## 8 The SCS Instrument
### SCS Instrumentation and Capabilities  
One of the major goals of the technical design was to implement a diverse platform for spectroscopy and coherent scattering techniques that is realized in a modular instrumentation of experiment stations and detectors. The mirror benders of the SCS Kirckpatrick-Baez refocusing optics deliver the beam to two X-ray interaction regions separated by 2 m (see Figure 7). This allows not only a small beam focus of 1-2 \(\upmu\)m for CDI experiments but also a variable beam diameter of up to 500 \(\upmu\)m. In this way, time-resolved spectroscopic studies can be carried out making the best use of the high-average photon flux without further beam attenuation for avoiding sample damage. The SCS instrument comprises two distinct experimental setups, the Forward-scattering Fixed-Target (FFT) chamber and the XRD chamber. Both chambers have the same mechanics on their base that locks to three fixation points on the floor, one set per interaction region. This allows for faster exchange of experiment stations and reproducible repositioning of the chambers. The FFT chamber is optimized for forward-scattering geometries such as XAS in transmission, small-angle X-ray scattering (SAXS) and CDI experiments. Besides optical and THz beam delivery the sample environment encompasses static magnetic fields up to 0.5 T and a fast sample scanner that fits 50 \(\times\) 50 mm\({}^{2}\) sample arrays. The diffraction signal from the samples is collected downstream on the primary area detector, DSSC. The detector is mounted on a girder with a 5 m long translation stage. The closest sample-detector distance is 350 mm, corresponding to spatial frequencies near the wavelength limit of a few nm at soft X-ray energies. Objects of up to 3-5 \(\upmu\)m in diameter can be reconstructed using CDI at a sample-detector distance of 5 m and photon energies below 1.5 keV. The missing low-q data passes through a hole in the center of the detector and is recorded downstream as an integrated sample transmission signal. Since the monochromatic beam intensity jitter is large, data collected from low intensity pulses can be vetoed using the DSSC detector [33]. In this way, the signal to noise level of the data can be improved and data acquisition time is optimized. The XRD chamber enables a range of time-resolved spectroscopy and scattering methods for which a variable scattering angle is needed. The most relevant techniques are time-resolved XRD and RIXS as well as nonlinear X-ray studies (stimulated emission and scattering). The XRD setup is equipped with a diffractometer where a diode array can be rotated by nearly \(\pm\)180\({}^{\circ}\) in the horizontal scattering plane. The sample motion system provides six degrees of freedom and enables temperature-dependent studies between room temperature and cryogenic temperatures (liquid He cryostat). A detector flange with 90\({}^{\circ}\) continuous rotation can interface with large detectors and spectrometers. The Heisenberg-RIXS (hRIXS) User Consortium is contributing a high-resolution spectrometer (\(\Delta\)E/E = 0.25 - 1 \(\times\) 10\({}^{-4}\)) that facilitates state-of-the-art RIXS experiments with unprecedented time-resolution at the SCS instrument. The 5 m long hRIXS spectrometer can rotate around the sample position, hovering 50 \(\upmu\)m above a high-planarity floor (250 \(\upmu\)m peak-to-valley over 37 m\({}^{2}\)) on air pads. Both experiment chambers are designed for solid targets and operate in the 10\({}^{-9}\) mbar pressure regime depending on the detector vacuum. The chambers are equipped with a sample transfer system for exchanging samples under vacuum conditions. Optical laser delivery can be either collinear to the X-ray beam or arranged in off-axis geometry. THz generation and focusing takes place close to the interaction region and temporal diagnostics at the sample interaction point is realized. The hRIXS  
Figure 7: Schematic outline of the SCS scientific instrument at the SASE3 FEL.