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If you want to know gross values, such as pulse duration, the timing between two pulses, etc, then if you have reconstruction agreement, you can be quite confident your analysis will work with ~3 fs precision in time and ~10 eV precision in energy, though exact values depend strongly on the XTCAV settings – discuss with ACR if you care! If you are studying the power structure of the pulse, then the honest answer is that we do not know exactly how good the reconstruction is – this is an open research question. We are currently working on ways to experimentally validate existing reconstruction methods and improve them. This is seen as a high priority by LCLS management and is funded through the FEL R&D program (as of time of writing, Oct 2018).

I see a "phase error".  What do I do?

This warning can cause events to be thrown away, impacting analysis:

The phase of the bunch with the RF field is far from 0 or 180 degrees

To disable this throwing away of events, set an environment variable:

export XTCAV_IGNORE_PHASE_WARNING=1

When this happens ACR should also be notified so they can adjust the phase on their end.  Tim Maxwell wrote on Dec. 11, 2022:

"I also see that the operating phase is indeed getting close to 0. I suspect the wording of the error message itself just had it the wrong way around. Seems to be the phase shifted after changing to low charge. We can also walk back the offset so that it no longer throws the error. (The physical phase is still actually +90 currently, so this is okay.)"

Who Do I Contact for More Help?

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