LHC Accelerator Upgrade 20/03/2000 LHC Accelerator Upgrade J.-P. Koutchouk CERN/AT 11/16/2018 Talk to IoP/JPK

Outline Introduction Goals (phases I and II, energy upgrade) Phase I: the consolidation Phase II: the luminosity upgrade How to increase further the luminosity? Increasing the beam current Focusing more Luminosity issues Technological challenges The energy upgrade Conclusions 11/16/2018 Talk to IoP/JPK

1- Introduction The present focus of the accelerator sector is obviously the baseline LHC. Planning the upgrade is nevertheless timely as it is largely technology-driven with lead times of 5 to 15 years, depending on goals and complexity. Yet, several choices require LHC results (machine and physics) Hence upgrade studies aim primarily at identifying the necessary hardware to launch in time the R&D programmes and give clear goals to the action of CERN partners (US-LHC, CARE-HHH and NED) 11/16/2018 Talk to IoP/JPK

2a- The goals tentativeplanning goal Phase I: LHC+ 2012 (or SLHC1) 2012 Triplet consolidation for high integrated luminosity; Luminosity 1 to  2; no interference with detectors Phase II: SLHC (or SLHC2) 2016 Luminosity  10: Phase III: LHC-D or LHC-T 2020-25 energy doubler or tripler 11/16/2018 Talk to IoP/JPK

2b- The goals: the luminosity profile LHC baseline SLHC LHC+ & SLHC 11/16/2018 Talk to IoP/JPK

3a- Phase I (LHC+) Motivations: Boundary conditions: Facilitate reaching the ultimate luminosity of 2.31034cm-2s-1 (made difficult following increase of crossing angle, introduction of a beam screen and collimator impedance) Improve the running efficiency at nominal performance & create margins if some of the design parameters would not be reached. Boundary conditions: no interference with detectors, fastest implementation: Nb-Ti s.c. technology; fast performance increase: no new beam dynamics 11/16/2018 Talk to IoP/JPK

3b- Phase I (LHC+) Solution: change the IR1 & IR5 triplets (70mm) for larger aperture ones (130mm). This gives the potential to recover the “ultimate” luminosity with a safety margin of ~50%. D1 may have to be changed. The superconducting cable is available (spare LHC dipole cable). Status: Feasibility studies done Included in Proposal SLHC-PP to FP7-Infrastr.-2007-1 coord. L. Evans, issued in May 2007. Project coordinator appointed (R. Ostojic) to evaluate cost and manpower requirements. Timescale: operational in 2012 Budget: remains to be found 11/16/2018 Talk to IoP/JPK

4a- Phase II (SLHC) Challenge: LHC baseline was pushed to “maximum” in the competition with SSC. Going beyond requires creative solutions. Luminosity goal: ~ 101034cm-2s-1 Boundary conditions: For such a significant upgrade, the added complexity should be minimized for a fast progress of performance and the risks mitigated for a graceful degradation in case of unexpected. 11/16/2018 Talk to IoP/JPK

4b- P.II: The luminosity formula crossing angle standard Variation of β along bunch F decreases with decreasing b*, increasing kb, Nb and ss. H is in the range {0.9, 1} for practical b*. A constraint is the “beam-beam limit”, usually given by: 11/16/2018 Talk to IoP/JPK

Luminosity at the beam-beam limit: 4c- P.II: The strategies Luminosity at the beam-beam limit: Two main tracks: Luminosity increase by increasing the beam current Luminosity increase by lowering b* + work on form factors and beam-beam limit 11/16/2018 Talk to IoP/JPK

4d- P.II: Increase of beam current Strategy: Increase significantly the bunch charge Nb (*4). Respect the beam-beam limit (that would be exceeded) by a change of regime: lengthen the bunch to reach a quasi coasting beam regime by longitudinal emittance blow-up. Reduce the number of bunches (50 ns spacing) to control e-cloud and image current heat deposition & beam stability. Recover the lost factor of 2 by reducing beta* by a factor of 2 (25 cm) Reduce the crossing angle by wire compensation 11/16/2018 Talk to IoP/JPK

4e- P.II: Increase of beam current Merits: no elements in detectors; quasi nominal insertion beam optics with small chromatic aberrations; higher average luminosity per run. Challenges: new beam dynamics: novel beam-beam regime not experienced at this level of performance; higher peak beam current coupling to machine elements, sophisticated rectangular beam distribution; machine protection: higher bunch/beam power; higher collimator robustness required; radiation protection: protection to be re-assessment when exceeding the ultimate beam current in the LHC (INB). injectors: new beam preparation; injectors’ upgrade for full operational performance: Linac4, PS2, SPS improvement. 11/16/2018 Talk to IoP/JPK

