TTC Meeting, Frascati, 5-7 December 2005 1

Summary of EP discussions at Oct. 2005 SMTF meeting at FNAL

T. Tajima (LANL), C. Boffo (FNAL)

TTC Meeting, Frascati, 5-7 December 2005 2

KEK and Nomura Plating Company in Japan developed the horizontal continuously-

rotating 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 3

New World Records (single-cell) KEK/Cornell 52.3 MV/m !! (T. Saeki)

TTC Meeting, Frascati, 5-7 December 2005 4

EP system for single-cell cavity

Cavity

Reservoirtank (100L)

Voltage/currentControlAnd operator

EP acid

Nomura Plating Co., Ltd.

TTC Meeting, Frascati, 5-7 December 2005 5

Cavity

Beam Pipe

Cathode

Cathodebag

AcidLevel

EP acid

EP acid

TTC Meeting, Frascati, 5-7 December 2005 6

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 7

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 8

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 9

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 10

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 11

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 12

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??