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