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Sixtrack simulations for the study of C rab cavity failures in HL-LHC

Sixtrack simulations for the study of C rab cavity failures in HL-LHC. LBS#48 meeting 16 September 2013. F. Bouly. LAYOUT.  - Introduction  - Initial conditions – Starting point  - First run and crab cavity - F ailure scenario : 1 example  - Conclusion. F.B.

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Sixtrack simulations for the study of C rab cavity failures in HL-LHC

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  1. Sixtrack simulations for the study of Crabcavityfailures in HL-LHC LBS#48 meeting 16 September 2013 F. Bouly

  2. LAYOUT •  - Introduction •  - Initial conditions – Starting point •  - First run and crabcavity • - Failure scenario : 1 example •  - Conclusion F.B. LBS#48 16/09/2013

  3.  - Introduction Context • HL-LHC WP8 : Collider experiment interface • Evaluate the inherent constraints on beam pipe design for various options for the high luminosity insertions at HL-LHC. It will take into account physics requirements at the interaction point and in the forward region along with LHC machine constraints. • Key point • What will be the consequences of the aperture changes for HL-LHC in terms of background, radiation and protection of the central detector regions. • TAS and triplets Opened whereas the size of the detector chambers will be reduced  Background issues : Beam gas scattering – showers from TCT – IR cross-talk …  Machine protection issues and possible failure scenarios : - Crab cavity failure scenarios ◄ - Dump failures : asynchronous beam dump - UFOs - Beam-beam kick missing - Fast vacuum valves - (D1 failure scenarios) - (…) F.B. LBS#48 16/09/2013

  4.  - Introduction Goals & failure scenarios • Evaluate the risks and possible issues close to the interaction regions (IP1 &IP5) when a crab cavity fails (i.e amount of particles lost) • Maximal transverse displacement (assuming optimal voltage to compensate the crossing angle) ~1.35 (ATS optics, β*=0.15 m,ncc = 3) •  Simulations achieved with SixTrack (collimation version) : a SixTrack update was done to enable the control (ramp and change voltage and phase). Bruce Yee Rendón • Optics configuration for the study • We only look at BEAM 1 in the simulations F.B. LBS#48 16/09/2013

  5. LAYOUT • - Introduction • - Initial conditions – starting point •  - First run and crabcavity • - Failure scenario : 1 example •  - Conclusion F.B. LBS#48 16/09/2013

  6. - Initial beam distribution Starting point • All the simulations start from IP1. The distributions are given according to the twiss parameters at IP1. The distributions are assumed to be (simple) Gaussian. • 2 types of distribution were used for the simulations 1st type : Halo distribution 2nd type : Core distribution ~0.012% of a full bunch ~97.790 % of a full bunch  x-x’ plan : 3 to 5 σ  y-y’ plan : 3 to 5 σ  Z-ΔE/E plan : 0 to 4 σ+ ‘pseudo-matching’ condition  x-x’ plan : 0 to 3 σ  y-y’ plan : 0 to 3 σ  Z-ΔE/E plan : 0 to 4 σ + ‘pseudo-matching’ condition

  7. - Initial beam distribution Longitudinal (pseudo-)matching For the longitudinal plan we first assume a 2D Gaussian distribution, with particle between 0 σ to 4σ. Still we added a condition for the matching : in our case all the particles are kept inside the area delimited by the which is at 4σz (when ΔE/E = 0 ) (Pseudo-)Matched Not Matched  Particles trajectories in the longitudinal phase-space : Can be derived with the Hamiltonian : H(ΔE/E,Δφ) = H(0,Δφ0) and V = total RF accelerating voltage λRF = RF wavelength ϕs = synchronous phase h = harmonic number η = γ-2 – αc αc = momentum compaction factor F.B. LBS#48 16/09/2013

  8. - Initial settings Simulation configuration with SixTrack Collimators settings: • All the simulations start from IP1 • Run of 6.4 *106 particles for 500 turns • For these first simulations the crab cavities are kept switched-off • Simulations carried out with both distributions (“halo” & “core” ) 12 10 A Marsili et al. Collimation cleaning with ATS optics for HL-LHC Collimation Review, 2013/30/05 Aperture modifications at IP1 and IP5 : In the aperture file allapert_ats_20121023b1: _ beam pipes diameterat IP reduced _ TAN wasmissing on the left of IP1  added F.B. LBS#48 16/09/2013

  9. LAYOUT • - Introduction • - Initial conditions – Startingpoint • - First run and crab cavity • - Failure scenario : 1 example •  - Conclusion F.B. LBS#48 16/09/2013

  10. - First run and crab Halo simulation (1st Run) • Core simulation : no losses observed • Halo simulation : (9714 / 6.4*106 ) particles lost halo Final distribution after 500 turns at IP1 F.B. LBS#48 16/09/2013

  11. - First run and crab Halo simulation (1st Run) _ Initial number of particles : 6400000 _ Number of particles absorbed by collimators : 9714 _ Number of particles hitting apertures : 3 _ Number of particles lost : 9717 -> MEANING : 0.152% of the initial distribution One particular collimator is absorbing the particles : TCP.B6L7.B1 F.B. LBS#48 16/09/2013

