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6/14/11 Collimation Upgrade Plan & Questions R. Assmann, CERN for the collimation team 14/6/2011 LHC Collimation Project Review

6/14/11 Collimation Upgrade Plan & Questions R. Assmann, CERN for the collimation team 14/6/2011 LHC Collimation Project Review

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6/14/11

Collimation Upgrade Plan & Questions

R. Assmann, CERN

for the collimation team14/6/2011

LHC Collimation Project Review

LHC Collimation as Staged System

• LHC collimation was conceived in 2003 as a staged system.

• Phase 1: – For initial beam commissioning and early years of LHC operation.

– Predicted not adequate for nominal and ultimate intensity.

– Designed, constructed and commissioned 2003 – 2009.

• Phase 2: – Upgrade for nominal, ultimate and higher beam intensities.

– Solves issues in efficiency, impedance and radiation impact.

– Originally not clear what the solution would be.

– By now various upgrade solutions worked out and under design.

• IR upgrade:– Adaptation to changes in IR upgrades: space and losses.

– Adaptation to phase space modifications (ATS, crab cavities).

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Overall Collimation Upgrade Plan(as defined in 2009)

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Initial collimation system (2009 – 2012)Inefficiency: 0.02 % (p)b* ~ 1 – 1.5 m, 3.5 TeVR2E limits in IR7?> 4 days per setup

Full collimation system (2018 onwards)Inefficiency: 0.0004 % (p)b* ~ 0.55 m, 7 TeVL not limited (p and ions)30 s per high accuracy setupRadiation optimization

Interim collimation system (2014 – 2016)Inefficiency: 0.002 % (p)b* ~ 1 – 2 m, 7 TeVGain ~100 in R2E (IR7IR3)L ≤ 5 × 1033 cm-2 s-1 nominal ion intensity> 2 days per setup

2013 shutdown: IR3 DScombined cleaning, IR2 TCT’s, TCLP installation?

2017 shutdown:IR(1)/2/(5)/7 DSPhase 2: integrated BPM’s, robust materials, red. impedance.Radiation opt.

Collimation IR Upgrade (2022 onwards)Low b*, 7 TeVTCT’s integrated into IR upgradeCompatibility with crab cavities

2021 shutdown: tbd

Prepared, Empty Secondary Collimator Slots for Phase 2

EMPTY PHASE II TCSM SLOT (30 IN TOTAL)

PHASE I TCSG SLOT

1st advanced phase 2 collimator CERN

SLAC design

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Luminosity

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Triplet aperture

and collimation

setup accuracy

R. Bruce

Loss limits: collimation, (UFO’s), … D. Woll- mann, A. Rossi, G. Bellodi

Beam-beam,

brightness & robust-

ness limits

A. Dalloc-chio (new materials)

• Good news:– Available aperture about 50% larger than guaranteed by design (smaller orbit

errors, better alignment, …). Gain here for luminosity!

– Optics very well controlled (5-10% beta beat, … for b* = 1.5m). Gain here!

• As expected:– Very challenging to achieve collimation & protection tolerances (only

infrequent setups possible, drifts over months, …) b* limited.

– Addressed by collimators with integrated beam position pickups (almost all to be equipped). Not discussed in details for this review.

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• Good news:– Collided successfully three times nominal brightness (head-on). Long-range

beam-beam soon to be checked. Gain factor 3 here, if LR beam-beam OK as well!

• Under study:– Robustness of collimators for the high achieved brightness. Simulation of

realistic scenarios, tests in HiRadMat facility starting in autumn.

– Development of more robust collimator materials ( EuCARD/ColMat program since 2009, report A. Dallocchio).

– Not discussed in details for this review.

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• Good news:– Since middle of May: ~ complete experimental assessment at 3.5 TeV done.

– Reached the design 500 kW peak beam loss (protons) at primary collimators without quench of a super-conducting magnet!

– Reached 80 MJ without a single quench from stored beam losses.

– Transverse damper stabilizes beam at 3.5 TeV high impedance OK.

– Reached 99.995% collimation efficiency with 50% smaller gaps than design (low emittance, high impedance) and due to much less impact of imperfections than predicted (better orbit, lower beta beat, …).

– Minimum beam lifetime at 3.5 TeV is ~4 times better than specified.

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Collimation of High Power Loss

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No quench of any magnet!

Ultra-High Efficiency

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99.995 %

worse

better

MD

99.960 %

Achieved Stored Energy: 80 MJ

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80 kg TNT

Stored Energy Comparedto 2010 Goals

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Therefore some questions I

• It runs so well: Do we really need to invest a lot of work for a better collimation efficiency in the first long LHC shutdown (2013/14)?

