SAT detector counts, NET, and overall efficiency from DSR

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Colin Bischoff, 2019-11-12


As an input for time-domain sims, I reproduce below the detector counts and per-detector NET from Table 3-1 of the Decadal Survey Report.

IMPORTANT NOTE: In the arXiv version of the DSR, we accidentally swapped the per-detector NET for 95 and 145 GHz. This has been fixed in the Github repo (thanks Ben!) and it is noted in this google doc. The table below has correct values.

Frequency # of optics tubes total # of detectors NET per-detector [μK sqrt(s)] beam FWHM [arcmin]
30 GHz 2 576 177 72.8
40 GHz 2 576 224 72.8
85 GHz 6 21144 270 25.5
95 GHz 6 21144 238 22.7
145 GHz 6 21144 309 25.5
155 GHz 6 21144 331 22.7
220 GHz 4 33752 747 13
270 GHz 4 33752 1281 13

The DSR also contains Table 2-1 (reproduced below), which lists the map depth and total survey weight (Q and U) for the ultra-deep survey. These are the numbers that are used for parameter forecasts, map-based Data Challenge simulations, etc.

We can use the detector counts and per-detector NET from the table above to calculate an idealized version of total survey weight (for a seven-year survey):

   τ = 7 years × 365 days / year × 86400 seconds / day = 2.2e8 seconds
   sw_ideal [μK-2] = τ × Ndet / NET2

If we take the ratio of the Table 2-1 forecast survey weight to this idealized survey weight, we obtain a value for the end-to-end efficiency that is being assumed in forecasting. The performance-based forecasting method uses the difference between idealized and achieved performance from BICEP/Keck, with SAT 30/40/85/95 GHz efficiency extrapolated from BK 95 GHz, SAT 145/155 GHz efficiency extrapolated from BK 150 GHz, and SAT 220/270 GHz efficiency extrapolated from BK 220 GHz, which accounts for the pattern of efficiency values shown below.

Frequency Q/U rms [μK arcmin] Total survey weight [μK-2] End-to-end efficiency
30 GHz 3.5 0.69e6 17%
40 GHz 4.5 0.43e6 17%
85 GHz 0.88 11.0e6 17%
95 GHz 0.78 14.1e6 17%
145 GHz 1.2 5.7e6 11.5%
155 GHz 1.3 4.8e6 11.5%
220 GHz 3.5 0.71e6 5.3%
270 GHz 6.0 0.24e6 5.3%