Detection and Analysis of Uncontrolled Beam Loss in the High Luminosity LHC - halvtidsseminarium

1. Detection and Analysis of Uncontrolled Beam Loss in the High Luminosity LHC- halvtidsseminarium Björn Lindström CERN and Uppsala University With input from 4th April 2019

2. Outline Project definition and motivation Failures CLIQ UFOs Crab Cavities Experiments

3. Dump LHC pp and ions 7 TeV/c – up to now 6.5 TeV/c 26.7 km Circumference CMS LHCb ATLAS ALICE LHC overview Switzerland Lake Geneva LHC Accelerator (100 m down) Collimation CERN-Prevessin SPS Accelerator CERN Main Site France

4. Beam induced damage • 1.52 MJ deposited energy Courtesy of F.Burkart

5. SPS vacuum leak • 2 MJ lost in 15 ms • LHC is cryogenic:SPS downtime ~3 days – LHC downtime ~3 months K. Li – 168th MPP meeting

6. Scope of project • Study of uncontrolled beam loss scenarios • How failure occurs • Effect on the beam • Subsequent beam losses (intensity, location) • Time scales • Detection of failures • How to limit time between detection of failure and beam dump Goal: Understand criticality of failures to determine protection strategy / how to design safer system

7. High Luminosity LHC (HL-LHC) changes • To attain higher luminosity, higher bunch intensity and smaller beam size in collision point • Many changes in layout (e.g. Triplet quadrupoles, crab cavities ... )

8. Methodology Example • Observed quench in Final Focusing magnet • Measured orbit offset (250 µm) • Calculate magnetic field change (0.7 mT) • Input from Magnet Simulation (colleagues) • Beam Tracking Simulations for similar scenarios (e.g. HiLumi) • Calculate resulting beam losses • Time to Critical losses (damage) Need min 3 turns to dump beams

9. Outline Project definition and motivation Failures CLIQ UFOs Crab Cavities Experiments

10. Overviewof Fast Failures Magnet Protection Active Equipment Other Failures Triplet Quench ADT UFO D1, D2 power loss Crab Cavities UFO type 2 Quench Heaters Beam-Beam Wire Beam-beam Kick CLIQ

11. Overviewof Fast Failures • aa

12. Overviewof Fast Failures • aa

13. Outline Project definition and motivation Failures CLIQ UFOs Crab Cavities Experiments

14. Magnet protection • High current in magnets (up to ~16 kA) • Quench – loss of superconductivity • Burn cables • Need active system to protect magnet • Active system changes current – magnetic field in beam region Until now, magnet protection did not consider effects on beam

15. CLIQ – Coupling Loss InducedQuench • New system for Final focusing magnets around Experiments • 2.5 kA deposited in magnet coil Imperative to study effect on beam CLIQ discharge current in magnet CLIQ current

16. CLIQ – inducedmagneticfields Three magnets – two different connection schemes Dipolar field → beam kick Octupolar field → beam size Courtesy of A. Navarro

17. Dipolar connection – beam orbit change Time to dump beams: min 3 turns Magnet protection design must takeeffects on beamintoaccount! Physicalaperture 1 MJ deposited in Collimators 0.14 % of full beam

18. Solution? • Only use Octupolarconnectionscheme • Possibilityunder discussion • EnsuringCLIQ canneverfirespuriously • Cannotbe 100 % failsafe, expensive, and increases the risk for magnet protection 18

19. Octupolar connection – beam orbit change 17 turns until damage Can safely dump within 10 turns Little margin – still critical Physicalaperture 1 MJ deposited in Collimators 0.14 % of full beam

20. Outline Project definition and motivation Failures CLIQ UFOs Crab Cavities Experiments

21. UFO observations in the LHC • Sudden beam loss spikes started appearing in 2010 • Cause beam dumps and magnet quenches • up to 12 hours downtime! • Probability of quench will increase (7 TeV beam energy) Long Shutdown 2 courtesyof A. Lechner Bjorn Lindstrom

22. Macroparticle interaction with beam beam loss monitor (BLM) • Many unknowns: origin? release mechanism? mitigation? future behavior (increased beam intensity/energy)? UFO + beam losses e- + beam e- Studying the UFO dynamics could provideclues Bjorn Lindstrom

23. Beam Loss Monitors (BLM) particle showers UFO scattered protons dBLM ICBLM Collimator beam Collimator Bjorn Lindstrom

