The ESRF machine is routinely operated at 6 GeV electron energy with a maximum current of 200 mA. The horizontal source emittance is 3.8 10-9 m.rad and the coupling is usually 1%. Beamline ID21 is installed on a 4.8 m long low beta straight (small source but larger divergence). The larger horizontal divergence limits the heat load on the first optical components by spreading the power over a larger surface.


RMS Photon source parameters
  7.0 keV 2.0 keV
Horizontal source size [µm] 50 50
Vertical source size [µm] 4.1 4.6
Horizontal source divergence [µrad] 108 109
Vertical source divergence [µrad] 10.8 19.8


The straight section is equipped with 3 different insertion devices: Two in-phase 42 period undulators and one 32 period. The two U42 can be used simultaneously for a gain in flux of at least a factor of 2 . The U32 offers a significant gain for the analysis of 3d transition metals (4-8KeV) as it provides two times more flux compared to a single U42.


On–axis brilliance of the fundamental (n=1) and third harmonic (n=3) of the insertion devices used on ID21.


ID21 is a windowless UHV beamline. The white beam from the undulatory source is conditioned in the lead shielded optics hutch principally by means of a fixed exit double mirror system (M0), acting as a low band-pass filter. The grazing angle of this device can be varied from 7 to 20 mad using either Rh, Si, or Ni reflective coatings. The Si coating is usually used to cover the 2-4 KeV range, the Ni coating to cover the 4-7.5 KeV, and Rh for energies higher than 7.5 KeV.