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EDR Lattice Evaluation Page

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GDE Sendai Meeting Lattice Evaluation

• GDE Sendai Meeting Lattice Evaluation: DRLatticeEvaluation_2008_0306.pdf (Version of March 6, 2008)

Responses to Lattice Evaluation

Response from Jie Gao

Dear All,

After reading the evaluation tables, I recommend FODO5 to be the baseine since FODO5
get the highest point in the performance among the four choices " Lattice design and 
dynamical properties" which is the most important for ILC damping design at this stage 
after cost saving compared with OCS8, and I hope our colleagueus make a good choice 
for ILC DR which has the best performance, and focused on the EDR design.

Best regards

Jie GAO

Response from Susanna Guiducci

Hi Mark, Andy and Junji

I mainly agree with ranking reported in the lattice evaluation document; below just a few comments:

*1) * Lattice design and dynamical problems

I think that the optimal value of the momentum compaction for RF and bunch length is around 
2 e-4 and therefore the choice is between *FODO5* and *DCO*, which are centered on this value.

*FODO4* has a satisfactory dynamic aperture at ac=2e-4. This is the result of an accurate 
optimization work  and  shows that FODO lattice  has a large flexibility  ( 4-fold   
and 8-fold symmetry, ac=6 e-4 -  1.7 e-4) and  it can achieve a satisfactory  dynamic aperture.

*DCO* has a dynamic aperture satisfying the minimum design requirements for ac=2.8e-4 and 1.7e-4. 
I'm confident that it can be improved with dedicated work.

*2) *Conventional facilities and services

For the EDR phase the choice of the layout is crucial since it is strictly connected to the 
choices of the CFS.  The racetrak layout of the *DCO *lattice with 2 long straights, where 
the major components are clustered in alcoves within a few hundred meters from the access 
shafts, seems to me the optimal solution for costs reduction and operational efficiency.

Therefore I agree with the choice of the *DCO* lattice for the EDR.

I think that the choice of the arc cell is less critical than the layout choice; more or 
less all the lattices can achieve the design parameters but it is important to fix one and  
to concentrate all the efforts on dynamic aperture optimization, evaluation of low emittance 
tuning and  collective effects and on cost/benefits optimization.

Thank you for the exhaustive work done for the comparison,

Susanna 

Response from Craig Burkhart

Mark,
 
Unfortunately, I had to leave yesterday's discussion just as you started into the evaluation 
table.  My interpretation of the Table and the comments that have been subsequently exchanged 
is that all four approaches are technically sound, the DCO is marginally superior to either 
FODO and the OSC8 is marginally inferior.
 
That said, cost should then become a primary concern.  There are clearly cost components in 
the evaluation, but since the technically merits of the competing systems are similar shouldn't 
a greater weighting be placed on cost?
 
If you conclude that the present evaluation places sufficient weight on cost, I certainly 
support your conclusions.
 
Craig

Response from Mike Zisman

Folks:

  I do think there is merit in Craig's comments. In practice, I think it means that you should 
try to keep the FODO5 lattice "alive" until there is an opportunity to do a cost comparison. 
Insofar as we suspect that the DCO lattice will be less expensive, there should be no objection 
to using it as the baseline, with the FODO5 lattice serving as backup. From an engineering 
perspective, that probably means doing a bottom-up cost estimate for the DCO version with 
subsequent "deltas" to assess the relative costs of FODO5. This could even be a management 
milestone at some point, say one year from now.

 ...something to consider.

Cheers,
Mike

Response from Louis Emery

To all,

I agree with the relative scores in the tables.
I would weight the first table more. But I think
it would not change the order of the results.
I'm leaning towards the DCO cell structure because
of the reduced number of magnets, and I think the
DA problem is not insurmountable.

I missed the webex session on Tuesday, so I have some
comments and questions:

I'm not sure how the DCO lattice at 100 degrees/cell 
ended up with a (much?) smaller
dynamic aperture than the FODO5 lattice with 108 degree
per cell. I see that the cell length for DCO is shorter (making the
dispersion smaller) than the FODO5 FODO
cell, perhaps to partially compensate the larger I5 created by the
shorter and stronger dipole. I think the dynamic acceptance of FODO
cells with constant circumference should scale roughly as the cell
length squared. So a shorter dipole magnet resulted in a smaller dynamic
aperture.

Andy, was using a 2x field in the dipole for reducing the total dipole
magnet cost? Could the magnet be longer without disrupting
the mechanical layout much?

To rephrase a point by Aimin, if maintaining a 90 degree phase advance
is important for dynamic aperture, then an "upgrade" of momentum
compaction from 1.7e-4 to a value 25% lower can be done with the
conversion of the DCO cell to a TME-cell (keeping 90 degree
cell) by the insertion of one quad. This is, of course, at a cost of
192 magnets.

How does the lower symmetry of the DCO lattice affect the
dynamic aperture? Could we have the superconducting
stuff together in two groups at a 90 degree azimuth relative to 
the injection and extraction (like FODO4 but with doglegs added to
reduce heat load)? 

