[Ext-GDE-104] CCB Response to ML/Params Change Config Request of Jan.1, 2007 (CCR#24)

[N.Toge <toge@xxxxxxxxxxxx>]

Dear Colleagues,

I am announcing that the CCB response, with regards to the ILC Config
Change Request for the ML/Parameters sections of Jan.1, 2007 (CCR#24)
is now posted at

http://www.linearcollider.org/wiki/lib/exe/fetch.php?id=bcd:bcd_history&cache=cache&media=bcd:ccb-com-ml24_20070123.pdf

CCB received the first communication on what became this CCR#24
T.Raubenheimer on December 18, 2006.  Proposed replacement text for BCD
was transmitted by the requester on January 1, 2007 and CCB forwarded it to 
GDE on January 3, 2007. It was classified as Class-2 based on its near 
identity in scope with CCR #20. C. Pagani, W. Funk and S. Mishra were 
assigned as the CCB reviewers.

CCR#24 seeks to apply nearly the same three changes in the ML design 
baseline as were proposed in CCR#20, but supported by changes in 
the ILC parameters to address concerns raised in the CCB response to 
CCR#20 as follows.

CCR#24d: To modify the baseline parameters such that the number of
  bunches per pulse is reduced from 2820 to 2670 and beta_x* decreased
  from 21mm to 20mm.  This allows us to achieve still the same peak
  luminosity of 2E34 while reducing the beam current from 9.5mA to 9mA.

CCR#24a: Change of the cryomodule (CM) layout driven by each of 
  the 10MW klystron RF unit, as proposed originally in CCR#24a,
  as (8-8-8) --> (9-8-9). Thus, 26 cavities are to be driven by 
  one 10MW klystron rather than the previous 24. 

CCR#24b: 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. However, one difference from CCR#20b is 
  that the conventional facilities, including the tunnels, are to be 
  maintained to accommodate the missing 3.5% worth of RF systems if/when 
  determined needed.

CCR#24c: Elimination of the uncertainty factor in the cryogenic static 
  heat load. Previously, 50%. Now, 0%. This allows lowering the cryogenic 
  capacity by 13%.

The summary CCB response is as follows:

1. CCB found that CCR#24d has no directly associated cost impacts, since 
   in and of itself it proposes no changes of equipment or layout.

   During consideration of CCR#24, CCB learned that the cost impact of 
   the three changes CCR#24a, b and c amounts to a total 3% reduction of 
   the construction cost of the ML, including that of related conventional 
   facilities. CCB understands that the cost impacts of the matching 
   components of CCR#24 will be identical to what they were for CCR#20.

   If individually looked at, only CCR#24b qualifies as Class-2 (CCR#24a 
   and CCR#24c each are Class-1). In the light of the important coupling 
   among all four changes, however, CCB has decided to consider them 
   jointly, and to only make recommendations to the EC.

2. CCB recommends that the EC:

   A. To accept CCR#24a.
   B. To accept CCR#24b.
   C. To reject CCR#24c.
   D. To accept CCR#24d.

3. CCB finds that to proceed further on design development of ML system, 
   together with design and development of other systems that rely on 
   hardware derived from ML, clarifications in the BCD text are urgently 
   required in two areas. Thus, CCB recommends the EC:

   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.  
      (This repeats a recommendation in response to CCR #20.)

   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.

Several supplementary remarks, as extracted from discussion of each element 
of CCR#24 are reproduced below:

- It is important to understand in future design analysis how the individual 
  elements in the LLRF loss factors are to be added in actual operation. 
- It is important to understand the ranges of beam parameters, together with 
  their inter-dependence and constraints, so that the overall operability of 
  ILC becomes more thoroughly understood by all who are involved in the design 
  and development efforts. 
- All area groups should adequately update their baseline system descriptions, 
  without excessive delay. Possible subjects include descriptions of: bunchers 
  and subharmonic bunchers of electron sources, RF system layout for particle 
  sources and RTML, beam parameters and timing specifications in general.
- The actual magnitude of uncertainty factor to assume for the static heat 
  load calls for more expert discussion and consensus-forming.
- Aside from the formula and coefficients to adopt in calculating the total 
  heat load capacity of the cryogenic system, the conditions in which 
  the baseline values of both the static and dynamic heat loads call for more 
  expert discussion and consensus-forming.

Details of the discussion are available in the CCB report whose
URI is mentioned 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