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[Ext-GDE-75] ML Change Request - October 30, 2006 (CCR#20)



Dear Colleagues,

I am announcing that CCB has received a change request proposal for the
ML section of GDE/ILC BCD from C.Adolphsen, who is representing the ML AG.

This change request, besides corrections of outdated information and
addition of some more details previously lacking, seeks to introduce
the following three changes:

- Change of the cryomodule (CM) layout driven by each of the 10MW
  klystron RF unit. Previously, with two 8-cavity CM without a magnet
  and one 8-cavity CM with a magnet. Now, with two 9-cavity CM without
  a magnet and one 8-cavity CM with a magnet.

  Thus, 26 cavities are driven by a 10MW klystron rather than the
  previous 24. Consequently, the max achievable acc gradient is
  33.5 MV/m rather than 35MV/m assuming use of WR770 for improved
  RF power transmission.

- Elimination of RF unit overhead. Previously, 3.5%. Now, 0%.

  Thus, Ebeam = 250GeV/m is available only if no RF units are failed.

- Elimination of the uncertainty factor in the cryogenic static heat
  load. Previously, 50%. Now, 0%. This allows us to lower the
  cryogenic capacity by 13%.

I am taking the following actions.

- This change request is referred to as CCR#20 hereafter.
- The CCB tentatively assigns Class-2 to this proposal, as suggested
  by the proponent. The CCB reviewers for CCR#20 will be C.Pagani, S.Mishra
  and W.Funk, pending confirmation, besides the CCB Chair.
- The CCB will be holding a hearing on the cost impacts concerning
  CCR#20 during the time of Valencia meeting.

Now this request is brought to review by the 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 Saturday, Nov.4, 2006.

My thanks in advance for your cooperation.

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

Sincerely,

- Nobu Toge (KEK, Accelerator Lab)
  email: toge@xxxxxxxxxxxx
  voice: +81-29-864-5224
  fax:   +81-29-864-3182
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The Main Linac section of the BCD is attached and includes changes starting on page 35 (using Track Changes) for which we request approval by the Change Control Board. These changes are aimed at reducing the linac cost - the estimated savings are about 5% of the Main Linac cost, which makes this a Class 2 change.

Besides corrections of outdated information and the addition of more details, there are three changes to the Main Linac BCD. 

1) Two 9-cavity cryomodules plus one 8-cavity cryomodule that contains a quad (same as in the baseline design) are powered by one 10 MW klystron instead of three 8-cavity cryomodules. The lengths of the two types of cryomodules are nearly the same, so no increase in shaft size is required. The maximum possible gradient in this case is 33.5 MV/m (versus 35.0 MV/m in the current baseline) assuming WR770 waveguide would be used for the long waveguide runs (providing 2% more power to the cavities). The number of rf sources is reduced by 1/13 (as is the required cooling and AC power capacity to first order), but the number of cavities remains the same.

2) The 3.5% rf unit overhead is eliminated. If the average sustainable cavity gradient is 31.5 MV/m as in the baseline, 250 GeV beam energies could only be reached if there are no failed units. If the cavities would be able to operate at the power-limited gradient of 33.5 MV/m, there would be a 6% overhead.

3) The uncertainly factor in the cryogenic static heat load is eliminated (this load should be known at the time of machine construction). However, the 40% overcapacity factor on the total load (static and dynamic) is not changed. The static heat load uncertainty factor is 50%, and reducing it to zero lowers the required cryogenic capacity by 13%.

Attachment: Main Linac with Changes 10_29_06.doc
Description: Main Linac with Changes 10_29_06.doc


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