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) |