Source and optics
The photon source of the FinEstBeAMS beamline is an Elliptically Polarizing Undulator (EPU).
|Magnetic structure||95.2 mm period, 26 periods,
14 mm minimal gap, 2.475 m magnetic length, maximum magnetic field 1.13 T
|Design||APPLE II design with permanent magnets|
|Energy (wavelength) range||4.5 - 1300 eV|
|Polarization||Linear, circular and elliptical|
The optical layout of the FinEstBeAMS beamline is based on the plane grating monochromator illuminated with collimated light.
|Collimating optics||Side cooled toroidal collimating mirror|
|Monochromator (cPGM)||Collimating plane grating monochromator with 2 plane gratings (92 and 600 mm/l) , internally cooled plane mirror
|Focusing optics||Toroidal mirrors. Focusing mirrors are used to switch the beam between branch lines by moving one or other one in front of the beam path.|
|Exit slit||Rectangular high precision slits|
|Re-focusing optics||Single ellipsoidal mirror|
|Photon resolution||ΔE/E up to 1 x 10E-4 (~2.3 meV at 10 eV, ~3.8 meV at 50 eV , ~40 meV at 400 eV)
|Flux at sample (focused)||10E9 - 10E13 ph/s (4.5 – 1300 eV) for E/ΔE~5000 (Maximum flux is measured around 100 eV.)
|Beam size at sample||200 x 200 μm2 (horizontal x vertical), 50 x 50 μm2 when limiting exit slit and baffles
Figure. Estimated photon flux at experiment for the 92 l/mm grating (curve at left, black colour) and the 600 l/mm grating (curve at right, red colour) for resolving power of 5000, i.e. 0.02% band width. Beamline acceptance was set at 1 mrad × 0.2 mrad, and it was assumed that the most efficient undulator harmonic is tuned for each photon energy. A ring current of 500 mA was used in these calculations. Solid squares and open circles show the first order flux for the two gratings after using filters of 200 nm thickness under the condition that the sum of the second and third order flux is 1% or less of the first order flux. Horizontal bars depict the energy ranges of the different filters.