NOBUGS 2026

Our group at RWTH Aachen University is dedicated to advancing neutron time-of-flight (TOF) powder diffraction methods, particularly in relation to the POWTEX diffractometer at MLZ [1] and the DAPHNE4NFDI consortium. Both initiatives aim to extend the developed methodologies across suitable TOF diffractometers also on other sources. A key part of our work is the continuous development and application of GSAS-II 2D, a modified version of GSAS-II extended for multidimensional Rietveld refinements. Herein, new concepts such as the Fundamental Instrument Description (FID), whose parameters are also incorporated in our recent proposal for a meta-data schema for TOF neutron powder diffraction, are applied.[2] The software has recently been updated to the latest upstream GSAS‑II release [3], and a comprehensive automated test suite together with a CI/CD pipeline has been added. Moreover, a containerized deployment that also powers the AIXtal platform [4, 5] has been realized. Past results, e.g., on multidimensional Rietveld refinements of high-pressure neutron TOF powder diffraction data from SNAP or POWGEN at ORNL, USA [6-9], have convincingly demonstrated the advantage of our method.
In this work, we present the current development of a NeXus application definition for neutron TOF powder diffraction that includes many parameters that are both relevant to the development or our new analysis method and further allows easier access to instrument and experiment specific knowledge that otherwise cannot be obtained quickly and easily. While the parameters of the Fundamental Instrument Description are central, the definition also incorporates classical instrument parameters that traditionally would be stored in separate configuration files. Since this does not meet our requirements for a single source of truth, we would like to use our approach to propose an alternative solution that also takes parameter history and versioning into account.