Participants: Enzo, Terrence, Panwei, Hatoya, Fabian.

On Wednesday (15/08/2018) we found a DC coupling between the vertical displacement of the top filter keystone (F0) and the yaw of the optic measured by the optical lever. The reason for this effect is not clear yet and we're in the process of investigating it. As shown in the plot, for a vertical displacement of 250 um of the F0 keystone the yaw displacement of the optic is 215 urad. This is an approximate estimate as the oplev readout reaches its nonlinear region.It's worth mentionng that we still have not installed a yaw adjustment mechanism at F0 yet because the prototype is still being tested. We yaw position is likely not fixed in a robust reliable way and we should visually inspect it again. 

We found this bevaviour when we opened the vacuum chamber and added some weight on top of the keystone in order to bring it down to its nominal position (at zero according to the LVDT). This was done as preparation for the measurment of the optimum height of the magnetic damper ring wth respect to the top of the standard filter (F1). We lowered the keystone 1.7 mm by putting and additional mass of 333 grams. The keystone already had a PROMEC mass of 447 grams, giving a total of 780 grams.

The vertical displacement of 1.7 mm at F0 produced a movement of the optic in such that the oplev beam went out of range. We recovered the alignment by moving the position of the quadrant photodiode (QPD). The oplev readout was calibrated again and the result will be shown in a separate entry.