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Analysis of the quench tests in S56 in May and July 2011Arjan Verweij, TE-MPEOn behalf of all persons involved in the testsContents- Motivation for these tests- Geometry- Test results- Simulations- Open questions- ConclusionA. Verweij, CMAC, 22 Aug 20111During the Chamonix 2009 workshop it was pointed out that a 13 kA joint could burn-out in case of a quench, if there would be a bad bonding between the cable and the copper bus coinciding with a discontinuity in the copper stabiliser.Motivation

Since then, resistance measurements and -ray pictures have shown the presence of many of such defective joints in the machine, limiting the safe operating current to about 6 kA.A. Verweij, CMAC, 22 Aug 20112Prompt quench of a jointBeam lossesResistive losses in the spliceBurn-out of the jointCable/bus movementQuench of a magnetThermal propagation through the busThermal propagationthrough GHe Spurious trips/heater firings, .TrainingDelayed quench of a jointDuring the Chamonix 2011 workshop it was shown that the largest probability to quench a joint was caused by thermal propagation of the heat developed in the magnet and the diode by-pass. It was therefore concluded to remain at 3.5 TeV in 2011.It was also recommended to measure this propagation in the machine.A. Verweij, CMAC, 22 Aug 20113Magnet(1.8 MJ @ 6 kA)DiodeJointTypical powers at 6 kA:Diode: 6 kWDiode busbars: 2x25 WContacts: 200 W (assuming 2x3 mW)GeometryII

Magnet(1.8 MJ @ 6 kA)DiodeA. Verweij, CMAC, 22 Aug 2011half moon contactsheat sink contacts4

RB jointUpper diode busbar(partially flexible)Half moon contactMain busbarstowards diodeGeometry21 cm5The diodeRc,moon

Rc,hs

Diode box, Helium contents : 5 liter Lower diode busbarRc,diodeLower heat sinkUpper heat sinkA. Verweij, CMAC, 22 Aug 2011Reception tests in FRASCATI:Endurance tests: 10 current cycles with 13 kA, t=120 s.The diode voltage and Rc,diode were measured. Rc,hs has only been checked a few times.

Cold reception tests (in SM18):Each diode has only experienced one current pulse below 1 kA for less than 1 s.Rc,hs+Rc,moon has been measured during this transient and was always below 5 mW.6Contents: Motivation for these tests Geometry Test resultsMeasured magnetsForward voltage over the diodesPropagation into the busVoltage & resistance in the diode leads Simulations Open questions ConclusionA. Verweij, CMAC, 22 Aug 20117Measured magnetsMagnetIDTraining quenches in SM18Training quenches in the LHCSecondary quenches in the LHCTest quenches May 2011Test quenchesJuly 2011A15R5-318812.3 12.410.55.2 4.66B15R5-335312.2 6.3 7.4 6.86 2 5 0.76 4 6 6 3C15R5-333812.2 12.710.9 10.72.46A16R5-320411.6 12.211.2 2 0.76 4 6 3 5B16R5-336112.5 12.47.4 2 2 5 0.76 6 3 4C16R5-224611.5 11.8 12.4 12.80.6 5.2 2 6 4All numbers in kATotal: 28 heaterinduced quenches3 magnets with training3 magnets without training6 magnets from stable part of productionA. Verweij, CMAC, 22 Aug 20118Magnet(1.8 MJ @ 6 kA)DiodeJointUdiodeII

Test resultsMeasured magnetsForward voltage over the diodesPropagation into the busVoltage & resistance in the diode leadsA. Verweij, CMAC, 22 Aug 20119Diode voltages for 6 kA quenches

Magnet not yet fully s.c.,all current in magnetMagnet s.c.,all current in magnet, U=L*dI/dtDiode blocksDiode cooling downConclusion:Forward voltage (and hence the heating) over the 6 diodes is very uniform.

(s7 kA a magnet quench will almost always propagate to the closest 13 kA joint. No quenches in the bus have been observed at 6 kA due to propagation of warm helium gas.

A. Verweij, CMAC, 22 Aug 201126Conclusion (2/2)Diode lead voltages/resistances: The measured resistances (up to 50 mW) are much larger than measured during the cold reception in SM18 (