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


I would like to announce that the GDE Executive Committee has officially approved the Change Request for the Damping Ring section of the Baseline Configuration Document recommended by our Change Control Board. This change request was deemed a class 2 change, requiring EC approval. The change to a single positron damping ring is now our official baseline.

This change has been enabled by the studies of methods for mitigating electron cloud effects. These studies gave enough confidence to propose this change. The Damping Ring group will continue to work on the electron cloud mitigation and, in particular, we will give high priority to experimental demonstrations in our R&D program.

The design work on the damping rings will continue, and our guidance is that no allowance should be made to maintain the option of reverting to two positron rings.

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Date: Tue, 19 Sep 2006 08:46:04 +0900 (JST)
To: ml-ccb@xxxxxxxxxxxx, ml-ext-gde@xxxxxxxxxxxx
From: "N.Toge" <toge@xxxxxxxxxxxx>
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Subject: [Ext-GDE-64] CCB Response DR (single e+ ring) Change Config Request of Aug.4,
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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 -


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

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

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


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


With best regards,

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