[Kenata, Masayuki]
Oplev loop has been modified to have large gain below 0.5 Hz. We have done for ITMX pitch and ETMX pitch.
I checked that the pitch oplev loop does not contaminated the length motion by using the ALS DARM. As shown in the attached figure, the ALS DARM signal does not change with this new loop.
Here is OLTF of ETMX. U.G.F = ~ 1.7 Hz
Nakano, Kenta
PITCH
We applied the same loops for the IM stages ITMY and ETMY(Fig 1, 2). The UGF of ITMY is ~ 1.8 Hz. The one of ETMY is ~ 1.78 Hz.
Tomorow, I make the loop for MN stages of both ETMs.
YAW
Nakano san made the loop of ITMX for YAW direction(Fig 3). The U.G.F is 7 Hz It is used MN Oplev as sensor. Nakano-san will plot the spectra of ITMX YAW later. He said that from view of RMS, ITMX YAW only moves several nrad by 1 Hz !!
Tomorrow, We will check whether these control loops are disturbed ALS DARM.
none
Maybe did you also check the Yarm pitch treatment would not degrade the ALS DARM as you did in 15036, right??
> several nrad RMS
Majide?
[Kenta, Masayuki]
Now, all of the suspension has strong OL loop, and the ALS DARM does not have any difference from the privious oplev control.
As shown in the second spectra, the RMS is below 10 nrad. The YAW motion is still large below 1 Hz. This is because the TM oplev is not used for the YAW control, but only MN oplev. We should use the sensor which monitoring TM motion to reduce the yaw motion below 1 Hz, so we are trying to use GR QPD to reduce these frequencies.
BTW, above 3 Hz, the ALS DARM signal seems to be limitted by the GR RFPD dark noise used for GR-PDH loop. If we can increase the modulation index, the ALS performance would be improved.
