====== 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."