The%20LHC%20Beam%20Position%20System

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The LHC Beam Position System
BI Review CERN - 19th-20th November
2001 Christian Boccard, Eva Calvo-Giraldo,
Daniel Cocq, Lars Jensen, Rhodri Jones,
Jean-Pierre Papis, Jean-Jacques Savioz, Hermann
Schmickler. (CERN) Daryl Bishop, Bill Roberts,
Bill Rawnsley, Graham Waters. (TRIUMF, Canada)
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Outline

• The LHC Beam Position Monitors
• General Layout
• Arc BPM
• Insertion BPM
• The LHC BPM Acquisition System
• Layout
• Wide Band Time Normaliser
• Radiation Issues
• Digital Acquisition Board (TRIUMF)
• Expected Performance
• Current Status
• Summary

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LHC BPM System - General Layout
922 Button Electrode BPMs (24mm) for the Main
Arcs Dispersion Suppressors
Total of 1158 BPMs for the LHC and its Transfer
Lines
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The Arc BPM - SSS Layout
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Arc BPM - Detailed Layout
Beam Pipes
BPMs
Cryogenic Coaxial Cables
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Arc BPM - Button Feedthrough
Button Feedthrough
Beam Screen
Liquid Helium Cooling Capillary
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Arc BPM - Feedthrough Technology
Classical Ceramic Seal
Glass-Ceramic Seal
Ceramic
Glass-Ceramic
Metallic Pin
Brazing
Stainless Steel Body
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Arc BPM - Technical Specifications

• Button Feedthrough
• 24/34mm Diameter Stainless Steel Button
• Button Capacitance (8.0 ? 0.6)pF
• Glass Ceramic Dielectric
• Vacuum Seal to 10-11 Pa.m3.s-1
• (50 ? 1)W Impedance for coaxial line
• Normal Operation between 5-25K
• Radiation Resistant
• Signal Levels (after 40m cable 70MHz Low Pass
  Filter)
• Pilot bunch (5?109) gives 30mV peak
• Ultimate bunch (1.7?1011) gives 1V peak

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Arc BPM - Technical Specifications

• (50 ? 1)W Impedance, with Frequency range up to
  2GHz
• Electrical length difference in each quadruplet
  lt 10ps
• Copper Cladded Stainless Steel Inner Outer
  Conductors
• Good Electrical Conductivity Poor Thermal
  Conductivity
• Silicon Dioxide Foam Dielectric
• N-Type Connectors using Glass Ceramic Dielectric
  Seal
• Operation from 5K to room temperature
• Radiation Resistant

• Cryogenic Cables

• Warm Cryostat Feedthough
• (50 ? 1)W Impedance
• Electrical length differences lt 4ps
• Radiation Resistant

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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
• Not sufficient to give requested 50mm resolution

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Improving the Directivity
IP 1 or 5
Use Time Structure of Beams to Enhance Directivity
Original Coupler Locations
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Outline

• The LHC Beam Position Monitors
• General Layout
• Arc BPM
• Insertion BPM
• The LHC BPM Acquisition System
• Layout
• Wide Band Time Normaliser
• Radiation Issues
• Digital Acquisition Board (TRIUMF)
• Expected Performance
• Current Status
• Summary

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LHC Beam Position System Layout
Acquisition Chassis ? 4
Acquisition Chassis ? 4
Acquisition Chassis ? 4
Acquisition Chassis ? 4
Surface Point (1 of 8)
1/16th of LHC Tunnel
Up to 28 Quadrupoles
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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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WBTN - Radiation Issues

• The Front-end Electronics for the Arc BPMs will
  be located under the main quadrupoles
• can expect to see a dose of some 12Gy/year

• Tests in the SPS-TCC2 area during 2000 showed
  that use of DIGITAL components in the tunnel
  should be avoided
• Most memories and FPGAs too easily corrupted
• Qualification of components long difficult

