Alexa, Evan, Sheila, Ryan
We reached 0 carm offset with CARM on normalized reflair 9, and DARM on normalized AS 45 Q.
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We changed the sensor for the DHARD WFS from AS B 45 Q to AS A 45Q, based on what Ryan told us about the LLO experience. With this sensor we can keep the loops closed throughout the whole CARM offset reduction without flipping the sign.
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We reduced the PSL power to 2.8 Watts after locking DRMI and transitioning to TR_CARM. (this is added to the guardian)
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We let the guardian take us to the "10PM" state
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We added a boost to the REFL BIAS path, (FM2) which has a z2:p0.01.
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We adjusted the TR_CARM offset (to about -34 or -36) to get the offset in TR_REFLAIR input to -0.08
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We ramped on TR_REFL with 8 in the input matrix and 0 in TR_CARM.
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We reduced the TR_REFL offset to zero
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in this situation we had large angular fluctuations, and didn't hold the lock very long. Our arm buildups were around 800 times the single arm power, and REFL was less than 10%
Our next steps will be to check the loop gains before we try turning off the refl offset, and trying to increase the DHARD WFS bandwidth.
We also toggled the noise eater tonight (we thought it might have been oscillating but this probably wasn't the case). We also copied the invP2P and Y2Y filters from the drivealign matrix into the opLev servos so that we can work on the DHARD WFS loops independent of these filters.
Lock loss times: all Feb 4th UTC
4:14:00
5:00:00
7:09:00
I have attached two time series of the lock aquisition (a long and short version), which includes the power trend of DC REFL and the build up in the arms. The third attachement is of the CARM and DARM spectra during our short full lock.
Note: the oscillation at about 1800 sec in the first attachment arises from us trying to transition REFLAIR9 and sqrt(TRX+TRY) too early in the CARM offset reduction.
Once the new IMC power is taken into account, I think the arm buildup on resonance is more like 940 times the single-arm buildup. That means we've achieved an IFO recycling gain of 28 W/W during this lock stretch.
With REFL_A_LF at 21 mW with arms off resonance, and 0.7 mW with arms on resonance (see Alexa's plot above), this means the IFO visibility is greater than 95% if REFL_A_LF is giving an accurate measure of the power reflected back from the PRM.
Details
Back when we digitally normalized the TR sensors (LHO#16211), we did so at 10.95 W of power into the IMC. Correspondingly, the LSC power normalization was set to 10.0 W (i.e., there is a small mismatch).
However, for this lock we had 2.82 W of input power into the IMC, with the LSC power normalization at 3.0 W (another, different mismatch). That means the arm buildup value of 810 that we saw tonight should be corrected to 810×(10.95/2.82)×(3/10) = 944. With a 3% PRM transmissivity, the recycling gain is therefore 28 W/W.
Since we were at 2.8 W of input power to the mode cleaner rather than the "nominal" 10.9 W that we've been using previously, and since the LSC power normalization is only dialed in to the nearest integer watt, there is a small amount of systematic shift in the arm buildups during this lock.