Telecon 20170731

Agenda:

• Optics and Packing
  • Update on packing of optical systems (UMN) (.pdf)
  • Ray tracing examination of stray light and DLFOV comparison, Optics Study 2017-07-31 (.pdf) (UMN)
  • Firing up far sidelobe analysis, Tran et al. (2010) (.pdf) (Brad)
  • Anyone at JPL to run GRASP? (Amy)
  • Are we using the right shield geometry? (Amy)
  • Moving forward with deployables (Amy)
• Scan
  • Scan angles with current focal plane (Kris) and general trade-offs (Julian)
  • Hydrazine or flywheels? What are reasonable spin and precession rates? (Amy)
• Focal Plane
  • current baseline: multi-chroic TES; anyone interested in developing other options so that we can point to concrete alternatives (e.g. KIDs)? multi-chroic MKIDs (.pdf)
  • Questions for the baseline (Jeff, Roger)
    • what is the plan for detector technology for the high frequency bands of the imager?
      • absorber coupled above 660 GHz, conservative default
      • Nb-nitride or similar material to enable use of the same pixel architecture at higher frequencies, requires development
    • are the distribution of colors for pixels as described by the worksheet reasonable? Band Definitions worksheet as of 2017-07-31 (.xlsx)
    • yes, from a technological stand point
    • are the bandwidths assumed reasonable?
      • 2.2:1 is constant with horn and antenna coupled
      • more bands could likely fit in the low frequency horns
      • we may be space limited at the high frequencies, that could drive us to 2 bands at lower frequencies than assumed, however this depends on the pixel size.
    • what should we assume about beam sizes as a function of frequency, specifically for the high frequency bands? Is it reasonable to assume single mode coupling all the way to the highest frequencies?
      • we can assume it scales as lambda / D

Actions:

• UMN, investigate DLFOV trade-off between crossed and open dragone
• Amy, determine cost difference for larger mirrors
• Brad, determine sidelobe analysis done for EPIC. How was galaxy contamination accounted for.
• Amy, find if anyone at JPL to run GRASP analysis.
• Amy, begin a matrix of possible science outputs.

Notes:

Attending: Jeff, Mike, Jamie, Julian, Shaul, Karl, Qi, Amy, Roger, ??

Optics

• Packing the open dragone. The focal plane can be placed near the bus at 2-3 degree penalty in alpha.
• Ray trace of possible sidelobes
  • cross dragone has clipping sidelobe as discussed previously
  • open dragone has no similar sidelobe. Is straightforward to baffle.
• comparison of DLFOV
  • when scaled by F*lambda open Dragone gives ~60% of the focal plane diameter of the crossed
  • however crossed will require larger pixels (large edge taper) to control sidelobes, while open can have small pixels (low edge taper) since sidelobes are controlled by baffling.
  • UMN to further investigate DLFOV trade-off between the systems
• Goal of settling on system in 3-4 weeks. Amy to look into cost difference for larger physical mirrors in the open dragone case.
• Physical optics analysis:
  • Brad can run GRASP once a system is designed.
  • For EPIC GRASP simulations were convolved with galaxy map to get polarization leakage.
    • Brad will continue investigating details of what was done.
    • Julian can also run full time domain simulations if/when needed.
  • JPL has a GRASP license. Amy checking for person to run analysis.

Scan

• Julian points to work done for LiteBIRD(LiteBIRD Scan Internal Memo (.pdf)) and CORE (https://arxiv.org/pdf/1707.04224.pdf (.pdf)).
  • LiteBIRD looked at full focal plane and assessed uniformity of coverage, angle of attack of each pixel, beam distortion from spin and precession speeds, ability to calibrate on dipole.
    • saw broad minimum in coverage uniformity for alpha = 25-65 deg.
    • narrower range where dipole signal is strong for all scans.
    • condition is good with and without HWP (for full focal plane)
  • CORE looked at single detector maps to asses ability to control systematics.
  • further constraints on CMBP scans need our own simulation. The machinery for this exists.
• Decision to take alpha + beta = 95 deg as the standard for now, no reason for 100 deg.

Focal Plane

• delayed to next week due to time.
• one key question is the need to go to 800 GHz.
  • needs input from Galactic science group
  • Amy will start a matrix of science outputs to help communicate between science goals and design trade-offs.