  12. - First run and crab Halo simulation (1st Run) Particle absorbed at TCP.B6L7.B1 Initial position (at IP1) of the particles lost during the simulation F.B. LBS#48 16/09/2013

  13. - First run and crab Halo simulation (5th Run) 1stRun After 5 simulations : i.e. 2500turns 5th Run 5thRun of 500 turns _ Initial number of particles : 6400000 _ Number of particles absorbed by collimators : 402 _ Number of particles hitting apertures : 0 _ Number of particles lost : 402 -> MEANING : 0.006% of the initial distribution F.B. LBS#48 16/09/2013

  14. - First run and crab Crab cavities switched on • During the 5th simulation the average number of absorbed particles was below: 1/turn • It was chosen to keep this distribution as a starting point • simulations were carried out to evaluate the crabbing effect : • - 1st turn : crab cavities are switched off • - 2nd turn to 11th turn : crab cavities voltage are ramped up to their nominal voltage (for 10 turns) at IP1 and IP5. • - Last 39 turns : the crab cavities are kept switched on F.B. LBS#48 16/09/2013

  15. - First run and crab Crab cavities switched on _ Initial number of particles : 6400000 _ Number of particles absorbed by collimators : 87 _ Number of particles hitting apertures :0 _ Number of particles lost : 87 -> MEANING : 0.0013594% of the initial distribution Ramp The collimation cleaning is still dominated by: TCP.B6L7.B1 Slight increase of the losses : acceptable (?) Number of turns a bit low (?) F.B. LBS#48 16/09/2013

  16. - First run and crab Crab cavities (distributions) Final distribution after 50 turns at IP1 HALO  Both distributions were used as starting point for the study of the failure scenario  For the core simulation : No losses observed over 6.4 millions particles CORE F.B. LBS#48 16/09/2013

  17. LAYOUT • - Introduction • - Initial conditions – Startingpoint • - First run and crab cavity • - Failure scenario : 1 example •  - Conclusion F.B. LBS#48 16/09/2013

  18. - Failure scenario Failure scenario description • Phase Failure of the first crab cavity at IP5 on the left side (Beam 1) • Failure in 1 turn : the phase of the cavity drops from 0˚ to 90˚ Realistic case? • 11 turns in the simulation : 1st turn with all the CCs in normal operation Failed • NB : no losses observed for the core distribution - only the results for the halo distribution are presented F.B. LBS#48 16/09/2013

  19. - Failure scenario Losses after the failure 10 turns after the failures failure _ Initial number of particles : 6400000 _ Number of particles absorbed by collimators : 53006 _ Number of particles hitting apertures :2 _ Number of particles lost : 53026 -> MEANING : 0.82853% of the initial distribution F.B. LBS#48 16/09/2013

  20. - Failure scenario Very row estimation of the losses • The “halos distribution” represents ~ 0.0123 % of a total bunch •  Energy in the HL-LHC beam : • 2808* 2.2*1011 * 7*1012 * 1.602*10-19≈ 693 MJ • Part of the beam that we consider in the simulation • 0.0123 % * 693 *106 = 85.2 kJ Tentative of Energy deposition estimation for this specific failure scenario F.B. LBS#48 16/09/2013

  21. Some particles trajectories Normal Beam 1- IP5 – horizontal plan Immediately after the failure Failure “Left part” of IP1 Increase ~27% F.B. LBS#48 16/09/2013

  22. - Failure scenario Some particles trajectories Normal Beam 1- IP5 – horizontal plan 3 turns after the failure Failure ~5% F.B. LBS#48 16/09/2013

  23. - Failure scenario Some particles trajectories Normal Beam 1- IP5 – horizontal plan 5 turns after the failure Failure ~14% F.B. LBS#48 16/09/2013

  24. - Failure scenario 10 turns after the failure Final distribution at IP1 - 10 turns after the failure The effect of the failure at IR5 is seen at IP1 F.B. LBS#48 16/09/2013

  25. LAYOUT • - Introduction • - Initial conditions – Startingpoint • - First run and crab cavity • - Failure scenario : 1 example •  - Conclusion F.B. LBS#48 16/09/2013

  26. Conclusion • From the first picture of “halo ” simulations : risks for the experiments seem to be very low (even with a beam dump in 10 turns) • Extensive number of simulations are carried out by B.Y. Rendón (BE/ABP). Losses from the “halo distribution” for different types of failure at IP5 • Very strong failures were simulated here : phase shift of 90° in 1 turn (~100 µs) But what happen in reality? The phase and voltage shift may take more than 1 turn • A mitigation strategy can be implemented in case of a failure : switch off the crab cavities if one failure is detected. Courtesy of B.Y.Rendón • Still : _ We need more statistics (different/complementary distributions) to evaluate the global losses (apertures and collimators) _ The simulations assumed no errors : misalignement, fields _ We need a better description of the cavity discharge with a beam. F.B. LBS#48 16/09/2013

  27. Thank you F.B. LBS#48 16/09/2013

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