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[Ext-GDE-76] Request for Comments re: ILC Main Linac Config Change Request



Dear Jim, Richard, Hitoshi,

I am writing you to request comments from the WWS concerning the Change
Configuration Request that has been submitted by C.Adolphsen today
(Oct.30, 2006) of the Main Linac (ML) systems.

The notice of this Change Conriguration Request (CCR#20) has been 
circulated within GDE and is available at

   http://lcdev.kek.jp/ML/PubCCB/msg00095.html

A topic of particular relevance to you colleagues in the physics
community is bullet 2, which seeks to eliminate the previously
assumed 3.5% RF unit overhead. This is part of attempts by the
ML Area Group leaders to reduce the ML construction cost by
up to 5%.

This means that with the proposed new baseline, the IP beam energy of 
250GeV will be available only when ALL the RF units are in operation, 
giving the beams an acc grdient of 31.5MV/m on average. 

Although hard to quantify, if a similar availability assumption is made 
for the ML units as before, a practically likely standard beam energy 
could be as low as ~240GeV (This is a reference number that Toge is 
offering; not a statement by ML AG leaders).

While I surmise that this change is most likely acceptable to you, 
the CCB would like to hear your opinion, comments or remarks (yes, no,
maybe, etc) in writing, for our record of the Change Config process.

While I hear that the entire GDE team is hoping to "freeze" the pre-RDR 
ILC configuration towards the end of November, because of the
competing CCRs that CCB have to process simultaneously, I would
greatly appreciate if you could give me your WWS statements

     Before the end of Valencia GDE meeting

Thank you in advance for your understanding and cooperation on this
matter.

Sincerely,

- Nobu Toge (KEK, Accelerator Lab)
  email: toge@xxxxxxxxxxxx
  voice: +81-29-864-5224
  fax:   +81-29-864-3182