Telecon 20180206

Attending: Brian, Roger, Jacques, Julian, Tom, Toki, Kris, Hannes, Shaul, Karl, Qi

Notes by : Karl/Qi

• Focal Plane Configuration (Kris, Karl, others) focal plane slides (.pdf)
  • including ADR and Readout boards
    • (.jpg)
    • ADR drawing:PIPER ADR CAD (.pdf)
• Cosmic Rays (Jeff f.; Roger)

Focal Plane Configuration

• Orientation of scan VS orientation of detector rows
  • Kris repeated the concern again from last week; with the hexagone wafers and current scan strategy, is it important to align rows of detectors with direction of scan?
  • multiple detectors on a row can scan over the same track if they are aligned with direction of scan
  • Shaul pointed out that even now there are detectors are one row, every other column though
  • It's not very clear if this matters
  • Spin rate is dominant over precession, so scan direction is about straight from left to right as shown
  • Shaul: each pixel has both polarizations; we want Q and U pairs, thus the word “detector” may be misleading here
  • Jacques: arrangement of focal plane, cross scan sampling; shaul: we will take look into Jaques's paper about cross scan sampling in terms of spin, precession etc.
  • Kris: faster precession, if compare 10 days to 10 hrs, gives better sky map coverage; however, if compare 10 hrs to 2 hrs, not sure if it makes a big difference
  • Jacques: holes on sky map will affect systematics over the focal plane
  • Shaul: fundamental questions have not be addressed, Q and U layout has not been done
  • Q and U alignment is flexible within wafer

• ADR
  • shaul: current model has a tank next to focal plane for ADR, but it does not need to be there there
  • Tom: PIPER ADR
    • continuous ADR, 4 stages
    • stage 1, attached to brown color plate, which attach the focal plane
    • about 9 by 8 by 3''
    • For PICO, one more intermediate stage, stable temperature; every 6 days, one extra ADR stage; so 5 stages in arrangement, slight larger than PIPER's
    • 0.1 K fluctuates between magging and demagging; Tom will look into it how large the fluctuation is for next week

• Focal Plane
  • change: 1)central wafer, split into three: F and GHI;2) 4mm space between edges of wafers based on different experiments (4.2mm for EBEX, 4-5mm for POLARBEAR, 5.5mm for BICEP)
  • Shaul: let's make space to 5mm
  • less F detectors, more GHI, same numbers for others
  • wire bonding
    • traditional: edge of wafer, constrains # you can bond; for F G H I, not enough space
    • “bump-bonding”, instead of the edge, you can wire bond the entire wafer, needed for GHI
  • readout
    • for TDM, 4 mm^2; for FDM, mainly due to large capacitors, 50-80 mm^2
    • FGHI need some special packing, working on

• sizes of mirrors
  • we need to increase mirror sizes if we want to use more diffraction limited field of view
  • dimensions are shown in the slides

Cosmic Rays

• Roger: signals long-time constant spikes
• TES for X-rays, they do not see it as a driven issue; worth looking into it