Cold L-Band Cavity BPM: Design Status July 2006

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Cold L-Band Cavity BPMDesign Status July 2006
Gennady Romanov Linda Valerio Manfred
Wendt Fermilab July 21, 2006
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Backup Cold BPM Requirements and Issues

• BPM location in the cryostat, at the SC-quad
• Every 3rd cryostat is equipped with a BPM/quad
  650x cold BPMs total.
• Real estate 170 mm length, 78 mm beam pipe
  diameter (???).
• Cryogenic environment ( 4 K)
• Cleanroom class 100 certification (SC-cavities
  nearby!)
• UHV certification
• lt 1 µm single bunch resolution, i.e. measurement
  (integration) time lt 300 ns.
• lt 200 µm error between electrical BPM center and
  magnetic center of the quad.
• Related issues
• RF signal feedthroughs.
• Cabling in the cryostat
• Read-out System

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Possible Cold BPM Solutions

• Dedicated, high resolution BPM (baseline design)
• Cavity BPM, based on the characterization of
  beam excited dipole eigenmodes, also requires the
  measurement of the monopole modes for
  normalization and evt. sign of the beam
  displacement.
• Combination of dedicated, lower resolution BPMs
  and HOM coupler signal BPMs (alternative
  design)
• Simple, button style BPMs ( 50 µm resolution)
  for machine tune-up and single bunch orbit
  measurements.
• HOM coupler BPM signal processor as high
  resolution BPM

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Cold Cavity BPM Development

• Problems with simple
• Pill-Box Cavity BPMs
• TM010 monopole common mode (CM)
• Cross-talk (xy-axes, polarization)
• Transient response (single-bunch measurements)
• Wake-potential (heat-load, BBU)
• Cryogenic and cleanroom requirements

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• Waveguide-loaded pillbox with slot coupling.
• Dimensioning for f010 and f110 symmetric to fRF,
  fRF 1.3 GHz, f010 1.1 GHz, f110 1.5 GHz.
• Dipole- and monopole ports, no reference cavity
  for intensity signal normalization and signal
  phase (sign).
• Qload 600 ( 10 cross-talk at 300 ns
  bunch-to-bunch spacing).
• Minimization of the X-Y cross-talk (isolation).
• Simple (cleanable) mechanics.
• Iteration of EM-simulations for optimizing all
  dimensions.
• Vacuum/cryo tests of the ceramic slot window.
• Copper model for bench measurements.

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Discrete port (current) x10 mm y30 mm
Cavity-BPMSLAC style
Excitation signal
Ports
General view
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Eigen modes
Dipole

• Mode Frequency
• 1.017 Parasitic E11-like
• 1.023 Parasitic E21-like
• 1.121 Monopole E01
• 1.198 - Waveguide
• 1.465 - Dipole E11
• 1.627

Parasitic mode Ez distribution
Parasitic mode. Coupling through horizontal slots
is clearly seen
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Transient solution. Probe magnitude
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Cavity-BPM Pillbox with WG slot coupling
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Optimization of slot dimensions
EM - Eigen mode solver. FD frequency domain
solver. Slot_L55 mm and Slot_W 5 mm -gt Qload
678
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Ceramic windows in coupling slots
Window Ceramic brick of alumina 96 er
9.4 Size the same as slot
Frequency, GHz 1.46
Loaded Q 600
Beam pipe radius, mm 39
Cell radius, mm 114
Cell gap, mm 10
Waveguide, mm 122x110x25
Coupling slot, mm 47x5x3
N type receptacle, 50 Ohm, D9.75 mm d3.05 mm
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Pick-up dimensions
11.13 mm
8.9 mm
47.03.mm
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Diam. 4.46 mm
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Dipole Mode Sensitivity (Resolution)
with
with
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Monopole mode damping using simple pin-antennas
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Damping with antennas Transmission-line Combiner.
180 degrees for dipole. Standing wave with some
frequency detuning. lTL 200 mm to avoid
resonances around 1.46 GHz (SW eigenmodes for
lTL 200 mm at f3 1.1 GHz, f5 1.9 GHz)
In phase for monopole
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Appropriate length of combiner reasonable
length and non-resonant Interaction with dipole
mode
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