====== Telecon 20170731 ======



__Agenda:__ 
  * Optics and Packing
    *  {{::opendragone_packing_20170731.pdf|Update on packing of optical systems (UMN)}}
    * Ray tracing examination of stray light and DLFOV comparison, {{::opticsstudy_20170731.pdf|Optics Study 2017-07-31}} (UMN)
    * Firing up far sidelobe analysis, {{::tran_et_al_2010.pdf|Tran et al. (2010)}} (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)? {{::2017_bjohnson_ltd17.pdf|multi-chroic MKIDs}}
    * 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?  {{::banddefinitionsv2.1.xlsx|Band Definitions worksheet as of 2017-07-31}}
       * 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_toast_20170123.pdf|LiteBIRD Scan Internal Memo}}) and CORE (https://arxiv.org/pdf/1707.04224.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.