Before you move on to multigrain indexing, you will need to know:

• what phases you are looking for,
• their crystal structures and cell parameters.

If you have a decent powder diffraction pattern to work with, you can try to do so with typical software people use in DAC experiments: dioptas, maud, etc.

There is a second option:

• collect diffraction peaks using peak-search,
• generate a 2-theta histogram of peaks.

This will be discussed below.

Generating a 2-theta histogram of peaks identified with a peak search has several advantages:

• most of the background signal (diamonds, shadows, etc) has been removed,
• a strong powder signal from the pressure medium will be partly removed,
• the signal from the sample you are trying to index is stronger,
• the histogram is based on the peak center of mass only, and hence removes the broadening due to grain size or internal strains.

Some drawbacks

• this is not a true powder diffraction pattern, peak broadening, in particular, is different,
• current easy-to-use versions do not sum intensities, but count the number of peaks for a given 2theta. The recovered intensity is proportional to the multiplicity, and not the structure factor. Diffraction intensities are messed up an can be used for structural refinements.

This can be done in ImageD11. Once calibrated for tilts, beam center, detector distance, etc, you can select

• Transformation → Load Filtered Peaks
• Transformation → Plot tth histogram

ImageD11 will ask for a number of bins (10000 is good) and you will get something like the screenshot below