Cheryl, Jenne, Varun

We had a lockloss because I set the offset too high. So I had to start over again. The alignment was having issue so I ran initial alignment and then helped the X and Y arms by hand. I manualled skipping OMC whitening so that Cheryl could work with Voilin damping without affecting the broadband sensitivity. We had another lockloss but the detector locked itself easily after the initial alignment setup earlier.

Next, I moved the switch the OMC ASC from QPD to Dither as described in alog 58960. I waited for the loops to converge monitoring both the loop output and the KAPPA_C.

Measurements for different OMC-ASC: 

1. I spent the night struggling with the measurement but then I just realized I was being stupid. The sneaky OMC dither master switch was off. I turned it on and tried the switch again.
   • I had checked that all the ADS loops had converged before I started making any changes to the OMC setup.
   • There do seem to be some issue with the dither loops however. There is large length, pitch and yaw drive output when the dither loops are turned on. The outputs converged in 45 mins so we are ready yo do the test! The nominal kappa value was 1. 
   • However, we think that as we didn't actually check the phasing of the dither loops, so maybe there's an offset there?
     • Jenne has noted this and we can look into when we get the interferometer back in the next few weeks.

For now I will give one last try at these measurements to get an estimated of the OMC-ASC coupling to DARM.

1.  Starting the measurement with POS-X offset. The loop is extremely slop to converge takes upto 10-15 mins between changes in the offsets. 
   • I increased the offsets from 1e-4 to 5e-4. No excess noise in darm.
   • I increased it to 1e-3. No excess noise in darm.
   • I increased it to 2e-3. No excess noise in darm at 1305223828. Ref 2 and 3.
   • I increased it to 8e-3. No excess noise visible in darm. Ref 6 and 7.
   • Running out of patience transitioned to bigger steps. Now at an offset of 0.2 some excess noise in darm. Ref 8 and 9.
     • Interesting note that the 90 Hz wide peak has worsened. The peak amplitude is approximately a factor of 3 above the overall broadband darm noise. Still waiting for the loops to converge.
     • The kappa_c fell to 0.83 however as the loops converged, it recovered to 0.97.
   • Increased the offset to 0.4. The noise spectrum is high above darm saving the reference and moving on with excitations! Finally! Saved as reference 10 and 11. The kappa_c drops to 0.82.
   • Starting the excitations at offset 0.3, 0.2, 0.1 and 0.
     • offset at 0.3: Ref 12 and 13.
     • offset at 0.2: Ref 14 and 15.
     • offset at 0.1: Ref 16 and 17.
     • offset at 0: Ref 18 and 19.
   • file saved at /ligo/home/varun.srivastava/LHO_work/O4_comm/2021_05_15_OMC-ASC_NB/OMC_ASC_POS_corX.xml
   • This measurement is interesting, using Anamaria's script, I estimate crossing at 0.14, using either CAL-CFTD_DELTAL or CAL-DELTAL, Plot attached. 
2. Starting the measurement with POS-Y offset. 
   • Knowing the offset values from POS-X measurement, I ramped the POSY-OFFSET to 0.4 from 0 in 4 steps. However, I stopped at POSY-OFFSET of 0.3. First, the L_OUT was getting close to saturation (32k counts). Second, I could see the excess noise in DARM. Kappa_c close to 0.72.
   • Quite and no EXC.
     • Ref 0 and 1 are quite DARM
     • Offset 0.3 and no EXC,  Ref 2 and 3.
   • Starting the excitations at offset 0.3, 0.2, 0.1 and 0
     • offset at 0.3: Ref 4 and 5.
     • offset at 0.2: Ref 6 and 7.
     • offset at 0.1: Ref 8 and 9.
     • offset at 0: Ref 10 and 11.
   • file saved at /ligo/home/varun.srivastava/LHO_work/O4_comm/2021_05_15_OMC-ASC_NB/OMC_ASC_POS_corY.xml
   • using Anamaria's script, I estimate crossing at 0.09, using either CAL-CFTD_DELTAL or CAL-DELTAL, Plot attached. 

It is important to note that there is some non-zero coupling between the OMC-ASC loops -- POS_X, POS_Y, ANG_X and ANG_Y. We assume in the above calculation that these have no coupling.

Combining the above two, POS-X and POS-Y, the OMC-ASC contributes almost 45% of the DARM noise in frequency band of 30-40 Hz at LHO. Although these numbers need to be checked for noise projections. I will take the measurements of ANG_X and ANG_Y later tonight. Robert is using the IFO to move shakers.