Merlin software

Software used on MERLIN

Software on MERLIN
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The Excitations group maintains a wide range of software for data reduction, visualisation and analysis.

The majority of the programs used on Merlin, either to assist in planning your experiment, or to undertake the analysis of your data, are performed in Mantid and Matlab. For more details see the Excitations Group software page.

 

 

Experiment planning software

Following on from chop, and mchop, Pychop has now been implemented in Mantid by Jon Taylor, to enable you to estimate your neutron flux and the percentage energy resolution for a given chopper configuration. Pychop can be added to your instance of MantidPlot via View->Manage Custom Menus, to create a new menu into which the Pychop script from /MantidInstall/scripts/PyChop.py can be added.

Now that Merlin has the capability to run in Rep-rate multiplication mode, flux and resolution are no longer the only considerations when choosing your chopper configuration. It may also be important to determine which incident energies will be transmitted by the chopper, and what the frame overlap will be like. To assist with this, Rob Bewley has written a matlab script Multi_rep_MERLIN.m. It has three arguments, the first and second are identical, and are the incident energy chosen, the third is the proposed chopper frequency. As shown below this will return which energies are transmitted. You can then play with the energies and frequencies to try and optimise the useful energies, however, any extra energy reps should be viewed as a bonus, and it will not necessarily be possible to choose one configuration that will provide all the energies you might be interested in.

How Multi_rep_MERLIN.m works

How Multi_rep_MERLIN.m works
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Data analysis software

Specific to MERLIN is Horace, a new suite of programs for the generation, visualisation, simulation and fitting of large 4-dimensional datasets obtained by making multiple measurements of a single crystal with varying sample orientation or incident energy. 

The feature of Horace that is new compared to existing software, such as MSlice, is that it allows you to combine multiple SPE files and thus build up a 4-dimensional dataset that, in principle, covers Q and energy in all directions.

To understand why this is not possible with a single SPE file consider the diagram. 

ToF QE coupling

ToF QE coupling
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For a single incident energy and crystal orientation it is clear that one of the components of Q, that parallel to the scattered beam (Q2), is coupled to time-of-flight rather than detector position. This means that this component of Q is coupled to neutron energy transfer. Put simply, the effect of this is that a linear “scan” in Q actually follows a curved path in either energy or Q2. Clearly this can be avoided by taking measurements with a different orientation of the sample with respect to the incident beam, since for different orientations the coupling between Q and energy will be different. By making measurements at lots of different sample orientations, Q and energy can be completely decoupled.

Horace is a set of programs that can be used to build, visualise and analyse such a dateset. Much of the functionality of Horace is built on top of the Libisis software package, which is designed to allow you to analyse and plot time-of-flight neutron data and triple-axis data.

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