Rebaselining Progress D. Schulte for the CLIC rebaselining team Davide Aguglia, Roberto Corsini, Steffen Doebert, Konrad Elsener, Alexej Grudiev, Erk Jensen, Andrea Latina, Philippe Lebrun, Lucie Linssen, Gerard McMonagle, David Nisbet, John Andrew Osborne, Yannis Papaphilippou, Germana Riddone, Lenny Rivkin, Giovanni Rumolo, Hermann Schmickler, Kyrre Sjobak, Steinar Stapnes, Igor Syratchev, Rogelio Tomas Garcia, Rolf Wegner, Walter Wuensch D. Schulte, CLIC Rebaselining Progress, February 2014

Simplified Parameter Diagram Drive Beam Generation Complex P klystron, N klystron, L DBA, … Main Beam Generation Complex P klystron, … Two-Beam Acceleration Complex L module, Δ structure, … I drive E drive τ RF N sector N combine f r N n b n cycle E 0 f r Parameter Routine Luminosity, RF+beam constraints L structure, , a 1, a 2, d 1, d 2, G E cms, G, L structure VariableMeaningCurrent value I drive Drive beam current101A E drive Drive beam energy2.37GeV τ RF Main linac RF pulse length244ns N sector Number of drive beam sectors per linac 4 N combine Combination number24 frfr Repetition rate50Hz NMain beam bunch charge in linac 3.72e9 nbnb MB bunches per pulse312 n cycle Spacing between MB bunches 6 cycles E0E0 MB energy at linac entrance 9GeV E cms Centre-of-mass energy500GeV GMain linac gradient100MV/m D. Schulte, CLIC Rebaselining Progress, February 2014

Simplified Parameter Diagram Drive Beam Generation Complex P klystron, N klystron, L DBA, … Main Beam Generation Complex P klystron, … Two-Beam Acceleration Complex L module, Δ structure, … Parameter Routine Luminosity, … C inestment, C operation,P VariableMeaning C investment Investment cost C operation Operation cost/year PPower consumption D. Schulte, CLIC Rebaselining Progress, February 2014 C inestment, C operation,P C inestment, C operation,P Infrastructure and Services Controls and operational infrastructure C inestment, C operation,P

Beam Studies Horizontal beta-function can be reduced from 8mm to 4mm (H. Garcia Morales, R. Tomas) – Used as a reserve Scaling of damping ring emittance as function of charge to keep the same risk level (F. Antoniou, Y. Pappaphilippou) Collective limitations in damping ring studied (G. Rumolo, G. Iadarola) – More difficult at higher charges, but does not seem prohibitive Scaling of charge with gradient – Different levels possible Keep local stability NW T (2  z )=const Same emittance growth NW T (2  z )˜sqrt(G) Same coherent residual effect NW T (2  z )˜G – Can use first one (J. Pfingstner) Tolerances change with gradient, but are always better than at 3TeV D. Schulte, CLIC Rebaselining Progress, February 2014

Summary on the high-power RF constraints RF breakdown and pulsed surface heating constraints used for CLIC_G design (2007): E s max < 250 MV/m P in /C in ·(t p P ) 1/3 = 18 MW·ns 1/3 /mm ΔT max (H s max, t p ) < 56 K Optimistic RF breakdown and pulsed surface heating constraints for BDR=10 -6 bpp/m: E s max ·(t p P ) 1/6 < 250 MV/m · (200ns) 1/6 P in /C in ·(t p P ) 1/3 < 2.8 MW/mm · (200ns) 1/3 = 17 [Wu] S c max ·(t p P ) 1/3 < 5 MW/mm 2 · (200ns) 1/3 and ΔT max (H s max, t p ) < 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 Since new year in database D. Schulte, CLIC Rebaselining Progress, February 2014

Old Cell Database Does NOT take S c into account => likely overestimating K. Sjobak, A. Grudiev D. Schulte, CLIC Rebaselining Progress, February 2014

New Cell Database K. Sjobak, A. Grudiev D. Schulte, CLIC Rebaselining Progress, February 2014 Improved cell design is on the way Will help larger apertures more

Cost and Power Not all cost is in cost model – Only the varying part for which we established the cost Cost model – Drive beam (Robert Corsini, Igor Syratchev, Davide Aguglia) – Main linac (Alexej Grudiev) – Civil engineering and infrastructure (Philippe Lebrun) – Cost for 500Gev based on CLIC_G is consistent with CDR (4.5 a.u.) Some cost savings identified in rebaselining – Conventional facilities for second drive beam accelerator (Philippe Lebrun) – Higher power klystrons for drive beam accelerator (Igor Syratchev) – Revised modulator cost (Davide Aguglia) – No electron pre-damping ring required (Yannis Papaphilippou, Steffen Doebert) Power model (Bernard Jeanneret) – Made some update D. Schulte, CLIC Rebaselining Progress, February 2014

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/alignment tolerances can vary but stay below 3TeV limit Integrate upgrade considerations later D. Schulte, CLIC Rebaselining Progress, February 2014

Specific Structure Luminosity Potential D. Schulte, CLIC Rebaselining Progress, February 2014 Using the same structure at different gradients, assume that we use full possible pulse length Safety factor S: Structure can tolerate S-times the nominal gradient for the full pulse length

