1. Proposed Button Design for a Series of High Power Button Tests Arash Zarrebini-Esfahani 22 nd August 2007

2. MICE 2 RFCC module each containing 4 cavities High gradients up 16 MV/m at 201 MHz Normal conducting Rounded Pillbox cavities – Lower peak surface field – High accelerating efficiency – Lower RF power

3. 201 MHz Cavity Design Cavity body + water cooling lines Four ports and flanges RF loop couplers Cavity support structure Cavity tuners Ceramic RF windows Curved Be windows

4. 201 MHz Cavity Fabrication 1 - Half shell spinning 2 - Fabrication of stiffener ring

5. 201 MHZ Cavity Fabrication 3 – Nose hole and half shell lip machining 4 – Half shell electro polishing

6. 201 MHz Cavity Fabrication 5 – Equator electron beam welding 6 – Fabrication of nose ring

7. 201 MHz Cavity Fabrication 7 – Cavity port pulling 8 – Cooling pipes TIG welding

8. What are the Problems? 1) Production techniques offer poor reproducibility 2) Achievable gradients are poor Surface features are one of main limiting factors − Field emission not an issue when average surface roughness, R A < 2 µm − Current Electro polishing techniques offers R A < 1 µm, But it is a `Black Art ‘  Surface Impurities or Defects are dominant cause of limited accelerating gradient ? (Must be verified)

9. What is the solution? To introduce New manufacturing processes This can improve: Reproducibility of cavity half shells Surface quality before and after cleaning process Welding quality Final assembly

10. Who Are We? U.K Cavity Development Consortium: Imperial College Cockcroft Institute Brunel University Liverpool University

11. Proposed research program A series of Button Tests to investigate the effect of manufacturing and surface treatment processes This aims to study and understand the factors limiting: Achievable accelerating gradients Reproducibility

12. Button Design MuCool Single part New Design 2 Individual Parts

13. Button Design The new design would allow testing of: Wider range of material Wider range of manufacturing and surface treatment process Cap Holder

14. Manufacturing Procedure Cap Forming Surface Characterisation Holder Forming Cap Material Selection Surface Characterisation Final Cap Surface Characterisation High Power Testing Cap Surface Treatment Surface Characterisation

15. Surface Preparation Ultrasonic Cleaning Surface Characterisation Deoxidation/etch Surface characterisation Electro-Polish Surface Characterisation Deionised Water high-pressure rinse Surface Characterisation

16. Surface Preparation Initially we investigate two chemistries for Electro-polishing Standard Phosphoric/butanol (J-Lab recipe) Phosphoric, butanol, PEG, Citric acid  PEG, known to prevent etch pitting  Citric acid, known to increase surface planarisation

17. Surface Characterisation Atomic Force Microscope (AFM) / Scanning Electron Microscope (SEM) –Surface topology –Average roughness –Stress –Planarisation X-ray photoelectron Spectrometer (XPS) –Chemical make up of the surface layers of the RF surface –Identifying Orbitals involved in bonding impurities, etc

18. What Do We Get? From processes: surface topology (roughness, planarisation, stresses, defects) surface chemical composition identify how the fabrication processes alters Topology and Chemistry From characterisation techniques: statistical models to predict the expected surface topology of a cavity produced, using each of the evaluated manufacturing techniques Hence, being able to extrapolate the manufacturing reliability and performance of high gradient cavities

19. Future plans Expanding the button test by introducing: –Other manufacturing techniques –Different EP chemical compositions –Other Surface preparation techniques Design and Manufacture a high frequency pillbox cavity –Smaller in size –Lower in cost –Closer to MICE cavity, hence better results

20. Overall Outcome Understanding the effect of limiting factors Understanding the effect of various techniques on performance Development of better manufacturing and processing techniques

21. References 201 MHz NC RF Cavity R&D, Derun Li, April 26, 2005 and July 28, 2004 RFCC Module Design Update, Steve Virostek, June 13, 2007 MICE RF Cavity Design and Fabrication Update, Steve Virostek, October 27, 2004 Neutrino Factory and Muon Collider R&D in the US “Two Mints in One?, Alan Bross, June 14, 2007 Proposed Investigation of High Gradient RF Cavity Limitations, Dr. Matthew Stables, Dr. Rebecca Seviour, 5th June 2007