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

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 -

CONTEXT 05/10/2007 - Fabien Eozénou -

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 -

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 -

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  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 05/10/2007 - Fabien Eozénou -

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

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 -

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 -

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

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

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

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 -

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

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

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 [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 -

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 05/10/2007 - Fabien Eozénou -

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

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 -

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 05/10/2007 - Fabien Eozénou -

« 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 -

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 -

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