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A COMMON R&D ON THE HIGH GRADIENT Nb CAVITIES

A COMMON R&D ON THE HIGH GRADIENT Nb CAVITIES. Kenji Saito Takayuki Saeki Yasuo Higashi Fumio Furuta. Bernard Visentin Fabien Eozénou Mélanie Bruchon. A CRUCIAL R&D ON HIGH GRADIENT Nb CAVITIES. International Linear Collider ~ 17000 Superconductive Nb cavities > 31.5 MV/m 1 Tev.

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A COMMON R&D ON THE HIGH GRADIENT Nb CAVITIES

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  1. A COMMON R&D ON THE HIGH GRADIENT Nb CAVITIES Kenji Saito Takayuki Saeki Yasuo Higashi Fumio Furuta Bernard Visentin Fabien Eozénou Mélanie Bruchon - Fabien Eozénou - FJPPL 2008 A_RD_04

  2. A CRUCIAL R&D ON HIGH GRADIENT Nb CAVITIES - Fabien Eozénou - FJPPL 2008 A_RD_04

  3. International Linear Collider ~17000 Superconductive Nb cavities > 31.5 MV/m 1 Tev TWO MAIN ROJECTS RELATED TO THE “COLD” TECHNOLOGY • XFEL (X-Ray Free-Electron Laser) • 17.5 GeV λ=0.1nm • 808 cavities E=23.5 MV/m assembled in 101 cryomodules - Fabien Eozénou - FJPPL 2008 A_RD_04

  4. Electro-Polishing (EP) And Baking: Reminder ‘Standard’ preparation to reach high gradients: Barrel Polishing + EP + Anneal + Final EP + HPR + Rinse + Baking Electro-Polishing: Internal Surface Treatment of the Cavity filled with acid in presence of Current Standard Baking: Cavity is baked under vacuum to remove high field Q-Slope whose origin remains mysterious ‘Standard’ parameters: 120°C: 48h - Fabien Eozénou - FJPPL 2008 A_RD_04

  5. 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 Electro-Polishing (EP): More details - Fabien Eozénou - FJPPL 2008 A_RD_04

  6. Electro-Polishing (EP) and Baking: Main Breakthroughs Nb Cavity Performances ( 1991 - 1999 ) Continuous improvements with Heat Treatments @ 800 and 1400°C, High Pressure Rinse, Baking & ElectroPolishing. 42 MV/m hard barrier (  2004 ) - Fabien Eozénou - FJPPL 2008 A_RD_04

  7. GOALS OF THE COMMON R&D PROGRAM • Improvement of the Baking Procedure: • Facilitate the baking procedure • Decrease the baking time • Improvement of Electro-Polishing: • Obtaining of high reproducible gradients • Better understanding of the process (use of modelling) - Fabien Eozénou - FJPPL 2008 A_RD_04

  8. IMPROVING THE BAKING PARAMETERS - Fabien Eozénou - FJPPL 2008 A_RD_04

  9. FAST ARGON BAKING B.Visentin IR baking system in Clean Room at Saclay. Use of Argon Instead of high Vacuum 120°C 48h 145°C 3h In terms of Oxygen diffusion in the bulk niobium - Fabien Eozénou - FJPPL 2008 A_RD_04

  10. BAKING RESULTS ON ICHIRO CAVITIES “Ichiro” (or Low Loss) Geometry makes it possible to reach higher gradients → Two cavities received from KEK IS8 Baked under argon during 1 hour at 145°C → + 9MV/m + 1hour additional baking : removal of residual slope. 2 hours = optimal duration for “fast argon” baking Will be presented at EPAC 2008: MoPP154 (B. Visentin et al.) An additional test will be done to reach the quench - Fabien Eozénou - FJPPL 2008 A_RD_04

  11. IMPROVING THE EP PARAMETERS - Fabien Eozénou - FJPPL 2008 A_RD_04

  12. LOW REPEATITIBILITY TESTS ON 9-CELL CAVITIES SHOW A LOW REPEATITIBLITY OF THE GRADIENT COMPARED TO THE CHEMICAL POLISHING. MANY CAVITIES ARE LIMITED BY FIELD EMISSION. IT IS NECESSARY TO IMPROVE RINSING PROCEDURES. - Fabien Eozénou - FJPPL 2008 A_RD_04

  13. ILC GDE S0 PROGRAM ON SINGLE CELL ILC S0 International Program on single-cell cavity: Different Rinsing procedures are evaluated: 6 tests for each “recipe” to have statistics: - Fabien Eozénou - FJPPL 2008 A_RD_04

  14. EXAMPLE: EVALUATION OF FRESH EP AT KEK - Fabien Eozénou - FJPPL 2008 A_RD_04

  15. RESULTS WITH ETHANOL RINSING WITHIN GDE S0 PROGRAM ON 1-CELL Test Within S0 program on single cell: Recipe: Light EP + 30’ Ethanol Rinsing + HPR Mixture: HF(40%) - H2SO4 (95%) with ratio 1 – 9 3 Cavities (Tesla Shape): Before EP at Saclay: • 1DE1: 37 MV/m • 1DE3: 30 MV/m • 1C03: 40 MV/m - Fabien Eozénou - FJPPL 2008 A_RD_04

  16. RESULTS FOR 1DE1 AND 1DE3 CAVITIES - Fabien Eozénou - FJPPL 2008 A_RD_04

  17. SUMMARY FOR THE 6 TESTS FOR S0 - Fabien Eozénou - FJPPL 2008 A_RD_04

  18. FINAL TABLE AND AVERAGE GRADIENT *Additional HPR At Saclay before Test #2 For the 5 EP on Desy Cavities Eacc Max = 41.35 +/- 1.27 Q0 @ Eacc Max= 1.29E10 +/- 5.27E9 ETHANOL RINSING + HPR SHOULD BE CONSIDERED AS A RELIABLE RECIPE! - Fabien Eozénou - FJPPL 2008 A_RD_04

