Dan, Kiwamu

We tried PRX, PRY, MICH and PRMI. PRMI did not lock, but the other configuration locked. Also I am worried that either ITMs or BS may be moving a lot.

(MICH)

• ASAIR_A_RF45_Q
  • demod phase = -91 deg
• whitening gain = 18 dB, stage 1 and 2 ON.
• servo gain -200
• we did not change the digital filters at all (i.e. the same old filters were used)
• UGF --> forgot to measure, must be higher than 10 Hz.
• The BS pitch was wobbly with an amplitude of about 2 urad in peak-to-peak, observed by oplev. Engaging the oplev damping servo successfully got rid of the pitch wobbliness.

(PRX and PRY)

• REFL_A_RF45_I
  • demod phase = -2.2 and 12 deg for PRX and PRY sideband resonance respectively
• Also checked the demod phase for REFL_A_RF9_I (out-of-loop)
  • demod phase = 77.0 and 79.7 deg for PRX and PRY sideband lock respectively
• whitening = 0 dB, no whitening stages engaged.
• servo gain = -200
• we did not change the digital filters at all (i.e. the same old filters were used)
• UGF --> 60-ish Hz

(PRMI)

• tried a smaller gain in PRCL and MICH by a factor of 500 and 20 respectively according to LLO's locking instruction (DCC-T1300991).
  • I did not see a momentary lock at all
• fiddled with the gains. No momentary lock was observed

(ITMX mysterious oscillation in pitch)

At the beginning, we saw a quite steady oscillation in pitch of ITMX at 0.5 Hz with an amplitude of 2 urad according to the uncalibrated oplev. We suspected a hidden excitation somewhere and therefore cleared all the excitation using the diag command. This did not solve the oscillation. Then I increased the pitch damping gain by a factor of 3 to suppress the oscillation and this worked well. Setting the gain back to the nominal value (i.e. -1), I saw no ring up in pitch and the oscillation still stayed small. So I left the damping gain as nominal. Strange. Since ITMY oplev is off from the QPD, we did not check the angular motion in ITMY.

(I feel that the mirror motion is bigger than it used to be. Maybe ?)

Since the last PRMI commissioning in this winter, we have kept a couple of limiters in LSC and SUS for preventing the servos from unnecessarily kicking the optics during lock acquisition. The limiter values and their associated filters had been carefully adjusted so that they don't limit the in-lock DC values but they limit some impulsive signals. However, the limiters were limiting the in-lock feedback signal at DC when PRX(Y) or MICH was locked. I had to increase some of the limiter values by more than a factor of 5 or take them out last night.

I have not done a quantitative spectral analysis yet, but I am feeling that the motion of the suspensions are greater than before.