Georgia, Jenne, Craig, TJ, Daniel, Keita, Varun
- The ITMY ring-heater were on overnight and the IFO wasn't able to relock itself.
- ITM ring heaters did use to have non-zero values in O3, but since we've been doing very well without that (and as Daniel / I pointed out that changes the vertex more than the arms) We turned the ITMs ring heaters off for now.
- We realized that the ETM ring heaters were turned off. However, for PI damping they were on at nominal values duing O3. Jenne turned on the ETM ring heaters to
- ETMX Upper: 0.45W; ETMX Lower: 0.45W;
- ETMY Upper: 0.4W; ETMY Lower: 0.4W;
- Next, we started initial alignment. ITM camera was putting signal far off from the WFS, so the initial alignment was done without the ALS-Y camera. Next, TJ and Jenne did the INIT_ALIGN. Details of green alignment in Jenne's alog 58782.
- We increased the input power to 46W and lost lock due to CSOFT-P ringing up at 0.5 Hz. During this power-up we didn't see PI mode at 14755 Hz ringing up. But we managed to stay locked for only a few minutes at high power.
- The IFO was able to relock upto 25 W. We increased the input power to 40W without any obvious problems in ASC/PI. We increased to 47 W of input power and lost lock. We had analog saturations and saw some glitching (unexplained) in the ASC signals ~ 10 s before lockloss.
- We relocked and were able to increase the input power to 47 W. 40 W into the PMC:
- We reduced the CSOFT_Y gain to 20 to suppress the 0.5 Hz oscillations.
- Later we increased the CSOFT_P gain from 15 to 30 ro suppress a ring-up.
- Daniel noted that the locklosses yesterday from PI occured when HOM spacing in Xarm = 5370 and Yarm = 5410.
- We are sitting atthe power as the IFO thermalizes to see if PI still ring up. Changed ETMX RH to 0.5 W and ETMY RH to 0.45 W.
- So far we seem to have beaten the PI. The HOM spacing asymptotes to Xarm ~ 5350 Yarm ~ 5403.
- In the meanwhile Craig made frequency noise injection measurements. I took a quick arm power measurement with SRCL dither using Craig's template.
When ETMY ring heater was first turned on there was a 0.07W discrepancy between the requested and measured power on the lower segment. DIAG_MAIN complained that the segment might be dead.
We found an SDF diff where, on April 6, the resistance of the lower segment (H1:TCS-ETMY_LOWRESISTANCE) had been modified from 43.6 Ohms to 36 Ohms. Not sure why this would ever change, maybe with a computer restart? Reverting this diff removed the discrepancy, and our ring heater is heating uniformly.
Before fixing this issue we had a lockloss from 46W input power, where a 0.46Hz CSOFT_P instability rang up. Unclear if the mismatched ring heater powers contributed of not.