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Parallel session P1-1: Detectors (chair: T. Cecil)

  • Introduction: 10mins Intro Slides
  • Discussion: 45 mins
  • Wrap-up: 5 mins


Notes from session (Tuesday, March 6, 08:45-09:45)

Four main topics to discuss: Bands / Dichroic groups, Detectors, Operating Temperature, and RF coupling

  • Bands / Dicroic groups - discussion of bands as laid out in the CDT report
    • Question - are there advantages to trichroic pixels, or to having simplified optics
      • Suzanne: Are the MF bands in the CDT report a wide band? Why not make it as wide as possible
      • Adrian: this is a multidimensional space of cost, risk and sensitivity. What is the target? Trichroics would be more sensitive - more detector for the same telescope - but could be more cost or risk, e.g. 20/30/40 GHz tricrhoic would save real estate but is not sky demonstrated
      • Cecil - we want to lean towards deployed technology for the reference design and then highlight thing under development in the options section
      • Suzanne we need to make sure that in the detector section write assumption are compatible with those made in forcasting
      • suggestion to begin moving through bands from high to low to target areas with more agreement
    • Motion to use 220/270 as a dichroic grouping for both large and small apperture
      • Motion passes, one opposed
    • Discussion on band selection in MF between large and small aperture telescopes
      • Clarence - need to be mindful of detector bandpass requirements. Can we make and test them to verify the benefit to the experiment
      • Is there an advantage to the extra split in MF for the small aperture telescopes (assume so, otherwise why include it)
      • foregroups are varying across the band. Narrower bands make the foregrounds easier. But this small change may not make a big difference.
    • Motion to do small aperture telescope at dichroic (no mention of changes from CDT report)
      • Motion passed, no opposition
    • Motion to do large MF dichroic for large aperture telescope, with trichroic (90/150/220) as possible in options section
      • Motion passes, no opposition
    • Discussion on band selection for LF
      • Do we want LF on large aperture telescope to be dichroic, or trichroic (20/30/40). Suggestion to put trichroic in options section
    • Motion to make LF in small aperture dicrhoic
      • Motion passes
    • Motion to make LF in large aperture dicrhoic (30/40) with stand along 20 GHz
      • Motion passes, one opposed (last motion of session and sense that topic may have been rushed)
  • Detectors
    • Motion from Jeff that MKIDs not be considered for the reference design, but be included in the reference design, especially as an option for higher frequencies.
      • Second by Suzanne
      • motion passed, but not unanimous
  • Base temperature
    • CDT calls for dilution fridge operation (~ 100mK operating temperature)
    • Question on what are power requirements? Is it just an extra pulse tube, or needed to circulate the mix? Is this a detector problem or site problem?
    • Dil fridge has been demonstrated in the field.
      • Has been demonstrated in the field (ACT and CLASS)
      • more information was requested on any limitations on boresight rotation with a dil fridge
    • Motion to use dil fridge for reference design
      • Motion passed
  • Coupling to free space
    • Do we want to have just one technology in the reference design, or list multiple viable options
      • Feedhorn and Lenslet have both been shown for dichroic bands, planar antenna is under development
    • Motion to not consider planar antenna for reference design, but put into options
      • Motion passed, one opposed
    • For SO the technologies are split, with lenslet at LF, feedhorn at HF, and both at MF
      • feedhorn OMT fab can be an issue at LF (ACT has made 24 GHz, but not down to 20 GHz)
      • small lenslet fab can be an issue at HF (shown in mm-wave but not by CMB community)
    • Question on if this is a case where we have two good options, and do not need to pick one. Is the availability of two good options actually a plus for the decadal?
    • Discussion about what more information is needed. Can also see further discussion from Wed splinter session:
    • No final motions on RF coupling were voted on. Issue was put on hold for further discussion.