Telecon 20180131

Attending: Brian, Julian, Hannes, Amy, Tom, Kris, Shaul, Karl, Qi, Roger, Graca

Notes by : Karl/Qi

• Preparing the next Teamx-I (.pdf)
• Report about systematics work (delayed to next week)
• Cleaned up focal plane version 4 (.pdf)
• GRASP status (.pdf)

Preparing the next Teamx-I – By learning from previous one.

• response from TeamX, 90 slides on sub-systems.
• Section summaries in presentation. No cost discussion today. 15 pages in each sub-system.
• Need to do homework on some items before next TeamX
• Systems:
  • I&T will be analyzed in next teamX, was not analyzed here. Still marked as weakness due to complexity.
  • telescope systems at various temperatures (40 K, 4 K, 100 mK) make testing the end to end alignment challenging.
  • Will continue discussion with Bill J. and Tomo next week.
  • Definition: OGSE, optical ground support equipment. Testing equipment that doesn't fly.
  • Future threats: add “cost of cooler” Comments: this is a cost threat more than a technology threat
• FP and detectors
  • Str: TES have ground based heritage. detector 1/f shown to be acceptable. future options for MKIDS.
    • Roger will lead 1/f story for final report. Tomasso is running gain variation and per rotation calibration options (assuming 10 mHz 1/f knee)
    • General comment: detector 1/f isn't the only important 1/f term. Other issues (temperature stability) may dominate.
    • Only modulation is sky rotation and scan speed.
  • Weak + future threat: Impact of cosmic rays.
    • Jeff Fillipini has looked into this. As has Roger. Roger will lead report summary.
    • Work to reduce impact is also being done at Berkeley.
  • Hannes: What about optical coupling?
    • This hasn't been finalized. Roger: coupling via lenslets hasn't been shown at high frequencies.
• Electronics
  • Weak: Temperature limits.
    • TeamX assumed what is currently used. but would used space qualified electronics, so this won't be an issue
    • Amy: TeamX usually gives reports to science teams, not reviewers. Amy is talking with TeamX/NASA to point out that reports need to be crafted so a general review audience understands the issues. Easily address comments like this risk getting blown out of porportion.
• Optics:
  • Weakness: maturity of mechanical and thermal design of focal plane.
    • this work is in progress for next TeamX
• Thermal:
  • 3HE, testing for MIRI was expensive. even if those tests done for PICO, < $1M so ignore it.
  • Cost is large. $900M for cooling, 50% of instrument cost. This is largest thermal risk point.
• Mechanical:
  • Strength: scalable, simple, nothing radical
  • Weakness: optics alignment complex.
    • Address by pointing out WMAP and Planck have done this successfully, should not be weakness, will address in next TeamX
• Configuration
  • Threat: No volume margin for primary mirror inside the shade
    • Shaul: this is being worked on, should have some margin by next TeamX

Focal Plane V4 (Karl)

• simpler focal plane, 2 wafer sizes.
• roughly 1000 more detectors at high frequency. Sensitivity same. (0.61 uK vs 0.62)
• FP could go further out in X,
• Current reflectors need to be larger if we increase focal plane; but we can increase focal plane with current strehl limits.
• Central wafer issues:
  • multi- and mono band pixels coexist
  • insufficient bond pads for number of bolos on this wafer.
    • 4000 bolos on 4“ wafer. Hannes: fit ~2000 bolos on 6” wafer in past.
    • We are assuming 100 um per bond pad. 4 inch wafer.
• 2 mm between tiles, may be too small. For EBEX, ~5 mm. Karl to check
  • Roger to get spacing number from recent BICEP arrays
• Kris: We need to think about how pixels are aligned to scan direction and how this impacts map making.
  • are we making single detector maps? multi detector maps? do pixels need to follow the same path on the sky as a neighbor?
  • This may require slight rotations of the focal plain.