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Fast Failures of LHC Crab Cavities

Fast Failures of LHC Crab Cavities. Tobias Baer 4 th LHC Crab Cavity Workshop 16 th December 2010. Thanks to: R. Calaga, R. de Maria, J. T ü ckmantel , J . Wenninger , K . Fuchsberger. Content. Content. KEK Crab Cavity Quench. Full decay of crab cavity in ≈100µs .

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Fast Failures of LHC Crab Cavities

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  1. Fast Failures of LHC Crab Cavities • Tobias Baer • 4th LHC Crab Cavity Workshop • 16th December 2010 • Thanks to:R. Calaga, R. de Maria, J. Tückmantel, J. Wenninger, K. Fuchsberger

  2. Content

  3. Content

  4. KEK Crab Cavity Quench • Full decay of crab cavity in ≈100µs. • Oscillations of Crab Cavity phase (up to 50° in 50µs). K. Nakanishi et al., Beam Behaviour due to Crab Cavity Breakdown, Proceedings of IPAC’10, Kyoto 100µs

  5. Analytical Approach • Horizontal kick by crab cavity: optimal voltage (local scheme, IP5): maximal displacement: q = particle charge E = particle Energy (7 TeV) V = voltage of crab cavity Φ = phase of crab cavity Ѳ = full crossing angle (580/285 µrad) φ = phase advance CC ->IP (≈ π/2) ω = angular frequency of CC (2 π∙400 MHz) z = longitudinal position of particle c = speed of light = 3.98 (1.02 for nominal optics)

  6. Analytical Approach • Beamloss approximation with simple Monte Carlo (upgrade optics): • Failure of single cavity (V -> 0): • Particle is lost if |x + xcc(z) ∙ k(ΔφCC->TCP)| > 5.7 ∙ σx • -> expected loss: (0.88 ± 0.06)% • Phase error of single cavity (Φ -> π/2): • Particle is lost if |x + xcc(z, Φ = π/2)∙k - xcc(z, Φ = 0)∙k| > 5.7σx • -> expected loss: (24.8 ± 0.3)% Scaling factor (≈ 1.12) 1. Gaussian Distribution 2. Gaussian Distribution CC with failure CC without failure

  7. Content

  8. Failure of CRAB.R5.B1 • Voltage of Crab.R5.B1 = 0. • Total beam loss: 1.3% in 2 turns (2% in first 10 turns), mainly at TCP.C6L7.B1. IP1 IP5 Losses CC failure • Upgrade optics SLHCV3.0 4444_thin, IP1/5: β* = 0.15m, Θ=580μrad, CC Local scheme IP5, 400/10,000 particles

  9. Failure of CRAB.R5.B1 • Bunchshape at TCP.C6L7.B1 directly after failure.

  10. Failure of CRAB.R5.B1 • Bunchshape at TCP.C6L7.B1, 1 turn after failure.

  11. Failure of CRAB.R5.B1 • Bunchshape at TCP.C6L7.B1, 2 turns after failure.

  12. Failure of CRAB.R5.B1 • Bunchshape at TCP.C6L7.B1, 3 turns after failure.

  13. Failure of CRAB.R5.B1 • Bunchshape at TCP.C6L7.B1, 4 turns after failure.

  14. Content

  15. Phase Error of CRAB.L5.B1 • Upgrade Optics, Phase of Crab.L5.B1 = -π/2. • Total beam loss: 15% - 35%in 2 turns, mainly at TCP.C6L7.B1 IP1 IP5 Losses CC failure • Upgrade optics SLHCV3.0 4444_thin, IP1/5: β* = 0.15m, Θ=580μrad, CC Local scheme IP5, 400/10,000 particles

  16. Beam Losses • Most beam losses occur one turn after the failure. Failure

  17. Phase Error of CRAB.L5.B1 • Bunchshape at TCP.C6L7.B1 directly after failure.

  18. Phase Error of CRAB.L5.B1 • Bunchshape at TCP.C6L7.B1, 1 turn after failure.

  19. Content

  20. Mitigation strategy ω = angular frequency of crab cavity β* = beta function at IP NCC = number of independent crab cavities on each side of IP Maximal displacement by single CC (local scheme IP5) Beam losses for 90⁰ phase shift of single CC (local scheme IP5)

  21. Content

  22. Conclusion • Upgrade optics: • Fast voltage decay: Losses of 1-2% in first turns. • Phase error: Losses of up to 15-35% in first turns. (assuming instantaneous, constant phase shift by 90°) • Nominal LHC optics -> see R. Calaga‘s slides for halo losses. • Losses mainly at primary collimators one turn after the failure. • Mitigation options: • Larger β* (>30cm). • Higher frequency. • Crab kick by several INDEPENDENT crab cavities. • Hollow electron lens against beam halo.

  23. Thank you • for your Attention • Tobias Baer • CERN BE/OP • Tobias.Baer@cern.ch • Office: +41 22 76 75379

  24. Backup slides

  25. Analysis Conditions • Optics: • SLHCV3.0 4444_thin, β* = 0.15m (IP1/5), β* = 10.0m (IP2/8) • Nominal optics, β* = 0.55m (IP1/5), β* = 10.0m (IP2/8) • Crab cavity local scheme IP5, CCs at Q4 • Abrupt failure at defined turn • Tracking of 400 – 10,000 particles for ≈20 turns.

  26. Bunchshape at IP5 • Bunchshape at IP5 in nominal operation (Horizontal)

  27. Bunchshape at IP5 • Bunchshape at IP5 in nominal operation (Vertical)

  28. Phase Error of CRAB.L5.B1 • Bunchshape at TCP.C6L7.B1, 2 turns after failure.

  29. Phase Error of CRAB.L5.B1 • Bunchshape at TCP.C6L7.B1, 3 turns after failure.

  30. Phase Error of CRAB.L5.B1 • Bunchshape at TCP.C6L7.B1, 4 turns after failure.

  31. Next steps • Improve simulation • Time dependent failures (based on KEK measurements) • Realistic model of tail population • Other failure scenarios • Failure crab cavities IP1 • Beam 2 • Global Crab Cavity scheme

  32. Collimation 3.5TeV, β*=3.5m TCSG.4R6.B1 TCSG.6R7.B1 TCSG.B4L7.B1 TCP.C6L7.B1 12.1σ TCSG.D5R7.B1 TCSG.D4L7.B1 TCSG.A4R7.B1 TCP.D6L7.B1

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