imagerteleconnotes20170911 [Probe Mission Study Wiki]

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====== Telecon 20170911 ======

Attending: Al, Shaul, Amy, Brad, Julian, Brian, Roger, Bill, Jacques, Jeff \\

__Agenda:__ 
  * New Permanent Telecon Time: Tuesday 2 pm
  * White noise and focal plane model {{::pico_noise_open_v_crossed_20170911.pdf|Noise model status}}  (Karl)
    * Focal plane size comparison {{:fov_comparison_09112017.pdf|}} (Qi) 
  * White noise comparison; 1/f noise (Roger, Jeff)
    * TDM noise :{{::Noise_for_CMB_Probe_v2.pdf|TDM noise Study}}
    * 1/f noise summary : {{::flicker_noise_CMB_probe.pdf| 1/f noise Study}}

__Notes:__


New telecon time.  **Tuesdays 2 pm CDT** starting 9/19.

Noise model (Karl)
  * Added multichroic pixels
    * stop illumination changes with frequency
    * Comments:
      * **A/I** should set lowest band at 25 dB to be conservative.
      * illuminations, diffraction, spillover may need study with GRASP.
        * Amy can look for person or software access at JPL. **A/I**: pending discussion with Shaul.
  * 100 mK bath temperature added.
    * effects low frequencies where phonon noise was dominate at 100 mK bath.
  * Single detector NET, Open performs better, particularly at high frequency.
  * DLFOV calculated.
    * in F*lambda units, crossed diameter is 2x open diameter.
    * pixels numbers added which satisfy DLFOV requirements.  Hex packing assumed
  * Final polarization weights are similar
    * crossed is 0-20% better at most bands.
    * open 5% better at only 3 bands.
  * Discussion:
    * Since roughly equal sensitivity open is probably preferred as focal plane is smaller, fewer detectors, less massive, easier to cool, overall cheaper.  Also lower sidelobes.
    * may need to consider diffraction pattern on primary of open.  Does primary need to be oversize?  How much?  A GRASP calculation could be done.

Focal plane sizes (Qi)
  * Past report said DLFOV for Open/Crossed ~ 75%.  This was stop at primary.
  * DLFOV reduced for stop between primary and secondary on open dragone.
  * Key points:
    * stop location matters and reduces DLFOV.
    * results consistent with and explain focal plane sizes in noise presentation.

1/f noise and TDM (Roger)
  * presentation tied up in JPL release procedure.  Should be shared with 1 week.
  * brief summary of work done:
    * TDM version of white noise calc in rough agreement with UMN numbers.
    * Likely to need 100 mK bath temperature just so bolometers are build-able.  Need a very low G and low T_bath helps achieve this.
    * little to no 1/f input from readout developers yet.
    * total instrument 1/f compiled from various deployed sources
    * how low has been achieved?  Unclear, most experiments use modulators or focus on higher l science.
    * Comments: 
      * SPIDER has a non-scanning data set which can be examined for 1/f levels. **A/I** Roger to follow-up.
      * Niemack may have data on TDM showing 10 mHz 1/f knee.
      * will the community doubt 1/f knee as low as needed is possible?  This is a critical component.
      * what 1/f knee is needed?  if 1 RPM need 16 mHz. 
      * 1 RPM is fast.  Past experiments are 0.5-1 RPM.
      * Large broadband HWP is not possible.  Need to address/understand 1/f.
      * (Jacques) 1/f not terrible problem if uncorrelated.  only reduces low l sensitivity.
        * Gain changes and temperature stability are large problems.
      * (Julian) making single detector maps is useful in dealing with 1/f, i.e. scan stratagey matters.
        * Has pipeline to do large scale simulations.  "Space is easy."
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