• Do operational experience and MD measurements not prove to us sufficiently well that we can reach nominal 7 TeV luminosity in 2014/15 (with the efficiency of the present collimation system)?

• Do the potential gains in b* and beam brightness (beam-beam) not provide an additional margin to increase luminosity (without pushing stored energy)?

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Reference p goal 2014 – 2017:

L ≥ 1 × 1034 cm-2 s-1 at 7 TeV

Could be reached with ~50% of nominal intensity?

On the Other Side

• Predicted leakage mechanisms and locations are fully confirmed, both for protons and ions.

• Proposed upgrade plan will gain factor ~10 in efficiency: can be used for higher stored energy and/or larger collimation gaps (relaxed tolerances and lower impedance). Lowest risk approach.

• All experience relies on 3.5 TeV beam energy (higher quench margin, larger collimation gaps, lower impedance, easier operation for transverse damper, lower cross-section single-diffractive scattering, …).

• All experience relies on operation with 1/2 of nominal emittance (50 ns) beam core far away from jaw surface, lower loss spikes, more room to close collimator gaps.

• It is assumed that 7 TeV beam is as stable as 3.5 TeV, that quench limits and efficiency scale as predicted and that losses do not become more localized at 7 TeV.

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Protons: Simulations vs MeasurementB1v, 3.5TeV, β*=3.5m, IR7

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B1

Losses in SC magnets understood: location and magnitude

Simulated (ideal)

Measured

Cle

anin

g I

nef

fici

ency

3.5 TeV: Luminosity Operation Collimation

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Fill #1645, 200 bunches, 2.4e13 p per beam, peak luminosity 2.5e32

Collimation IR3

Colli-mationIR7

ATLAS

CMSLHCb

Colli-mation IR6

Origin of Dispersion Suppressor Losses

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Quad Quad Dipole Dipole

Coll

Coll Coll

Quad Quad Dipole Dipole

Coll Coll

Collisionp – pPb – Pb

Collisionp – CColl. Mat.

on energy

on energy

off energy

Zoom IR7(and illustration of 2013 upgrade for IR3)

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D. Wollmann, G. Valentino, F. Burkart, R. Assmann, …

quench level

Proton losses phase II:Zoom into DS downstream of IR7

Impact pattern on cryogenic collimator 1

Impact pattern on cryogenic collimator 2

Simulation T. Weiler

Very low load on SC magnets less radiation damage, much longer lifetime.

99.997 %/m 99.99992 %/m

Cryo-collimators can be one-sided!Simulation

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Phase 1

Phase 2

Gap × 1× 1.2

× 1.5

× 2

Idea

l Ine

ffici

ency

[1/m

]

Impedance

bett

er

better

Better Efficiency and/or Lower Impedance

Acceptable Area

R. AssmannT. WeilerE. Metral

Target Inefficiency(nominal intensity, design peak loss rate)

Installation of collimation phase IIincluding collimators in cryogenic dispersion suppressors

WARNING: Grid simulation here for non-nominal optics and perfect machine!

Increase gaps by factor 1.5Nominal I. Larger triplet/IR aperture or lower b*

Impedance Target Phase 1

(full octupoles, no transv. feedback,

nominal chromaticity)

Impedance Target Phase 2(full octupoles,no transv. feedback,nominal chromaticity)

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Ions: Beam 2 Leakage from IR7 Collimation (much worse, as expected)

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Therefore some questions II

• Can the upgrade of the IR3 dispersion suppressors be delayed without any danger for magnet lifetime (SC magnets as halo dumps)?

• Is later upgrade work feasible in dispersion suppressors (activation)?

• Are we sufficiently sure about 7 TeV beam behavior to give up the improvement in collimation efficiency and/or impedance for 2014?

• Is the presently predicted “proton” safety factor ~4 above nominal intensity big enough ( assumptions and energy scaling)?

• Do we need an upgrade of the IR3 dispersion suppressors for reaching nominal ion luminosity?

• Will a delay of the IR3 dispersion suppressors lead to unacceptable knock-on effects for other dispersion suppressor work (IR2 for ions, IR1/5 losses into dispersion suppressors, …)?

• Will decision force us to work with small emittances (impact on 25 ns)?

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Overall Collimation Plan(possible modification, acceptable risk?)

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Initial collimation system (2009 – 2012)Inefficiency: 0.005 % (p)b* ~ 1 – 1.5 m, 3.5 TeVR2E limits in IR7?> 4 days per setup

Full collimation system (2018 onwards)Inefficiency: 0.0004 % (p)b* ~ 0.55 m, 7 TeVL not limited (p and ions)30 s per high accuracy setupRadiation optimization

Initial collimation system (2014 – 2016)Inefficiency: 0.005 % (p)b* ~ 1 – 2 m, 7 TeVGain ~100 in R2E (IR7IR3)L ~ 1 × 1034 cm-2 s-1 Ion intensity and lumi limits> 2 days per setup

IR2 TCT’s, combined cleaning IR3,TCLP installation?

