[Ext-GDE-95] CCB Response to ML Config Request of Oct.30, 2006 (CCR#20)

[N.Toge <toge@xxxxxxxxxxxx>]

Dear Colleagues,

I am announcing that the CCB response, with regards to the ILC Config 
Change Request for the ML section of Oct.30, 2006 (CCR#20), 
is now posted at -

   http://www.linearcollider.org/wiki/lib/exe/fetch.php?cache=cache&media=bcd:ccb-com-ml20061127.pdf

The change request was submitted by C.Adolphsen on Oct.30, 2006.
It seeks to to apply three changes in the ML design baseline:

   CCR#20a: Change of the cryomodule (CM) layout driven by each of 
      the 10MW klystron RF unit. Previously, with two 8-cavity without 
      a magnet and one 8-cavity with a magnet (8-8-8). 
      Now, with two 9-cavity CM without a magnet and one 8-cavity with 
      a magnet (9-8-9). Thus, 26 cavities are driven by one 10MW klystron 
      rather than the previous 24. Consequently, the maximum achievable 
      accelerating gradient is 33.5MV/m rather than 35MV/m assuming use 
      of WR770 waveguides for improved RF transmission.

   CCR#20b: Elimination of RF unit overhead. Previously, 3.5%. 
      Now, 0%. Thus, maximum beam energy 250GeV is available only if 
      all RF units are in operation and all CMs together with their cavities.

   CCR#20c: Elimination of the uncertainty factor in the cryogenic static  
      heat load. Previously, 50%. Now, 0%. This allows to lower 
      the cryogenic capacity by 13%.

This CCR was initially classified as Class-2 and it was confirmed
as such at the CCB hearing that was held at Valencia on Nov.9, 2006,
whose minutes is available at

   http://www.linearcollider.org/wiki/lib/exe/fetch.php?cache=cache&media=bcd:ccr20hearingml20061109.pdf

CCB reviewers were C.Pagani, W.Funk and S.Mishra.

The summary CCB response is as follows -

1. CCB found that the cost impact of the three changes CCR#20a, 
   b and c amounts to a total 5.2% reduction of the construction cost 
   of ML, including that of related conventional facilities. 
   If individually looked at, only CCR#20-b qualifies as Class-2 
   (CCR#20-a and CCR#20-c each belong to Class-1 category). 
   In the light of important implications and relative relationship 
   among three changes, however, CCB has decided to make recommendations 
   to EC for all of CCR#20-a, #20-b and #20-c, rather than to make 
   a final configuration change decision separately for #20a and #20c.

2. CCB recommends EC, on the basis of its review as detailed in the 
    "Discussion" session of the full report:

    A.  To not accept CCR#20a.
    B.  To not accept CCR#20b.
    C.  To not accept CCR#20c.

3. CCB finds that to proceed further on design development of ML 
   system, together with design development of other systems who rely 
   on the hardware equipment derived from ML, some clarifications in 
   the BCD text is urgently required in at least three areas. CCB recommends 
   EC:

   D.  To instruct relevant parties to resolve conflicting descriptions 
       of beam parameter specifications in the BCD.
   E.  To instruct relevant parties to introduce a place holder for 
       clear and unmistakable definition of the energy reach and luminosity 
       reach of ILC phase-1 in the BCD and to introduce descriptive entries 
       there.
   F.  To instruct relevant parties to redraft a specification table as part 
       of BCD for the main linac RF unit, together with cavities and cryomodule, 
       on the basis of a firm consensus of all subgroups who are involved such 
       as: parameters, high-level RF, low-level RF, cavities, cryomodules, 
       cryogenics, commissioning, operation and availability. This specification 
       table has to allocate reasonable provisions for absorbing the current 
       technical ambiguities, has to be internally consistent, and has to be 
       consistent with respect to the definition of the "energy reach" above.

Full details of the evaluation of related issues, discussion and assessment
are available in the CCB report at the URI quoted above.

Additional communication and reference materials are available for
viewing, under CCR #20, at

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

With best regards,

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