Electropolishing at ANL

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Electropolishing at ANL
SMTF Meeting Oct. 5, 2005

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Electropolishing at Argonne

• Argonne has electropolished niobium cavities for
  over 30 years
• All of the 150 SC cavities produced at Argonne
  were processed by electropolishing
• Experience has been developed in adapting EP to
  many different geometries
• Argonne has all of the infrastructure required to
  polish large SC cavities

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EP at Argonne based on Siemens Process
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Examples of Various Electropolished Geometries
Quarter-wave
Co-axial half-wave
Double spoke
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Recent Activities Electropolished Triple-Spoke
Resonator RF surface area 1.5 m2
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Surface smoothness Have used EP to produce very
smooth and brilliant surfaces
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A Joint ANL/FNAL Cavity Processing Facility
Chemical Processing Rooms
Air Scrubber
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Capability at Argonne

• Comprehensive chemical processing capability
  suitable for several cavities per week
• Primary infrastructure

• A pair of large chemistry rooms
• A large air scrubber
• Three clean room areas for post-processing
  (high-pressure rinsing)
• A high-capacity de-ionized water system
• Procedures for procurement, storage, handling,
  disposal
• Hardware power supplies, acid pumps, water
  chiller

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ANL Proposal in SCRF for the ILC (FY06)
Motivation
It was generally agreed at the first
International ILC Workshop (KEK, Nov. 2004) that
a U.S. capability to build, process and operate
high-performance 9-cell elliptical cavities is
required for the proposed International Linear
Collider
Proposal
To leverage the existing infrastructure and
expertise at Argonne to build a complete
electropolish apparatus for ILC-type 9-cell
elliptical cavities and perform electropolishing
on 9-cell cavities for SMTF
Deliverables
FY06 An operational electropolishing
facility for 9-cell cavities
Resources Required
FY06 1.5 FTE (0.75 Scientist, 0.75
Designer/Technician) 135K MS
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ANL Recipe for EP
Based on the Siemens process from the early
1970s Cavity (anode) - observed no polishing
rate sensitivity to electrical connection point
even for large cavities High purity Al cathode
(3000 series or better) tailored to the cavity
cathode area 10 or more surface area of Nb Acid
composition 8510 mixture of 96 H2SO4, 40 HF,
reagent grade trouble with vendor mixing losing
HF Temperature 28-32o C (chilled water through
the cathode) Typically have used intermittent EP
(1 min on 1 off) Average anode current density
40 mA/cm2, acid replaced when value drops below
30 mA/cm2
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EP Cathodes

• Cathodes hand wound from ½ OD 3003 series Al
  tubing (50 ft spools)
• White paste (elemental sulfur?) typically seen at
  cathode

Housing cathode
End plate cathode
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Technical Issues with EP

• Thoughts on horizontal versus vertical polishing
• Vertical EP
• Downward facing Nb surfaces polish much faster
  than upward facing surfaces.
• Bubble streaming from the cathode can cause
  grooves, streaks (Teflon bag?)
• Strong temperature gradients (top-to-bottom) in
  the acid bath can lead to differential polishing
• Horizontal EP
• 1. Polishing is slower since cavity is only half
  full

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Vertical Polishing Differential polishing always
seen in upward vs. downward surfaces
Surface facing down
Surface facing up
Cavity flipped after every 50 cycles