Optic scheme

ID24-DCM is a new instrument replacing the historical energy dispersive XAS-S branch of ID24. ID24-DCM benefits from a photon flux that is up to four orders of magnitude greater than BM23 and accommodates the most demanding experiments. The main characteristics of this beamline are listed in Table 2. It couples a bright undulator X-ray source with a fixed-exit double-crystal monochromator with very high angular resolution specifically designed for spectroscopic purposes. As today, the ID24 undulator X-ray source is composed of two U27 and one U27/U32 in revolver mode. In 2025, they will be replaced by two new 2.3 m long U27/U32 revolver undulators (minimum gap 11 mm). The DCM is combined with two harmonic rejection mirrors positioned between the monochromator and the undulator. KB focusing mirrors (Pt-coated) are employed to achieve micron to sub-micron (0.5 x 0.5 µm2) spatial resolution. The optical scheme of ID24-DCM is fully optimized for the EBS and permits to perform nano-, long-range-, time- and energy-resolved EXAFS (one EXAFS/second over 1000 eV) in a wide energy domain from 4.5 to 45 keV. 

 

Table 2: ID24 main characteristics.

Source

U27, U32

Slits

0.3-0.6x0.5 mm2

Harmonic rejection mirrors

Fixed exit double mirrors 2-4 mrad Si/Pt/Rh stripes (MH2/MH3)

Monochromator

Fixed exit Double Crystal Monochromator Si(111) (311)

Focusing mirrors

Pt coated mirrors in KB geometry (2-8 mrad inclination)

Energy range

4.5-45 keV

Beamsize

0.5x0.5 µm2 to 1x1 mm2

Flux (ph/sec)

3x1011 – 2x1013

Time resolution

one EXAFS/sec

one XANES/0.3 sec

Additional detection schemes

Ionization chambers, diodes

µXRF using a single-element Vortex coupled to a polycapillary, multi-element fluorescence detector

5-crystal analyzer system (5-28 keV)

Foreseen for 2025: Von Hamos spectrometer designed by ID20

XRD (Pilatus 2 M)

Pressure ruby luminescence system

Microscope for sample visualization

Experimental hutch:

The experimental hutch of ID24-DCM, that is located ~60 m from the source, comprises a polished granite floor on top of which mobile granite blocks can be freely positioned using air pads. The individual granite blocks are optimized for limited and defined sample environment and detector systems. The mobile blocks are then fixed and fine positioned along the X-ray beam on a reference L-shaped granite block, that also hosts the first ionization chamber, a fast shutter and the KB-system. The incidence angle of the two KB mirrors can be varied between 2 to 8 mrad allowing XAS operation in focused mode from 4.5 to 45 keV. The KB mirrors yields to a stable focal spot of less than 0.5x0.5 µm2 (FWHM) independent of the incoming energy and at a distance of 0.5 m from the centre of the second horizontal focusing mirror, which is a significant improvement of the spatial resolution compared to the former ID24-S (varying from 5 x 5 µm2 FWHM at 7 keV and 10 x 10  µm2  FWHM  at 12 keV). By adjusting the focusing distance between 0.4 m and 1 m the focal spot size at ID24-DCM can be selected between 0.4x0.4 µm2 and 2x2 µm2.