4f- P.II: Increase of beam current Investments: new triplet (b*= 25 cm) & D1, install the 200 MHz RF system, possibly more resistant collimators, upgrade of dumping system, extend the dynamic range of some beam instruments, upgrade radiation protection, upgrade of injectors (SPS, PS, Booster and Linac). What if: - if beam current cannot be reached or if new beam-beam regime inefficient or if injectors not ready, return to 25 ns spacing to recover the Phase I performance (nominal  1 to 2) Could then gain +30% luminosity with additional crab crossing. Recover Phase II performance if new triplet is b*= 10cm type AND if larger angle crab crossing would be successful. 11/16/2018 Talk to IoP/JPK

4g- P.II: Decrease of beta* To improve significantly the luminosity by a b* reduction, a modification of the crossing scheme or parameters is mandatory (Sep1 = 5) (Sep1 = 3) (Sep1 = 3) PAC07 11/16/2018 Talk to IoP/JPK

4h- P.II: Early separation D0 Full Early Separation (50 ns only if D0 not in inner detector) First encounter D0 First encounter Partial Early Separation (25 or 50 ns) We need a residual crossing angle 11/16/2018 Talk to IoP/JPK

4i- P.II: Detector geometrical constraints We cannot put the D0 in the inner detector. There are potential slots starting at 3.5 m and 6.8 m (ATLAS). A “partial” early separation should be considered Courtesy of M. Nessi, ‘Machine upgrade, ATLAS considerations’, June 2006 11/16/2018 Talk to IoP/JPK

4j- P.II: Decrease of beta* Merits: modification of LHC only in IR’s with no consequence for the global machine; no beam current increase beyond the agreed LHC & INB programs (collimation, machine and radiation protection); same beam dynamics mode and operations strategy; easy luminosity leveling, expected faster build-up of performance related to a lower complexity; compatible with 25 and 50 ns spacing (with reduced performance by 2), mild upgrade of injectors but benefits from an injector upgrade program. Challenges: installation of dipoles deep inside the detectors, higher chromatic aberrations, a few encounters at a reduced beam separation, lower integrated luminosity per run. 11/16/2018 Talk to IoP/JPK

4k- P.II: Decrease of beta* Investments: {new triplet (b*= 10 cm), D1}, D2, one matching quad?, 4 early sep. dipoles, optional crab cavities and electron lenses, improvements in injectors. What if: - if reduced separation not acceptable: full recovery possible but using new untested solutions: i) e-lens compensation or ii) increase separation and use crab or iii) turn to 50 ns operation with a loss by  2, that could be compensated by some current and bunch length increase (other strategy). if chromatic aberrations too large: fast decrease with increase of beta*, reduction of l*, Q0, or achromatic collimation insertions? If conceptual problem, turn to intensity increase with same hardware in IR’s. 11/16/2018 Talk to IoP/JPK

two draft upgrade scenarios compromises between heat load 20/03/2000 parameter symbol 25 ns, small b* 50 ns, long transverse emittance e [mm] 3.75 protons per bunch Nb [1011] 1.7 4.9 bunch spacing Dt [ns] 25 50 beam current I [A] 0.86 1.22 longitudinal profile Gauss Flat rms bunch length sz [cm] 7.55 11.8 beta* at IP1&5 b* [m] 0.08 0.25 full crossing angle qc [mrad] 381 Piwinski parameter f=qcsz/(2*sx*) 2.0 hourglass reduction 0.99 peak luminosity L [1034 cm-2s-1] 15.5 10.7 peak events per crossing 294 403 initial lumi lifetime tL [h] 2.2 4.5 effective luminosity (Tturnaround=5 h) Leff [1034 cm-2s-1] 3.6 3.5 Trun,opt [h] 4.6 6.7 e-c heat SEY=1.4(1.3) P [W/m] 1.04 (0.59) 0.36 (0.1) SR heat load 4.6-20 K PSR [W/m] 0.36 image current heat PIC [W/m] 0.33 0.78 gas-s. 100 h (10 h) tb Pgas [W/m] 0.06 (0.56) 0.09 (0.9) extent luminous region sl [cm] 3.7 5.3 comment D0 + crab wire comp. two draft upgrade scenarios (courtesy F. Zimmermann, Valencia 2006) compromises between heat load and # pile up events 11/16/2018 Talk to IoP/JPK

