1. Cold Diode Project TE/MPE - TM
Introduction
Aim of Project
Diode stack inventory
Procurement of new parts
Complementary activities on diodes
New diode Lab in Bd 272
Coming steps
Conclusion
Giorgio on behalf of M.Bednarek, S.Deleage, M.Favre, S.Pemberton, G.Seweryn, K.Stachon, Z.Toch,

2. Introduction
The cold diode assembly is a protective component of the superconducting magnets: in case of a quench, the diode bypass the magnet:
Like the other components of the circuit, the cold diode has to carry 12 kA during the current decay: 100 s. for RB and 30 s. for RQ
Schematic of the RB circuit (main dipole)

3. Introduction: dipole and quadrupole stack
Main Quadrupole busbar
Diode 1
Diode 2
Ansys model from S. Izquierdo
Main Dipole busbar
Diode Heat Sink
Diode 1
Diode Heat Sink

4. Introduction: dipole diode stack
Rbus-bus
(‘half moon’)
R < 2 µΩ (300K)
Upper diode busbar
Diode box,
Helium contents : 5 liter
RHS-bus
R < 2 µΩ (300K)
Upper
heat sink
Voltage taps on the diode press-pack
Rdiode-HS
Lower
heat sink

5. Aim of the Project
The aim of the project is to have enough spare diode stacks, MB and MQ type, to cope magnet replacement during next LS2 and have some spares.
Dipole diode stack (MDA or MDB): 30 pc
+ 10 optional
Quadrupole diode stack (MQA or MQD): 10 pc
Reminder: during LS1 we replaced 17 MDs
(dipole type) and 4 MQs (quadrupole type)
Restart R&D program on protection diode.

6. Diode stack inventory (actual status)
Spares diode stacks on stock
Spares diode stacks under preparation
MDA : 10
MDB: 13
MQAs: 1
MQBs: 5
MDA-0185
MDB- 0200
MQA 0441 (*)
MQB 2003
MDA-0213
MDB-01179
MQB 2004
MDA-0673
MDB-2008
MQB 2006
MDA-2004
MDB-2010
MQB 2007
MDA-2013
MDB-2011
MQB 2008
MDA-2015
MDB-2017
MDA-2021
MDB-2018
MDA-2022
MDB-2019
MDA-2023
MDB-2020
MDA-2024
MDB-2025
MDB-2026
MDB-2027
MDB-2028
MDAs : 3
MDBs: 13
MQAs: 1
MQBs: 5
MDA-0302
MDB-0107
MQA 0401 (*)
MQB 0528 (*)
MDA-1281
MDB-0111
MQA 0280
MQB 2001 (*)
MDA-1353
MDB-0131
MQA 0312
MQB 0203
MDB-0169
MQA 2101
MQB 0456
MDB-0333
MDB-1334
(*) Diode “grignotée”
(*) Ready for cold testing in SM18
MQA 2101: assembled with new components from 2016

7. New parts procurement
Main components of diode stack: more than 25 parts into a dipole stack:
Lower diode bus bar
Upper diode bus bar
Top plate
Bus bar insulator
Upper
heat sink
Spring washers
Tie rod
Diode press-pack
Lower
heat sink
Bottom plate
Dipole stack insulator
Quadrupole stack

8. New parts procurement
The order DO-27528, went through in Feb.2016 with the main improvements:
Dipole bus bar in one piece (no e-beam welding)
Isolating parts (molded instead of machined)
Prototypes received in May 2016
Quadrupole’s copper parts: (DSM)
dimensional verification
visual inspection
dummy assembly
Electrical contact resistance measurement
OK for series production !
Series production received in September 2016
Dipole’s bus bars…OFE copper (TRIPLECUT)
dimensional verification, visual inspection

9. New parts procurement Dipole’s copper parts…(HST)
dimensional verification
visual inspection: heat sink circular shape…
dummy assembly
Electrical contact resistance measurement
Dipole heat sink not OK for series production !
Exchange of samples, finally satisfactory on a dummy heat sink (Alu)!
Production of new copper prototype (Nov.2016), before launching series production…
Final series production received after CERN acceptance (Jan.2017)

10. New parts procurement Belleville washers Isolating pieces…
dimensional verification
visual inspection
dummy assembly
Apply correction
Improve varnishing
Insulation test on dummy assembly
OK for series production !
Series production received in September 2016
Belleville washers
Large stock of used one : 700 pc. 8/stacks 87 stacks
Mechanical lab testing of new and used washers
Confirmation from manufacturer that they can be re-used
No need to buy new Belleville washers !

