Merlin software
17 Oct 2008
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The Excitations group maintains a wide range of software for data reduction, visualisation and analysis.

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Software on MERLIN 
 

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 Excitat​ions Group software page.

Experiment planning software

To assist you in planning your experiment on Merlin, two MANTID utilities have been developed: QEcoverage and Pychop. QEcoverage aims to show you the coverage of the detectors on different instruments for a given incident energy, and can be found in MantidPlot under Interfaces>Utility>QEcoverage. Examples below compare the coverage for different instruments for the same energy, and just on Merlin for different incident energies.


Pychop, which is under Interfaces>Direct>Pychop is the latest version of the chop software that has been integrated with multirep, such that you can determine for a given instrument, incident energy and frequency, what the flux and energy resolution should be, but also which incident energies you will be able to measure. The different information is displayed under four different tabs as shown below. Obviously there is a play off between flux and resolution based on the chopper settings, but pychop also shows you how this affects the different reps that can be measured simultaneously. Generally it is not possible to demand a certain set of energy reps, but instead you should concentrate on optimising your flux and resolution for your main energy of choice, and then determine which other energies you get for free.

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

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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