First, I show what appears to be a clear correlation between the TPC field cage currents on day 134 (May 14th) and Jeff's metric of the "big" events that we understand to be associated with abort gap cleaning (see Jeff's blog post). The IFCW (blue) and OFCE (red) currents during data acquisition runs are shown below versus hour (EDT) on that day, lined up with Jeff's plot in time:

NB: the long time-scale drop in currents is understood to be a different issue related to humidity impacts on the TPC cathode power supply and should be ignored here.



The correlation is hard to miss with spikes well over 0.1 muA. A likely hypothesis, given that both inner and outer field cage currents are impacted, though inner more so, is that there is enough ionic space charge in the TPC created by the abort gap events that its self-repulsion pushes ions to the field cages where they steal electrons from the field cage currents. They are thus an artifact of large space charge.
 
Here are the same currents from the first 8 hours of today (day 117, May 17th):



The scale of the spikes is now much smaller (0.015 muA), which gives hope that the situation has improved.


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A separate question has been asked if whether this issue can be seen in AuAu27 taken during Run 11. Here are the same two currents vs. day during that period of operations:



The large and common fluctuations seen in the two currents are likely again due to humidity (it was June). To remove those, I show hear IFCW - OFCE:


This shows small spikes that are generally around 0.01 muA at most, at or below the level we are seeing today (on day 117). These do not appear to be significant.

I also took a look at the AuAu19 data taken during Run 11, and there I do see larger spikes. Here is the current difference, which shows lots of large spiking (1 muA?!?)! The large blob on day 119 appears to be due to a temporary resistor short as well.



To get a closer look at the spiking, I zoomed in on a smaller period of time around the start of day 115:


I'm not quite sure what is going on, but it may be that the really big spikes are the TPC cathode voltage being raised and lowered during non-TPC runs for beam dumps and injection??? Not sure. But even outside of those, there are notable spikes of the order of 0.1 muA.

So, maybe there was some space charge in AuAu19 due to the abort gap events? I don't think I've definitively answered that yet (nor am I sure I need to).

-Gene