Indico : https://indico.cern.ch/event/608554/

Present: Michal, Christos, Ray, Alberto, JJ, Rhod, Adriana, Sotiris, Gerhard, Thibaut, Enrico, RHUL by video link

E/O BPM Status (Alberto)

• 2 Possible set-ups
  • Polarizer/Analyser
  • Interferometer
    • Should be more sensitive
• SPS prototype set-up
  • LiNbO3 crystal
  • 750nm wavelength with narrow bandwidth laser <200kHz
  • Polarisation maintaining fibre for incoming path and normal single mode fibre for the outgoing path 
  • Photodiode signal amplified by 28dB
  • Switch from negative to positive signal due to incoming polarisation state observed
• EM Simulations
  • Big drop when EM field reaches crystal due to change in dielectric constant of the material 1/30
  • Expecting 1.27uW but measures 5 times less ~230nW
    • Needs more careful calculation & set-up optimisation before drawing conclusions
• Test Bench
  • Coaxial line being set-up in RHUL
  • Now functional ready for testing
• Next Steps
  • New PU design
    • Longer crystal, metallic button on beam side & grounding on outer side
    • Overall increase in sensitivity of factor 10 expected
  • Longer term
    • Look at interferometric detection system
    • Look at waveguide structures in very thin crystals to enhance field across crystal
• Questions / ACTIONS
  • Rad hardness of crystal?
    • SPS crystal did not suffer after 1 year in the machine
    • Irradiation tests to be foreseen
  • Comparison of expected performance from HT & E/O
    • Ballpark figure required

New IR BPM Status (Thibaut)

• Locations
  • Now all placed >57cm (2ns) from long range encounters
  • https://espace.cern.ch/HiLumi/WP15/default.aspx
• Open questions
  • Can warm BPM in front of D2 be placed inside D2
  • Aperture of BPTX & APWL
  • BI & RF to decide on APWL or not
• Design of BPMQT
  • Q2a, Q2b,Q3,CP,D1
  • Inermet shielding requested for reducing radiation to front-face of Q2
  • 2W deposited power in BPM from collision debris - needs cooling
  • Latest design
    • Octagonal shape
    • Transitions are inserts welded on
    • Inermet on outside of 1mm walls
      • Is 1mm too thin?
      • Needs to withstand pressure differential
  • Can the pick-up be entirely out of inermet?
    • How to braze/fix transitions & feedthroughs
    • May need to look at other high Z materials - Tungsten, Molybdenum?
• To do
  • Thermal calculation / heat load & cooling
  • Coating for RF - can we do this with inermet?
  • Need input from MME
• Stripline design
  • 3D printing does not seem feasible in terms of tolerances
    • To be checked with ML
  • New "buildable" design being investigated by Michal
    • Include feedthroughs
• Plans
  • Functional specifications by March 2017
    • Report back in April WP13 meeting
  • First design by end 2017
  • Prototype BPM in 2018