Note, ground and HVC (high voltage common) are used interchangeably here.
Monday, December 16, 2024, in the previous test, elog 1038, it was found that the cathode was unable to hold any voltage and was shorted to HVC. The cathode was shorted directly to ground, with the cathode supply current limiting upon being powered, unable to reach even 1V.
After testing, the ANODE power supply stopped functioning and was unable to provide and voltage or current.
When the target was removed, it was found that the TBHT terminal was just ~100Ω from HVC. When I shorted the TGHT to TBHT terminal, as they are when the target is installed, the resistance from TBHT to HVC dropped to just 1Ω. Prior to the anode power supply stopping, it was found that when it was powered on with no target present, it was able to hold voltage, but still drew significant current: up to 400mA when provided less that 20V. This should be completely open, losing no current at all.
Keiko and the controls team have been looped in to address the issue with the ANODE power supply as it may be a controls issue. They believe there are a few possibilities for its error that must be investigated prior to deferring to the power supplies group. This will continue to be investigated
********** UPDATE: ISSUE RESOLVED ********* There is simply a physically triggered interlock that requires the faraday cage door to be closed to operate the ANODE power supply
When investigating the resistive short from the TBHT, I first noted the resistances between each of the channels: TGHT(-) to TGHT(+) 30↨Ω; TBHT(-) to TBHT(+) 20Ω; TBHT(-) to TGHT(-) 100Ω; TBHT(+) to TGHT(+) 140Ω. I also reconfirmed and noted relevant connections at the feedthroughs: There are NO visible shorts to HVC from the TGHT or TBHT feedthroughs. From TGHT(-), there is one 50kΩ resistor with varistor, between TGHT(-) and TGHT(+) there is a100Ω with varistor. I then removed the back of the faraday cage to investigate possible paths to ground from the TGHT and/or TBHT. This showed that TGHT- was grounded through a varistor (checked, functioning correctly, OL at low voltage), TGHT- to + has varistor||100Ω, TBHT- to + has varistor||100Ω, and TBHT- to TGHT- has varistor||100Ω. These fit in accordance with the observed resistances between the terminals.
I also disconnected the ANODE power supply from its output wire to further investigate without possible issues from the power supply. At this point, (after I had remade the varistor connections) I began to observe that the TGHT and TBHT terminals were all detached from ground by 50kΩ (expected amount, given that there is a 100k||100k resistor from TBHT- feedthrough to ground). When I reattached the anode power supply, that value dropped to 35kΩ, I assume due to internal resistance of the power supply. I placed everything back in position and (repeatedly) ensured that the 35kΩ separation persisted. It seems that this shorting issue has resolved itself. It may be that the was an accidental connection made from an unshielded wire inside the faraday cage.
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