I obtained the field cage currents from Runs 3 through 13 (years 2003-2013) and plotted them versus time [years]. The individual Run periods are easily discerned over this time range. Here are the results:

(open each image in a new window or tab to see higher resolution)

Legend:

top left: OFCE (outer east)
bottom left: IFCE (inner east)
top right: OFCW (outer west)
bottom right: IFCW (inner west)

...and...

all recorded data in red
only during during TPC runs in blue

First observation: all the currents show a common downward trend over time of ~13.16 nAmps/year (cathode power supply voltage dropping? Keithley meter calibration drifting?)

Attempting to subtract off the common downward trend, and overall magnitude, helps obviate other features:

Common:
- Run 3 (and the very beginning of Run 4) and Runs 8 & 9 all have slightly elevated currents (on the ~100 nAmp scale, or ~0.1% scale)
- Huge dips seen near the end of Run 13 (see this blog) also occurred in Runs 10-12 (but went unnoticed?)
OFCE:
- Generally no unique issues
IFCE:
- A short near ring 169.5 occurred at start of Run 4, but a compensating resistor was put in place for most of Runs 4 and 5
- The first attemt to patch this short caused flucuating currents in Runs 6 and 7
- The short was permanently fixed before Run 8
OFCW:
- The partial short believed to be near ring 80.5 persisted from Run 5-9 (but went unnoticed for a few years and was only corrected in the data for Runs 8-9?)
- The short between the last two rings (181 & 182) occurred part way through Run 9
IFCW:
- Some Run 9 data looked like a short, but other evidence does not support this (see this blog)

-Gene


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Here is a list of all of the cathode and field cage information available from the online database archives, along with shortnames I have assigned for them in parentheses:

currentInnerFieldCageEast_1 (Ioe)
currentOuterFieldCageEast_1 (Iie)
currentInnerFieldCageWest_1 (Iow)
currentOuterFieldCageWest_1 (Iiw)
voltageInnerFieldCageEast_0 (Vie0)
voltageOuterFieldCageEast_0 (Voe0)
voltageInnerFieldCageWest_0 (Viw0)
voltageOuterFieldCageWest_0 (Vow0)
voltageInnerFieldCageEast_1 (Vie1)
voltageOuterFieldCageEast_1 (Voe1)
voltageInnerFieldCageWest_1 (Viw1)
voltageOuterFieldCageWest_1 (Vow1)
CathodeCurrentReadback (Icr)
CathodeVoltageReadback (Vcr)
CathodeVoltageSetpoint (Vcs)
groundShellCurrent (Igs or gsc)

The inner/outer label is known to be backwards on the first four currents, which is reflected in the short titles I've given them.

I found that Icr is always 0, so it is not helpful. The readouts of voltages labeled 0 and 1 are explained here (and are expected to be different for inner vs. outer field cages). Here are the quadruplet of voltage readings [V] on the field cages (arranged as with the currents in the original post), for 0 first, and 1 second, where I have taken the liberty of adding 7 V to OFC west's voltage 0 during the period that rings 181 and 182 are shorted together, and subtractacted 137 V from voltage 1 on the same cage for the same period (the two voltages are identical during the short, and sit near -40 V):

___________________________________________________

There are some fluctuations in these field cage voltages that I do not understand, and there is no global trend to explain the steady drop in the currents over time (though some of the voltage 0 readings tend towards zero a little in later years). Also, voltage 0 for OFC west appears to be much more noisy than the other voltages, and is offset from OFC east for all years as well, perhaps due to how the pots were set for these two field cages?

Next, here is the cathode voltage setpoint and its profile:

It is unclear to me why this has values near 0.305, nor what units it is in (I was expecting volts). The precision is kept only to 0.001 of whatever the units are. The profile plot allows us to see that it has an upward trend.

Here is the readback voltage on the cathode and its profile:

These are probably recorded in [kV] with a precision of 0.001 (or 1 volt). The profile shows there is a curious rise during each Run year, and a notable step downward for Run 10 that does not appear to coincide with the OFC west short that occurred before the end of Run 9.

And now the profile of the ratio of readback/setpoint, showing a downward trend of losing about a half a percent over the past decade:

Lastly, here is the ground shell current and its profile:

I have no idea how to interpret what is seen here for the ground shell current.

-Gene

Here are the TPC drift velocities [cm/μs] recorded over the same years. There is no obvious correlation here with respect to the field cage currents, but given that we are on (or near) the drift velocity vs. E-field plateau, we would expect the dependence on cathode voltage to be rather small. Other contributing factors to the drift velocity would probably need to be removed first in order to look for a true correlation with field cage currents.

-Gene

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A decade of voltages and cathode readings

A decade of drift velocities