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LHC- Longitudinal Profile Monitor.

LHC- Longitudinal Profile Monitor. Non intercepting diagnostics based on synchrotron light from a bending magnet (started as “piggy back” on transverse profile system) Longitudinal Beam profile (3564 bunches) Abort Gap Population Bunched/Debunched beam at injection

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LHC- Longitudinal Profile Monitor.

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  1. LHC- Longitudinal Profile Monitor. Non intercepting diagnostics based on synchrotron light from a bending magnet (started as “piggy back” on transverse profile system) • Longitudinal Beam profile (3564 bunches) • Abort Gap Population • Bunched/Debunched beam at injection • Empty RF Buckets (aka “ghost bunches”) • Longitudinal wings (high resolution) • Core Measurements: length, distribution, oscil.. Functional Specification: CERN/EDMS Doc. 328145 SCH: LEADE LPM+AG 15/12/03

  2. Point 4: Echenevex RF accelerating cavities SCH: LEADE LPM+AG 15/12/03

  3. MODE Ultra-high sensitivity High sensitivity Standard sensitivity Sensitivity (p/ps) 60 104 106 Sensitivity/Ult. Peak Density 3x10-7 5x10-5 5x10-3 Dynamic range (p/ps) 60 to 6x104 6x104 to 3x108 5x106 to 5x108 Sampling period 100 ns 50 ps 50 ps Integration time 100 ms 10 s 1 ms Accuracy  30 p/ps  4x103 p/ps  1% Transmission rate < 1 s 1 min 100 ms APPLICATIONS Abort gap monitor X Tails X Ghost bunches X De-bunched beam X Core parameters X Specification Requirements SCH: LEADE LPM+AG 15/12/03

  4. Longitudinal Profile Monitor: situation Sept. 2003 LPM is a LARP contribution/“collaboration”, not in-house project LPM is studied by Berkeley lab, (need similar instrument in ALS) (n.b. same group responsible for LHC Luminosity measurement) Initial plan: 2002 R&D (APD/ Laser mixing) 2003 Choice of technology + Prototype design 2004 Production electronics and instruments 2005 Install in LHC (2006 reserved for transverse instruments) SCH: LEADE LPM+AG 15/12/03

  5. Light production at injection energy too low: SC undulator added Undulator and D3 magnet at LHC Point 4 SCH: LEADE LPM+AG 15/12/03

  6. Abort gap, 3s (Protons) For Ions: spacing 100ns, total 890 bunches, 1:40 RF cycles SCH: LEADE LPM+AG 15/12/03

  7. LHC Beam profile 3564 bunches+ 32,076 empty buckets, RMS Bunch length 0.28ns: sample time 50 ps 89s/50ps = 1,780,000 data bins…. Integrate over 40ms… …50,000,000 data points/second SCH: LEADE LPM+AG 15/12/03

  8. Fast Photon Detectors: Commercial Avalanche Photodiode modules PC card for Time-correlated Single Photon Counting: TimeHarp 200 3MHz count rate, <40ps resolution …but only 4096 time-bins… SCH: LEADE LPM+AG 15/12/03

  9. Fast Photon Detectors: Avalanche Photodiodes C-SPAD: Cooled Single-Photon Avalanche Diode With active quenching circuit: laser range-finding of satellite in flight, T.Otsubo, CRL, Tokyo 100ps, 16 bins SCH: LEADE LPM+AG 15/12/03

  10. Photon Counting: MCP PMT Hammamatsu R3809U Photon counting has its problems too, For high dynamic range, there must be no systematic false counts SCH: LEADE LPM+AG 15/12/03

  11. MCP-PMT: Dynamic range Self-generated false counts after event: need to gate detector off for 1us after each event: count rate drops to 10’s of kHz. 102 900 ns SCH: LEADE LPM+AG 15/12/03

  12. Proposed Laser Mixing System: filters Synch light, 633nm 8 bit Detector 350nm Mixing crystal 40 MHz Laser Ti:Sapphire 800nm Very narrow light spectrum is used, ~3nm (1% of available) Laser pulse timing phase-locked to Machine RF, with offset Laser used to sample with 10ps pulses at 40MHz Max. Data rate at laser frequency, could be 80MHz? SCH: LEADE LPM+AG 15/12/03

  13. Laser Mixing: LPM High Sensitivity Mode 25ns laser sample interval, 500 sample points/scan 400MHz Bucket 2.5ns Increment delay by 50 ps / machine rev If PMT is 1% accurate, still need to integrate over 1000 samples to get spec accuracy: 55s + settling time ( Spec. 10-4 in 10s ) SCH: LEADE LPM+AG 15/12/03

  14. Compress Scale... SET3 SCH: LEADE LPM+AG 15/12/03

  15. LM Concerns: • Low wavelength conversion efficiency • - single photon counting • - needs longer integration time • Requires exclusive operating modes • -std/high resolution modes • High res. integration time too long: • - 10 sec: increase to 1min SCH: LEADE LPM+AG 15/12/03

  16. LM system is unlikely to meet specs for integration time, and is not suitable for abort gap protection (too complex) • If LM system is used, 3 separate instruments will be needed. • Avalanche Photon counting has its problems too: as the count rate reduces, the number of detectors becomes large. • No work is being done on the APD method. SCH: LEADE LPM+AG 15/12/03

  17. Photon Production and the Abort Gap Monitor Calculated photon production (450-900nm) : 0.0014 photons/proton at the extraction mirror (…& ions?) At injection energy, abort level is now x700: 60p/ps x 700 = 5.88^6 photons/100ns/turn = 6 10^9 photons / 100ms integration The 7TeV abort level remains at 60p/ps: 840 000 000 photons/integrated over 100ms =0.3nJ signal (n.b.this is corrected from the value given in talk, the D3 bending magnet is more efficient at 7TeV) From this must be taken transmission losses, detector efficiency(10%), bandwidth(1%), background noise… SCH: LEADE LPM+AG 15/12/03

  18. Abort Gap monitor is important machine operating instrument; needs simple robust solution. A separate instrument is considered. 2003: LARP priority for LPM reduced, no funding given (no work done) LBNL team concentrates on Luminosity. 2004: LDM priority raised: ¾ FTE available for LPM+AG (no material) Priorities now set: 1/ Abort Gap monitor 2/ Luminosity 3/ LPM (R&D tool?) To increase the reliability/availability and performance of the AG and LPM, separate, warm undulators are considered, cost and initial design for March ‘04 SCH: LEADE LPM+AG 15/12/03

  19. AG 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 SCH: LEADE LPM+AG 15/12/03 (3.3 µs)

  20. Hamamatsu R5916U-50 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) SCH: LEADE LPM+AG 15/12/03

  21. (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 SCH: LEADE LPM+AG 15/12/03

  22. Empty buckets (gap) Regular bunches Parasitic bunch Camshaft SCH: LEADE LPM+AG 15/12/03

  23. Parasitic bunch Gate signal on Gate signal delayed 28 ns Gate signal on Parasitic bunches SCH: LEADE LPM+AG 15/12/03

  24. The Situation 12/03: Tests to establish Sensitivity and Dynamic range of MCP-PMT …answers for Chamonix? Studies to establish reliable AG design: accessibility, few interventions AG data needed for warm undulator design. More effort should be available in 2005/6 for LPM system: technology choice still open but time very short. SCH: LEADE LPM+AG 15/12/03

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