Dipole diode lead resistance measurement Introduction Where are we now? All data Highest resistances V-tap swaps detected NCs

Origin Quench propagation measurements Diode working group started Unexpected diode lead behaviour. Diode working group started MPE and MSC groups Comprehensive study, SM18 test stand, Weak points identified. Quadrupole connection plate consolidation All contacts measured when the diode container is open. Dipole diode leads remained unknown CSCM test may be not executed. Global dipole diode lead measurement at warm and at low current was developed.

What can be measured? V Only a sum of all 3 contacts and the copper bus can be measured!

Electrical diagram Diode branch assures a bypass of the magnet in case of quench Complete procedure available on EDMS: 1334252

What is measured? Components that have never seen current and thus have never been tested! T-junction, Copper flexible, 3 contacts per diode lead. CSCM cannot be substituted by this measurement. CSCM will qualify these components with high current. DLM cannot guarantee good performance at nominal conditions! V

Schematics of the set-up By moving from magnet to magnet we switch between MBA and MBB lines 3 people are required to move the system smoothly

Measurement Current is applied in steps of 30%, 60%, 80% and 100% of the maximum current value. For reversed mode the max current is 1.5 A. For forward mode the max current is 10 A. Plateau length is 10 s. Linear fit is calculated to get the final resistance value and cancel the offset.

If more than 15.5 μΩ is measured, the diode lead may be weak. Acceptance criteria Global diode lead measurement: 3 contacts together. The most critical is the half-moon contact Simulation => 450K if R = 14.5 μΩ, Details → Arjan Verweij and Zinur Charifoulline Remaining 2 contacts are unlikely to be below 0.5 μΩ. If more than 15.5 μΩ is measured, the diode lead may be weak. Diode container opening is needed!

Where are we now with the measurements? What are the results so far?

Diode lead measurements Current situation Diode lead measurements 4 5 6 7 8 1 2 3

Data from all sectors Note: logarithmic vertical scale! Diode lead contact resistances from sectors: 1-2, 2-3, partly 3-4, 5-6, 6-7, 7-8 and 8-1 1856 diode leads 15.5 µΩ (threshold set by the Diode Working Group) Represented is the sum of 3 contact resistances.

Highest resistances - all sectors Location MTF_ID Diode lead Contact resistance [Ω] A15L8 HCLBARB000-IN003058 Anode 210.0 µ Cathode 89.8 µ C14L6 HCLBBRA000-IN003341 41.6 µ C30R5 HCLBARB000-IN003320 34.4 µ B32R5 HCLBBRA000-IN003315 & Anode 23.1 µ C34R2 HCLBALB000-IN001394 19.1 μ A18L8 HCLBBRD000-IN003012 18.9 µ A21R7 HCLBBRA000-IN003014 16.6 µ B26R2 HCLBBLA000-IN003126 16.1 μ

A15L8 Diode container opened on Tuesday, 25.02.2014 Photo by Ludovic Grand-Clement

90 μΩ 210 μΩ A15L8 - zoom Washers are not as specified by the design! Photo by Ludovic Grand-Clement

A15L8 – number 3058 High resistance located in the half-moons… Possible consequences? If this magnet quenches at Inom → Half-moon burn-out, → Magnet takes back the current, → Magnet burn-out, → Open circuit… like in September 2008… We are lucky that this magnet has not quenched… … and that this measurement was introduced – we have detected it! Otherwise only CSCM could detect it (if carried out) Large delay for: Warm-up, Repair the diode assembly, Redo all tests, Cool-down, Repeat CSCM.

All low resistance diode leads Note: Linear vertical scale 5 diode leads are higher! Narrow distribution of diode leads, Mean value at about 3 μΩ.

Summary of NCs Bad V-tap (no continuity) V-tap swaps EDMS 1347363 V-tap swaps EDMS 1347357 EDMS 1347364 EDMS 1352457 EDMS 1352459 EDMS 1352460 EDMS 1352461 EDMS 1352462 EDMS 1352463 Diode lead contact resistance above 15.5 μΩ EDMS 1347322 EDMS 1347329 EDMS 1347330 EDMS 1347331 EDMS 1347332 EDMS 1347333 EDMS 1358362 EDMS 1358676

Summary of NCs Bad V-tap (no continuity) V-tap swaps EDMS 1347363 V-tap swaps EDMS 1347357: Problem solved, NC CLOSED with warnings EDMS 1347364 EDMS 1352457: Problem solved, NC CLOSED with warnings EDMS 1352459: Problem solved, NC CLOSED with warnings EDMS 1352460 EDMS 1352461: Problem solved, NC CLOSED with warnings EDMS 1352462 EDMS 1352463 Diode lead contact resistance above 15.5 μΩ EDMS 1347322 EDMS 1347329: Diode stack exchanged, NC CLOSED EDMS 1347330: Diode stack exchanged, NC CLOSED EDMS 1347331: Diode stack exchanged, NC CLOSED EDMS 1347332 EDMS 1347333 EDMS 1358362 EDMS 1358676

Summary 1-2, 2-3, 5-6, 6-7, 7-8 and 8-1 are done! 8 diode stacks where the contact resistances exceed the threshold of 15.5 μΩ, One diode stack with extremely high half-moon resistances: 210 μΩ and 90 μΩ Discovered several V-tap swaps that are very difficult to detect, For each case an NCR was opened, and is followed-up, This measurement will help to interpret the result of the warm bus-bar measurement carried out before opening the machine.

Thank you for your attention!

Back-up slides…

Other observed outliers T_BB_Anode Expected distribution EE212 and EE213 V-tap swap Not yet understood 7 V-tap swaps, 7 more cases for other measurements where outliers are observed, no explanation so far, Local diagnostics needed.

Types of faults observed EE012 swapped with EE014 in A34L8 Swapped I-tap and V-tap, More local diagnostics needed, Already noticed by Reiner: logbook entry Removed from interlock since 23/02/2010, QPS compensations did not work for this magnet. Courtesy of Zinur Charifoulline