Data processing for the SNS EQ-SANS diffractometer

The scattering data on the Extended Q-range Small Angle Scattering Diffractometer at the spallation neutron source are stored as neutron events. Each event has two parts: the time of fight of the detected neutron, and an identifier for the neutron's location on the detector. In addition, each event is associated with the source pulse from which the neutron is originated. Due to Spallation Neutron Source's (SNS) high neutron flux, the size of the stored data files can easily exceed several Gigabytes. Processing and reducing these data can be very time consuming. In the present work, we implement a data processing scheme for the EQ-SANS diffractometer that is fast, versatile, and highly automated. The data are processed directly from the event files into neutron scattering intensity versus momentum transfer data sets, or other desired formats. Speed gains are obtained by the implementation of parallel computing under the Message Passing Interface framework. In addition, the implementation allows for time-slicing of the scattering data, which will enable fast time-dependency studies on the EQ-SANS instrument, such as temperature jump and fast shears. Finally, our work implements the handling of scattering data from the innovative frame-skipping operation of the EQ-SANS instrument.