1. Development of Chemical-Mechanical Polishing for Superconducting Cavities
Shekhar Mishra, Fermilab
Mark J. Oreglia, Univ. of Chicago
Cliff Spiro, Cabot Microelectronics

2. ANL-FNAL-UofC Collaboration Meeting
Project Summary
High Gradient (~35 MV/m) and high yield of the SRF cavities are needed for
International Linear Collider (ILC) and High Intensity Proton Accelerator (Project-X).
State of the art cavity manufacturing and processing :
Electo-polishing and High Pressure Rinse
Remove the damaged Niobium layer
Average Gradient is 20% lower
Yield is less than 25%
Limitation:
Complicated procedure, dangerous chemical, expensive
Niobium surface contamination and/or surface imperfection caused by either manufacturing or processing (Sulfur contamination)
Proposal:
Chemical-Mechanical Planarization technology to remove the damaged Niobium layer
4/21/2017
ANL-FNAL-UofC Collaboration Meeting

3. ANL-FNAL-UofC Collaboration Meeting
9-cell Test Results
ILC
Goal
Average A6-8, AES2,4 = 32 MV/m
A9 reprocess at Jlab
4/21/2017
ANL-FNAL-UofC Collaboration Meeting 3

4. Why alternate technique ?
The electrolyte is a mixture of hydrofluoric and sulfuric acid. Details not fully understood.
Manufacturing or acid related defect:
1mm θ z
~600µm beads
on Nb cavity
Acid related contamination
Sulfur Deposit
Surface Smoothness: RMS:
1247 nm fine grain BCP
27 nm single crystal BCP
251 nm fine grain ep
These two problems will require mechanical polishing that can make a smooth surface.
4/21/2017
ANL-FNAL-UofC Collaboration Meeting

5. Introduction to Cabot Microlectronics and Chemical Mechanical Planarization (CMP)
Leader in CMP slurries
Pioneer in CMP technology
Copper, Tungsten, Dielectric, Data Storage
CMP pad offering in early stage commercialization
ESF consumable and service offering in non-semiconductor applications
Unparalleled track record
Deliver tens of millions of gallons to customers globally
Outstanding technology and manufacturing infrastructure
Robust ramp of new products to high volume production
Provide global support and service
World-class team of scientists and technologists
Non-planarized IC product
Planarized IC product
© 2005 Cabot Microelectronics Corporation

6. CMP of Nb 20X Field of View (approx. 230um x 300um)
BEFORE
Rq = 603nm
Heavily cratered surface from machining
AFTER
Rq = 3.5nm
Small islands appear to be grains.
Highest point to lowest point around 18.6nm.
© 2005 Cabot Microelectronics Corporation

7. Fermilab Tumbling Machine
Not installed.
Design and Engineering needed to hold the cavity in place and liquid flow etc.
4/21/2017
ANL-FNAL-UofC Collaboration Meeting

8. New Vertical Test @ FNAL
Nine-cell Tesla-style cavity
Recently commissioned (IB1)
Existing 1.8 K Cryogenic plant
RF system in collaboration with Jlab
Capable of testing ~50 Cavities/yr
Evolutionary upgrades:
Thermometry for 9-cells, 2 cavities at a time, 2 top plates, Cryo upgrades
Plan for two additional VTS cryostats
Ultimate capacity ~ 264 cavity tests/yr
Plan for 2 more
VTS pits
VTS Cryostat:IB1
New RF & Control Room
4/21/2017
ANL-FNAL-UofC Collaboration Meeting

9. Plans and Possibilities
Development of the chemical that would be used in the Chemical Mechanical Polishing (CMP) of Niobium
Small sample test
Accelerating Gradient Test:
Polish 1-cell (1.3 GHz) Nb cavity using the Fermilab Tumbling machine
Rinse with high purity water
RF test in the Fermilab Vertical Test Facility
Possible Advantage
No dangerous chemical
A much simplified procedure that could lead to considerable cost saving
Could potentially reduce acid related defects and contamination
Could eliminate surface defects produced during manufacturing
Small size R&D project with great potential
Excellent training opportunities for students in Accelerator R&D
4/21/2017
ANL-FNAL-UofC Collaboration Meeting

10. ANL-FNAL-UofC Collaboration Meeting
Budget
%FTE
UofC
Fermilab
Cabot
Salary and Fringe Benefits
- Post-doctoral
-Graduate Student Assistant
-Undergraduate Student Assistant
-Engineers
-Technician
100% 5%
20%
$12,500
$6,500
$26,000
Graduate Student Tution
Material and Supplies
$1,000
$17,500
$35,000
Publication Cost (Conference)
$1,500
Total Direct Cost
$15,000
$50,000
Build on Surface science Research
Student training in Accelerator R&D (Fermilab Accelerator Ph.d Program)
Local Industry involvement
Leverage existing laboratory infrastructure
4/21/2017
ANL-FNAL-UofC Collaboration Meeting