From: Francesco Ruggiero
Sent: Monday, September 05, 2005 3:36 PM
To: Sergio Calatroni
Cc: martind@nikhef.nl; Delio Duarte Ramos; Massimiliano Ferro-Luzzi;
Leonel Marques Antunes Ferreira
Subject: [Fwd: LHC Velo wake field suppressor]

Attachments: LHC Velo wake field suppressor; Au coating

Dear Sergio,

I have discussed with Delio Ramos about the possibility of avoiding the gold coating foreseen on the Al chamber of the VELO wake field suppressor at the transition with the LHCb UX85/1 Beryllium beampipe. I am keen to give my green light to the proposed solution, but I have a few questions that I hope you or some colleague at NIKHEF may be able to answer:

- 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."

- 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?

- 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?

thank you for a prompt reply
ciao Francesco

-- 
E-mail:    Francesco.Ruggiero@cern.ch,      Location: Building 9/1-008
Address:   CERN, A&B Department, CH-1211 Geneva 23, Switzerland
Telephone: +41 (22) 767 3726 or 767 5272,    TeleFax: +41 (22) 783 0552
WWW:       http://wwwslap.cern.ch/~rgo/