Some more information on how to interpret the archived signals:
The compton photon detector trigger rates are shown in light blue (compton:RATE_G). The current in the detector PMT (MF2b1461_11ch1property.E) is shown in green.
The trigger rates are the best routine measurement of steady background rates, and rates around 100 Hz/uA are desireable. These rates are normalized to beam current. There are a couple of important details to know about this: the normalization to beam current creates large, spurious spikes in this measure when the beam ramps up after a trip. Also, the rate variable does not update quickly in EPICS, so fast spikes in rate are not visible in this.
The PMT current is a better measure of fast background spikes. The current increases at high rates, and large spikes in the background pushes the average rate up high enough to produce large spikes in (negative) current. You can see these start to occur around 18:40 in the plot, and increase in magnitude and frequency as the problem grows. These spikes in rate also occasionally trip the detector high-voltage, causing the current to drop to zero, before returning when the HV is reset.
To summarize: when we are running smoothly, the PMT current is very stable (like before 18:00 in the plot) and the laser-off RATE_G is around 100 Hz/uA. When the average photon rate goes above a few hundred Hz/uA, or the PMT current starts shown intermittent spikes, then we have a problem.