BL29 BOREAS
Beamline fOr REsonant Absorption and Scattering
The variable polarization soft X-ray beamline is dedicated to polarization-dependent spectroscopic investigations of advanced materials of fundamental as well as applied interest: namely magnetic, oxide, ferroelectric or polymer materials for micro- and nano-technology devices, usually in the fields of spintronics and information storage.
The beamline is equipped with two cutting edge end-stations, a High-field vector magnet (HECTOR) for absorption methods and a UHV reflectometer (MARES) for scattering and reflection approaches, which allow spectroscopic studies under high magnetic fields (from 2 up to 6 Tesla) at sample temperatures between 1.5 and 340K.
BOREAS beamline instrumentation and ambitious x-ray optical design at the service of these two complementary endstations make possible soft x-ray (magnetic) circular and linear dichroism (XMCD/XMLD) measurements and other related characterization techniques at the frontier of materials science studies.
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Status
User operation
The beamline and its first endstation, Hector vector magnet, are fully operational and open to users since May 2012. The scattering endstation is expected to be completed by summer 2014, and start operation end 2014.
The data quality so far is very encouraging on the beamline performance for XAS, XMCD measurements in a very extended energy range. Status update presentations (October 2013) are available here (staus slides) and here (slides2_oct2013).
Beamline characteristics
Photon energy range | 80 to >3000 eV |
Calculated flux at the sample (at a resolving power of 5000 and for 100mA current) |
5x1012 photons/s @ 150 eV 2x1012 photons/s @ 700 eV 1.5x1012 photons/s @ 1500 eV 5x1011 photons/s @ 2000 eV 1x1010 photons/s @ 3000 eV 1.5x109 photons/s @ 4000 eV |
Maximum resolving power |
15000 for 80 eV < E < 1500 eV 5000 for E > 1500 eV |
Beam size at the sample | variable between a minimum of 100(H)x20(V) micron2 and >1x1 mm2 |
The beamline is optimized for highest photon flux and energy resolution in the range between 150 eV and 2000 eV. However, the monochromator and undulator allow us to reach a lowest energy of 80 eV in circular polarization, thus covering the Si L edges. Above 2000 eV, the optics of the beamline has a reduced performance as compared to typical hard x-ray beamlines, but the flux and energy resolution should be high enough to perform x-ray absorption experiments at important edges (L edges of all the 4d metals, etc).
Here below are shown some plots of the typical beamline photon flux using the different gratings and mirror combinations available at the beamline, and for the various polarizations of the EPU. Flux values are estimated from intensity measurements using a AUXV100G diode downstream the last beamline optical component.
In the measurements, the accumulated storage ring current was around 100mA (September 2012 to February 2012), and nominal slit settings were used, i.e. 15 micron opening for the vertical entrance (VES) and exit slits(VXS). Resolving power is about 7500-10,000 with VES/VXS=15/15 micron slits. Higher resolving power, approx 15,000 or larger, can be attained for more extreme exit slit settings, such as 15/5 micron slit settings, whereas intensities are almost linear on the vertical exit slit opening (achieved vertical beam FWHM at the entrance slit is estimated to be typically within 5.5-7.5 micron range). A number of combinations, including choices between Gold or Nickel or Silicon(uncoated) stripes on the first plane mirror, slits, etc...can result in slightly different numbers, but these values are representative.
The EU71 undulator might be used as a wiggler for energies above the cut-off of the first harmonics (about 1000 eV), improving the flux in elliptical polarization especially for energies above 2000 eV. (This is still under exploration).