Thanks.
Louis Emery

Response from Andy Wolski

Dear Louis,

Thanks for your comments.  You raise some good questions: the dynamic aperture in particular 
is something that we should look at carefully, to make sure that we understand the issues, 
and arrive at an optimum solution.

Regarding the dipole field, this (or, equivalently, the dipole length) was used as a variable 
in the cell design of the DCO lattice to control the momentum compaction factor.  But the 
dependencies are not strong, and there is plenty of space in the lattice if it is found that 
a longer magnet would be preferable.  I'm not sure that cost is a real issue.  My guess is 
that to first order, the dipole cost depends on the beam energy and total bend angle.  Since 
all the lattices we considered for the baseline have a total bend of 2pi and all operate at 
5 GeV, I would expect any differences in dipole cost to be small.  The installation costs may 
depend more on the number of dipoles (so, a smaller number of dipoles may be cheaper to install, 
even if each individual dipole is heavier), but I'm not sure about this.

I thought the comparison between the OCS-style and DCO-style arc cells presented by Aimin was 
extremely interesting.  I had not viewed a TME cell in that way before.  It does raise some 
interesting upgrade possibilities, as you point out.

The layout is also an issue that we need to pursue.  While it is necessary at this stage to have 
a single lattice identified as the baseline, it is very important to maintain at least one 
alternate, so that we can understand the influence of things like the layout on cost, dynamics, 
etc.

Best regards,

Andy. 

Response from Mark Palmer

Hi All,

I would like to say thank you to everyone who sent a response to the lattice evaluation 
exercise.  An updated version of the lattice evaluation document has just been placed on 
the lattice evaluation page (%SCRIPTURLPATH%/view/ILC/DampingRings/LatEvalPage) 
along with copies of the responses.  The direct document link is:  
%PUBURLPATH%/ILC/DampingRings/LatEvalPage/DRLatticeEvaluation_2008_0306.pdf

At this point, both of the lattices which can accommodate 6 mm bunch lengths (FODO5 and DCO) 
appear promising.  The growing consensus is that both should be maintained while further 
investigations of the beam dynamics, technical issues, and costing are explored further.  The 
cost, reliability and availability  issues that appeared both directly and indirectly in the 
evaluations favor DCO because of the clustering of many technically challenging components in 
the rings as close as possible to the two access shafts.  It is also the case that most feel 
that any dynamics issues remaining in the designs can likely be successfully dealt with. 
Thus the recommendation that has been passed to the project managers is that the DCO be 
specified as the baseline lattice and FODO5 as the alternative lattice for the ILC Technical Design Phase.

If there are further comments/concerns, please continue to send them to the full mailing list.

Cheers,
Mark

Lattice Evaluation and Comparison Information

• Specifications for EDR lattice: EDRLatticeSpecifications.pdf
• Comparison of parameters for lattice options (OCS8, FODO, DCO): LatticeOptionsParameters.pdf

OCS8 Lattice (Developed from RDR baseline)

Lattice Documentation

• ILCDR07-KEK (Dec 07) presentation of the OCS8 lattice: Emery.pdf
• ALCPG07 (Oct 07) presentation describing status of the OCS8 lattice: OCS8_DR_Lattice_Xiao.pdf

MAD Deck

• OCS8 lattice file (xsif format): ocs8.xsif
• OCS8 MAD job file: OCS8.Run.mad8

Comments and Results

• See below for instructions on submitting comments
• Comments Received:
  • None

FODO4/5 Lattices (Variable momentum compaction factor, two dipoles per arc cell)

Lattice Documentation

• Introduction to FODO4 lattice: Introduction_to_FODO4.pdf
• ILCDR07-KEK (Dec 07) presentation on the FODO lattice: ILC_DR_FODO_lattice-sunyp.pdf
• ALCPG07 (Oct 07) presentation describing the alternate FODO lattice: FODO_DR_Lattice_Gao.pdf

MAD Deck: FODO4

• FODO4 lattice file: FODO4.xsif

MAD Deck: FODO5

• FODO5 lattice file: ILC_DR_FODO5.mad8

Comments and Results

• See below for instructions on submitting comments
• Comments Received:
  • None

DCO Lattice (Variable momentum compaction factor, one dipole per arc cell)

Lattice Documentation

• DCO lattice description: Wolski.pdf

MAD Deck: DCO

• DCO lattice file: DCO.xsif
• Magnet settings for 72 degree phase advance arc cell DCO (alpha = 2.8x10-4): kvals.72deg.xsif
• Magnet settings for 90 degree phase advance arc cell DCO (alpha = 1.7x10-4): kvals.90deg.xsif
• Magnet settings for 100 degree phase advance arc cell DCO (alpha = 1.3x10-4): kvals.108deg.xsif
• MAD job file for DCO lattice: DCO.mad8

Comments and Results

• See below for instructions on submitting comments
• Comments Received:
  • None

Lattice Evaluation Submissions

• Please submit comments and lattice evaluation studies by email.