1. Guillaume Olry, Sébastien Bousson CNRS/IN2P3/ IPN Orsay – Paris-Sud University Experience on Spiral2 cavity cleanliness degradation during clean room assembly

2. S. Bousson – Spiral-2 cavity baking in clean room – TTC Topical Workshop – 13 th Nov 2014 - Saclay  High  Spiral-2 QWRs 2 Cryomodules A sectionCryomodules B section Cryomodule B housing two beta 0.12 QWR

3. S. Bousson – Spiral-2 cavity baking in clean room – TTC Topical Workshop – 13 th Nov 2014 - Saclay  Spiral2 cavities clean room assembly Clean room assembly procedure was developed and tested during the prototyping phase of Spiral2 The high beta SP2 cryomodule prototype had performances within specifications For the series production, we applied the same protocol, mainly based on cleaning and assembly procedures, with few QC (particle counting)… BIG MISTAKE ! Parts suppliers, production procedure,… were different for the series than for the prototype -> initial cleanliness of several parts was different (vacuum tubes, power coupler,…) -> as a consequence final cleanliness was also different (unfortunately, it was worse…)

4. S. Bousson – Spiral-2 cavity baking in clean room – TTC Topical Workshop – 13 th Nov 2014 - Saclay  Cavity VT results vs cryomodule perf. High beta Spiral2 Cryomodule assembly and results: early days situation (in 2011): CMB1 : Eacc max 4.4 MV/m (8.9 in VT) & 5.1 MV/m (8.7 in VT) CMB2 : Eacc max 5.2 MV/m (10.4 in VT) & 8.4 MV/m (10.4 in VT) CMB3 : Eacc max 3.9 MV/m (10.0 in VT) & 6.7 MV/m (10.3 in VT) Vacuum level always OK Power coupler RF conditioning: no specific issue (both @ warm & cold T) Cryo losses OK Cavity Qo OK BUT Early quenches (wrt VT tests) & very strong field emission (from 30 to > 100 mSv/h

5. S. Bousson – Spiral-2 cavity baking in clean room – TTC Topical Workshop – 13 th Nov 2014 - Saclay  Then particle hunting started… We have introduced systematic checks of parts and sub- assembly quality control wrt particulate contamination.

6. S. Bousson – Spiral-2 cavity baking in clean room – TTC Topical Workshop – 13 th Nov 2014 - Saclay  Vacuum tube contamination First finding: particle contamination of vacuum tubes Contamination problems on two pumping tubes: CF16 tube with bellow (coupler) and CF40 tube (bended tubes used for connection to cryomodule)  Even after cleaning (= US cleaning and UPW rinsing), still « dirty » and observation of dust !

7. S. Bousson – Spiral-2 cavity baking in clean room – TTC Topical Workshop – 13 th Nov 2014 - Saclay  Vacuum tube contamination First finding: particle contamination of vacuum tubes CF 16 : Some had traces of rust (strange on stainless steel material…)

8. S. Bousson – Spiral-2 cavity baking in clean room – TTC Topical Workshop – 13 th Nov 2014 - Saclay  Vacuum tube contamination First finding: particle contamination of vacuum tubes CF 40 : All of them showed traces of rust !

9. S. Bousson – Spiral-2 cavity baking in clean room – TTC Topical Workshop – 13 th Nov 2014 - Saclay  Vacuum tube contamination First finding: particle contamination of vacuum tubes The source of it is during fabrication, where non-SS tools are used to bend the tubes… Cure: all tubes have been reprocessed

10. S. Bousson – Spiral-2 cavity baking in clean room – TTC Topical Workshop – 13 th Nov 2014 - Saclay  Power coupler contamination Second finding: issues with power coupler cleanliness. After cryomodule test, after dis-assembly, we observed obvious signs of strong FE:

11. S. Bousson – Spiral-2 cavity baking in clean room – TTC Topical Workshop – 13 th Nov 2014 - Saclay  Power coupler contamination Second finding: particle contamination coming from the power couplers. Series power couplers appeared to be very difficult to clean, contrary to what we experienced with the prototype Not produced by the same vendor…  antenna surface quality different Particle size0.3 µ0.5 µ1 µ5 µ10 µ25 µ Blow thru CF16 port31812633000 Blow thru antenna port4474172053360144

12. S. Bousson – Spiral-2 cavity baking in clean room – TTC Topical Workshop – 13 th Nov 2014 - Saclay  Power coupler contamination Second finding: particle contamination coming from the power couplers.  SOLUTIONS :  All couplers have been electro-polished (50 µm)  Assembly procedures upgraded and particule counting on all components before mounting

13. S. Bousson – Spiral-2 cavity baking in clean room – TTC Topical Workshop – 13 th Nov 2014 - Saclay  Contamination risks with gate valve Third finding: risk of cavity pollution with EPDM gate valve (used on warm unit and and power coupler) We found out that EPDM (ethylene propylene diene monomer) seals of the gate and angle valves were outgasing heavy elements. The flow rate was so high that it limited the vacuum in the chambers above 2e-8 mbar (specifications: 1e-9 mbar without beam) Inter-cryomodules warm sections during clean room assembly and on alignment bench. Courtesy P.E. Bernaudin (Ganil)

14. S. Bousson – Spiral-2 cavity baking in clean room – TTC Topical Workshop – 13 th Nov 2014 - Saclay  Contamination risks with gate valve Third finding: risk of cavity pollution with EPDM gate valve (used on warm unit and and power coupler) Cure: changing seals to viton ones (after cross-checking the integrated radiation doses requirements for the linac) Baking also helps to reduce mass > 45 Courtesy P.E. Bernaudin (Ganil)