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WBTN - Radiation Issues

• In 2001 Fibre-Optic Link added to LHC BPM
  system
• only the minimum of analogue electronics kept in
  tunnel
• all sensitive digital electronics located on the
  surface
• allows easy access to most of the acquisition
  system

• Cost of large scale fibre-optic installation
  compensated by
• elimination of 13km of expensive low loss
  coaxial cable
• reduction in number of acquisition crates
• no bunch synchronous timing required in the
  tunnel

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WBTN - Radiation Test Results
2001 Test results of the very front-end WBTN
card with Fibre-Optic Link
Initial performance
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The LHC BPM Acquisition System
Tunnel
Surface
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TRIUMF Digital Acquisition Board

• Average of all bunches over T turns
• LEP experience - default T set to 224 turns
  (20ms) for 50Hz elimination
• Average of each individual batch over N turns
• Capture Mode (Triggered on demand)
• Acquisition of N bunches for T turns where N?T ?
  100000
• i.e. 1 bunch for 100000 turns or 100 bunches for
  1000 turns
• Average of all bunches or individual batches for
  gt1000 turns
• Post-Mortem (Continuously updated)
• Average of all bunches over 1 turn for last 1000
  turns
• Last 1000 orbit acquisitions
• Calibration Mode (Asynchronous Mode)
• Allows acquisitions in absence of bunch
  synchronous clock

• Orbit Mode (Real time acquisition at up to 10Hz)

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Operational Prototype Results in 2001
System extensively used in SPS for electron cloud
instability studies.
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Outline

• The LHC Beam Position Monitors
• General Layout
• Arc BPM
• Insertion BPM
• The LHC BPM Acquisition System
• Layout
• Wide Band Time Normaliser
• Radiation Issues
• Digital Acquisition Board (TRIUMF)
• Expected Performance
• Current Status
• Summary

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Accuracy and Resolution
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Current Status

• Beam Position Monitors

• Button Feedthrough
• Contract for 4250 placed with CERAMASEAL (USA)
• pre-series delivery foreseen for Dec 2001
• Coupler Feedthrough
• Contract for 280 placed with CERAMASEAL (USA)
• Cryogenic Cable
• Contract for 4250 placed with KAMAN (USA)
• pre-series production awaiting final approval of
  SSS integration issues.
• Warm Cryostat Feedthrough
• Contract for 1000 placed with HUBERSUHNER (CH)
• pre-series delivery Feb 2002
• Arc BPM body
• Under construction - responsibility of LHC/VAC

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Current Status (cont.)

• WBTN 70MHz Low Pass Filters
• Contract placed by TRIUMF with LORCH MICROWAVE
  (USA)
• 140 pre-series pairs delivered accepted
• remaining 2360 pairs to be delivered by mid 2002
• WBTN Front-end and Mezzanine Cards
• Prototypes successfully tested in 2001
• Front-end card qualified for radiation
  environment
• Manufacture of pre-series to begin in 2002
• Fibre-optic Transmission Components
• Transmitters and receptors under test
• Radiation qualification final component choice
  foreseen in 2002
• Fibre-Optic cable - call for tender in progress
  (responsibility of ST/EL)
• Digital Acquisition Board (TRIUMF)
• Prototype successfully tested in 2001
• Pre-series to be delivered by mid 2002

• Acquisition System

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Summary

• Arc Button BPMs
• All hardware designed and in production
• Directional Couplers
• Locations fixed design underway
• Acquisition system
• Single complete prototype tested successfully in
  2001
• Prototype of a complete operational acquisition
  chain to be installed and tested on 6 BPMs in the
  SPS during 2002

• Outstanding Issues
• Precision requirements and integration of BPMs in
  the Collimator Regions
• Integration issues in the Dispersion Suppressor
  and Interaction Regions
• Approval of the routing for the Cryogenic Cables
  of the Arc BPMs
• WorldFIP fieldbus yet to be tested
• Software development for real-time orbit
  acquisition