The European Spallation Source (ESS) will operate a suite of diffractometers, with the DREAM diffractometer  among the first instruments to be commissioned with neutrons. In order to take full advantage of this powerful source and to ensure smooth operation even for first-time users, the ESS Data Management and Software Centre is developing an integrated data pipeline linking all the steps from data acquisition and live visualisation to data analysis. The software used in the data pipeline should be efficient enough to deal with large amounts of data and respond to requirements from the scientific community while providing an intuitive workflow at the same time.
To test this pipeline during the construction phase of ESS and of its instruments, we use instrument simulations with McStas , which has to be combined with GEANT4  due to the complex three-dimensional geometry of the new 10B detectors of the ESS diffractometers.
Here we report on preliminary tests of the reduction of powder diffraction data using McStas and GEANT4 simulations of the DREAM instrument and Scipp  for the reduction.
 Andersen et al., Nucl. Inst. and Methods in Physics Research A 957, 163402 (2020).
 Willendrup and Lefmann, Journal of Neutron Research 22, 1 (2020) and 23, 7 (2021).
 Allison et al., Nucl. Inst. and Methods in Physics Research Section A 835, 186 (2016).
 Heybrock et al., Journal of Neutron Research 22, 169 (2020) and scipp.github.io