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[Ext-GDE-64] CCB Response DR (single e+ ring) Change Config Request of Aug.4, 2006



Dear Colleagues,

I am announcing that the CCB response, with regards to the latest
Change Request for the Damping Ring section, is now posted at -

   http://www.linearcollider.org/wiki/lib/exe/fetch.php?cache=cache&media=bcd:ccb-com-dr20060919.pdf

The change request was submitted by A.Wolski on Aug.4, 2006.
It relates to reconfiguration of the two-DR layout on the
positron side. The proposal is to revise the baseline of the
positron DR to consist of one ring, given the promising prospects
for resolving the electron cloud instability issues with
introduction of grooved vacuum chambers and/or clearing electrodes.
Provisions for building two positron DRs, however, are to be
maintained.

The requester suggested Class 2 for this request, to which
CCB concurred after evaluation of the cost impact.
CCB gratefully acknowledges the detailed assessment reports offered
by colleagues from the the DR Area Group and the GDE Cost Engineering
team.

The summary CCB response is as follows -

1. CCB agrees that the cost change (in this case, reduction) expected 
   from this change request is substantial, such that it qualifies as 
   Class-2. Consequently, CCB assumes that its role concerning this 
   change request is to assess its merits and make a recommendation to 
   EC, rather than to make a final configuration change decision.
2. CCB recommends EC to adopt this change request as is, for reasons 
   detailed below in the Discussion section in the PDF document that
   is available at the URI above.
3. CCB will encourage the relevant parties, and will work with them, to 
   update the "Parameters and Layout" section of BCD in accordance with 
   the updated damping ring population.
4. CCB notes the need for conducting systematic R&D associated with 
   the vacuum chamber system, simulation and validation of all mitigation 
   techniques for electron cloud effects. CCB recognizes that the GDE R&D 
   board is currently in the process of evaluating, organizing and facilitating 
   these research programs. CCB recommends that the GDE Executive Committee 
   create an effective review process by which the progress of such R&D efforts 
   be evaluated so as to re-confirm the adequacy of the baseline design at 
   appropriate intervals. This applies equally to other design development 
   issues with the damping ring baseline, such as the 650MHz RF and fast 
   kickers, as well as to other systems such as high-gradient SRF cavities 
   or extraction magnets in the beam delivery sections.

Additional communication and reference materials are available for
viewing, under CCR #15, at

   http://www.linearcollider.org/wiki/doku.php?id=bcd:bcd_history

When GDE EC makes the final decision and approves this change request,
CCB will update the DR section under

   http://www.linearcollider.org/wiki/doku.php?id=bcd:bcd_home

With best regards,

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