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[Ext-GDE-104] CCB Response to ML/Params Change Config Request of Jan.1, 2007 (CCR#24)
- Subject: [Ext-GDE-104] CCB Response to ML/Params Change Config Request of Jan.1, 2007 (CCR#24)
- From: N.Toge <toge@xxxxxxxxxxxx>
- Date: Tue, 23 Jan 2007 14:16:03 +0900 (JST)
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
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
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
With best regards,
- Nobu Toge (KEK, Accelerator Lab)