From: Sergio Calatroni
Sent: Tuesday, September 06, 2005 4:26 PM
To: Francesco Ruggiero
Cc: martind@nikhef.nl; Delio Duarte Ramos; Massimiliano Ferro-Luzzi;
Leonel Marques Antunes Ferreira
Subject: RE: [Fwd: LHC Velo wake field suppressor]

Attachments: ETR 2005-1.doc; rf.pdf

Hello Francesco,

first of all my apologies for not having being able to take part to the meeting yesterday.
I copy here your questions and add my answers

> - what is the contact resistance originally specified for the gold 
> coating solution? Is there an EDMS document where I can find this 
> specification?
> The only technical information I could find on RF measurements of the 
> VELO wake field suppressor by Frans Kroes were discussed at a VELO 
> Engineering Design Review held on
> 16/12/2002 but they do not mention contact resistance (see 
> http://agenda.cern.ch/fullAgenda.php?ida=a021804). On the other hand, 
> in the minutes of a NIKHEF vertex MT meeting held on 04/12/2003 I can 
> read that "Bad contacts will spark and melt under the 35 A image 
> currents."

I have not more information than you have, except maybe what is reported in the attached document by F. Kroes (I received it from H. de Vries), page 18: 0.08 mOhm were measured on the mock-up (both sides gold plated), but it is not clear to me whether this value should be considered as a specification or simply as an information concerning a specific installation.

> - are we sure that a contact resistance of about 1 mOhm can be 
> achieved by an increased contact force of the CuBe fingers on the NEG 
> coating of the Beryllium chamber? and is there a simple mechanical 
> solution to increase this contact force well above 50 grams per 
> finger?

I have no doubts on the first point, due to the experience gained on different types of contacts in the last few years. Unfortunately I don't have precise mechanical drawings of how the contact is implemented but I believe it should be easily feasible. Of course a few screws would help....
 
> - is there a risk that the NEG coating be scratched away by the RF 
> fingers during the assembly of the chamber? Can we imagine an in-situ 
> measurement of the total contact resistance before the final 
> installation of the chamber?

The risk exists, it is correct. However even in such a case we would be in contact with the aluminium surface below. I have made no mesaurements for contacts onto aluminium, but I don't see many reasons why it should be any worse than the NEG (thickness of the oxides are approximativley equivalent). However I believe your suggestion of an in-situ measurement to be the good one. From the drawings I have (attached) it should be easy to perform after the NEG coating, without risks of contaminating the NEG.

Ciao e grazie, Sergio