-detector distance is fixed at 10 cm. ESA Flex is a flexible instrument that allows users to build up the experiment as required. It is mounted on a motorized table, allowing user-supplied chambers to be installed for the measurement. ESA Flex also includes a configurable X-ray spectrometer that can be mounted in a variety of positions to measure a range of scattering angles, in both vertical and horizontal geometries. The 3-crystal spectrometer can be used from 40\({}^{\circ}\) to 85\({}^{\circ}\) Bragg angles, and uses a 1.5 M JUNGFRAU pixel detector.