Telecon 20171114

Attending: Brian, Richard, Shaul, Karl, Qi, Roger, Jeff F, Joy, Graca, Jacques, Kris

Agenda:

Delayed to next week:

Notes:

New items to consider: Readout - drivers and open questions (Shaul)

Largely information from S4
Options: FDM, TDM,
Two issues: wire count requiring cooling power, power consumed by warm electronics.
Power use – back of envelope 500 W for 10k detectors (FDM)
TDM - more wires at 100 mK. lower power use ~ 100 W for 10k detectors
None of this has been optimized for power use. ASICs have not been included.
- FDM has thought about this somewhat, Shaul to pull out numbers from LiteBIRD assumptions
- TDM, Roger will work on TDM estimates. Contact Mike Niemack and/or Hannes.
3rd option: microwave mux, in demo stage on MUSTANG. Not sufficient TRL yet. Consider for future phases.

Cooling - drivers and open questions (Shaul)

Initial discussions with Chris Paine (JPL)
primary 30 K (passive), may need to be tweaked to 40 K
secondary 4-6.5 K (MIRI 3-stage PT, MIRI from JWST high TRL, as precooler for JT)
- currently at 6.5, could change to 4K.
- UMN calculate stop at 6.5 K.
focal plane, 100 mK.
- UMN calculate sensitivity change if 50-150 mK?
- options: Continuous ADR (Goddard), single shot ADR from Duband
  - Jacques: dilution option at TRL 4, present at space cryo workshop in April. engineering model in 2 years.
To still consider:
- thermal loads from supports, wiring, coolers, optical loads from IR filters.
- How to implement IR filters – stop is 1.2 m. Needs tech development.
  - questions on how to get diameters, how large areas effect optics, etc.
  - Needs a leader to interface with tech group: UMN to find point person.
- Chris Paine is in charge of loads based on structure being developed at JPL. Roger will provider wiring counts.

Cosmic Rays (Jeff)

mitigation in light of Planck. Jeff spearheading. Finishing up lab tests will report on that in ~1 month.
Jeff knows TDM. does anyone have FMD experience? Especially relating to crosstalk.
- cosmic rays are large signal. can have larger effect.
- Qi to work with Jeff to provide EBEX numbers.

Grasp (Brad)

get better primary illumination and sidelobe information.
- will calculate sidelobe response to moon, earth, etc.
our 140cm Open dragone is in GRASP.
ready for physical optics calculations.
Richard: start with gaussian, but need to quickly consider actual beams from detectors. These will matter.
Kris: Planck was limited in what GRASP could do. Time intensive. Are there any time savers, efficiencies implemented?
- Shaul: Doing rough case for now. Just get location of significant sidelobes, polarization response for few detectors, other major features. Not planning to do full case, specifically to allow rough numbers on short timescales.

larger diffraction limited field of view (Hills)

More detailed notes here: coma_correction_of_open_design.docx note_on_apertures.docx fov_open_v3d_wide.xlsx
adjusting mirrors to correct for coma. Done via Zemax optimization.
plots of FOV at pixel frequencies.
10x area improvement at low frequencies.
also can include curved focal plane. ~ 3m radius of curvature. ~ 1 cm shift at edge of FOV
- also astigmatism in X direction is cancelled.
- fov ~ 50% larger in area, some of this is at very wide X angles, would require larger mirrors.
- curved focal plane also slightly improves telecentricity.
- UMN to check if larger mirrors fit in sun shade cone
Open optics have large distortion in Y as you move in X across the FP.
- square grid of points on sky end up in curved pattern on focal plane.
- you're calibrating to locate beams anyway, so not issue.
- need to check polarization effects. this may indicate an issue, but check with basic GRASP study.
- Crossed design doesn't have this distortion.
lack of telecentricity affects stop illumination.
- curved FP improves this slightly over flat case.
- also needs to be checked in GRASP. Not necessarily a problem.