1. LHC magnet protection diodes status and recommendations for LS1 October 10 th, 2012 F. Savary on behalf of the diode working group (TE-MSC and MPE Groups + EN-MME) M. Bajko, M. J. Bednarek, L. Bottura, R. Bouvier, Z. Charifoulline, K. Dahlerup- Petersen, G. D'Angelo, G. Dib, F. A. Duprat, M. Duret, M. Favre, C. Giloux, L. Grand-Clement, M. Guinchard, S. Izquierdo Bermudez, M. Ky, P. Perret, H. Prin, V. Roger, D. Tommasini, A. Siemko, J-P. Tock, A. Verweij, G. Willering, More information available at https://espace.cern.ch/Diodeshttps://espace.cern.ch/Diodes

2. Outlook Reminder Diode to heat sink contact Heat sink to bus bar contact Bus to bus contact Outcome of the tests and analysis Recommendations & actions Impact on LS1 22012-10-10Protection diodes status and recommendations for LS1

3. Lower diode bus bar Reminder – Dipole diode stack 3 R Bus-bus (‘half moon’) R HS-bus Diode box, He content:  5 liter R Diode-HS Voltage taps on the diode Upper Heat Sink Lower Heat Sink Bolted contacts with 4 M6 + helicoil, 4 spring washers, 10 Nm Diode compressed by a stack of spring washers to 40 kN All copper parts Ni-plated, 2-3 µm 2012-10-10Protection diodes status and recommendations for LS1

4. Diode bus bar Nickel plated everywhere SSS bus bar Silver plated over 40 mm Connection plate Nickel plated everywhere Reminder – Quad. diode stack 2012-10-104Protection diodes status and recommendations for LS1 R Diode-HS R HS-bus R Bus-bus

5. Diode to heat sink contact R Diode-HS : has typical behavior, confirmed by production data, tests in Bloc 4, and more recent tests @ 4.2 K in SM18 Not stable 2012-10-10Protection diodes status and recommendations for LS15 First run @ 13 kA MQB0112

6. Diode to heat sink contact The diode is protected against excessive temperature by the heat sink (T DIODE < 300 K and T HEAT SINK < 230 K) 2012-10-10Protection diodes status and recommendations for LS16 First run @ 13 kA Test run Standard @ 4.2 K Spec. [µΩ] # of contacts measured Min. measured [µΩ] Max. measured [µΩ] Average [µΩ] rms [µΩ] First run @ 13 kA-311.47307.966.89 Last run @ 13 kA< 5 µΩ300.5620.43.663.97 # of contacts measured Contact resistance [µΩ] Bad assemblies 7.5 µΩ 14 µΩ 4.5 µΩ 30 µΩ

7. Heat sink to bus contact R HS-bus is stable at cold/high current, for both dipoles and quadrupoles stacks (also for 24 stacks measured in Bloc 4 after incident in S34) Like the diode to heat sink contact, is not an issue thanks to the HS 2012-10-10Protection diodes status and recommendations for LS17 @ 4.2 K, standard tests Test typeSpec. [µΩ] # of contacts measured Min. measured [µΩ] Max. measured [µΩ] Average [µΩ] rms [µΩ] Standard< 2 µΩ320.291.580.680.27 Special< 2 µΩ140.251.10.770.25 Contact resistance [µΩ] # of contacts measured

8. Bus to bus contact - dipole R Bus-bus – ½ moons contacts for dipoles Measured for the first time in SM18 in February 2012 Are stable at cold/high current 2012-10-10Protection diodes status and recommendations for LS18 R < 2 µΩ required R < 1 µΩ measured

9. Bus to bus contact - quadrupole R Bus-bus – connection plate contacts for quadrupoles Measured for the first time in SM18 in July 2012 2012-10-10Protection diodes status and recommendations for LS19 R < 2 µΩ required R > 2 µΩ measured

10. Outcome of the tests and analysis The assembly procedure of the stacks is (re)understood Lots of efforts to rebuild the experience lost after the series production All the contacts were studied at RT, 77 K, and 4.2 K The measurements in SM18 (4.2 K) indicate that The diode to heat sink contacts, even if not stable, are safe thanks to the heat sink, which was designed for 13 kA, tau = 120 s / 50 s The heat sink to bus and ½ moons contacts are stable with small resistances, hence safe The resistance of the connection plate contacts (quads) depends on the current and current history. We cannot guarantee that all (400 x 8) contacts in the machine can safely carry one or more current decays of 12 kA, tau=30 s. The bolted assembly lacks rigidity and robustness, hence is not safe 2012-10-10Protection diodes status and recommendations for LS110

11. Recommendations and actions Re-do all the bus bar to connection plate contacts of the almost 400 quad. diode stacks installed in the machine 2 stacks with reinforced bolted connection are now under test @ 4.2 K in SM18 The consolidation procedure will be verified, and repeated, on representative mock-up in B-180 >>> can be done without removing the stacks from its container 2012-10-10Protection diodes status and recommendations for LS111 R BB Diode/Plate R BB SSS/Plate R BB Diode/Plate @ RT (  ) R BB SSS/Plate @ RT (  0.4< 0.1

12. Impact on LS1 2012-10-10Protection diodes status and recommendations for LS112 9 additional persons 1 staff (L. Grand-Clément) + 8 FSU’s: cut-open the diode container, re-do the bolted connections, carry out ELQC, re-weld the cover, carry out helium leak test … the size of SMACC is currently 240 persons The diode consolidation needs to be integrated with the existing activities, meaning more coactivity/coordination Globally, one month Dip-Dip Dip-Quad