Collimation Upgrade Plan Questions R Assmann CERN for

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

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). 6/14/11

Overall Collimation Upgrade Plan (as defined in 2009) Interim collimation system (2014 – 2016) Inefficiency: 0. 002 % (p) b* ~ 1 – 2 m, 7 Te. V Gain ~100 in R 2 E (IR 7 IR 3) L ≤ 5 × 1033 cm-2 s-1 nominal ion intensity > 2 days per setup 2017 shutdown: IR(1)/2/(5)/7 DS Phase 2: integrated BPM’s, robust materials, red. impedance. Radiation opt. 2013 shutdown: IR 3 DS combined cleaning, IR 2 TCT’s, TCLP installation? Initial collimation system (2009 – 2012) Inefficiency: 0. 02 % (p) b* ~ 1 – 1. 5 m, 3. 5 Te. V R 2 E limits in IR 7? > 4 days per setup 6/14/11 Full collimation system (2018 onwards) Inefficiency: 0. 0004 % (p) b* ~ 0. 55 m, 7 Te. V L not limited (p and ions) 30 s per high accuracy setup Radiation optimization 2021 shutdown: tbd Collimation IR Upgrade (2022 onwards) Low b*, 7 Te. V TCT’s integrated into IR upgrade Compatibility with crab cavities

Prepared, Empty Secondary Collimator Slots for Phase 2 SLAC design PHASE I TCSG SLOT 1 st advanced phase 2 collimator CERN EMPTY PHASE II TCSM SLOT (30 IN TOTAL) 6/14/11

Luminosity Triplet aperture and collimation setup accuracy R. Bruce 6/14/11 Beambeam, brightness & robustness limits A. Dallocchio (new materials) Loss limits: collimation, (UFO’s), … D. Wollmann, A. Rossi, G. Bellodi

• 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. 5 m). 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. 6/14/11

• 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 Hi. Rad. Mat facility starting in autumn. – Development of more robust collimator materials ( Eu. CARD/Col. Mat program since 2009, report A. Dallocchio). – Not discussed in details for this review. 6/14/11

• Good news: – Since middle of May: ~ complete experimental assessment at 3. 5 Te. V done. – Reached the design 500 k. W 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 Te. V 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 Te. V is ~4 times better than specified. 6/14/11

Collimation of High Power Loss No quench of any magnet! 6/14/11

Ultra-High Efficiency 99. 960 % worse 99. 995 % MD better 6/14/11

Achieved Stored Energy: 80 MJ 80 kg TNT 6/14/11

Stored Energy Compared to 2010 Goals 6/14/11

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 Te. V 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)? Reference p goal 2014 – 2017: L ≥ 1 × 1034 cm-2 s-1 at 7 Te. V Could be reached with ~50% of nominal intensity? 6/14/11

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 Te. V 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 Te. V beam is as stable as 3. 5 Te. V, that quench limits and efficiency scale as predicted and that losses do not become more localized at 7 Te. V. 6/14/11

Protons: Simulations vs Measurement Cleaning Inefficiency B 1 v, 3. 5 Te. V, β*=3. 5 m, IR 7 B 1 Measured Simulated (ideal) Losses in SC magnets understood: location and magnitude 6/14/11

3. 5 Te. V: Luminosity Operation Collimation IR 7 CMS ATLAS Collimation IR 3 LHCb Collimation IR 6 Fill #1645, 200 bunches, 2. 4 e 13 p per beam, peak luminosity 2. 5 e 32 6/14/11

Origin of Dispersion Suppressor Losses Coll on energy Collision p–C Coll. Mat. Collision p–p Pb – Pb Quad Coll Quad Dipole Dip ole on energy Quad Coll off energy 6/14/11 Coll Dipole Dip ole

Zoom IR 7 (and illustration of 2013 upgrade for IR 3) D. Wollmann, G. Valentino, F. Burkart, R. Assmann, … 6/14/11

Proton losses phase II: Zoom into DS downstream of IR 7 99. 997 %/m 99. 99992 %/m quench level Very low load on SC magnets less radiation damage, much longer lifetime. Simulation T. Weiler Impact pattern on cryogenic collimator 2 Impact pattern on cryogenic collimator 1 imu n o i lat S 6/14/11 Cryo-collimators can be one-sided!

