Contact: Jim Viccaro,
+1 630.252.0464 (APS) or +1 773.702.1598 (The University of Chicago), viccaro@cars.uchicago.edu
A SAXS facility can only succeed if parasitic scattering is kept to a minimum.
This is achieved at 15-ID-D using a number of crossed slits at different distances from the source point.
The x-ray source is an APS Type-A undulator with a cooled double-bounce diamond (111) crystal monochromator.
Good SAXS data relies heavily on the ability to accurately photon fluxes incident on the sample, as well as the transmission through the sample.
A detector in the beam stop greatly simplifies the process of instrument alignment and provides ‘real time’ transmission monitoring during SAXS exposures.
Beamline Control and Historical Data
The 15-ID beamline is controlled via the distributed system known as EPICS.
User interface to optics motors as well as beam flux and beam position monitors is done through the graphical user software MEDM.
Historical records of important beamline parameters are constantly being recorded and are available for consultation.
In general, users of the 15-ID-D SAXS facility only need to do small adjustments or ‘tweaks’ to the beam delivery optics.
The MEDM / EPICS control is mostly used to align samples via the sample positioning motors.
A typical example of this is scanning a capillary sample through the beam – monitoring transmission to find the optimal sample position.
SAXS15id - Camera Control Version
The SAXS control program ‘saxs15id’ is a purpose-built package.
It is designed to allow the user to acquire SAXS exposures from samples using a CCD x-ray detector.
It takes account of incident and transmission x-ray fluxes and automatically integrates each SAXS/WAXS image into a one dimensional plot.
It is possible to take time sequenced SAXS measurements, or tie successive exposures in with one or two changing experimental variables - like sample position or temperature.
Saxs15id Data Files
With the ability to take SAXS exposures every five seconds or so, data can pile up at a reasonably fast rate.
This data is most usually burnt onto DVDs or CD-ROMS and taken home by the user.
Note: each SAXS/WAXS image requires from 0.5 to 2 Mbytes of disk storage.
There are four main types of file that are generated by users in normal operation:
- Image files – these binary files encoded in a format dictated by whichever CCD x-ray detector we are currently using.
One example of this is the Bruker SMART CCD format.
In the case of Bruker format – these files usually have a file names of the form: XXXXX.NNN where XXXX is any combination of alphanumerics (no spaces or special characters) and NNN is a three digit number such as: 003 or 144
- LOG files – these are ASCII files containing a record line for every transmission measurement or SAXS exposure.
This file should sit on the same sub-directory as the SAXS image files (see above). The naming convention for these files is XXXX.log
- SAX files – these are ASCII files containing all the camera parameters such as camera length, x-ray wavelength, position of beam center on SAXS images etc.
This file should also occupy the same sub-directory as the relevant SAXS image files.
- DATA files – these are ASCII files holding processed profile data generated by the users as they analyze their data.
These data files usually contain columns of q values as well as normalized/calibrated/subtracted intensity data.
Specifications
