## 4 Experimental Stations
### Experimental Station Alvra
#### 4.1.1 X-ray Optics and Diagnostics  
A detailed summary of the X-ray optics is given in Section 3.1 and of the X-ray diagnostics in Section 3.3, here we will focus on the aspects specific to Alvra. The layout of the Aramis-1 beamline is shown in Figure 14. The key components are two horizontal offset mirrors that work at incidence angles of 6 mrad, for a total deflection angle of 12 mrad, followed by a fixed-exit double-crystal monochromator which deflects the beam vertically, and two harmonic rejection mirrors which return the beam vertically to its original beam path. This allows both monochromatic and pink beam paths to be identical downstream of the optical elements (see insets A and B in Figure 6). The monochromator contains 3 crystal pairs, which include Si(111), Si(311), and InSb(111) to cover the full Aramis photon energy range with varying bandwidth and energy resolution. The final optical components are two KB mirrors, with a working distance of 1.5 m from the center of the last mirror. These achromatic focusing optics are capable of achieving a 1.5 m focal spot (FWHM). The optics have been designed to be used over the full range of the Aramis X-ray energies: 1.77-12.4 keV.  
Figure 13: The Experimental Station Alvra X-ray hutch. The X-rays come from the Optics hutch, to the left of the schematic and move from left to right in the figure. The various components located in the hutch are labelled. The ESB beam pipe chicane is a motorized beam pipe that can be moved vertically to either allow the XFEL beam to be delivered to Bernina, or to allow easy access to the Alvra instruments. The same motorized elements will be used in a similar fashion for an ESC beam pipe chicane in the future.  
One crucial aspect of the Aramis-1 beamline is to allow for measurements in the 2-5 keV energy range. At these photon energies the optics will all function flawlessly at the higher harmonic energies as well, providing no discrimination for these photons. The HRM optics allow the incidence beam angle to be tuned, allowing the harmonics to be greatly suppressed when the monochromator is used. Calculations for the HRMs indicate we can achieve a contrast of at least \(10^{-3}\) for these higher photon energies, with up to \(10^{-5}\) achievable under certain optics configurations [88]. Note that the expected harmonic contribution from the XFEL is \(\sim\)1% for each subsequent odd harmonic, which could result in up to \(10^{9}\) photons per pulse in the 3 rd harmonic if no suppression is used.  
The photon diagnostics described in Section 3.3 have all either been tested with or designed for X-ray photon energies above 4 keV. This implies the development of these diagnostics components in the 2-4 keV range will need to be evaluated once SwissFEL is operational. Several of the elements are capable of lower energy measurements, including the gas-based photon beam intensity and position monitor (PBIG and PBIM). The solid photon backscattering monitors (PBPS) can be used with thinner scattering films, such as 200 nm of Si\({}_{3}\)N\({}_{4}\), which will allow them to be used at lower photon energies.