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

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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
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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
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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

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LHC Specifications(C. Fischer, LHC-B-ES-0005)

• Maximum allowable charge density 60 p/ps (4 104
  p/ps) average over 100 ns _at_ 7 Tev (450 GeV).
• Accuracy 50 (5) _at_ 7 TeV (450 GeV).
• Integration time 100 ms (1000 turns)

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Hamamatsu R5916U-50 Gated Photomultiplier Tube
Gate min. raise time 1 ns lt2.5 ns RF bucket
spacing Gate voltage 10 V Low voltage switching
required Gain at 3.4 kV 106 High gain lt 10
dark counts/sec Low noise Max duty cycle
1 100 ns -gt 100 kHz max sampling rate -gt 3 ms
to measure entire abort gap (w/o integration)
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Light Source in the LHC
Superconducting undulator (5T) _at_ IR4 Used for
both longitudinal and transverse
diagnostics. Possible permanent magnets undulator
dedicated to longitudinal diagnostics only. (R.
Jung M. Facchini)
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Tests at the ALS
(LHC parameters)
328 RF buckets 2761 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)
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MCP-PMT experimental setup (old)
SROC
Hamamatsu Streak Trigger Unit
Stanford DG535 Delay
1.5 MHz
100 kHz
HP8114A Pulser
10 V Gate
MCP PMT
Visible Light
Tektronix TDS3052
Bending dipole
Hamamatsu C3360 HV
-3 kV
(neutral density filter)
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Gate signal on
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(No Transcript)
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Gate signal on
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MCP-PMT experimental setup (present)
SROC
Hamamatsu Streak Trigger Unit
Stanford DG535 Delay
1.5 MHz
100 kHz
HP8114A Pulser
10 V Gate
MCP PMT
Visible Light
Tektronix TDS754D
Hamamatsu C3360 HV
-3 kV
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Empty buckets (gap)
Regular bunches
Parasitic bunch
Camshaft
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Parasitic bunch
Gate signal on
Gate signal delayed 28 ns
Gate signal on
Parasitic bunches
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Gate signal on
Parasitic bunch
Last bunch in train
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MCP-PMT looks promising

• Can be easily switched at the required speed
• S/N ratio seems adequate
• Fast photocatode recovery (100s 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)