2017 shutdown:IR(1)/2/3/(5)/7 DSPhase 2: integrated BPM’s, robust materials, reduced impedance.Radiation opt.

Collimation IR Upgrade (2022 onwards)Low b*, 7 TeVTCT’s integrated into IR upgradeCompatibility with crab cavities

2021 shutdown: tbd

Conclusion

• Equipping the IR3 dispersion suppressors with collimators improves the performance reach for LHC and has the lowest risk for LHC performance. It was defined as a minimal plan some years ago.

• There are a number of recent good news at 3.5 TeV in collimation and other LHC areas that must be taken into account:– It opens the possibility to discuss delaying the IR3 collimation upgrade in the

dispersion suppressors by three years.

– Some important issues were summarized and some questions put up that require attention and advice.

– Subsequent talks will go into more details.

• Predicting performance at 7 TeV is tricky and quite involved: loss spikes, quench limit, nuclear physics p/ions, energy deposition details, small collimation gaps, high impedance, …

• Your advice is very much welcome!

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Additional Info

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Origin of Losses in Dispersion Suppressor

• Effect understood and predicted as early as 2003.

• Collimators in straight sections “generate” off-momentum p and ions (effectively).

• Off-momentum particles pass through straight sections and are deflected by first dipoles in dispersion suppressors.

• Downstream magnets act as off-momentum halo beam dump.

• SC regions off-hands: Impossible to put collimators in dispersion suppressors (as in LEP).

• Clear physics sources: p have single-diffractive scattering in matter, ions dissociate/fragment!

• Now confirmed by experimental data (also in horizontal plane).

• Loose factor ~10 with non-smooth aperture (alignment)!

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p – C Interaction: Multiple Coulomb &Single-Diffractive Scattering

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Analytically Derived Simple Scaling Law (E0 = 1 TeV)

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MCSSD

R. Assmann, Proc. HE-LHC Workshop

Monte-Carlo Simulation of Realistic Beam Halo and Interactions

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Why Off-Energy Hadrons can be so Disturbing

• Loss pattern cannot be compared to case of point scatterers like UFO’s or wire scanners very diluted showers.

• Off energy hadrons produce a very sharp impact line.

• BLM’s cannot distinguish the two cases!

• Important uncertainties about BLM response and thresholds with such a concentrated loss.

• Plan quench tests for this case.

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Point scatterer (e.g. UFO)

Low energy tail after V bend

(A)

(B)

Interaction

Interaction

Halo/shower

Halo/shower

(A) Very diluted Very low risk for quench “Fixed” by relaxing BLM limits (small T)

(B) Concentrated losses High risk for quench Protect by tight BLM limits (medium – large T)

3.5 TeV: Losses in DS of IR5 (CMS)

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Fill #1647, 200 bunches, 2.4e13 p per beam, peak luminosity 2.5e32

Simple Extrapolation of Losses in Dispersion Supressor of IR5

Parameter Fill #1645, 3.5 TeV 7 TeV scaled

Luminosity 0.025 × 1034 cm-2 s-1 1 × 1034 cm-2 s-1

Loss @ BLM 3.1 × 10-6 Gy/s 2.4 × 10-4 Gy/s

Limit @ BLM 5 × 10-4 Gy/s ~3 × 10-4 Gy/s

Int. loss @ BLM for 200 d at 75% efficiency

0.039 kGy/y 3.1 kGy/y

Int. peak loss magnet coil (must be much higher)

? ?

Limit for int loss in dipole ? ?

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Note:Does not include significant loads from ion operation.Does not include effect of b*.Does not include steeper scaling of losses with lumi (up to factor 5 higher paper Annika Nordt). Win with monitor factor?Should be able to gain something with TCL/TCLP collimators (cannot fix problem due to zero dispersion).In the past strong concerns about dipoles with this load (K.H. Mess). Now OK?

Clear conclusion:NOT AT ALL COMFORTABLE!

Quench Limit vs Energy

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Where to Find Links to Info (New and Old)?

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https://espace.cern.ch/lhc-collimation-workspace

Links to past meetings, minutes, presentations, …

Where to Find or Put Reference Info for Upgrade?

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https://espace.cern.ch/lhc-collimation-upgrade

Minutes from collimation upgrade management meetings, agreed production and installation, tables, agreed planning, safety, …