Mark B. & Szymon S.

On Thursday June 7, 2012 we tried testing the L2 (penultimate mass) OSEMs after Jeff G. reported a problem with the upper right OSEM.

We saved a DTT template under: 
/ligo/svncommon/SusSVN/sus/trunk/QUAD/H2/ETMY/SAGL2/ETMY_L2_OSEM_testing_template

Shaking the top mass M0 in the longitudinal direction [H2:SUS-ETMY_M0_TEST_L_EXC] and monitoring the OSEM readback signals [H2:SUS-ETMY_L2_OSEMINF_UR_OUTMON] in DataViewer, we found that the UR OSEM was only responding with 1/5 of the amplitude as the other three OSEMs on that stage.

Setting up a 0.43 Hz (at around the first pendulum mode) sinusoidal drive with about 50 counts of amplitude in the reaction chain top mass [H2:SUS-ETMY_R0_TEST_L_EXC], we saw that there was no cross coupling between the main and reaction chains which indicates that they weren't rubbing together.

We then took a passive measurement of the L2 OSEMs, by looking at the power spectra of the channels:

H2:SUS-ETMY_L2_OSEMINF_UL_OUTMON
H2:SUS-ETMY_L2_OSEMINF_UR_OUTMON
H2:SUS-ETMY_L2_OSEMINF_LL_OUTMON
H2:SUS-ETMY_L2_OSEMINF_LR_OUTMON

In the attached plot we noticed that the UR OSEM on L2 did not have a magnitude consistent with the other three OSEMs around the 0.99 Hz mode.  We also picked up a transverse mode around 1.03 Hz from the UR, LR, and UL OSEM sensors - something that should not be present in these OSEMs, which are ideally only longitudinal sensors.  These features lead us to suspect that the stage L2 UR OSEM is misaligned, despite the painstaking efforts of members of the suspension team to get it right.

At this time, we don't think this problem merits going into the chamber to diagnose because of the delay that would be introduced from pumping.