====== Telecon 20171017 ====== Attending: Brian, Julian, Shaul, Karl, Qi, Roger, Kris, Jacques __Agenda:__ * optical system + noise model + focal plane options (Young, Wen) * {{:open_dragone_optics_20171017.pdf| 1.4 m Open Dragone Options }} * {{:crossdragone_d120cm_f2.5_fov4_10deg.pdf| 1.2 m Crossed Dragone}} * TM rates for large/small aperture systems (??) * {{::probe_scanning.pdf|Scan angles}} * Scan angles + full sky scan simulations + integration with systematics (Gorski, Delabrouille, + all) __Notes:__ Open Dragone: optical system + noise model + focal plane options (Young) * Size of pixel defined on lowest or middle frequency band. * middle band means smaller pixel, higher sensitivity * 10 dB edge taper + middle band size, overall the best in terms of mapping speed * lowest band has 4.8 dB edge taper * edge taper is at 4K stop * Using 10 dB at middle of band moving forward. * For Open Dragone, the DLFOV is small. The outer area of the focal plane is not usable for high frequency, thus it’s hard to trade low -frequency detectors for more high-frequency detectors. * We don’t know what we need for low frequency, it depends on the synchrotron structures. * Plan is to optimize mirror shapes to increase ~150 GHZ DLFOV so trading low sensitivity for high sensitivity is an option. * Open Dragone Optics * V3.D: focal plane further from stop, linearly 10% more focal plane compared to baseline * looks good, has room for mechanical structure of focal plane * Karl is working on coma correction to this telescope, and hopefully we will have larger DLFOV **(AI)** * V4: 10% less DLFOV compared to baseline. Overall smaller telescope, allows roughly 2-3 deg. increase in alpha. * sensitivity calculation uses edge taper defined as lowest band, can be done using middle band Large-aperture Cross Dragone (Wen) * Follow-up to matrix from previous week. Now we have a baffled, large cross dragone. * Reminder: Why 50cm? De-scoped to save cost, if imager + spectrometer is emplemented. * Still questions as to whether just 140cm -- 50 cm saves cost. * Idea here is to provide options to cost and be decided on by the EC. * Cross Dragone has large DLFOV if not limited by vignetting (blockage, mirror sizes etc) * current case is limited by vignetting and blockage, not image quality. * unlike Open Dragone case, we can trade detectors at low frequency for high-frequency detectors more easily * ~ 3K detectors (Open) VS ~ 5K detectors (Cross) * F number: 1.5 (Open) VS 2.5 (Cross) * more detectors + larger F#, means Cross Dragone has larger focal plane * We have filled the matrix of telescope categories * optics design is wrapping up. Polishing will be done to improve sensitivities. * the large/small, open/cross options provide input to trade-off decisions. Scan (Kris) * Simulation * note WMAP Q/U map in V band; Probe with alpha = 22 deg, beta = 73 deg, is close to WMAP * fast spin + different precession (fast, slow, very slow) * for T spin 20s (3 rpm) is fast, Kris do 1 rpm **(AI)** * slowest precession, more non-smooth features, higher resolution needed * LiteBird & Core use same convention of alpha and beta, Kris will change his definition * The simulations are the average over 1 year * simulating over other different periods will be very useful, give more opportunities to look into the scanning. * Jacques: maps with no holes over week timescales are useful. * Kris will do two-week simulation **(AI)** Scanning strategy * Julian: 6 + 1 parameters; precession angle alpha, spin angle beta, 3 rotation rates (spin, precession, HWP), radius of L2 orbit, + data (or sample) rate. * Jacques will lead to make table of scan drivers, wants, and evaluation metrics in wiki **(AI)** * Shaul to make table of hardware or engineering limits on 6 + 1 parameters **(AI)** * Brian: there may not be many options of the L2 orbits * there could be, we need more information input from project * Jacques: Planck had radius L2 = 300,000 km, small. Needed 380 kg fuel for insertion. * Brian and Amy to check details of L2 orbit **(AI)** * Amy told Shaul that we will probably have a steerable antenna for tele-communication; also fly wheels for pointing * Kris: demonstration of full scan + systematics + map making is also important * Julian: Agree, the machinery exists to do these sims. They need to be in time domain. They're computationally cheap. Need limits on the input parameters and evaluation metrics. * Shaul’s comments on this scan parameters study: 1) optimization of parameters; 2) systematics given parameters * When mapping + noise correlation? Julian: As soon as we have the tables from Jacques, we will have a range of parameters.