Proposed Button Design for a Series
of High Power Button Tests
Arash Zarrebini-Esfahani22nd August 2007
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
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
201 MHz Cavity Fabrication
1 - Half shell spinning
2 - Fabrication of stiffener ring
201 MHZ Cavity Fabrication
3 – Nose hole and half shell lip machining
4 – Half shell electro polishing
201 MHz Cavity Fabrication
5 – Equator electron beam welding
6 – Fabrication of nose ring
201 MHz Cavity Fabrication
7 – Cavity port pulling
8 – Cooling pipes TIG welding
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, RA < 2 µm
− Current Electro polishing techniques offers RA < 1 µm , But it is a `Black Art ‘
Surface Impurities or Defects are dominant cause of limited accelerating gradient ? (Must be verified)
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
Who Are We?
U.K Cavity Development Consortium:
• Imperial College
• Cockcroft Institute
• Brunel University
• Liverpool University
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
Button Design
MuCool
• Single part
New Design
• 2 Individual Parts
Button Design
The new design would allow testing of:
• Wider range of material
• Wider range of manufacturing and surface treatment process
Cap Holder
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
Surface Preparation
Ultrasonic Cleaning
Surface Characterisation
Deoxidation/etchSurface characterisation
Electro-Polish Surface Characterisation
Deionised Water high-pressure rinse Surface Characterisation
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
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
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
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
Overall Outcome
• Understanding the effect of limiting factors
• Understanding the effect of various techniques on performance
• Development of better manufacturing and processing techniques
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