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

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 LS Protection diodes status and recommendations for LS1

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 Protection diodes status and recommendations for LS1

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

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

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) Protection diodes status and recommendations for LS16 First 13 kA Test run 4.2 K Spec. [µΩ] # of contacts measured Min. measured [µΩ] Max. measured [µΩ] Average [µΩ] rms [µΩ] First 13 kA Last 13 kA< 5 µΩ # of contacts measured Contact resistance [µΩ] Bad assemblies 7.5 µΩ 14 µΩ 4.5 µΩ 30 µΩ

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 Protection diodes status and recommendations for 4.2 K, standard tests Test typeSpec. [µΩ] # of contacts measured Min. measured [µΩ] Max. measured [µΩ] Average [µΩ] rms [µΩ] Standard< 2 µΩ Special< 2 µΩ Contact resistance [µΩ] # of contacts measured

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 Protection diodes status and recommendations for LS18 R < 2 µΩ required R < 1 µΩ measured

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

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 Protection diodes status and recommendations for LS110

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 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 Protection diodes status and recommendations for LS111 R BB Diode/Plate R BB SSS/Plate R BB RT (  ) R BB RT (  0.4< 0.1

Impact on LS Protection 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