Beamline construction
ASTRA is a compact beamline without Al or Be windows, which commonly are used to protect the vacuum of the storage ring.
The only window in the beamline is a thin polypropylene foil between the monochromator and the first ionization chamber. This beamline design allows challenging XAS measurements at low photon energies, e.g., at the Al K absorption edge.
Due to this straightforward and user-friendly concept without any additional optical components such as lenses or mirrors, ASTRA can be quickly aligned and easily operated.
Figure 1. ASTRA beamline construction.
Figure 2. ASTRA beamline photo.
Source
Radiation source in the ASTRA beamline is a double bend achromatic 1.3 Tesla bending magnet with critical energy of ~2keV.Beamline optics
In the front end section, the synchrotron beam is defined by two fixed apertures. Downstream from SOLARIS´s radiation shield wall a diagnostic module with a fluorescence screen and a wire-type X-ray beam position monitor (XBPM) allows to visualize and determine the position of the white beam and its profile.
A compact differential ion pump maintains the pressure difference of 4–5 orders of magnitude between the diagnostic module (ultra-high vacuum chamber, base pressure in the 10-10 mbar range) and the monochromator (high-vacuum system, 10-6 mbar range).
The monochromator is a modified Lemonnier type double crystal monochromator (DCM). The first and second crystals are mounted parallel on a motorized rotation stage (range ~ 15° - 65°) driven by a stepper motor (angular resolution ~ 0.0001°). The Bragg axis rotation is mechanically linked to a translation of the second crystal perpendicular to its surface via a fixed curved cam, providing a fixed position of the exit (monochromatic) beam during energy scanning.
Energy range (keV) | Crystal | 2d spacing (Å) | Accessible K absorption edges | Beam size at sample FWHM | Flux at sample (ph/sec) at 450 mA |
---|---|---|---|---|---|
0.5 - 1.8 | KAP (100) + multilayer | 26.63 | Na, Mg, Al | 10 x 1 mm | 4.0·108 |
0.85 - 1.6 | Beryl (10-10) | 15.95 | Na, Mg | 10 x 1 mm | 3.0·108 |
1.8 - 3.7 | InSb (111) | 7.48 | Si - K | 10 x 1 mm | 1011 |
2.0 - 7.6 | Si (111) | 6.27 | P - Fe | 10 x 1 mm | 3.0·1010 |
3.4 - 12.0 | Ge (220) | 4.00 | K - Zn | 10 x 1 mm | 5.0·1010 |
5.0 - 15.0 | Si (400) | 2.71 | V - Se | 10 x 1 mm | cooming soon |