24. Beam Loss Monitors (BLM) • ICBLM: • Main beam loss monitoring system of LHC • 40 ms time resolution (half LHC turn) • dBLM: • ns resolution (bunch-by-bunch, 25 ns) particle showers UFO scattered protons dBLM ICBLM Collimator beam Collimator Bjorn Lindstrom

25. Beam Loss Monitors (BLM) 1 cm2 • ICBLM: • Main beam loss monitoring system of LHC • 40 ms time resolution (half LHC turn) • dBLM: • ns resolution, bunch-by-bunch particle showers UFO scattered protons dBLM ICBLM Collimator beam Collimator Bjorn Lindstrom

26. UFO simulated using a Wire Wire-scanner: Thin carbon wire, ~30 µm, similar dimension to UFO Beam losses detected by fast diamond BLM wire beam Bjorn Lindstrom

27. UFO simulated using a Wire Wire-scanner: Thin carbon wire, ~30 µm, similar dimension to UFO Beam losses detected by fast diamond BLM Consecutive LHC turns Detected 7 turns earlier bunches wire Can study movement of matter intercepting the beam Bjorn Lindstrom

28. Real UFO observations • Implemented reliable UFO detection system in diamond BLM • 2 blown-up bunches, all physics fills end of pp, Run II • Recorded 12 events in two weeks bunch size proportional to

29. Example of measurement • Dust moves horizontally • Negatively charged(?) • Important clue for further understanding, e.g. release mechanism

30. Outline Project definition and motivation Failures CLIQ UFOs Crab Cavities Experiments

31. Crab Cavities Luminosity: Geometric Factor

32. Crab Cavities • Cavity with sinusoidal transverse kick - bunch is tilted - better overlap at crossing point E

33. Crab Cavities in the SPS Two vertical Crab Cavities installed • Horizontal CCs to be tested in 2021 Courtesy of T. Levens

34. Failure Scenarios • Voltage drop (not relevant for the SPS) • Phase jump • Detuning (continuous phase shift) • Quenches (not observed, tested without beam) 270 GeV, 2 MV, coherent excitation: Physical aperture

35. First Machine Protection experiments with crabbed hadron beams • Detuningduringbeamenergy ramp (26 GeV -> 270 GeV) • Was predicted and agrees well with simulations • -> gives confidence in HiLumipredictions start of ramp intensity BLM

36. Conclusions and Outlook • Criticality of failures in Magnet System, Active Elements, and other scenarios has been determined • CLIQ system would create the fastest failure in the LHC– potential mitigation methods have been proposed • Simulations validated by dedicated experiments / beam observations • Proposed & validated novel method for studying UFOs– strong indication UFO movement also horizontal • First Machine Protection experiments with Crab Cavities in a hadron beam– observations confirm expectations, fast interlocks are required • UFO dynamics studies ongoing • Wrap-up failure studies – write papers

37. Many thanks toL. Bortot, A. Lechner, A. Navarro, M. Valette, M. Väänänen, V. Raginel, E. Ravaioli, R. Schmidt, C. Wiesner, D. Wollmann

38. Beam beam kick • The two beams interact • Transverse kick (orbit change, main issue) • Beamsize growth • Beams cannot be dumped simultaneously: . Remaining beam is kicked due to missing beam-beam

39. Combined failures – beam beam effect • Previously predicted and observed for LHC • In HiLumi: Missing beam-beam in itself is critical • Added on top of any other failure Imperative to dump both beams at same time (Rewrite) delayed dump

40. Q2 – Beta Beating • Beta beating of up to 100 % at the collimators • Beam size increases by factor 1.4 -> losses

41. Q2 – OrbitExcursion • In Q2, inducedfield is mainlyOctupolar • Beamsaredisplacedup to +- 20 mm • -> orbitdistortiondespite no dipolarfield Beams 1 & 2

42. Triplet Quench • Quench in an ATLAS Q1 last summer • Not detected by magnet protection system • 1.7 A current change (0.02 % of nominal current) • 250 µm orbit distortion, beam losses, dump

43. Superconducting strands / tapes Image from C. Senatore, CAS Zuerich 2018 Daniel Wollmann Nb-Ti strand (LHC) Nb3Sn strand (HL-LHC) HTS tapes (future acc. magnets..?)