[Ext-GDE-101] CCB Response to PES Change Request - Nov.17, 2006 (CCR#22)

[N.Toge <toge@xxxxxxxxxxxx>]

Dear Colleagues,

I am announcing that the CCB response, with regards to the ILC Config
Change Request for the Polarized Electron Source (PES) section of 
Nov. 16, 2006 (CCR#22, http://lcdev.kek.jp/ML/PubCCB/msg00110.html)
is now posted as

   http://www.linearcollider.org/wiki/lib/exe/fetch.php?cache=cache&media=bcd:ccb-com-pes20061201.pdf

The change request was submitted by A.Brachmann on Nov.16, 2006.
Request was treated as Class-1. N.Toge and M. Kuriki were assigned as 
the CCB reviewers. 

The CCR#22a proposed the following four revisions:

CCR#22a: Eliminate second (backup/redundant) normal conducting beam 
         line.
CCR#22b: Eliminate cavern for laser system; locate laser system in 
         above ground building and addition of a small diameter shaft 
         (d = 1.5 m) for laser beam transport.
CCR#22c: Modification of "dogleg" section of beamline - Replace 
         with vertical chicane.
CCR#22d: Replace 2 L-band bunchers and NC pre-accelerator with combined 
         TW tapered L-band bunching and pre-acceleration section.

The main motivation for this CCR to the electron source baseline design 
is to reduce the overall cost of this area. CCR#22a and #22b will 
significantly reduce the cost of the injector, mainly through reduction of 
the lengths of beam and service tunnels and through elimination of a large 
cavernous space that would have been used to house the laser system. 

A second set of cost savings results from elimination of beam line 
components. The new beam line layout allows the modification of the "dogleg"
section of the beam line into a vertically oriented chicane, which is 
advantageous from an operational point of view. In addition, recent 
(but still preliminary) simulations of the L-band bunching section show 
significant improvements of injector efficiency if a tapered (beta-match) 
TW bunching section is used, instead of two L-band buncher sections of 
the baseline design. 

The last two subjects (#22c and #22d) are not expected to have a significant 
impact on the cost of the injector.

The summary CCB response is as follows -

1.  CCB agrees that the cost change (in this case, reduction) expected 
    from this change request is substantial, such that it qualifies as 
    Class-1. 
2.  CCB finds that the revisions to the baseline configuration of the PES 
    system reasonable and acceptable and accepts this change request as is. 

For record's sake here is an excerpt from overall CCB assessment:

   CCB notes that a careful consideration is critically required for 
   the pointing jitter issues of the laser spot on the cathode. 
   Some ways (optical fibers within a temperature-controlled conduit 
   with possibly some active feedback elements, etc) to control 
   the disturbance along the laser beam transport should be provided 
   and be made part of the BC description of PES in a near future.

Additional communication and reference materials are available for
viewing, under CCR #22, at

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

The BCD files for PES section at the BCD/CCB wiki

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

has been updated as follows -

   http://www.linearcollider.org/wiki/lib/exe/fetch.php?cache=cache&media=bcd:electrons.20061201.doc

All-in-one BCD files will be updated shortly (within a day or two).

With best regards,

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