Beamline layout/specifications

P10 uses a 5m long U29 undulator device. The figure (Fig. 4.1.1 of the PETRA III TDR) shows the calculated brilliance for the PETRA III standard undulator for low and high beta source configurations at 2m or 5m length.

This table (Tab. 4.1.1 of the PETRA III TDR) shows the nomimal parameters for PETRA III undulators.

Flux calculations for the P10 beamline (by XTRACE) in low beta configuration using a Si(111) monochromator. The X-ray energy was set to 8keV and the source to slit distance was set to 90m for these calculations. The important 'ball park' number for coherent scattering experiments in low beta configuration is 109 cps in a 10x10µm2 slit at 90m. The low beta full beam size at this distance is 5.2 x 1.1mm2.

Flux calculations for the P10 beamline (by XTRACE) in high beta configuration using a Si(111) monochromator. The x-ray energy was 8keV and the source to slit distance was 90m for these calculations. The important 'ball park' number for coherent scattering experiments in high beta configuration is 3 x 109 cps in a 10x10µm2 slit at 90m. The high beta full beam size at this distance is 1.8 x 1.1mm2.

P10 operates with an effective energy gap in between ~10.5keV to ~11.5keV since the specification for the minimum undulator gap of 9.5mm could not be reached. The actual minimum gap is ~9.8mm. This shifts the lower energy cutoff for the first harmonic to ~3.8keV (or ~11.5keV for the 3rd harmonic). The increase of the 1st harmonic cutoff is not a problem for P10 but the energy gap might cause problems for some experiments.

Flux measurements at P10:

P10 undertook an attempt to determine the delivered photon flux in December 2010. At this time the beamline was in a high beta configuration and PETRA III was running in a reduced current mode at 55mA. The measurements used an undulator gap of 16.525 and the monochromator was set to 8.05keV. An X-ray eye was used to check that the undulator setting was correct, i.e. no vertical beam splitting did occur. The mirrors were used to suppress the higher harmonics with an incident angle of ~0.158 degree. A calibrated PIN diode (H.-P. Liermann, P02, calibrated at APS) was used to measure the intensity. The measurements are in good agreement with the XTRACE calculations (~10% deviation).

Coherent flux estimate for P10 (8keV, Si(111), 90m):

These are estimates of the expected coherent flux or (in other words) the intensity behind a slit of a size, which matches the transverse coherence area. To make numbers comparable, here is the formula used for the transverse coherence length in these estimates:
xit = 1/(2 x √π) x R/(2.35 x sigma) x lambda
'lambda' is the X-ray wavelength, 'R' is the distance between source and slit and 'sigma' is the 1-sigma source size of PETRA III (see last two rows of table 4.1.1 above). Sometimes the coherence length is estimated using different prefactors, normally resulting in larger values.
At 90m from the source and at 8keV photon energy, the transverse coherence length is 277 µm in the vertical direction and 46 µm in the horizontal direction in low beta configuration. The predicted intensity behind a slit of this size is 1.3 x 1011 cps.