= Simulation meeting 2021 Nov 25 15:00 =
Zoom2: https://zoom.us/j/6676627462

== Participants ==
Naoki Koyama, Matteo Leonardi, Yoichi Aso, Keiko Kokeyama, Haoyu Wang


== Agenda ==
=== Updates from Projects ===
 * Birefringence
   * Slide for updates [[ https://gwdoc.icrr.u-tokyo.ac.jp/cgi-bin/private/DocDB/ShowDocument?docid=13335|link]]
   * The rotation error of TWE maps can contribute -20% to +60% errors for birefringence loss estimation.
   * The beam position on ITM also has an influence in loss estimation:
     * If we suppose the errors are (+10, -10) degrees for 45 TWE and 135 TWE maps, we calculated the losses when beams have different decenters.
     * According to birefringence loss measurements of KAGRA (6.1% for ITMX and 10.8% for ITMYs), both ITMX and ITMY give a suggestion that the decenter is around 1.6cm.
   * Aso-san proposed an idea to recover the real rotation angle by scanning parameters (rotation angles). As we have TWE maps at 8 different rotation angles, we can scan the rotation angle until using different 4 maps will generate exactly the same birefringence map. However, TWE maps of 0 and 180 (or 45 and 225, ...) look very similar except a rotation angle between them. This may affect the effectiveness of this method.
   * Similar with Aso-san's method, if we can construct TWE maps at any angle with TWE maps at 3 different rotation angles, we may be able to know the real rotation angle.
   * Check HR maps again.
   * If possible, ask Hirose-san how he rotated the mirrors.
   * Simulation results between single bounce model and MZ model with 20 order's higher order modes still do not match. Possibly due to symmetry problem which we can't understand. We are still investigating this problem.

 * GUI
   * The 'model check window' is added and the interface is under careful design.