CSCM type test: Diode Leads and Diodes Gerard Willering & Vincent Roger TE-MSC With thanks to Bernhard Auchmann, Zinour Charifoulline, Scott Rowan, Arjan Verweij, Daniel Wollmann and all involved in the CSCM test MPE-TM

Outline Diode leads Test parameters and conditions Measurements Comparison with test station data Diodes Test parameters and conditions Measurements Concluding remarks Gerard Willering – TE-MSC-TF - CSCM type test - 16/05/2013

Diode leads: Measured voltages Board A Board B Large data set acquired: RB156 voltage signals RQF 51 voltage signals QPS Board A: BB + interconnections QPS Board B: BB + interconnections + diode leads

Diode lead resistance Gerard Willering – TE-MSC-TF - CSCM type test - 16/05/2013 Diode leads Include 3 types of contact - Diode – Heatsink (clamped) - Heatsink – busbar (bolted) - Busbar – busbar (bolted) - About 60 cm of bus bar In total 6 contacts per voltage signal.

Diode lead resistance Gerard Willering – TE-MSC-TF - CSCM type test - 16/05/2013 Low-resistance RB lead

Diode lead resistance Gerard Willering – TE-MSC-TF - CSCM type test - 16/05/2013 Highest resistance RB lead -At 2 kA run still low resistance -Resistance increase from the first 4 kA run onwards -Resistance reduction during long 7 kA run after short 8 kA run. -Low-current characteristics used for statistical analysis.

Typical behavior: 1.At the first ramp to a higher current the resistance increase is significant 2.After a prolonged run at the similar current the resistance is reduced. For the RQF diode leads similar behavior is seen.

During CSCM R max = 70 µΩ in 6 contacts combined In Block-4 R max > 35 µΩ in 1 diode-heatsink contact. Note: - Different current profiles - Different cooling Diode lead resistance - Comparison to test station data ?

Fast jumps in diode lead resistance Fast jumps identified as the main risk: possibly mechanical movement in bolted joints WhereTypeI (kA) Step (mv) Step ( μΩ) Time (ms) LHC ’11Quad lead416040<50 LHC ‘13Dip lead4307< 120 LHC ’13Quad lead45012< 120 LHC ’13Quad Lead6508< 120 LHC ‘13Quad lead < 120 SM18HS-diode – LHC quad - Verweij 2013 – CSCM type test 2012 – SM18 test station Heatsink-busbar The SM18 test shows that heatsink-busbar contacts can have fast jumps.

Remarks on Diode lead resistance Gerard Willering – TE-MSC-TF - CSCM type test - 16/05/2013 Data analysis -Maximum resistance is in the range as observed for diode-heatsink contact -Fast jumps may occur as well in diode-heatsink contact -A resistance increase in the other two contacts are not identified, but cannot be excluded. -The high-resistances are all “self-healing” as was seen before for diode- heatsink contacts Impact on the test after LS1 -No unexpected results → No show stoppers. Note: the part that was deemed most risky is consolidated during LS1 (the connection plates of the quad diode leads).

Diode opening Gerard Willering – TE-MSC-TF - CSCM type test - 16/05/2013 Prior to high current runs the diodes need to be opened. 1. PC initialization 2. Ramp to 400 A 3. Warmup of magnets and gradual opening of diodes 4. Warmup of diodes → reduction of V forward 5. High current ramp In stage 1 and 2 most current is in the magnet From stage 3 on the current shifts more to the diode circuit. “Slow” opening is required to allow the PC to respond.

Diode opening – Forward voltage Gerard Willering – TE-MSC-TF - CSCM type test - 16/05/2013 Typical opening 1.Increase in I magnet and V 2.V forward reached 3.Warming of the diode – decrease in V forward Dip in voltage after opening -Only in Quad diodes at I = 400 A in 47 out of 364 cases. -Quick decrease in voltage suggest quick increase in temperature → local warm-spot -Regular pattern, always 1.55 to 1.65 V -At 1.5 V the temperature is well below 70 K. -In all the cases the voltage characteristics is the same within ± 1 % and the dip seems to have no permanent effect.

Remarks on V forward of the diodes Gerard Willering – TE-MSC-TF - CSCM type test - 16/05/2013 Data analysis -Strange dip seen only in 13 % of Quad diode openings -At high currents these diodes did not show any deviation from normal behavior. Comments for LS1 qualification test -Since V forward remains at 1.6 V the temperature is much less than 70 K. -After the dip all diodes show similar values of V forward.

Concluding remarks on diodes and diode leads Gerard Willering – TE-MSC-TF - CSCM type test - 16/05/2013 -No show stoppers identified on diodes and diode leads for the CSCM test in LS1 -Large sets of data on diode leads show resistance variations in the range that has been seen before. -Variations in diode opening voltage were unexpected, but are deemed not to be a risk for the test.

Spare slides

Diode opening – statistics of dips With a lower opening temperature (higher voltage) the dip is occurring more often.

Increasing to 6 kA Increasing in to 13 kA