CLIC Energy Stages Meeting D. Schulte1 D. Schulte for the CLIC team

Motivation Advantages of a staged approach of CLIC over a single stage – Operation at lower energies is better, luminosity will be higher – The cost per stage is reduced, overall project cost is spread out in time – One could reduce the technical risk of the first stage Staged approach will be part of CDR volume 3 – Used as input for the European strategy

Current CLIC Energy Stages D. Schulte3

Main Beam Generation Complex Drive Beam Generation Complex Layout at 3 TeV D. Schulte4

Main Beam Generation Complex Drive beam Main beam Drive Beam Generation Complex Layout for 500 GeV Only one DB complex Shorter main linac Shorter drive beam pulse 2.5 km 797 klystrons 15 MW, 2x29µs=58µs D. Schulte5

Reminder: 3TeV Parameter Optimisation Optimisation 1 – Luminosity per linac input power Optimisation 2 – 3TeV total project cost A.Grudiev, W. Wuensch, H. Braun, D.S. D. Schulte

Staging Consideration The staged approach should have a good physics case for its stages It should have a good technical design at each stage with a reasonable evolution The stages must have changes to be funded Physics case is mostly not known – Will use one example case to illustrate how CLIC could be staged – But need also to develop flexibility to adjust to LHC findings

Workplan Three components – Quick staged scenario for Volume 3 for next year Currently three stages based on CLIC 500GeV and CLIC 3TeV Some changes in beam emittances and IP sizes are possible – Longer term full optimisation Needs adjustment to physics ever so often Requires input from the cost working group Overall optimisation of parameters Optimisation of components Might require iteration – Potential intermediate optimisation for CDR Can we have an improved structure/parameter set?

Potential Energy Stages Strategy D. Schulte9 Use three stages Last stage consistent with current CLIC 3TeV site and components First stage derived from physics needs obvious candidates are Higgs top at threshold Low mass SUSY, if found … Second stage can be defined in different ways practical considerations from the machine physics case

Beam Parameters at Other Energies Preliminary, Indicative Choice D. Schulte10 Based on design at energy E max we can easily derive indicative parameters for E<E max leave injection complex the same shorten the linac adjust BDS but could profit from some parameter changes (ε,β) Obviously the beam parameters do not change before the BDS slight changes would yield slightly better performance correction with O(E -1/8 ) could be possible Currently we use the CLIC 3TeV and 500GeV structure to design lower energy versions of CLIC will have to do full optimisation at some time

Example: Luminosity at 260GeV Current structure would require ε x =1.4μm for L 0.01 /L total =65%

Potential CLIC Luminosity Above 500GeV D. Schulte12 Blue line indicates luminosity that we can achieve with current BDS design

Potential CLIC Parameters Based on 3TeV D. Schulte13 B. Dalena, D.S.

Potential CLIC Parameters Based on 500GeV D. Schulte14

Potential CLIC Staged Parameters D. Schulte15 First stage ML structures are re-used

Concept First Stage D. Schulte16 Concept! Not to scale

Concept Second Stage D. Schulte17

Concept Third Stage D. Schulte18

Alternative CLIC Staged Parameters D. Schulte19 First stage ML structures are not re-used

Workplan for First Stage Decide on strategy for first stage – Energies and luminosities required (physics) – Accelerating structure – PETS/decelerator, gradient – Sub-staging strategy Develop solution – Lattice design – Long transfer line lattice and integration into tunnel, if needed – Performance studies, background, etc.

Sub-Stages: 1 rst Stage of CLIC D. Schulte21 Could consist of two (three) installation sub-stages Build tunnel long enough for top (or 500GeV), install only enough structures for Higgs and run Then add structures for top and run If needed add structures for 500Gev and run Or build full stage run only at full energy, i.e. top threshold or 500GeV or run also at lower energies

Natural First Stages No of decelerators potential80/1.07 MV/mFewer structures Note: a small problem with the fill factor needs to be overcome Some issue with energy granularity Current 500GeV structures require 16% more power than 3TeV structures just live with it reduce gradient and main beam current by 8% reduce the number of PETS per decelerator and drive beam energy by 16% (check decelerator stability)

