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Parallel session P3-1: Status of reference design overview from P1 and P2 (chair: J. Ruhl)

Reference Instrument spreadsheet

Notes from session (Tuesday, March 6, 11:15-12:45)

Reference Design Discussion Notes: 06-Mar-2018

Telescope (Nils Halverson):

  • Small aperture tel. design: Motion to require <46 cm refractor, to enable silicon lenses. Comment from Kovac that simulations assumed something larger, he thinks 55 cm. Simulation group needs to check this. One backup would to allow larger (alumina) lenses for LF band.
  • Ruhl: Did you discuss multiple telescopes per mount for small aperture? Nils: No, we didnt. Some concern about BiCEP-array with 4 tubes might change requirements on mount. Kovac: Mentions that BICEP-array has costing for 4-tubes / small aperture option to help Reference design.

Cryostat and Optics (Abby Vieregg):

  • Overall, group made a lot of decisions, and moved surprisingly fast.

Detectors (Tom Cecil):

  • Also lots of progress on decisions
  • Only outstanding decision on spreadsheet was coupling technology, but agreed there should be some cost / sch / sci analysis, with others listed as strong options.

Readout (Amy Bender):

  • Decided we should use one technology, but couldn’t settle on which one.


  • How do we move Readout decision forward? Can we get teams / advocates for each technology and they can report back with more info that would help?
  • Keith mentioned that beam and polarization calibration wasnt discussed, would hope that its important aspect that goes into Reference design.
  • Ruhl mentions that detector testing wasnt discussed, e.g., but other things are missing too, that we might have missed.
  • Question about how TD group will be organized in future. Brad comments about proposal to organize telecons+groups around Reference design writing assignments. Carlstrom agrees, and that will be the place for TD group to give input.

Action Items / Homework:

  • Forecasting: Push through forecasting for 46 cm small aperture telescopes (CDT assumed 52 cm).
  • Forecasting: Push through forecasting for low-ell performance in Chile with just detector differencing.
  • Readout: Assemble a team in the next ~week, to assemble spec’s for readout to compare. Comparison should include NEP’s (e.g., phonon, photon, readout, etc.), and on-sky vs in-lab performance (different rows).
  • Readout: Need input from Reference Design writing team, to understand relative waiting for on-sky performance vs future technical promise. Action item uncertain.
  • Readout: Need input about Cost. Padin was volunteered to do this for uMUX, fMUX, tMUX.
  • Detectors: Toki and Sara will compare lenslet vs horn-coupled technology, and optimization for CMB-S4.

Notes from Plenary (Tuesday, March 6, 2:00-3:45)

Reference Design Status (Ruhl)

  • Small aperture telescope: Some discussion about 46 cm limit, and if it would be worth updating sims. Agreement that the difference will be small, but seemed like some preference of still re-doing the sims to understand tradeoff.
    • Action: Still re-do sims.
  • Small aperture telescope: Also it was brought up that alumina would work as lens tech for smaller apertures. Note that was also brought up in parallel session as a viable option to bring up in book.
  • Cryostat / Optics: Question about how we got 19 tubes per cryostat. From discussion it sounds like SO put some thought into this, and came to reasonable conclusion.
    • Action: Can we get more info on SO baseline about large aperture design cryostat, e.g., number of tubes, silicon lens diameter, number of wafers per tube, which could help inform us if we want to explore any variations for S4 reference design.
  • Small aperture telescope: Is there an easy solution to do 360 deg bore-sight rotation for DR fridge? Sounded like CLASS was only DR project doing +/-45 deg rotation, some research / TD might be needed to make this possible.
    • Action: Do more research about boresight rotation for DR system.