Ushiba, Takano, Fujimoto, Hirose, Tanaka

## Abstract

We found that PR3 IM OSEM H3 has large gilitch frequently. This glitch shakes PR3 largely, more than 10 urads and disturbs PRMI/SRMI lock.

## Details

As reported in klog36978, PR3 moved largely again during today's commissioning.

First, GAS LVDT signals seem to become glitchy at this moment. We turned off only GAS controls and monitored the local sensor signals. Although GAS LVDT signal seems to be not changed, PR3 moved largely (fig.1). So GASs are not gulity.

Second, We turned off TM OLDAMP controls after restoring GAS controls. Similarly, PR3 moved largely (fig.2). So, TM oplev seems to be innocent.

Third, we turned off IM DAMP. Actually, we requested PR3 guardian to be the PAY_FLAOT state. Then, we found that IM OSEM H3 has large glitch, ~10 cnts? in the view from K1:VIS-PR3_IM_OSEMINF_H3_OUT (fig.3). This time, TM oplev seems to be stable(fig.4). IM OSEM H3 seems to be used for IM DAMP T and Y. We turned on the PAYLOAD controls (actually we requested the guardian to be LOCK_ACQUISITION) and then we turned off the IM DAMP T and Y. In this state, TM OLDAMP started oscillate 1.15 Hz. Except for this 1.15 Hz oscillation, PR3 seems not to move largely (fig.5). 

Finally, we closed the laser shutter in order to confime whether this glitches are caused by the scattered light from IFO. The glitch is still in the OSEM signals even though the laser shutter was closed (K1:PSL-BEAM_SHUTTER = 0) (fig.6). This indicates this glitch comes from OSEM itself.

According to OSEM2EUL matrix, the coefficient from DGS cnts to urad? in Y direction is 5.8. So This 10 cnts glitch is relavant with ~58 urad.  

OSEM giltch seems to appear in only one direction, that is in negative direction in K1:VIS-PR3_IM_OSEMINF_H3_OUT. we suspect that somethin ex. OSEM LED intensity? or LED current? gets weak.

We left PR3 in the PAY_FLOAT state overnight to check how frequent this glitch occurrs.