Specific Structure Cost D. Schulte, CLIC Rebaselining Progress, February 2014 Higher gradient reduces linac length -> lower linac cost But requires more instantaneous power -> increased drive beam cost Higher luminosity requires more energy per pulse -> higher drive beam cost Using the same structure at different gradients and change the whole design accordingly Lowest cost at highest allowed gradient Almost no exception L=0.5x10 34 cm -2 s -1 L=1x10 34 cm -2 s -1 L=2x10 34 cm -2 s -1

Cost vs. Bunch Charge D. Schulte, CLIC Rebaselining Progress, February 2014 CLIC_G parameters are no solution Train can only have 245 bunches not 312 Cannot reach cm -2 s -1 at 350GeV with 50Hz repetition rate Luminosity goal significantly impact minimum cost For L=1x10 34 cm -2 s -1 to L=2x10 34 cm -2 s -1 costs 0.5 a.u. S=1.1 Cost [a.u.] N [10 9 ] L=0.5x10 34 cm -2 s -1 L=1x10 34 cm -2 s -1 L=2x10 34 cm -2 s

Impact of RF Constraints D. Schulte, CLIC Rebaselining Progress, February 2014 Safety factor S: Structure can tolerate S- times the nominal gradient for the full pulse length Cost [a.u.] S=1.0 L=1.1 L=1.2 a/ L=10 34 cm -2 s -1 10% safety in gradient cost about 0.1 a.u.

Luminosity Spectrum Quality D. Schulte, CLIC Rebaselining Progress, February 2014 Used L 0.99 /L total >0.6 As constraint -> Cheaper designs toward this limit Not a surprise Cost [a.u.] L 0.99 /L total L=0.5x10 34 cm -2 s -1 L=1x10 34 cm -2 s -1 L=2x10 34 cm -2 s -1 Safety factor S=1.1

Good Structure Options D. Schulte, CLIC Rebaselining Progress, February 2014 Cheapest design Highest gradient design (< 3% overcost) Longest structure design (< 3% overcost) L=1x10 34 cm -2 s -1, S=1.1

Good Structure Options D. Schulte, CLIC Rebaselining Progress, February 2014 Cheapest design Highest gradient design (< 3% overcost) Longest structure design (< 3% overcost) L=1x10 34 cm -2 s -1, S=1.1

Good Structure Options D. Schulte, CLIC Rebaselining Progress, February 2014 Cheapest design Highest gradient design (< 3% overcost) Longest structure design (< 3% overcost) L=1x10 34 cm -2 s -1, S=1.1

Some Examples D. Schulte, CLIC Rebaselining Progress, February 2014 longHigh gradientcheap L [10 34 cm -2 s -1 ]111 a 1 /λ a 2 /λ0.105 D 1 /L cell D 2 /L cell N cell G [MV/m] P [MW] N [10 9 ] Δz [λ]866 nbnb τ RF [ns] C [a.u.] L=1x10 34 cm -2 s -1, S=1.1

Study of Klystron-based Alternative For first energy stage at 375GeV cms Would need ~30,000 klystrons at 3TeV Studied CLIC_G with klystrons Similar cost as with drive beam but more detailed cost model in preparation Defined RF unit based on this structure and achieved klystron performances D. Schulte, CLIC Rebaselining Progress, February 2014 I. Syratchev et al.

Klystron vs. Drive-beam Cost D. Schulte, CLIC Rebaselining Progress, February Cost K [a.u.] Cost DB [a.u.] Very simple cost model

Preliminary FEL Structure Choice? a 1 /λ=0.15, a 2 /λ=0.1 d 1 /λ=0.9mm, d 2 /λ=1.7mm L=0.75m, G=65MV/m P in =41.8MW, τ=149.6ns 11 RF units -> structure per unit -> 10 Cost=49.7 a.u. This structure has happened to be the cheapest Should we use it as a GUINEA-PIG to set up the simulations? Preliminary, old database, simple cost model D. Schulte, CLIC Rebaselining Progress, February 2014

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 Minimum cost for gradient margin is 0.1 a.u./10% Minimum cost of doubling luminosity from cm -2 s -1 is 0.5 a.u. If we pick one structure the gradient is still aa free parameter – Can change the safety margin 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 Do klystrons in more detail Need to define the staging strategy D. Schulte, CLIC Rebaselining Progress, February 2014

Reserve D. Schulte, CLIC Rebaselining Progress, February 2014

Algorithm Go through different sets, i.e. combinations (1.6x10 9 ) of L structure, a 1, a 2, d 1, d 2, 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 n f =24 and f DBA =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 D. Schulte, CLIC Rebaselining Progress, February 2014

Impact of RF Constraints D. Schulte, CLIC Rebaselining Progress, February 2014 L=10 34 cm -2 s -1

Operation at Different Margins D. Schulte, CLIC Rebaselining Progress, February 2014 S=1.0S=1.1S=1.2S=1.0S=1.2 L [10 34 cm -2 s -1 ]11122 G [MV/m] P [MW] N [10 9 ] Δz [λ]66668 nbnb τ RF [ns] C [a.u.] C opt [a.u.] P wall [MW] P opt [MW] Using the optimum structure for S=1.2, L=1e34 does lead to little cost Increase for other parameters (50MCHF at L=1e34 and at most 110MCHF at L=1e34) Good robust choice for L=1e34, but bunch spacing changes at S=1.2 and L=1e34

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, G. Rumolo, 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) – Made some update 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 D. Schulte, CLIC Rebaselining Progress, February 2014

Specific Structure Total Cost D. Schulte, CLIC Rebaselining Progress, February 2014 Lowest cost at highest allowed gradient Almost no exception