The LHC Beam Position System

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The LHC Beam Position System
Ad-hoc Working Group on LHC Experiment-Machine
Parameter and Signal Exchange 26th March
2002 Rhodri Jones (SL/BI)
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LHC BPM System - General

• 100 Warm, Button Electrode BPMs (LEP) for TI2
  TI8
• 922 Button Electrode BPMs (24mm) for Arc DS
• 44 Warm Button Electrodes BPMs for IR3 IR7
• 44 Enlarged Button BPMs (34mm) for IR1,2,5 8
• 24 Directional Couplers for IR1,2,5 8
• 24 Special BPMs for Transverse Damper, Tune
  Chromaticity Measurements in IR4
• 1 BPTX timing pick-up per incoming beam for
  IR1,2,5 8
• Total of 1166 BPMs for the LHC and its Transfer
  Lines

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The Arc BPM - SSS Layout
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Arc BPM - Button Feedthrough
Button Feedthrough
Beam Screen
Liquid Helium Cooling Capillary
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Interaction Region BPMs
Liquid Helium Capillaries
Stripline Electrode
Q2 Coupler

• Stripline length 120mm to give same response as
  button
• 2 Types
• Warm Coupler - capable of withstanding bake-out
  to 200C
• Cold Coupler - located in Q2 cryostat (tilted by
  45 for cryostat integration)
• Directivity measured as 28dB at 200MHz

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The Front-End Electronics
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The Wide Band Time Normaliser
A
B
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The Wide Band Time Normaliser
A (B 1.5ns)
A
B
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The Wide Band Time Normaliser
A
B
A(B1.5ns)
B(A1.5ns)10ns
Interval 10 ? 1.5ns
System output
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The Wide Band Time Normaliser
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WBTN - Linearity v Intensity
For LHC Arc BPMs 1 130mm
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WBTN - Linearity v Position
For LHC Arc BPMs 1 130mm
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The LHC BPM Acquisition System
Tunnel
Surface
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Accuracy and Resolution
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Timing Pick-up for the Experiments(BPTX)

• Located 150m from the IP in front of the D2
  Magnet
• One BPTX either side of the IP on the incoming
  beam
• Exclusively used by the experiments

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BPTX Requirements?

• Choice of Pick-up?
• Stripline Coupler?
• Peak voltage (one button) of 20V after 200m of
  cable for nominal bunch
• Peak voltage (one button) of 1V after 200m of
  cable for pilot bunch
• Button Electrode BPM?
• Peak voltage (one button) of 5V after 200m of
  cable for nominal bunch
• Peak voltage (one button) of 250mV after 200m of
  cable for pilot bunch
• Other Type of Pick-up?
• Type of Signal?
• Sum signal (sum of all 4 pick-up electrodes ? 2 ?
  peak voltage)?
• Virtually independent of position requires only
  1 cable
• Sum and Delta Signal?
• Requires 3 cables to give sum, horizontal
  position vertical position
• Other Type of Signal?

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Next Steps

• SL/BI will supply
• 2 BPTX Pick-ups per Experiment
• Choice of pick-up in collaboration with
  Experiments
• Experiments responsible for
• Cabling
• All machine cabling to be defined by 15th March
  2002!
• All machine cabling to be ordered by 15th May
  2002
• Any subsequent electronics
• Keep in mind radiation resistance for
  electronics in the tunnel