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BL4-2 Hardware Overview

The beamline 4-2 at SSRL is a dedicated experimental station for small-angle x-ray scattering and diffraction (SAXS) experiments. It focuses on the application of SAXS in the areas of structural biology and biophysics and provides state-of-the-art facilities for a large variety of different experiments.


The beamline uses the central part of the radiation fan producesd by a 20-pole, 2 T wiggler as its source. A Rhodium coated mirror at mid-point between the source and the detector provides a 1:1 image of the source at the detector plane. The monochromator with the choice of either a pair of Si111 crystals or a multilayer pair as diffractive elements is LN2 cooled. The beamline end-station features a pin-hole SAXS camera with a set of beam defining/collimating slits  and two sets of guard slits. The evacuated flight tube has a choice  of seven different sample-to-detector distances that can be semi-automatically changed and houses at the downstream end a small beamstop with integrated photodiode for measuring the transmitted photon flux. For the data collection there are two large area detectors available: a Pilatus3 X 1M pixel array detector and a gap-less Rayonix225 HE CCD detector. 

Basic beamline parameters:

Source Type insertion device, wiggler
Optics focusing bent cylinder mirror,
Rh coated (cutoff energy 17.5keV)
upward reflecting,
Magnification 1
Monochromator Si111
Mo/B4C Multilayer
energy range 6 - 17 keV (for Si111)
8 - 14 keV (for Multilayer)
energy resolution 5 x 10-4 (for Si111)
3 x 10-2 (for Multilayer)
flux (in full beam) 3 x 1012 ph/s (for Si111)
1 x 1014 ph/s (for Multilayer)
spot size at detector (0.2 x 1.0) mm2
Detectors Dectris Pilatus3 X 1M
Rayonix MX225HE
sample-detector-distance 0.25 - 3.5 m,
variable in seven discrete steps
x-ray source-detector-distance 32 m
typical q - range [Å-1]
(at 11keV)
0.045   - 3.6   (for 0.25m)
0.024   - 2.2   (for 0.5m)
0.016   - 1.7   (for 0.75m)
0.010   - 1.0   (for 1.1m)
0.0068 - 0.67 (for 1.7m)
0.0045 - 0.46 (for 2.5m)
0.0034 - 0.33 (for 3.4m)