  19. SEARCH FOR NEW PARAMETERS: EP at LOWER VOLTAGE (5V) PROCESS EASY TO CONTROL! = Current Oscillation Regime at any Temperature and stirring conditions. + It does not seem to depend on bath aging. + Low heating of the Bath Surface after 130 µm EP at 5V • Tests With 1C21 Cavity: 2 sequences: 80 µm + 50 µm +Ethanol Rinsing. EP at low temperature first (~20°C) • Very Bright and little grainy surface Ratio Removal @ Iris / Removal @ Equator seems promising 110 µm / 90 µm in the half cell were acid is better renewed Lower than for Standard EP (17V) ? → To be confirmed What is the result in terms of RF performance?... - Fabien Eozénou - FJPPL 2008 A_RD_04

  20. RF RESULTS AFTER LOW VOLTAGE EP Promising Result :1C21 cavity belong to a batch of cavities that show poor results after BCP (Baking Resistant cavities! Eacc<20 MV/m) OUTLOOK: → EP at low Voltage with ICHIRO/1DE1 Cavities + Standard EP on 1C21 → EP at higher temperature to increase the removal rate - Fabien Eozénou - FJPPL 2008 A_RD_04

  21. IMPROVING THE EP PROCESS - Fabien Eozénou - FJPPL 2008 A_RD_04

  22. IMPORTANCE OF THE FLUID DISTRIBUTION Example of study of the process by E. Kako (KEK) - Fabien Eozénou - FJPPL 2008 A_RD_04

  23. Composition of the bath: In practice: Mixture of hydrofluoric and sulfuric acids (1:9 in volumes) Modelling: Density and viscosity of sulfuric acid Nb oxydation: 2 Nb + 5 H2O → 5 H2 + Nb2O5 (1) Nb2O5 + 10 HF → 2 H2NbOF5 + 3 H2O (2) Modelling: Only equation 2, Nb2O5 is continuously formed Kinetic equation: HOW CAN MODELLING HELP US? STUDY WITH COMSOL SOFTWARE M. Bruchon Is the standard EP responsible for the dissymmetric attack of the surface? →Modelling of fluid dynamics and chemical reactions in 2D • x is the production of H2NbOF5 at time t, α and β the initial concentration of Nb2O5 and HF - Fabien Eozénou - FJPPL 2008 A_RD_04

  24. Phenomenon transport : High concentrated electrolyte Diffusion Migration Convection • Navier Stockes equation (incompressible fluid) • Electroneutrality • Gravity effect • HF concentration versus time and fluid velocity GENERAL EQUATIONS • Mass balance equation: - Fabien Eozénou - FJPPL 2008 A_RD_04

  25. ASSYMETRIC EP FOR SINGLE-CELL CAVITIES Modelling of Saclay EP Set-up for different shapesof single cell Velocity LL TESLA HF Left beam tube is badly swept by the acid Acid “rebounds” on the right iris HF Velocity - Fabien Eozénou - FJPPL 2008 A_RD_04

  26. Velocity field HF at 20 000s IMPROVEMENT FOR SINGLE-CELL CAVITIES Inflow and outflow like 9-cells cavities New symmetric acid distribution → more uniformattack (be careful for the irises) Will be experimentally testedat Saclay - Fabien Eozénou - FJPPL 2008 A_RD_04

  27. Specifications from KEK (size of holes, inflow and outflow of acid) Fluid velocity [HF] at 4 000 s [HF] at 20 000 s 9-CELL CAVITIES MODELLING ICHIRO Cavities TESLA Cavities HF Velocity Good electropolishing of central cell #5 Electropolishing needs to be improved in the other cells Explanation to the field flatness degradation experimentally observed at KEK after electropolishing ? →Outlook: 3D Modelling, Alternative cathode shape - Fabien Eozénou - FJPPL 2008 A_RD_04

  28. IMPROVING THE INFRASTRUCTURES - Fabien Eozénou - FJPPL 2008 A_RD_04

  29. NEW EP FACILITY AT KEK 9-Cell Cavity EP at Nomura Plating Building of a new set-up for 9-Cell cavities EP at KEK http://www.linearcollider.org/newsline/readmore_20080327_atw.html - Fabien Eozénou - FJPPL 2008 A_RD_04

  30. STUDY FOR 9-CELL EP SET-UP IMPLEMENTATION AT SACLAY - Fabien Eozénou - FJPPL 2008 A_RD_04

  31. Ultra Pure water plant XFEL cold mass assembly 6.5 m X 14 m XFEL cryomodule assembly 4.4 m X 35 m SPIRAL2, SOLEIL, … cryomodule assembly10 m X 13 m NEW EQUIPMENT EXISTING EQUIPMENT Preparation and Assembly Facilitiesfor SRF Activities at Saclay Surface characterization (optical microscope, MEB, SIMS, …) chemical treatment of multicell cavities (+US and UP water rinsing) CLEAN ROOMS ISO 7 (class 10000) 6 x 7.5 m ISO 5 (class 100) 6 x 6 m ISO 4 (class 10) 6 x 14.4 m EP multi-cells Chemistry storage area Gas cleaning plant CP monocell EP monocell R&D on samples - Fabien Eozénou - FJPPL 2008 A_RD_04

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