First TCS with broken RF finger

The RF finger which was lost is not a longitudinal but a transverse finger. Rocio called the transverse finger a longitudinal one (maybe there is a different notation at the engineering side). I include a photo of the problem which should solve all mis-understandings. I think this is exactly the problem that we discussed before. Please correct me if I am wrong. In addition there was a problem with the contact of a longitudinal RF finger, as they wanted to adjust the mechanical stops to a maximum gap of 62 mm. This was solved to my information.

_________________________________________
Ralph W. Assmann
CERN, Accelerator & Beams Department
CH-1211 Geneva 23
Switzerland

Tel.: +41 22 767 5231 (office Prevessin)
      +41 22 767 0681 (office Meyrin)
      +41 76 487 4543 (mobile)
Fax: +41 22 783 0552
Web: http://www.cern.ch/assmann
      http://www.cern.ch/lhc-collimation-project

From: Alexej Grudiev
Sent: Friday, May 05, 2006 12:26 PM
To: Ralph Wolfgang Assmann; Rocio Chamizo
Cc: Oliver Aberle; Alessandro Bertarelli; Jose Miguel Jimenez; Yacine Kadi; Jacques Lettry; Manfred Mayer; Roberto Losito; Michel Jonker; Thomas Weiler; Sergio Calatroni; Francesco Ruggiero
Subject: RE: First TCS with broken RF finger

Dear Ralph,

Francesco forwarded your e-mail to me for information. (Thank you Francesco for keeping me informed). In addition, he told me that the lost rf finger is the longitudinal one. I just want to comment on that.

The loss of a longitudinal rf finger is much more critical than the loss of 1 or 2 transverse rf fingers. It increases the rf power losses on the next rf finger by factor 2 in extreme case, when there is only one finger next to the lost one, or by 50% if there are 2 rf finger on both sides of the lost rf finger. So depending on the position of the lost rf finger, the rf power losses per finger can be significantly increased due to loss of even one finger.

To reduce the risk of failure of the rf finger(s) next to the broken one, I think, the collimator should be installed in place where there are at least less heating of the rf fingers due to beam losses. This will reduce the overall heating of rf fingers giving margin for the collimator with broken rf finger. So if it is possible I would recommend to do it.

For future, I would recommend to not accept collimators with broken longitudinal rf finger, in particular, if this finger is in the position where there is maximum of the rf power losses. It is the one which has only one rf finger next to it.

Best regards,

Alexej

From: Ralph Wolfgang Assmann
Sent: Thu 5/4/2006 5:10 PM
To: Rocio Chamizo
Cc: Oliver Aberle; Alessandro Bertarelli; Jose Miguel Jimenez; Yacine Kadi; Jacques Lettry; Manfred Mayer; Roberto Losito; Michel Jonker; Thomas Weiler; Sergio Calatroni; Francesco Ruggiero; Ralph Wolfgang Assmann
Subject: First TCS with broken RF finger

Dear Rocio,

After discussion with Francesco Ruggiero, we herewith approve the first
TCS collimator with the broken RF finger, assuming the foreseen
installation at point 8. Please note that this is an exception and does
not constitute any rule for acceptance of future non-conformities of
this kind.

It is very important that such problems are avoided in future. In
particular we will reject every collimator with 2 broken RF fingers and,
if required, also collimators with 1 broken RF finger.

Please transfer this message very clearly to CERCA. Please also make
sure that the final steps of production for the first TCS are proceeding
with maximum speed. It must be installed still in May. Many thanks.

Best regards,

Ralph

_________________________________________
Ralph W. Assmann
CERN, Accelerator & Beams Department
CH-1211 Geneva 23
Switzerland

Tel.: +41 22 767 5231 (office Prevessin)
      +41 22 767 0681 (office Meyrin)
      +41 76 487 4543 (mobile)
Fax: +41 22 783 0552
Web: http://www.cern.ch/assmann
      http://www.cern.ch/lhc-collimation-project

-----Original Message-----
From: Rocio Chamizo
Sent: Wednesday, May 03, 2006 10:27 AM
To: Oliver Aberle; Ralph Wolfgang Assmann; Alessandro Bertarelli; Jose
Miguel Jimenez; Yacine Kadi; Jacques Lettry; Manfred Mayer; Roberto
Losito; Michel Jonker; Thomas Weiler
Subject: Collimators - NC and data - MTF

Dear colleagues,
Here are some of the files that we discussed about yesterday. Access for
MTF have been requested for you all. Best regards,

Rocio