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From an email thread with RIX scientists on July 9, 2021:

Executive summary: now that you’ve set the preamp gain to 4 (we think you did that today, following Matt’s advice) we think you’re running with the same settings we used for sxrx30416 run 83, as best we can tell.  Note that the manual describes an EM (electron-multiplying) gain setting that is useful for single photon counting

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but we believe the LCLS cameras are Newton CCDs, not Newton EMCCDs.  See manual https://andor.oxinst.com/downloads/view/newton-ccd-emccd-hardware-guide
Details: Dan and I looked at the settings from sxrx30416 run 83 vs. the current running.  These are the settings we had:

In [2]: andorconfig.highCapacity()
Out[2]: 0

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This is

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not settable in the IOC, but Dan looked and it defaults to 0 now, which we think is right (highCapacity=1 corresponds to large dynamic range, which you don’t want for single-photon regime)

In [3]: andorconfig.readoutSpeedIndex()
Out[3]: 0

This corresponds to 3MHz which is what you are running now, and it is correct: this increases the readout speed so we can run at 120Hz, but also increases noise.

In [4]: andorconfig.gainIndex()
Out[4]: 2

This “gain enum index” corresponds to the factor 4 you have just set (today) for the highest preamp gain, as Matt

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Seaberg suggested.