A decade of TPC Field Cage Currents

 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)

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