All of the data produced at SOLEIL is stored in NeXus(1) files. Each file is associated with a set of contextual data, i.e. data describing the environment in which the experiment took place, amongst other things (a comment describing the sample, the list of users present, type of experiment, beamline and synchrotron parameters, etc.). In TWIST, this information provides search criteria to help you find NeXus files.
Once the NeXus files have been found, you can view their content using the “View” tab. It is an embedded version of the standalone application, Baladi, which is available at the BeamLines.
This application lets you explore NeXus files and display experimental data, whether in scalar form, text strings, spectra, or images. For spectra, you can compare them, for example, or superimpose them, or compare one as a function of the other (y as a function of x), etc.
| From scalar values, e.g. machine current, a spectrum can be created to display the machine current curve with respect to time. If the scientist wishes to download the data viewed, or other data, the files can be downloaded: - Directly in NeXus format.
- In another format by choosing the appropriate conversion script from the download dialogue box. The file can be, for example, an EDF file, a text file, or an image file (BMP format, etc.).
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When downloading has been launched, its status can be monitored in real time in an appropriate tab of the application.
A few statistics about its use at SOLEIL:
• 13 beamlines currently use data storage in NeXus format.
• More than 137,000 NeXus files have been created since October 2007.
This total breaks down as follows(2):
- ODE : 70,000
- SWING : 33,000
- DIFFABS : 13,300
- CRISTAL : 7,500
- PROXIMA1 : 7,000
- LUCIA : 2,750
- CASSIOPEE : 1,600
- MARS : 900
- TEMPO : 800
- ANTARES & SAMBA: 200
- DISCO & DEIMOS : < 100
(1) NeXus : It is the file format adopted at SOLEIL to store the experimental data. This format is comparable to XML in the public domain, but in binary form. It is self-descriptive, open-ended, extensible, and based on a logical organisation of data. It provides a means of linking contextual data (experimental parameters, instrumentation, etc.) with experimental data. NeXus is used by several communities: DIAMOND, LLB, ISIS, SNS and, recently, the ESRF, amongst others. This common format was chosen for the purpose of facilitating the exchange of data between institutes. For further details, see the website: http://www.nexusformat.org/Main_Page
(2) Values as of June 2009.
