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Development of An Abort Gap Monitor for High-Energy Proton Rings

Development of An Abort Gap Monitor for High-Energy Proton Rings. J.-F. Beche, J. Byrd, S. De Santis , P. Denes, M. Placidi,W. Turner, M. Zolotorev. Lawrence Berkeley National Laboratory. LHC Accelerator Research Program.

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Development of An Abort Gap Monitor for High-Energy Proton Rings

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  1. Development of An Abort Gap Monitor for High-Energy Proton Rings J.-F. Beche, J. Byrd, S. De Santis, P. Denes, M. Placidi,W. Turner, M. Zolotorev Lawrence Berkeley National Laboratory

  2. LHC Accelerator Research Program Instrument under development at LBNL as part of the US contribution to LHC. Historically, a Longitudinal Density Monitor project spin-off aimed to provide a reliable and simple device suitable for being included in the LHC interlock chain. work in progress

  3. What is the Abort Gap and Reasons for Monitoring It • 3.3 ms gap in the machine fill, corresponding to the raise time of the abort kicker. • Gap can populate by: • Injection errors (450 GeV, fast mechanism) • Diffusion (mainly 7 TeV, slow mechanism) • Debunching (mainly 7 TeV, slow mechanism) • SC magnets quenching

  4. LHC Specifications(C. Fischer, LHC-B-ES-0005) • Maximum allowable charge density: 60 p/ps (4 104 p/ps) average over 100 ns @ 7 Tev (450 GeV). • Accuracy: 50% (5%) @ 7 TeV (450 GeV). • Integration time: 100 ms (~1000 turns)

  5. Hamamatsu R5916U-50 Gated Photomultiplier Tube Gate min. raise time: 1 ns <2.5 ns RF bucket spacing Gate voltage: 10 V Low voltage switching required Gain at –3.4 kV: 106 High gain < 10 dark counts/sec Low noise Max duty cycle: 1% 100 ns -> 100 kHz max sampling rate -> 3 ms to measure entire abort gap (w/o integration)

  6. Light Source in the LHC Superconducting undulator (5T) @ IR4 Used for both longitudinal and transverse diagnostics. Possible permanent magnets undulator dedicated to longitudinal diagnostics only. (R. Jung & M. Facchini)

  7. Tests at the ALS (LHC parameters) 328 RF buckets 276+1 filled (280-620 ps) Bunch width ~50 ps (2808/35640) (2.5 ns) Bunch spacing 2 ns “Camshaft” pulse ~120 ns gap (no camshaft) (3.3 µs)

  8. MCP-PMT experimental setup (old) SROC Hamamatsu Streak Trigger Unit Stanford DG535 Delay 1.5 MHz ~100 kHz HP8114A Pulser 10 V Gate Visible Light MCP PMT Tektronix TDS3052 Bending dipole Hamamatsu C3360 HV -3 kV (neutral density filter)

  9. Gate signal on

  10. Gate signal on

  11. (Pockels cell) MCP-PMT experimental setup (present) SROC Hamamatsu Streak Trigger Unit Stanford DG535 Delay 1.5 MHz ~100 kHz HP8114A Pulser 10 V Gate Visible Light MCP PMT Tektronix TDS754D Hamamatsu C3360 HV -3 kV

  12. Empty buckets (gap) Regular bunches Parasitic bunch Camshaft

  13. Parasitic bunch Gate signal on Gate signal delayed 28 ns Gate signal on Parasitic bunches

  14. Gate signal on Parasitic bunch Last bunch in train

  15. Can be easily switched at the required speed S/N ratio seems adequate Fast photocatode recovery (~100’s ps, Pockels cell not required) Can we simulate the expected LHC photon flux at the ALS (10-5 ph/p) ? MCP-PMT available in different bands. Which is the most suitable for LHC ? 100 ns integrating circuit ? Future test on the Tevatron (particularly for unbunched beam) MCP-PMT looks promising

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