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 16/05/2008 - Fabien Eozénou - FJPPL 2008 A_RD_04

R&D ON HIGH GRADIENT Nb CAVITIES A CRUCIAL R&D ON HIGH GRADIENT Nb CAVITIES 16/05/2008 - Fabien Eozénou - FJPPL 2008 A_RD_04

TWO MAIN ROJECTS RELATED TO THE “COLD” TECHNOLOGY International Linear Collider ~17000 Superconductive Nb cavities > 31.5 MV/m 1 Tev XFEL (X-Ray Free-Electron Laser) 17.5 GeV λ=0.1nm 808 cavities E=23.5 MV/m assembled in 101 cryomodules 16/05/2008 - Fabien Eozénou - FJPPL 2008 A_RD_04

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 16/05/2008 - Fabien Eozénou - FJPPL 2008 A_RD_04

Electro-Polishing (EP): More details 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 16/05/2008 - Fabien Eozénou - FJPPL 2008 A_RD_04

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 ) 16/05/2008 - Fabien Eozénou - FJPPL 2008 A_RD_04

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) 16/05/2008 - Fabien Eozénou - FJPPL 2008 A_RD_04

IMPROVING THE BAKING PARAMETERS 16/05/2008 - Fabien Eozénou - FJPPL 2008 A_RD_04

FAST ARGON BAKING B.Visentin Use of Argon Instead of high Vacuum 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 16/05/2008 - Fabien Eozénou - FJPPL 2008 A_RD_04

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 16/05/2008 - Fabien Eozénou - FJPPL 2008 A_RD_04

IMPROVING THE EP PARAMETERS 16/05/2008 - Fabien Eozénou - FJPPL 2008 A_RD_04

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. 16/05/2008 - Fabien Eozénou - FJPPL 2008 A_RD_04

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: 1) EP(20 µm) + HPR + Test 2) EP (20) + H2O2 Rinsing + HPR + Baking + Test RF 3)EP (20) + Degreasing + HPR + Baking + Test RF 4) EP (20) + Ethanol Rinsing + HPR + Baking + Test RF 5) EP (20) + HF Rinsing + HPR + Baking + Test RF 6) EP (20) + Boiling Water Rinsing + HPR + Baking + Test RF 7) EP (20) + EP (3μm fresh acid) + HPR + Baking + Test RF 8) EP (20) + Oxipolishing + HPR + Baking + Test RF 16/05/2008 - Fabien Eozénou - FJPPL 2008 A_RD_04

EXAMPLE: EVALUATION OF FRESH EP AT KEK 16/05/2008 - Fabien Eozénou - FJPPL 2008 A_RD_04

Light EP + 30’ Ethanol Rinsing + HPR 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 16/05/2008 - Fabien Eozénou - FJPPL 2008 A_RD_04

RESULTS FOR 1DE1 AND 1DE3 CAVITIES 16/05/2008 - Fabien Eozénou - FJPPL 2008 A_RD_04

SUMMARY FOR THE 6 TESTS FOR S0 16/05/2008 - Fabien Eozénou - FJPPL 2008 A_RD_04

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! 16/05/2008 - Fabien Eozénou - FJPPL 2008 A_RD_04

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?... 16/05/2008 - Fabien Eozénou - FJPPL 2008 A_RD_04

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 16/05/2008 - Fabien Eozénou - FJPPL 2008 A_RD_04

IMPROVING THE EP PROCESS 16/05/2008 - Fabien Eozénou - FJPPL 2008 A_RD_04

IMPORTANCE OF THE FLUID DISTRIBUTION Example of study of the process by E. Kako (KEK) 16/05/2008 - Fabien Eozénou - FJPPL 2008 A_RD_04

→ Modelling of fluid dynamics and chemical reactions in 2D 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 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: x is the production of H2NbOF5 at time t, α and β the initial concentration of Nb2O5 and HF 16/05/2008 - Fabien Eozénou - FJPPL 2008 A_RD_04

Phenomenon transport : GENERAL EQUATIONS Mass balance equation: Phenomenon transport : Diffusion Migration Convection Navier Stockes equation (incompressible fluid) Electroneutrality Gravity effect HF concentration versus time and fluid velocity High concentrated electrolyte 16/05/2008 - Fabien Eozénou - FJPPL 2008 A_RD_04

ASSYMETRIC EP FOR SINGLE-CELL CAVITIES Modelling of Saclay EP Set-up for different shapes of single cell Velocity LL TESLA HF Left beam tube is badly swept by the acid Acid “rebounds” on the right iris HF Velocity 16/05/2008 - Fabien Eozénou - FJPPL 2008 A_RD_04

IMPROVEMENT FOR SINGLE-CELL CAVITIES Inflow and outflow like 9-cells cavities Velocity field HF at 20 000s New symmetric acid distribution → more uniform attack (be careful for the irises) Will be experimentally tested at Saclay 16/05/2008 - Fabien Eozénou - FJPPL 2008 A_RD_04

9-CELL CAVITIES MODELLING Specifications from KEK (size of holes, inflow and outflow of acid) ICHIRO Cavities Fluid velocity [HF] at 4 000 s [HF] at 20 000 s TESLA Cavities HF Good electropolishing of central cell #5 Electropolishing needs to be improved in the other cells Velocity Explanation to the field flatness degradation experimentally observed at KEK after electropolishing ? →Outlook: 3D Modelling, Alternative cathode shape 16/05/2008 - Fabien Eozénou - FJPPL 2008 A_RD_04

IMPROVING THE INFRASTRUCTURES 16/05/2008 - Fabien Eozénou - FJPPL 2008 A_RD_04

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 16/05/2008 - Fabien Eozénou - FJPPL 2008 A_RD_04

STUDY FOR 9-CELL EP SET-UP IMPLEMENTATION AT SACLAY 16/05/2008 - Fabien Eozénou - FJPPL 2008 A_RD_04

Preparation and Assembly Facilities for SRF Activities at Saclay SPIRAL2, SOLEIL, … cryomodule assembly 10 m X 13 m XFEL cryomodule assembly 4.4 m X 35 m XFEL cold mass assembly 6.5 m X 14 m NEW EQUIPMENT EXISTING EQUIPMENT Surface characterization (optical microscope, MEB, SIMS, …) chemical treatment of multicell cavities (+US and UP water rinsing) Ultra Pure water plant 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 EP monocell R&D on samples CP monocell 16/05/2008 - Fabien Eozénou - FJPPL 2008 A_RD_04