Experience with Vertical ElectroPolishing at CEA Saclay Comparison

Experience with Vertical Electro-Polishing at CEA Saclay Comparison with Horizontal EP F. Eozénou 25/11/2020 CEA DSM Irfu - F. Eozénou - TTC Meeting 2012 JLab WG 2 1

STATUS AT TTC 2011 v Commissioning of the VEP set-up v First operation with 1 Cell 25/11/2020 CEA DSM Irfu - F. Eozénou - TTC Meeting 2011 IHEP WG 2 2

IMPROVEMENT OF THE INFRASTRUCTURE IN 2012 v Working area closed v Tooling for the preparation of the cavity • Cathode’s insertion in 9 Cells • Handling of cavities w/wo He vessel 25/11/2020 CEA DSM Irfu - F. Eozénou - TTC Meeting 2012 JLab WG 2 3

OPERATION IN 2012 Cavity Voltage (V) Acid flow L/min duration (min) Removal rate µm/min 1 C 21 1 AC 03 1 AC 02 1 C 21 1 AC 03 1 AC 01 C 1 -45 1 AC 03 TB 9 R 1025 1 AC 03 20 20 20 12 8 12 12 12 I(V) 7. 5 6. 5 I(V) 6 I(V) 7. 5 6 8 8 8 8 8. 5 - 11 11 17 15 15 -27 >20 24 60 180 293 140 300 98 110 105 30 96 184 120 127 270 360 106 120 330 0. 22 0. 25 0. 33 0. 16 0. 15 tbd 0. 27 0. 26 0. 39 0. 16 0. 19 ~0. 30 <0. 30 0. 16 1 AC 1 6 25 273 tbd v 19 EP sequences v Running time: 55 hours, no major failure v Trend: V↓ acid flow↑ 25/11/2020 CEA DSM Irfu - F. Eozénou - TTC Meeting 2012 JLab WG 2 4

STANDARD PARAMETERS FOR HORIZONTAL EP Easy removal of exhaust gases v High operating voltage: 14 - 17 V →Oscillating current v v Acid flow rate: ~ 10 L/min Acid temperature: T<35°C ω=1 rpm Because of ω, veq=10 -2 m. s-1 → Are these parameters suitable for VEP? ? ? 25/11/2020 CEA DSM Irfu - F. Eozénou - TTC Meeting 2012 JLab WG 2 5

VEP WITH INNAPROPRIATE PARAMETERS (1 Cells) 1 C 21 20 V - 8 L/min - T<25°C v Very bright surface… v … But fine stripes at § Iris § Equator (upper half cell) 1 AC 3 12 V <V<20 V - 8 L/min - 30°C<T<35°C v Local pitting (crown) v Asymmetric treatment Bubble traces Pitting + faster removal! ! Asymmetric treatment ! 25/11/2020 CEA DSM Irfu - F. Eozénou - TTC Meeting 2012 JLab WG 2 6

POSSIBLE EFFECTS OF HIGH V, HIGH T, LOW ACID FLOW v O 2 generated if V>12 V v If flow unsufficient: § Risk of heating (pits) § Risk of unsufficient removal of bubbles v Wider plateau with higher flow rate + low flow at cavity surface 25/11/2020 CEA DSM Irfu - F. Eozénou - TTC Meeting 2012 JLab WG 2 (COMSOL) 7

RF RESULTS WITH INITIAL PARAMETERS 1 C 21 Cavity v Eacc>30 MV/m with high voltage VEP. v Must be improved with optimized parameters. 25/11/2020 CEA DSM Irfu - F. Eozénou - TTC Meeting 2012 JLab WG 2 8

IMPROVEMENT OF THE PROCESS v Decrease in operating voltage: ~ 6 V § No change in performance (demonstrated for HEP) § No risk of O 2. H 2 risk remains § Less sulfur generated v Increase in the acid flowrate: >20 L/min § Better removal of bubbles § Less heating in the cavity v Increase in cathode’s diameter (or shaped cathode) § Higher flow at the cavity surface § More efficient bubble removal (less H 2/cathode surface) 25/11/2020 CEA DSM Irfu - F. Eozénou - TTC Meeting 2012 JLab WG 2 9

1 Cell VEP WITH NEW PARAMETERS →VEP of 1 AC 1 v v v Parameters: 6 V - 25 L/min – 19°C Bright surface of both half cells No bubble trace / No pitting No heating of the acid No sulfur odour Cavity assembled in Cleanroom. Waiting for VT. 25/11/2020 CEA DSM Irfu - F. Eozénou - TTC Meeting 2012 JLab WG 2 10

Additional RF RESULT 1 AC 3: pits due to unadapted parameters (total 250 µm VEP) → + 60 µm with optimized parameters. v Better surface achieved v Pits partially removed v In spite of pits, the cavity is tested → Quench at 34 MV/m at the pit area (Standard Q-Slope before baking) 25/11/2020 CEA DSM Irfu - F. Eozénou - TTC Meeting 2012 JLab WG 2 11

CATHODE’S OPTIMIZATION COMSOL modeling to optimize the shape of the cathode (K. Muller) v Method: Design Of Experiment v Response evaluated: uniformity of the removal (acid flow + electric field) v Parameters: § Shape geometry: cylindrical/ellipsoidal § Shape diameter § Length of the shape § Axis diameter Optimized cathode for 1 Cell Acid flow modelling with optimized cathode 25/11/2020 CEA DSM Irfu - F. Eozénou - TTC Meeting 2012 JLab WG 2 12

VEP OF 9 Cell CAVITY WITH OPTIMIZED PARAMETERS Treatment of TB 9 R 1025 ILC cavity from (previously H-EP) 6 V - 24 L/min - T<25°C Cathode: rod Ø 40 mm v v v 25/11/2020 CEA DSM Irfu - F. Eozénou - TTC Meeting 2012 JLab WG 2 ~ 60 µm removed Heating < +3°C Very bright surface… No bubble trace Brightness improved / previous HEP Promising Result! 13

TEST PREPARATION v Modification of infrastructure for 9 Cell 1. 3 GHz testing. v Cryostat prepared for test at 1. 8 K v Delay: Mistake occured during initial test v Final test planned for early December Before/after baking 25/11/2020 CEA DSM Irfu - F. Eozénou - TTC Meeting 2012 JLab WG 2 14

CONCLUSION v Desirable parameters for VEP are put forward: § Low voltage: 6 V § High acid flow § Low temperature § Large cathode v Results observed: § No bubble trace / No pitting § Nice surface finish § Symmetric brightening in the cell § Low heating in the cavity v 1 Cell and 9 Cell treated with new parameters: waiting for test v Eacc>30 MV/m with inappropriate parameters v Outlook § increase gradually the temperature and acid flowin coming treatments to increase the removal rate § VEP of SPL cavities in early 2013 25/11/2020 CEA DSM Irfu - F. Eozénou - TTC Meeting 2012 JLab WG 2 15

THANK YOU FOR YOUR ATTENTION 25/11/2020 CEA DSM Irfu - F. Eozénou - TTC Meeting 2012 JLab WG 2 16