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

2. 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.

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

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

5. 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

6. 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

7. 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.

8. 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!

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

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

11. 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.

12. 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

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

14. 90 μΩ 210 μΩ A15L8 - zoom Washers are not as specified by the design!
Photo by Ludovic Grand-Clement

15. 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.

16. 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.

17. Summary of NCs Bad V-tap (no continuity) V-tap swaps
EDMS
V-tap swaps
EDMS
EDMS
EDMS
EDMS
EDMS
EDMS
EDMS
EDMS
Diode lead contact resistance above
15.5 μΩ
EDMS
EDMS
EDMS
EDMS
EDMS
EDMS
EDMS
EDMS

18. Summary of NCs Bad V-tap (no continuity) V-tap swaps
EDMS
V-tap swaps
EDMS : Problem solved, NC CLOSED with warnings
EDMS
EDMS : Problem solved, NC CLOSED with warnings
EDMS : Problem solved, NC CLOSED with warnings
EDMS
EDMS : Problem solved, NC CLOSED with warnings
EDMS
EDMS
Diode lead contact resistance above
15.5 μΩ
EDMS
EDMS : Diode stack exchanged, NC CLOSED
EDMS : Diode stack exchanged, NC CLOSED
EDMS : Diode stack exchanged, NC CLOSED
EDMS
EDMS
EDMS
EDMS

19. 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.

20. Thank you for your attention!

21. Back-up slides…

22. 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.

23. 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