Alexa, Gabriele, Sheila, Evan

Summary

We have updated the DHARD P filters so that we have a 3 Hz BW when we are on resonance. When we first engage the WFS at 50pm CARM offset, the loop is stable at 100mHz BW. This loop would also be stable at 3 Hz BW; however, we don't want to have to adjust the loop gain as we reduce the CARM offset, so we have left the loop at low BW at 50pm CARM offset. The DHARD Y filters are installed for a high BW configuration; however, they have not been tested yet.

Details for Pitch

The old DHARD P configuration was as follows: FM3 (0.1:0), FM4(:0.01), FM7(SB3.8), FM8(invDhP), FM9 (SB9.8), FM10 (ELP10),Gain = 8. Note: this is the inverse plant that Evan measured in LHO#16520.

The new DHARD P configuration is as follows: FM2(zpk([-1.5+i*4;-1.5-i*4;-3.5+i*1.5;-3.5-i*1.5],[-41+i*70;-41-i*70;-46+i*100;-46-i*100],160000)*gain(2)), FM4(:0.01), FM7(SB3.8), FM9 (SB9.8), Gain = 21. Evidently, we have removed Evan's plant inversion and replaced it with a compensation filter which we designed from Gabriele's model. The attached image shows the difference between the old and new configuration modulo the gains.  

At 50pm CARM offset, we were able to close this loop first with a gain of 21 (low BW), and then with a gain of 165 (3 Hz BW). Since the optical gain changes as we reduce the CARM offset, we decided to leave the loop at 50pm CARM offset with a low BW. Once we were on resonance, this loop was stable and gave us a 3 Hz BW as desired. This is in the guardian now.

Details for Yaw

The old/nominal DHARD Y configuration is as follows: FM3 (0.1:0), FM4(:0.01), FM7(SB3,14), FM8(invDhP), FM9 (SB9.8), FM10 (ELP10),Gain = 8. Note: this is the inverse plant that Evan measured in LHO#16566.

In preperation for a higher BW loop we have installed FM2 (same compenstation as for P), and FM6 (zpk([-0.376+i*15.215;-0.376-i*15.215;0.22+i*19.22;0.22-i*19.22], [-0.405+i*18.071;-0.405-i*18.071;-0.207+i*11.314;-0.207-i*11.314],1)gain(0.488863)). FM6 is designed to compenstate the resonant peaks between 1.5-3Hz in Gabriele's model LHO#17001 (this was confirmed by measurement). The second attached image shows the comparision between the nominal/old configuration and these new filters modulo the gains.

This loop has not been test yet. The guardian currently sets this to the old configuration.