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CLIC Energy Stages Meeting

D. Schulte

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

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Current CLIC Energy Stages

D. Schulte

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Main Beam Generation Complex

Drive Beam Generation Complex

Layout at 3 TeV

D. Schulte

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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 pulse2.5 km

797 klystrons15 MW, 2x29µs=58µs

D. Schulte

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?

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Potential Energy Stages Strategy

D. Schulte

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

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Beam Parameters at Other EnergiesPreliminary, Indicative Choice

D. Schulte

Based on design at energy Emax we can easily derive indicative parameters for E<Emax

• 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 εx=1.4μmfor L0.01/Ltotal=65%

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Potential CLIC Luminosity Above 500GeV

D. SchulteBlue line indicates luminosity that we can achieve with current BDS design

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Potential CLIC Parameters Based on 3TeV

D. Schulte

B. Dalena, D.S.

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Potential CLIC Parameters Based on 500GeV

D. Schulte

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Potential CLIC Staged Parameters

D. Schulte First stage ML structures are re-used

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Concept First Stage

D. Schulte

Concept! Not to scale

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Concept Second Stage

D. Schulte

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Concept Third Stage

D. Schulte

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Alternative CLIC Staged Parameters

D. Schulte 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.

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Sub-Stages: 1rst Stage of CLIC

D. Schulte

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

potential 80/1.07 MV/m Fewer structures

3 316 294 2754 415 386 3615 515 478 446

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

baseline 80/1.065 MV/m

Fewer structures

3 307 290 2754 404 380 3615 500 471 446

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 RunningBaseline 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

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Issues for Energy Stages

D. Schulte

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

€

FoM ∝ L(E)w(E)dEE1

E2

∫

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Parameter and Structure Choice

Potential structures designs

RF limitationsBeam physics constraints

Parameter set

Cost model

Design choice

Physics requirementsStructure chosen to work for beam physics

Will tell the story as if we had a structure given

D. Schulte

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Luminosity and Parameter Drivers

Beam Quality(+bunch length)

D. Schulte

Luminosityspectrum Beam current

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Approximate Parameter Derivation

Damping ring and BDS define minimum horizontal beam size at IP

D. Schulte

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

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DR Challenge

D. Schulte

The horizontal beam size at the IP strongly depends on εx(N), which is dominatedAlso εy(N) and εz(N) at the damping ring are important

Need to fully understand εx(N), εy(N) and εz(N)

Need to make a robust choice for first stage

Currently use• εx≈ 500(660)nm and εy≈ 5(20)m at 3TeV• εx≈ 1800(2400)nm and εy≈ 5(25)m at 500GeV

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BDS and DR Challenges

D. Schulte

The BDS drives two main design parameters, σx and σy

• σx drives the overall parameter choice since it impacts the accelerating structure

• σy is directly relevant for the luminosityCurrently find βx≈ 8mm and βy≈ 0.1-0.15mm for all energies

Need to understand βx(E, βy, εx, εy, σE) and βy(E, βx, εx, εy, σE, σz)• 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.