ALBA Synchrotron
Layout
The overall layout of MSPD components is displayed above and positions of main components given below.
Physical separation between machine and beamline vacuum is achived by a 150 micron thick CVD window. An additional 320 micron thick CVD window is positioned ~20 cm upstream to reduce heat load. At the end of the OPTICS hutch, 254 micron Be windows are positioned as beamline UHV-air interface.
ID center | 0 m |
FE fix aperture mask | 10.6 m (14.4 x 3.9 mm2 H x V) |
FE variable aperture slits | 14 m (max 19 x 4.9 mm2 H x V) |
Gate valve of Front End FE | 18.2 m |
CVD window | 18.9 m (Front End-Beamline Optics interface) |
Collimating/Focusing Mirror | 21 m |
White Beam Slits | 22.9 m |
White Beam Fluorescence screen | 23.6 m |
Double Crystal Monochromator | 24.8 m |
Monochromatic Beam Slits | 25.6 m |
Be windows | 28.3 m (Beamline Optics UHV-air interface) |
Pre KB slits | ~29 m |
KB-mirror (vertical) | 29.9 m |
KB-mirror (horizontal) | 30.3 m |
HP station 1 | 31 m |
Pre PD slits | ~34 m |
PD station 2 | 35 m |
Collimating/focusing mirror
The white beam Mirror either collimates or focus the beam in vertical direction. Collimating the beam reduces the white beam divergence down to ~15 microradians (the residual divergence is essentially induced by slope errors of the mirror surface), thus improving the energy resolution after the monochromator. The mirror bending mechanism allows focusing the beam on the Powder Diffraction station, which is necessary when operating with the Position Sensitive Detector. Highest angular resolution over a wide 2Theta range is obtained with the Multi Analyzer Detection Setup and collimated beam. The radius of curvature for focus on PD and collimated modes are 10 km and 21 km , respectively.
The mirror is a 1200 long, 95 mm wide and 70mm thick single crystal block of silicon. It has three eeffctive stripes (uncoated Si, coated Rh and Pt) to adapt reflectivity and harmonic suppression within specific energy ranges. The working angle is fixed to 2 mrad grazing incidence.
Additionally, the mirror serves to reduce the heat load on the monochromator. It is indirectly cooled by two independent water circuits. Heat load is evacuted through water circulating pipes brazed to copper blocks partially immersed into grooves containing a liquid mixture of Ga-In-Sn.
Above 40keV, where reflectivity dropps down, the mirror must be removed and the white beam from the source directly impinges the monochormator. Vertical aperture is adjusted to mate the length of first crystal of monochormator and to reduce heat load. All mirror downstream components can be adjusted in height for either mirror or unmirror mode.
The mirror vessel and moving mechanism was manufactured by CINEL (Italy), the mirror block and bending mechanism by Winlight (France).
Fix exit Double Crystal Monochromator (DCM)
Energy selection is achieved through two successive Bragg reflexion of silicon (111, d-spacing 3.135 Angstroem). To preserve energy resolution and flux under high heat load, the crystals are externally cooled with liquid nitrogen.
Energy resolution is ΔE/E ~2 10-4, taking into account white beam divergence and Darwin Width. The length and the shadowing of the 2nd crystal limit the energy to 50keV and 7keV, respectively. The pitch of the second crystal is finely tuned by a piezo actuator. Outcoming versus Incoming beam ratio is continuously maintained through an electronic module, so called MOCO for MOnochromator COntroller.
The DCM was manufactured by BRUKER (Germany)
Type | Si(111) DCM with long 2nd crystal |
Fix Exit Gap Offset | 20 mm |
Absorbed power | 670 W (worst-case conditions) |
KB mirrors
For High-Pressure experiments, both a small beam spot and a high energy are required. The former triggers the maximal pressure achievable in Diamond Anvil Cells, the latter warrants enough transmission through the massive diamonds exerting the pressure on the sample. Focusing the beam down to a dozen micron beam size is obtained using Kirkpatrick-Baez (KB) mirror system. On BL04-MSPD, the KB system parameters have been optimally selected for 30keV operation, but ensures proper beam focus in the 20-50 keV energy range.
The small beam size offered by KB system is used as well for Micro Diffraction experiments in transmission geometry.
The KB system has been manucaftured by Irelec (France)
Vertical Focusing Mirror | Horizontal Focusing mirror | |
Type | Elliptically bent mirror | Elliptically bent mirror |
Substrate | Si | Si |
Coating material | Multilayer | Multilayer |
d-spacing | 2.97 nm | 2.56 nm |
Number of W/Si layers | 110 | 150 |
Angle of incidence | 5 - 10 mrad | 5 - 10 mrad |
Mirror length | 300 mm | 300 mm |
Reflectivity | ||
20 keV | 75% | 75% |
50 keV | 90% | 90% |
Mean resolution ΔE/E (20–50 keV) | 2.5% | 1.8% |
Beam size at HP station
The beam spot at the HP station is surveyed every time we configure the beamline with KB mirrors. It is achieved using a camera looking at a direct beam illuminated fluorescence screen. Optimization of the beam spot is perfomed by tuning the pitch angle and the bending radius of the vertical and horizontal focusing KB mirrors.
Refinement of the projections clearly reveals the Lorentzian character of the beam profile in horizontal and vertical directions causing the beam spot to extend up to 75 microns at 10% maximum. The tails are supressed by inserting a pinhole of variable diameter before the sample.