Natural First Stages No of decelerators baseline80/1.065 MV/m Fewer structures Note: a small problem with the fill factor needs to be overcome Some issue with energy granularity Current 500GeV structures require 16% more power than 3TeV structures just live with it reduce gradient and main beam current by 6.5% reduce the number of PETS per decelerator and drive beam energy by 13% (check decelerator stability)

Sub-stages Baseline 500GeV First sub-stage, option 1 First sub-stage, option 2

Low Energy Running Baseline 500GeV Early extraction, option 1 Early extraction, option 2 Reduced gradient

Workplan for Second Stage Need to understand if we can have physics input – Can only use knowledge derived from LHC and first stage experiments – Will then try to find a technical solution Otherwise need to use a technically justified second stage – E.g. go up to the maximum energy with one drive beam accelerator, i.e. about 50% of the final energy (current choice) – Or define step to have good luminosity at any energy between first and full second stage energy But would need some figure of merit/operational requirements for this – Will need to develop scheme to run at different energies Have one for the final stage, but needs to be reviewed for second stage

Thresholds Crossed as a function of Energy (GeV)

Workplan for Optimisation Need better models for – Cost – Power consumption Should review – RF limitations – Beam delivery system performance and trade-off – Damping ring emittances Will repeat previous exercise – Based on updated models – But also trying to include considerations on the stages

Issues for Energy Stages D. Schulte29 Consolidate the current cost/power model for 3TeV e.g. use of permanent magnets reduces power (J. Clarke et al.) Need to review figure of merit luminosity needs so far optimised for maximum energy will need (generic) running plan cost, cost and power/energy consumption, average or maximum power? cost of initial stage, integrated cost of all stages? Need to develop a cost/power/energy consumption model for other energies

Parameter and Structure Choice Potential structures designs RF limitations Beam physics constraints Parameter set Cost model Design choice Physics requirements Structure chosen to work for beam physics Will tell the story as if we had a structure given D. Schulte30

Luminosity and Parameter Drivers Beam Quality (+bunch length) D. Schulte31 Luminosity spectrum Beam current

Approximate Parameter Derivation Damping ring and BDS define minimum horizontal beam size at IP D. Schulte32 Not how we chose parameters but how parameters are driven by physics Beam-beam effects define minimum charge to have full luminosity efficiency Luminosity efficiency requires structure aperture consistent with minimum charge All parameters follow

DR Challenge D. Schulte33 The horizontal beam size at the IP strongly depends on ε x (N), which is dominated Also ε y (N) and ε z (N) at the damping ring are important Need to fully understand ε x (N), ε y (N) and ε z (N) Need to make a robust choice for first stage Currently use ε x ≈ 500(660)nm and ε y ≈ 5(20)m at 3TeV ε x ≈ 1800(2400)nm and ε y ≈ 5(25)m at 500GeV

BDS and DR Challenges D. Schulte34 The BDS drives two main design parameters, σ x and σ y σ x drives the overall parameter choice since it impacts the accelerating structure σ y is directly relevant for the luminosity Currently find β x ≈ 8mm and β y ≈ mm for all energies Need to understand β x (E, β y, ε x, ε y, σ E ) and β y (E, β x, ε x, ε y, σ E, σ z ) urgent as it affects all other parameters needs a reliable automatic optimisation of the designs, i.e. improved algorithms for MAPCLASS Need a robust choice for first stage

Klystron-based Approach Has been studied for 500GeV – Appears excluded for high energies – Did not seem more attractive than drive beam at 500GeV – But might be more attractive below 500GeV Considerations – Demonstration of klystron-based RF unit is reasonably simple – Might be cheaper at lower energy (compete with LEP 3 etc.) – Need to review efficiency considerations Should review findings for 500GeV at lower energy

Steps Forward Cost model -> Philippe Power model -> Bernard Emittances at DR -> Yannis Beam size at collision -> Rogelio RF constraints -> Walter Exploration of L for first stage options -> D. Design for first stage lattice -> D., Andrea Extraction lines/tunnel integration -> Andrea, D. Physics justification for second stage -> Lucie, James Physics requirements for first stage -> Lucie, James Potential for choice other structures -> Alexej, … Klystron-based approach -> Alexej, Bernard, Igor, Philippe, D.