rebaselining progress

D. Schulte, CLIC Rebaselining, October 2013

Rebaselining Progress

D. Schulte


Model Availability• RF structure limitations (Alexej Grudiev)

– Best guess from experiments, we will add a bit of extra margin

• RF structure database from (Kyrre Sjoback)– Update with new RF limitation coming soon

• Beam limitations (Yannis Papaphilippou, Rogelio Tomas, D.S.)– New minimum beta-function 4mm (Hector Garcia, Rogelio Tomas)

• But here continue with 8mm• Use 4mm as a margin• And to be able to improve for low energy running

• Power model (Bernard Jeanneret)– Needs to be validated

• Cost model– Drive beam (Robert Corsini, Igor Syratchev)– Main linac (Alexej Grudiev)– Civil engineering and infrastructure (Philippe Lebrun)– Cost for 500Gev based on CLIC_G is consistent with CDR

Summary on the high-power RF constraints

RF breakdown and pulsed surface heating constraints used for CLIC_G design (2007):

• Esmax < 250 MV/m

• Pin/Cin·(tpP)1/3 = 18 MW·ns1/3/mm

• ΔTmax(Hsmax, tp) < 56 K

Optimistic RF breakdown and pulsed surface heating constraints for BDR=10-6 bpp/m:

• Esmax ·(tp

P)1/6 < 250 MV/m · (200ns)1/6 • Pin/Cin·(tp

P)1/3 < 2.8 MW/mm · (200ns)1/3 = 17 [Wu]• Sc

max ·(tpP)1/3 < 5 MW/mm2 · (200ns)1/3

and

• ΔTmax(Hsmax, tp) < 50 K

• Depending on degree of our optimism a safety margin has to be applied. • Varying RF constraints in the optimization how much money one can save by being

optimistic.A. Grudiev

Not yet available in database

Remarks

• Not all cost is in cost model– Only the varying part for which we established the cost– Comparison with the CDR cost for this part we find very good

agreement with CLIC_G parameters

• But CLIC_G parameters are not consistent with RF limitations– Train can only have 245 bunches not 312– Cannot reach 1034cm-2s-1 at 350GeV with 50Hz repetition rate

• Some cost savings identified in rebaselining– Building for second drive beam accelerator– Higher power klystrons for drive beam accelerator– Revised modulator cost (Davide Aguglia)– No electron pre-damping ring required (Yannis, Steffen)

Choices

• Assume 50Hz operation– To minimise magnetic stray field effects– Only harmonics would be possible, but suffer from pulse-to-pulse

variation

• Target for one specific luminosity– Use only the pulse length good for this luminosity

• First consider 350GeV machine– Neglect impact of upgrade– i.e. gradients below 100MV/m are allowed– Charge scaling is for local stability

• Emittance growth can vary but stays below 3TeV limit

• Integrate upgrade considerations later

Algorithm

• Go through different sets, i.e. combinations of Lstructure, a1, a2 , d1, d2, G

• For each set– Identify highest bunch charge and use it– Determine minimum bunch distance and use it– Calculate input power, fill and rise time and maximum available beam time– If luminosity is below target got to next structure– Adjust beam pulse time according to luminosity– Determine number of drive beam sectors for nf=24 and fDBA=1GHz– Adjust to next larger integer– Calculate cost– While stretching linac by one decelerator is cheaper, stretch– Store parameter set

• Will store all acceptable sets– i.e. all that achieve the luminosity target


Example: Cost vs. Bunch Charge


Impact of RF Constraints

L=1034cm-2s-1


Example Structures: Cheapest ChoicesS=1.0 S=1.1 S=1.2 S=1.0 S=1.2

L [1034cm-2s-1] 1 1 1 2 2

a1/λ 0.15 0.15 0.15 0.15 0.15

a2/λ 0.09 0.09 0.085 0.09 0.085

D1/Lcell 0.26 0.185 0.35 0.22 0.278

D2/Lcell 0.11 0.11 0.11 0.11 0.203

Ncell 34 38 30 38 36

G [MV/m] 90 75 75 75 60

Pstructure [MW] 72.4 56.9 44.4 56.6 36.2

N [109] 4.46 4.06 3.85 4.06 4.28

Δz [λ] 6 6 6 6 8

nb 252 296 324 591 572

τRF [ns] 199.7 222.2 246.7 372.8 457.9

C [M. a.u.] 2,782 2,910 3,021 3,308 3,639

PRF [MW] 10.915 10.248 11.246 17.1 17.7

Pwall [MW] 143.6 142.4 144.3 171.3 163.4


Operation at Different MarginsS=1.0 S=1.1 S=1.2 S=1.0 S=1.2

L [1034cm-2s-1] 1 1 1 2 2

G [MV/m] 95 80 75 75 55

Pstructure [MW] 68.0 49.9 44.4 44.4 22.6

N [109] 4.36 3.98 3.85 3.85 3.3

Δz [λ] 6 6 6 6 8

nb 252 313 324 648 927

τRF [ns] 215.7 241.1 246.7 408.7 702.7

C [M a.u.] 2,834 2,969 3,021 3,444 4,026

Copt [M a.u.] 2,782 2,91 3,021 3,308 3,639

Pwall [MW] 155.6 147.4 144.3 174.5 182.6

Popt [MW] 143.6 142.4 144.3 171.3 163.4

Additional cost for S=1.2 potential 50M a.u. and 12MWFor use of S=1.2 cost is about 240M a.u.

Good robust choice for L=1e34, but issue with margin at 2e34


Choice of 3TeV StructuresA number of parametersare fixed• A gradient of 100MV/m to fit on the site• A luminosity in the peak of 2x1034cm-2s-1

• No safety margin

No structure with safety margin has reached the luminosity goal

The cost variation is quite small


Conclusions• We have a cost model for main linac and drive beam complex including civil engineering and

infrastructure– Injectors are being worked on

• Adjusted RF limitations to experimental results– CLIC_G cannot sustain the pulse length from the CDR– Further adjustments with new database

• Minimum cost for gradient margin is 120M a.u./10%

• Minimum cost of doubling luminosity from 1034cm-2s-1 is 530M a.u.

• Can change the safety margin for a structure by adjusting the beam and RF pulse parameters– Can adjust to RF testing results– But all other systems will have to redo work– And still some additional cost will occur

• No safety margin at 3TeV appears possible with G=100MV/m

• Can find compromise structure for 350GeV and 3TeV– But may not be a good idea given the long time between the energy stages


Outlook

• Work needs to continue– Agree on luminosity target

• Suggested baseline 1x1034cm-2s-1 @350+GeV?• Should we have alternative with 2x1034cm-2s-1 or more?

– Decide on exact energy target > 350GeV• Requires adjustments of decelerators and pulse lengths

– Get the new RF data base• Structures may change somewhat

– Define RF margin• Suggested value is 10% overhead in gradient

– Agree on structure choice strategy• Either a structure that is good for all energies• The best low energy structure

– Study the upgrade• In particular if we want to change the structure

– Do same exercise for klystrons?• Requires more detailed layout and cost model


Reserve


Bunch Charge


Bunch Spacing


Luminosity PotentialS=1.0 S=1.2

L=0.5x1034cm-2s-1 105MV/m 85MV/m

L=1x1034cm-2s-1 95MV/m 75MV/m

L=2x1034cm-2s-1 75MV/m 55MV/m


Pulse Charge


Number of Bunches


Cost


Total Cost


Preliminary Power Model


No of Decelerators

rebaselining progress

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