Training in AT for year 2008

What was wrong with thePlug-In Modules (PIMs) in thecold part of LHC?P. Strubin, based on documents from many colleagues17 April 20121LRFF Task ForceOutlineIntroductionWhat happened in August 2007?Fact findings and calculationsWhy did it happen?How did the non-conformity crop in?Local anomaliesANSYS simulation to confirm the diagnosticImpact on resistanceCorrective actionsMeans of detection of damaged PIMs 17 April 20122LRFF Task ForceSome key dimensions17 April 2012LRFF Task Force3

Original design verified in 2007 by Delio, who did not participate in the original design. Found correct.3What does a PIM look like?

17 April 2012LRFF Task Force44What happened in August 2007?After warm-up of sector 7-8A buckled PIM was discovered in interconnect QQBI.26.R7Was really found by chance!17 April 2012LRFF Task Force5

5 PIMs damaged in sector 7-8, all QQBI type. 12 faulty ones in sector 4-5, all QQBI type.5Why did it happen?Several ideas followed, but rapidly converging to a non conformity during manufacturing17 April 2012LRFF Task Force6

6How did the non-conformity crop in?SpecificationMeasured DC resistance of fingers was an acceptance criteriaDimensions and angles were defined via approved drawingsOnly OK on the traveller, no real measurements registeredDifficulties at the manufacturerMaximum value of resistance sometimes not met with nominal anglesOriginal reason was an incorrect height of the end of the finger, wrongly corrected by increasing an angleFingers were bent by hand, no tooling made, hence no reproducibility between PIMsCorrective actions not documented!

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6.7mm finger height12 bend angleProblem identified and mentioned to BINP during the readiness review, but no corrective action taken by BINP for the series. Traveller not filled in properly.Finger height found at 4mm and angle >19, up to 45 for first non conforming PIMs measured.7

Local anomaliesLength of interconnects sometime at the limit of acceptable17 April 2012LRFF Task Force8Stroke measured in situ during cool down on both sides of Q9L5 and found more or less as expected (+1 to 2 mm).8ANSYS simulationSimulations made on nominal and faulty PIMsCritical parameters, like friction coefficient, measured as accurately as possible17 April 2012LRFF Task Force9

Example with a faulty PIMExample with a conforming PIMFriction coefficient measured at cold, found within range used for design.9Impact on resistanceA buckled finger may loose contact when warmed-up17 April 2012LRFF Task Force10

A non conforming finger may loose contact after a partial warm up.10Corrective actionsA tooling was designed to restore the correct geometry of the fingers

Move the SSS by 2 mm to reduce the span of the QQBI17 April 2012LRFF Task Force11

A non-conforming RF contact assembly inserted in the correcting tool prototypeAn example of a non-conforming assembly, and a corrected assemblyNo damage on coatings with the corrective tooling. Stroke amplitude restored, DC resistance OK.11Means of detection of damaged PIMsQuite a few solutions analysedRolling a ball from one extremity of a sector to the other, localise the ball with the BPMs, move it by a draft created by pumping at one end

PhotometryPrinciple OK, but not adapted for the required lengthRF probe from the extremitiesNeeded at cold calibrationSensitivity at the limit for reliable detectionX-ray tomographyCan measure through the external bellows

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Ball speed around 2 m/s, draft around 4 m/sX-ray tomograph used in the LHC, also to try and diagnostic bad splices.12Follow-up (end 2008 beginning 2009)Finding ways to repair a broken PIM without global warm upLimit the warming up to one half-cellUse neon flushing to prevent condensation of gas in beam tubeAnalyse and mitigate risk at the extremity of the arcsMinimise the warm up during long cryogenic stand-by periodsAnalyse the situation in the stand-alone magnetsRelated problems after the 3-4 incidentDebris in the beam pipe and PIMs (could affect resistance)Buckling of the nested bellowsStrategy of PIM replacement17 April 2012LRFF Task Force13Partial warm up validate in SM18, used several times since then13SummaryThe PIM problem was purely mechanicalIt has been fully understoodNon conforming PIMs can be repairedStrategy for replacement has been defined and is appliedWith some accrobacy, a PIM can even be replaced in a cold sectoronly partial warm up of one cellA repaired PIM has a DC resistance as specifiedRF measurements were also made end 2008 and beginning 2009

But I cannot remember of a PIM crisisCould have been a supply problem after the 3-4 incident17 April 201214LRFF Task Force