1. A COMMON R&D ON THE HIGH GRADIENT Nb CAVITIES
Fabien Éozénou
WORKSHOP FJPPL 2007
May 10th 2007
05/10/2007
- Fabien Eozénou -

2. Why are Electropolishing and Baking crucial. MAJOR ISSUES
OUTLINE
CONTEXT: ILC
Why are Electropolishing and Baking crucial.
MAJOR ISSUES
LAST RESULTS PRESENTED AT TTC by KEK
LAST RESULTS PRESENTED AT TTC by SACLAY
COMMON R&D PROGRAM
05/10/2007
- Fabien Eozénou -

3. CONTEXT
05/10/2007
- Fabien Eozénou -

4. R&D NECESSARY FOR ILC International Linear Collider
16000 Superconductive Nb cavities > 35 MV/m
Surface treatments crucial for high gradients
R&D necessary (Ex GDE S0 program for reproducible gradients)
‘Standard preparation’ :
Barrel Polishing + EP + Anneal + Final EP + HPR + Rinse + Baking
EP = Electro-Polishing
HPR = High Pressure Rinsing
05/10/2007
- Fabien Eozénou -

5. R&D CRUCIAL ON TWO DIFFERENT TOPICS
Electropolishing
Baking
Electropolishing was a breakthrough to achieve high gradients
By H.Padamsee
Baking:
Cavity is baked under vacuum to remove high field Q-Slope whose origin remains mysterious
‘Standard’ parameters: 120°C: 48h
05/10/2007
- Fabien Eozénou -

6. 2 H+ + 2 e-  H2 (Teflon net to prevent H contamination)
WHAT IS ELECTROPOLISHING? (EP)
Process
- Nb polished internally with an electrolyte
(concentrated H2SO4 - HF mixture) under voltage
- Cavity = Anode & Cathode is an Al pipe inside the cavity
Chemical reactions
- Anode: Niobium oxidation
2 Nb + 5 H2O  Nb2O H e-
- Cathode: H2 generation
2 H+ + 2 e-  H2 (Teflon net to prevent H contamination)
- HF: dissolution of oxide Nb2O5 layer
- H2SO4: forming of a viscous layer
05/10/2007
- Fabien Eozénou -

7. MACROPOLISHING + MICROPOLISHING
ELECTROLYTE
Regrouper 13 et 14
Micropolishing smoothens irregularities < 1 µm
Better RF performances due to smoother surface?
05/10/2007
- Fabien Eozénou -

8. ELECTROPOLISHING AND BAKING SET-UP
Single Cell Ichiro Cavity EP At KEK/ Nomura Plating
Single Cell EP at Saclay
Infra Red cavity baking in Clean Room at Saclay
9-Cell EP For STF at NP
05/10/2007
- Fabien Eozénou -

9. Achieve a better reproducibility for high gradients Reduce impurities
MAJOR ISSUES
Achieve a better reproducibility for high gradients
Reduce impurities
Choose better rinsing procedures
Improve baking parameters
Better knowledge of acid quality
05/10/2007
- Fabien Eozénou -

10. LAST RESULTS FROM KEK ON SINGLE CELL PRESENTED AT TTC MEETING
05/10/2007
- Fabien Eozénou -

11. SINGLE CELL STUDY
05/10/2007
- Fabien Eozénou -

12. EFFICIENT RECIPE FOR LOW SCATTER
05/10/2007
- Fabien Eozénou -

13. ACID QUALITY CONTROL BY ICE
F- and SO42- in EP acid measured by Ion Capillary Electrophoresis (ICE)
HF losses due to degassing during acid preparation and EP are huge!
05/10/2007
- Fabien Eozénou -

14. LAST RESULTS FROM SACLAY ON SINGLE CELL PRESENTED AT TTC MEETING
05/10/2007
- Fabien Eozénou -

15. LAST RESULTS FOR NEW BAKING PARAMETERS
B. Visentin
05/10/2007
- Fabien Eozénou -

16. SINGLE CELL EP + MODELING
Single cell Electro-polishing:
First Results.
EP at constant voltage
Baking and RF DESY
42.73 after baking
+7MV/m / last treatment
[F-] at time 1 000s
Modeling: Influence of fluid circulation/cathode shape
COMSOL Software
Convection and diffusion
+ Chemical Reaction
By M. Bruchon
05/10/2007
- Fabien Eozénou -

17. SEARCH FOR BEST EP PARAMETERS
Voltage
New Voltage has been investigated. 5 Volt with standard mixture
Oscillation region → very shiny surface.
(Cavity 1C21 waiting for test).
Concerning the study for different HF-H2SO4-H2O mixtures
Standard mixture works well.
Water addition (Ex mixture) undesirable
(lower removal rate and deteriorated surface).
High HF concentrations promising on samples → mixture to be tested on single cell (low T, low voltage).
Diluted mixtures tested but Hydrogen contamination
Intensity
Voltage
05/10/2007
- Fabien Eozénou -

18. CROSS PROCESSING AND TESTING OF CAVITIES
COMMON R&D PROGRAM:
CROSS PROCESSING AND TESTING OF CAVITIES
05/10/2007
- Fabien Eozénou -

19. BAKING RESISTANT CAVITIES
Some cavity tested at Saclay are not cured by baking! Polluted Niobium?
Would heavy material removal by Barrel Polishing at KEK cure this batch of cavity?
05/10/2007
- Fabien Eozénou -

20. ELECTROPOLISHING AND MODELINGLL
comparative studies
between TTF, RE, LL, IS shapes
1500 s
to s
(mol.m-3)
DIFFERENT CATHODE SHAPES INVESTIGATED BY MODELING
→ comparative RF measurements
between TTF and IS shapes
05/10/2007
- Fabien Eozénou -

21. « 1 - HOUR » BAKING & TUNER TESTS
After positive result with “Fast Argon Baking” 145 °C / 3 hours …
New apparatus under fabrication at Saclay
for “1-Hour Baking” at 160°C (UHV or Argon)
RF Test on 1-cell LL Ichiro cavity
With a cavity from KEK
Performances Comparison between “standard UHV baking”
and “ 1-hour Argon baking”
Tests at KEK with Saclay tuners for Lorenz forces detuning at high gradients on 9-cells Ichiro cavities at 77K
05/10/2007
- Fabien Eozénou -

22. BETTER UNDERSTANDING OF BATH AGING
At Saclay, we use a simple (but not precise) way to evaluate degassed acid.
Scrubber for EP Set-Up:
Sodium hydroxide
+ BTB C27H28Br2O5S 
When the mixture becomes acidic, it turns yellow.
+ Ionic chromatography tested on sample electropolishing
ARE INVESTIGATIONS AT KEK AND SACLAY IN ACCORDANCE?
05/10/2007
- Fabien Eozénou -

23. Thank you!!!
05/10/2007
- Fabien Eozénou -