6/14/11 collimation upgrade plan & questions r. assmann, cern for the collimation team 14/6/2011...
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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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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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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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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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Analytically Derived Simple Scaling Law (E0 = 1 TeV)
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MCSSD
R. Assmann, Proc. HE-LHC Workshop
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!
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, …
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