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Summary of EP discussions at Oct.
2005 SMTF meeting at FNAL
T. Tajima (LANL), C. Boffo (FNAL)
TTC Meeting, Frascati, 5-7 December 2005
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KEK and Nomura Plating Company in Japan
developed the horizontal continuouslyrotating EP system that has been adopted
by DESY and JLAB.
• Kenji Saito’s paper in SRF89, KEK, (pp.
635-694) is still a valuable resource on
important parameters. Kenji is presently
writing an updated version of his paper.
• Results of new studies on EP parameters
at DESY and JLAB should be compared
with his data.
TTC Meeting, Frascati, 5-7 December 2005
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New World Records (single-cell)
KEK/Cornell 52.3 MV/m !! (T. Saeki)
TTC Meeting, Frascati, 5-7 December 2005
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EP system for single-cell cavity
Voltage/current
Control
And operator
Cavity
EP acid
Nomura Plating Co., Ltd.
Reservoir
tank (100L)
TTC Meeting, Frascati, 5-7 December 2005
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EP acid
Cavity
Beam Pipe
Acid
Level
EP acid
Cathode
bag
Cathode
TTC Meeting, Frascati, 5-7 December 2005
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Discussion was held to clarify the
following issues.
•
•
•
•
What do we agree upon?
What are the pitfalls ?
What are unknowns and need more R&D?
Action items
TTC Meeting, Frascati, 5-7 December 2005
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What we agreed upon (1)
• EP parameters
• Current density 30-100 mA/cm2
• Solution temperature 25-35 C
• Starting composition H2SO4 (96%):HF(48%)=9:1 by volume
• Materials to be used
•
•
•
•
Teflon should be used on the wetted surface
PVDF should not be used on the wetted surface
Viton should not be used on the wetted surface
Pure Al (1100) should be used for the cathode
• Following process
• HPR should be done as soon as EP is completed
TTC Meeting, Frascati, 5-7 December 2005
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What we agreed upon (2)
• Problems that could affect cavity performance
and possible measures to avoid them (=>)
– Generated hydrogen => Proper handling of hydrogen,
add HNO3?
– Reduced HF content generates sulfur => adjust the
concentration by monitoring the voltage to keep the
desired current intensity
– Chemical residues such as sulfur => maintaining HF
concentration, filtering and/or cleaning the system,
rinsing the cavity with H2O2,, etc.
– Polishing rate non-uniformity (DESY) => better control
of temperature variation and/or flow on the cavity
surface
TTC Meeting, Frascati, 5-7 December 2005
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What are the pitfalls ?
– Is there any? KEK does not think there is.
(True?)
– Something related to 9-cell cavities process
due to the longer structure and associated
difficulty in controlling the EP condition on all
the cavity surfaces.
– Complexity might lead to some error
TTC Meeting, Frascati, 5-7 December 2005
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What are the unknowns and need
further discussions in Frascati?
• How much higher can the current intensity go to
increase the polishing rate, which reduces time
and cost
• Should the electrodes contact each cell? If not,
we can EP dressed cavities using existing setup.
• Should the EP be done in a clean environment?
• Should we filter the EP solution? (KEK uses a
coarse filter, JLAB does not.)
• Nb content in the solution. When do you need to
refresh the acid?
• Do we need tumbling before EP and why?
TTC Meeting, Frascati, 5-7 December 2005
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Action items
• EP simulation (DESY, FNAL) to understand the
phenomena scientifically
• Parameters study at DESY and JLAB comparing to KEK
parameters
• Explore vertical EP system to reduce the cost
• Consider having reference cavities to calibrate the
system
• Write a brief report summarizing this meeting before the
Frascati TTC meeting (Almost done, but better to be
written after further discussion at the Frascati meeting.)
• Other
– accurate thickness monitoring with high resolution
TTC Meeting, Frascati, 5-7 December 2005
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Other items that were not discussed and
seem important
• Can pure aluminum be used as the heat
exchanger tubes? ANL has been using it
for a long time and seems confident to use
it.
• Rotational speed of the cavity
• Anything else??
TTC Meeting, Frascati, 5-7 December 2005
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