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[Ext-GDE-54] DR Change Config Request - August 4, 2006



Dear Colleagues,

I am announcing that CCB has received a change request for the Damping 
Ring (DR) section of ILC Baseline Config Doc from A.Wolski, who is
representing the DR AG for GDE.

This change request mainly relates to reconfiguring the positron
side DR to comprise only one ring, rather than two that has been
assumed so far. The main aim of this revision is to reduce the
construction, operation and maintenance cost of the damping ring
system. A potential risk of electron-cloud effects is recognized, 
and it continues to be investigated, according to the requester. 
For that reason, the proposed new baseline retains the provisions for 
reintroducing the second positron DR if found necessary.

Another element within this change request is substantial
simplification and clean-up of the DR BCD text, so as to cleanly
highlight the critical aspects of the design baseline and
alternatives.

The requesters suggest Class 2 as the classification for this change
request. The CCB chair tentatively agrees to treat this as Class 2,
pending analysis of the associated cost-delta and impacts, in 
particular, with respect to the DR beam dynamics issues and overall
machine parameter space.

The detailed description of this change request, as submitted by
Wolski is available as CCB-PositronRing.pdf at

    https://wiki.lepp.cornell.edu/ilc/bin/view/Public/DampingRings/ConfigStudy

The proposed replacement text for the DR section of BCD is posted as
dr.04aug2006.doc at the same URI.

According to the protocol for Class-2 change requests, I am doing
the following.

- I am assigning D.Schulte, K.Kubo, M.Kuriki (all to be confirmed), 
  plus myself, to act as CCB co-reviewers.
- I will be asking
  * GDE Cost Engineers for their assessment on the cost
    impact concerning this change request.
  * D.Schulte and K.Kubo for consulting the GDE Accelerator
    Physics Group for an assessment on the DR beam dynamics
    impact concerning this change request.
- A CCB recommendation report will be drafted within at most
  approximately two weeks, and will be sent to EC (with cc: to the 
  entire GDE) for their final decision.

Now this request is brought to review by CCB, and is also open to
general discussion. Any members of GDE or GDE-related task groups with
comments or questions on this request, please, direct them to
ml-ccb@xxxxxxxxxxxx and/or ml-ext-gde@xxxxxxxxxxxx by the end of
Friday, August 11, PDT. 

I urge the recipients of this notice to share the information
and discussion of this change request with non-GDE members within
the community. I ENCOURAGE the remarks and comments from non-GDE members 
be funneled through adequate channels of GDE (i.e. MDI contact,
WWS contact, Board chairs, AG/GG/TS group contacts).

My thanks in advance for your cooperation and understanding.

BCD is available at
   http://www.linearcollider.org/wiki/doku.php?id=bcd:bcd_home
BCD change history is available at
   http://www.linearcollider.org/wiki/doku.php?id=bcd:bcd_history
RDR-related information repository for DR is found at
   https://wiki.lepp.cornell.edu/ilc/bin/view/Public/DampingRings/ConfigStudy

Sincerely,

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

We wish to propose a change in the baseline configuration for the ILC
damping rings. Briefly, the change is to eliminate the second positron
damping ring, so that the damping rings system would consist simply of
two rings with circumference roughly 6.7 km (one ring for electrons, and
one for positrons) and the associated injection and extraction lines.
All other specifications would remain the same.

The main purpose of the configuration change is to reduce the costs of
the damping rings; though there are also technical benefits,
particularly to do with the injection and extraction (which no longer
have to divide the injected beams between two rings, or combine the
beams extracted from two rings), and with the alignment and support
systems. There is some increase in technical risk, mainly to do with the
electron cloud effect that was the original motivation for specifying
two positron damping rings; however, studies since the original baseline
decisions were made indicate significant progress with the development
and understanding of techniques that may be used to prevent build-up of
the electron cloud. It is now believed that, with continued R&D,
techniques can be applied that will allow the positron damping ring
subsystem to meet its performance goals with a single positron ring.

In our view, because of the cost and technical impact of this
configuration change, the appropriate classification is ?Class 2?
according to the CCB scheme. We should like to emphasise two important
points associated with this change: first, R&D into mitigation
techniques for the electron cloud should be continued as a very high
priority; second, design of the damping rings complex should not
preclude installation of a second positron damping ring as a later
upgrade, should electron cloud effects be found to be a limitation on
performance.

The documentation requested by the CCB to support this change request is
provided at the following web address:

https://wiki.lepp.cornell.edu/ilc/bin/view/Public/DampingRings/ConfigStudy

See under the heading "Configuration Changes - Positron Damping Ring".
In particular, you will find:

1. Requester?s contact details.
2. Concise summary of the change request.
3. Replacement text for relevant parts of the baseline configuration
descriptions.
4. Classification in requester?s view.
5. Reasonably detailed descriptions and reasons for the change request.
6. Assessment of the impacts of the change.
7. References to supporting materials.

Most of the above are in the document "CCB-PositronRing.pdf". The
replacement text for relevant parts of the baseline configuration
descriptions is in the document "dr.04aug2006.doc". The talks presented
at VLCW06, at which this change configuration was discussed by the
damping rings group, are all posted at the above site.

If you require further information or clarification of any details,
please let me know.

Yours sincerely,

Andy Wolski
for the ILC Damping Rings Area System Leaders.

--- End Message ---