ELOG CARME

AIDA GELINA BRIKEN nToF CRIB ISOLDE CIRCE nTOFCapture DESPEC DTAS EDI_PSA 179Ta CARME StellarModelling DCF K40

CARME

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Wed Jan 10 10:22:41 2024

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Started mounting some FEEs. We ran into some mechanical issues due to the new ERNI connectors on the new flexi-rigid adaptor PCBs. Davide skimmed 6.5 mm off the edge with the groove (the groove is gone). This is suffiicent to support the flexi-rigid and in spite of our earlier concerns, the flexi-rigid can be mated/un-mated with the FEEs without major alignment issues.

We still have issues for the bottom-right detector, where the FEE holder will just not fit - will probably figure something out with Davide.

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We observe a peculiar issue with the bottom-left detector. At 150V, the leakage current for this detector as tested with just the adaptor cards on the feedthroughs that carry the bias (no FEEs) is of the order of 3 uA.

We mounted all four flexi-rigid PCBs - still 3 uA.

We mounted the FEE that slots into the bottom-most feedthrough (which corresponds to the n-n bias). Still 3 uA.

We mounted the FEE that slots in to the second bottom feedthrough (not corresponding to bias). 15 uA! Upon lowerint the bias, the leakage current goes to zero around 30V as opposed to 0V like all the other detectors, and like this detector when this particular FEE is not mounted.

Tests were performed exchanging all PCBs, and all FEEs. The same behaviour is observed. It is not an issue with the FEE or the PCB. We suspect some cross-contact between detector bias and some strip that feeds into the second FEE? In any case, it is most likely a vacuum side issue - nothing we can do now.

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The detector can be biased to 80V or so without major issue, and it appears this behaviour improves over time, i.e. leaving the bias on reduces the leakage current dramatically so it may even be possible to reach 150V.

See plots attached. Note in 2nd plot the plotting script has some issues - detector names are correct until the bias in Ch#2 is brough to 150V, then the colours are incorrect. Only Ch#2 was being changed. Note the drop in leakage current by a factor 2 just increasing the bias to 150V for a few seconds and returning down.

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