better WARNING: Grid simulation here for nonnominal optics and perfect machine! Impedance Target Phase 1 R. Assmann T. Weiler E. Metral (full octupoles, no transv. feedback, nominal chromaticity) Phase 1 Target Inefficiency (nominal intensity, design peak loss rate) Gap × 1. 5 × 2 Impedance Target Phase 2 (full octupoles, no transv. feedback, nominal chromaticity) Acceptable Area × 1. 2 better Ideal Inefficiency [1/m] Better Efficiency and/or Lower Impedance Phase 2 Installation of collimation phase II including collimators in cryogenic dispersion suppressors 6/14/11 Impedance Increase gaps by factor 1. 5 Nominal I. Larger triplet/IR aperture or lower b*

Ions: Beam 2 Leakage from IR 7 Collimation (much worse, as expected) 6/14/11

Therefore some questions II • Can the upgrade of the IR 3 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 Te. V 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 IR 3 dispersion suppressors for reaching nominal ion luminosity? • Will a delay of the IR 3 dispersion suppressors lead to unacceptable knock -on effects for other dispersion suppressor work (IR 2 for ions, IR 1/5 losses into dispersion suppressors, …)? • Will decision force us to work with small emittances (impact on 25 ns)? 6/14/11

Overall Collimation Plan (possible modification, acceptable risk? ) Initial collimation system (2014 – 2016) Inefficiency: 0. 005 % (p) b* ~ 1 – 2 m, 7 Te. V Gain ~100 in R 2 E (IR 7 IR 3) L ~ 1 × 1034 cm-2 s-1 Ion intensity and lumi limits > 2 days per setup 2017 shutdown: IR(1)/2/3/(5)/7 DS Phase 2: integrated BPM’s, robust materials, reduced impedance. Radiation opt. IR 2 TCT’s, combined cleaning IR 3, TCLP installation? Initial collimation system (2009 – 2012) Inefficiency: 0. 005 % (p) b* ~ 1 – 1. 5 m, 3. 5 Te. V R 2 E limits in IR 7? > 4 days per setup 6/14/11 Full collimation system (2018 onwards) Inefficiency: 0. 0004 % (p) b* ~ 0. 55 m, 7 Te. V L not limited (p and ions) 30 s per high accuracy setup Radiation optimization 2021 shutdown: tbd Collimation IR Upgrade (2022 onwards) Low b*, 7 Te. V TCT’s integrated into IR upgrade Compatibility with crab cavities

Conclusion • Equipping the IR 3 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 a number of recent good news at 3. 5 Te. V in collimation and other LHC areas that must be taken into account: – It opens the possibility to discuss delaying the IR 3 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 Te. V 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! 6/14/11

Additional Info 6/14/11

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 offmomentum halo beam dump. • SC regions off-hands: Impossible to put collimators in dispersion suppressors (as in LEP). 6/14/11 • 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 nonsmooth aperture (alignment)!

p – C Interaction: Multiple Coulomb & Single-Diffractive Scattering 6/14/11

Analytically Derived Simple Scaling Law (E 0 = 1 Te. V) R. Assmann, Proc. HE-LHC Workshop 6/14/11 MCS SD

Monte-Carlo Simulation of Realistic Beam Halo and Interactions 6/14/11

Why Off-Energy Hadrons can be so Disturbing (A) Ve • 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. 6/14/11 (A) ry d low risk iluted Very for que Interaction nch “Fixed” by rela x limits ( small T ing BLM ) Halo/shower (B) Con centrat ed UFO) Hscatterer Point losses igh risk (e. g. f or quen Protect ch by tigh t limits ( medium BLM Interaction – large Halo/shower T) Low energy tail after V bend

3. 5 Te. V: Losses in DS of IR 5 (CMS) Fill #1647, 200 bunches, 2. 4 e 13 p per beam, peak luminosity 2. 5 e 32 6/14/11

Simple Extrapolation of Losses in Dispersion Supressor of IR 5 Parameter Fill #1645, 3. 5 Te. V 7 Te. V 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 0. 039 k. Gy/y 3. 1 k. Gy/y 75% efficiency Int. peak loss magnet coil ? ? (must be much higher) Limit for int loss in dipole Note: Clear c Does not include significant loads from ion operation. NOT A onclusion: Does not include effect of b*. T ALL C O Does not include steeper scaling of losses with lumi (up to factor 5 MFO RTAB higher paper Annika Nordt). Win with monitor factor? LE! 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? 6/14/11

Quench Limit vs Energy 6/14/11

Where to Find Links to Info (New and Old)? https: //espace. cern. ch/lhc-collimation-workspace Links to past meetings, minutes, presentations, … 6/14/11

Where to Find or Put Reference Info for Upgrade? https: //espace. cern. ch/lhc-collimation-upgrade Minutes from collimation upgrade management meetings, agreed production and installation, tables, agreed planning, safety, … 6/14/11