## 4 Experimental Stations
### Experimental Station Alvra
#### 4.1.2 ESA Prime and Flex
When used with large Bragg angles (>85\({}^{\circ}\)) and segmented X-ray crystals [150] this spectrometer is capable of 100 meV energy resolution. ESA Flex is shown on the left of Figure 15.  
Figure 15: The instruments installed at Experimental Station Alvra (ESA). The ESA Flex instrument **(left)** is a flexible X-ray spectrometer that can be positioned according to the experimental requirements. The ESA Prime instrument **(right)** is a combined scattering and spectroscopy chamber designed to allow experiments in neutral, vacuum, or He atmosphere. ESA Prime is focussed on allowing experiments to be performed in the 2–5 keV tender X-ray regime. The crystals available for both [PERSON] spectrometers are listed in Table 3. As noted in the caption of Table 3 the crystals are either curved or segmented. In general the curved crystals provide excellent focusing capabilities (2 \(\times\) X-ray spot size on the sample in the focusing direction), with some loss of energy resolution due to the crystal curvature, while the segmented crystals provide focal spots of 2 mm (2 \(\times\) 1 mm segment size) but much improved energy resolution (essentially the Darwin width of the crystal reflection). The contributions of the various components in the spectrometer to the final energy resolution, including X-ray focal spot, detector pixel size, and geometry Bragg angle, can be found in reference [150]. Figure 16: The tender X-ray energy range covered by the ESA Prime X-ray spectrometer. The dashed lines are the various crystals available for use with the spectrometer (see Table 3), covering the full range of energies at the various Bragg angles available in the spectrometer. The energies of various X-ray emission transitions are also marked to provide a sense as to what elements can be measured in this photon energy range. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Crystal** & **Miller Indices** & **2d Spacing** & **Radius of Curvature** & **Type** & **Crystal Area** \\ \hline TiAP & 002 & 12.95 Å & 25 cm & Curved & 5 \(\times\) 10 cm \\ ADP & 101 & 10.64 Å & 25 cm & Curved & 5 \(\times\) 10 cm \\ PET & 002 & 8.742 Å & 25 cm & Curved & 5 \(\times\) 10 cm \\ InSb & 111 & 7.4806 Å & 25 cm & Curved & 5 \(\times\) 6 cm \\ SiO\({}_{2}\) & 1010 & 6.687 Å & 25 cm & Curved & 5 \(\times\) 10 cm \\ Ge & 111 & 6.532 Å & 25 cm & 1 mm segments & 5 \(\times\) 10 cm \\ Si & 111 & 6.271 Å & 7 and 25 cm & 1 mm segments & 5 \(\times\) 10 cm \\ SiO\({}_{2}\) & 1120 & 4.912 Å & 25 cm & Curved & 5 \(\times\) 10 cm \\ SiO\({}_{2}\) & 1012 & 4.564 Å & 25 cm & Curved & 5 \(\times\) 10 cm \\ Ge & 220 & 4.0 Å & 25 cm & 1 mm segments & 5 \(\times\) 10 cm \\ Si & 220 & 3.840 Å & 25 cm & 1 mm segments & 5 \(\times\) 10 cm \\ Si & 311 & 3.274 Å & 25 cm & 1 mm segments & 5 \(\times\) 10 cm \\ Ge & 400 & 2.829 Å & 25 cm & 1 mm segments & 5 \(\times\) 10 cm \\ Si & 400 & 2.714 Å & 25 cm & 1 mm segments & 5 \(\times\) 10 cm \\ Si & 331 & 2.4916 Å & 25 cm & 1 mm segments & 5 \(\times\) 10 cm \\ Si & 531 & 1.836 Å & 25 cm & 1 mm segments & 5 \(\times\) 10 cm \\ \hline \hline \end{tabular}
\end{table} 
Table 3: List of von Hamos geometry spectrometer crystals available for use at either ESA Prime or ESA Flex. Note that higher-order reflections have been omitted for clarity. Curved means smooth crystals, segmented mean diced along the focusing axis, but perfect flat crystals along the dispersive axis [150].