## 5 The SPB/SFX Instrument
### SPB/SFX Instrumentation and Capabilities  
The SPB/SFX instrument is a 3 to 16 keV, forward scattering instrument [61] with a 1 \(\upmu\)m-scale and a 100 nm-scale focus in the upstream interaction region [69; 70], and optics to refocus the upstream focal point to a second interaction region further downstream (about 12 m) in the experiment hutch. This refocused beam allows for a second, in series, experiment to be performed simultaneously with a measurement in the upstream interaction region (see Figure 4). The Serial Femtosecond Crystallography (SFX) User Consortium provides the vast majority of the instrumentation for the downstream interaction region including, but not limited to, a 4 Mpixel detector (AGIPD) and an alternative detector (Jungfrau), the refocusing CRLs, sample delivery technologies (largely liquid jet delivery in various forms and fixed target systems) as well as various diagnostics and sundry apparatus. The 1 \(\upmu\)m-scale and 100 nm-scale focal spots for the upstream interaction region of the SPB/SFX instrument are to be produced by mirror optics due to their high transmission and potential for making very neat and well confined focal spots. The mirrors are all designed with 950 mm clear aperture, with working angles of 4 mrad and 3.5 mrad, respectively. Figure 4: Overview schematic of the SPB/SFX scientific instrument at the SASE1 FEL beamline. The sketch indicates major instrumentation items installed in the photon beam transport tunnel, optics and experiment hutch. Not shown is the PP-laser instrumentation. The 100 nm-scale design is a traditional Kirkpatrick-Baez (KB) design. The 1 um-scale mirrors are four-bounce--with a plan horizontal mirror followed by a focusing ellipse in the horizontal and then a focusing vertical mirror with a plane vertical mirror. This four bounce design mitigates vibrational issues and a large displacement from the direct beam over the long (\(\sim\)24 m) mirror to interaction region distance. For early user operation in 2017, the mirrors will not yet be installed. Instead, Beryllium compound refractive lenses (CRLs) will be used to produce an approximately 2.5 um spot in the interaction region. After mirror installation, the CRL unit will be moved to the refocusing position and new lenses installed to refocus the upstream spot to \(\sim\)3-5 um in the second interaction region downstream. In addition to focusing elements, a variety of beam conditioning apparatus (slits, apertures and attenuator) will be installed to aperture the beam upstream of the optics (the so-called power slits), clean up tails and streaks from the optics immediately downstream of them (the so-called cleanup slits) and apertures near the focal plane that further clean up the beam (termed apertures and will likely be sacrificial). This beam conditioning is essential for single particle imaging where a very neat, clean and well-understood beam is necessary for the successful observation and interpretation of the weak diffraction data collected. The primary 2D detector at SPB/SFX is a 1 Mpixel AGIPD detector [31]. It will be mounted in a vacuum chamber directly attached to the upstream sample chamber. Using a longitudinal translation, it can be placed as close as 129 mm from the interaction region, resulting in a better than 0.2 nm geometrical resolution limit for 9 keV photon energy. It can also be placed downstream as far as 6 m from the interaction region, allowing for appropriate sampling of diffraction data from samples as large as almost 1 um at the lowest energies. The detector mechanics consists of four panels mounted on x-y-translations to adjust the central hole for letting the X-ray beam pass. The destructive nature of these experiments and the high repetition rate of the European XFEL necessitate rapid delivery (and replenishment) of sample at the interaction region. Furthermore, for biological systems the samples must be appropriately hydrated and handled to ensure an intact and representative sample is brought to the XFEL beam.