IP1& 5 luminosity evolution for 25-ns and 50-ns spacing 20/03/2000 IP1& 5 luminosity evolution for 25-ns and 50-ns spacing F. Zimmermann 25 ns spacing 50 ns spacing average luminosity initial luminosity peak may not be useful for physics (set up & tuning?) 11/16/2018 Talk to IoP/JPK

4n-P.II: Luminosity leveling The relatively fast luminosity decay and high multiplicity call for Luminosity Leveling. …but the issue is how to do it efficiently: dynamic beta*: uses existing hardware; probably complex due to large number of side-effects in IR’s AND arcs. dynamic bunch length: needs new RF; possible side effects in whole machine related to modification of peak current. dynamic crossing angle: using the early separation hardware, no side effects identified. Even better: use crab. EXCEPT, valid for all, a modulation of the length of the luminous region. 11/16/2018 Talk to IoP/JPK

4p-P.II: Luminosity leveling Multiplicity around 50 G. Sterbini 11/16/2018 Talk to IoP/JPK

4p-P.II: Learning period Performance rise depends on complexity. Statistical law by V. Shiltsev. Using/extending his approach yields: complexity luminosity The strategy with beam current increase requires about 3 years after Phase I (4 years without). In the ISR, a comparable beta* decrease (/7) took a few weeks at reduced current; one year for the LHC at full current? 11/16/2018 Talk to IoP/JPK

4q- P.II: LHC technological challenges Triplets: the key issue (challenge, lead time, cost) The most promising technology is Nb3Sn for larger field (50%) and larger temperature margin. A very recent success for this delicate technology: US-LARP TQS02a reached ~ 11T peak. The aperture barrier of 90 to 110 mm is being jumped (stress limit) and the required length (~9 m) should not cause an additional problem. Fall-back solution: very large and long low gradient Nb-Ti triplet for larger temperature margin & ability to collect the collision debris on masks; presently considered for b*≥ 25 cm but might be pushed further (?) Energy deposition: being included in magnet design 11/16/2018 Talk to IoP/JPK

4r- P.II: LHC technological challenges Early separation dipoles: feasibility study done (e-m and power deposition). It appears so far technically doable. Before further studies, an assessment of its impact on the detection of particles is needed for ATLAS (organized) and CMS (to be organized). Wire compensation: promising results in SPS; implemented in RHIC by US-LARP and under study. Crab crossing: under test at KEK (electrons); being considered for US-LARP R&D: accuracy challenging. Electron lenses: implemented at Tevatron; considered for installation in RHIC and support by US-LARP: very challenging for full beam-beam compensation. 11/16/2018 Talk to IoP/JPK

5-The energy upgrade The progress of super-conducting magnet technologies opens the possibility to consider doubling the LHC energy with Nb3Sn (25 TeV c.m.) or perhaps tripling it with emerging technologies based on HTS superconductors. This would be a major upgrade of the CERN accelerator complex that requires feasibility studies yet to be done. The first and critical element is the availability of collider quality high-field superconducting magnets that can stand or are shielded from the emitted synchrotron radiation. The phase II studies do not include the energy upgrade but should be used to prepare and e.g. foster external contributions if the physics motivation is expressed/confirmed. 11/16/2018 Talk to IoP/JPK

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Conclusion The upgrade of the LHC luminosity is a natural and necessary development for such a unique facility; it is very challenging. A two-phase strategy minimizes the increments in complexity. Two roads are considered to reach the second phase with ~10 in peak luminosity. They are both promising with different challenges and risks. One should aim, if possible, at combining both for a robust solution. A tight collaboration with the experimentalists and sharing of risks is needed, e.g. for an early separation scheme, for the luminosity leveling options,… The technology needed requires the R&D program proposed in the White Paper and the joint effort of the community: US-LARP, CARE and, of course, the Experimenters… 11/16/2018 Talk to IoP/JPK

Annexes Variation of the luminous region with dynamic c Expression of the F factor Nominal LHC parameters Minimum crossing angle 11/16/2018 Talk to IoP/JPK

Variation of the luminous region with dynamic c Sterbini 11/16/2018 Talk to IoP/JPK

luminosity reduction factor from crossing angle 20/03/2000 luminosity reduction factor from crossing angle Piwinski angle nominal LHC Zimmermann 11/16/2018 Talk to IoP/JPK

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Ruggiero 11/16/2018 Talk to IoP/JPK