11. Prototypes with 2016 parts…
Finally, we received all new parts to assemble the new diodes stacks (30MBs and 10 MQs)

12. Complementary activities …
Temporary diode lab in Bd 867 (Thanks to Betty!)
Dedicated place with appropriate condition has been used !
Measuring equipment was transported to the new room.
Restarted the test setup (replacement of faulty power resistor, revised cabling)
Press-pack diode inventory and testing
Started wafer inventory and re-testing at
300K and 77K (Liquid Nitrogen)
Learning process for Zibi !
Available wafers : 191, to be sorted, classified!
Wafer tested
Wafer rejected
Wafer for testing
207 16

13. Electrical test on diode press-pack
All available press-pack (207) have been electrically tested at 300K and 77K:
Forward measurement: Ufwd (I)
Pulse test at different current
Forward characteristics
Limit applied:
Ufwd(12000A) < 1.05 [V] | 300 K
Ufwd(12000A) < 1.65 [V] | 77 K

14. Electrical test on diode press-pack
Reverse measurement: Urev (I)
Measure the leakage current under reverse voltage
Reverse characteristics
Limit applied:
Urev (1mA) > 550 [V] | 300 K
Urev (1mA) > 300 [V] | 77 K

15. Electrical test on diode press-pack
Krzysztof Stachon developed a new software, based on PXI crate, to automatize the testing of the diode:
Replace the oscilloscope
Improve the reliability of the measurement
Database storage of test results
To be finalized in the new diode lab

16. Geometrical measurement…
Wafer dimensional measurement by the metrology lab
In order to verify the dimensional criterion of the wafers, a sample of 20 wafers was given to metrology lab:
6 um
62 um
4um

17. Contact surface…under pressure
Fujifilm improvement…
Purchase a new scanner with dedicated software to quantify the contact surface and the pressure applied
Prototype parts were measured: report available
Quantitative analysis will be possible !

18. Contact surface…under pressure
All diode press-packs have been qualified with dummy diode (rectified cylinder):
Measure the flatness of the diode press-pack under 42 kN !
Sort the diode press-pack according to contact surface !

19. New diode Lab in Bd 272
New diode lab is being prepared in building 272:
The structure of the building was installed in August, but incomplete.
Electricity in the building was accepted (HSE) (Sept.2016).
Air conditioning and ventilation installation completed (Jan.2017).
Cupboards were ordered and installed for storage.
Dedicated workshop were ordered by Hera (long delay delivery) and are being finalized.
Other tooling have been ordered: new press, “chèvre”, pallet truck, packing device, etc…
We should have the new lab operational very soon (April)
Improvement are planned from hardware and software point of view in the diode stack testing procedure.

20. New diode Lab in Bd 272

21. Coming steps… Test and validation of 2016 quadrupole stack (MPE +MSC)
Refurbishing of 3 old MQA quadrupole stacks DONE OK !
Assembly of 1 new MQA quadrupole stack (2101) DONE OK !
Testing of the new MQA2101 stack at 300K and 77K, in Bd 272
4 stacks ready for testing in SM18 for April 2017
Installation of new diode lab, including new equipment
Furniture and workshop received.
Additional equipment received: New press, “Chèvre”, Pallet trucks
Setting up the test stand: ongoing
Improving hardware and software for the new test stand
Optimize the test stand
Upgrade with new equipment
Contacting Dynex to assure wafer production, know how for future press-pack orders…

22. Conclusion
Compare to the initial road map, there is some delay mainly due to:
OFE Copper purchasing procedure (Material request)
Priority was given to IGBT switch (Mathieu, Samuel and Zibi)
Training period of new test operator on diode press-pack
Re-installation in new building
Acceptance of dipole heat sink (machining process still to be approved)
Delivery of new diode lab, including furniture, air conditioning, tooling
Re-qualification of existing press-pack better than expected.
Enough diode stack for magnet replacement (except MQAs)
We should be able to have 30 new dipole stacks and 10 new quadrupole stack, fully qualified, by the end of 2017.
No showstopper for LS2 purpose

23. Thank you !