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High Gradient Nb Cavities: Electropolishing and Baking Research & Development

This workshop by Fabien Eozénou in May 2007 focuses on the crucial processes of electropolishing and baking for high-gradient Nb cavities in the context of the ILC. Major issues, last results and common R&D programs are discussed, shedding light on the significant advancements made in surface treatments to achieve reproducible gradients for the International Linear Collider project.

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High Gradient Nb Cavities: Electropolishing and Baking Research & Development

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

  2. 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 - Fabien Eozénou -

  3. CONTEXT - 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 - 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 - Fabien Eozénou -

  6. 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  Nb2O5 + 10 H+ + 10 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 - Fabien Eozénou -

  7. MACROPOLISHING + MICROPOLISHING ELECTROLYTE Micropolishing smoothens irregularities < 1 µm Better RF performances due to smoother surface? - 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 - Fabien Eozénou -

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

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

  11. SINGLE CELL STUDY - Fabien Eozénou -

  12. EFFICIENT RECIPE FOR LOW SCATTER - 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! - Fabien Eozénou -

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

  15. LAST RESULTS FOR NEW BAKING PARAMETERS B. Visentin - Fabien Eozénou -

  16. [F-] at time 1 000s SINGLE CELL EP + MODELING Single cell Electro-polishing: First Results. EP at constant voltage Baking and RF Test @ DESY 42.73 MV/m @1.8K after baking +7MV/m / last treatment Modeling: Influence of fluid circulation/cathode shape COMSOL Software Convection and diffusion + Chemical Reaction By M. Bruchon - 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 1-9-1 mixture) undesirable • (lower removal rate and deteriorated surface). • High HF concentrations promising on samples → 3 - 6.72 - 0.28 mixture to be tested on single cell (low T, low voltage). • Diluted mixtures tested but Hydrogen contamination Intensity Voltage - Fabien Eozénou -

  18. COMMON R&D PROGRAM: CROSS PROCESSING AND TESTING OF CAVITIES - 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? - Fabien Eozénou -

  20. ELECTROPOLISHING AND MODELING LL comparative studies between TTF, RE, LL, IS shapes 1500 s 13 000 to 30 000 s (mol.m-3) DIFFERENT CATHODE SHAPES INVESTIGATED BY MODELING → comparative RF measurements between TTF and IS shapes - 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 - 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? - Fabien Eozénou -

  23. Thank you!!! - Fabien Eozénou -

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