aLIGO LHO Logbook

H1 ISC (ISC)

stefan.ballmer@LIGO.ORG - posted 01:33, Thursday 16 July 2015 - last comment - 08:44, Thursday 16 July 2015(19675)

more ASC...

Jenne, Evan, Stefan

- Reverted the the ramp times in PREP_TR back to Monday's values - this seemed to be more reliable, and not produce any transients at that stage of the script.
- Repeatedly brought the machine up to 24W, but we still see a hint for the 0.41Hz CSOFT resonance, and occasionally a YAW gain oscillation at maybe 1.5Hz.
- The DC oplev PIT on SR3 was stuck on the limiter.
- We also cleaned up the Guardian flow chart. It now has a single flow line. (The previous spider web caused more lock losses than it was worth.)
- Since the 0.41Hz problem seems to come and go, we decided to kill it with a good CSOFT loop design - using a 2nd UGF at the resonance to damp it. Evan is still testing this filter.

Comments related to this report

evan.hall@LIGO.ORG - 04:39, Thursday 16 July 2015 (19676)

Link

Just to summarize, we seem to be suffering from several issues at 23+ W:

The intermittent apperance of an 0.4 Hz instability seen in the arm powers, the sideband powers, and various ASC loops (but particularly common soft pitch). [Some people claim this will be fixed by tuning the cSoft loop appropriately.]
The intermittent appearance of a 2.5 Hz instability seen on the AS port camera and the yaw ASC loops. Confusingly, it sort of looks like a pitch instability on the camera. [Some people claim this is an ASC loop instability.]
Random, sudden locklosses after a few minutes. [Some people claim this is a slow alignment drift.]

evan.hall@LIGO.ORG - 06:27, Thursday 16 July 2015 (19678)

Link

I was able to get a 30 minute lock at 23.7 W with the following:

dETM yaw gain increased from 14 to 22. I think this is what is needed to suppress the 2.5 Hz oscillations that we see at high power.
cETM pitch engaged with +20 dB filter and gain of -1. Unclear whether this helps or hurts us.
cETM yaw gain engaged with no +20 dB filter and with gain of -2. After 30 minutes I tried turning on the +20 dB boost, but this rang up the 2.5 Hz oscillation and broke the lock. So this loop configuration gets a thumbs down.
Common hard/soft actuation removed from the output matrices. I did this out of an abundance of caution. I'm not sure whether it is responsible for any of the high-power problems we've seen over the past 36 hours.

Other notes:

Over the past two days, I saw the following EPICS freezes:
- 2015-07-14 04:31:00 Z
- 2015-07-14 08:22:50 Z
- 2015-07-15 12:26:36 Z
- 2015-07-15 12:26:50 Z (this one lasted for about 20 s, and at the same time the SYS_DIAG guardian threw an NDS connection error)
Twice tonight we had locklosses when engaging the fiber mode damping in the Guardian.
Twice tonight we saw the DARM WFS fail to control the AS port spot during CARM offset reduction. This caused a lockloss both times. From the OPS overview screen, it seemed like the shutter was open both times.

evan.hall@LIGO.ORG - 08:44, Thursday 16 July 2015 (19679)

Link

We were able to get two more stable locks at 24 W, this time in the full low noise state.

However, Patrick and I found that EY L2 was periodically saturating, with the quadrants having something like 50,000 ct rms, coming primarily from the microseism. So the EY L1/L2 crossover is now increased in the Guardian (the L1 filter gain was 0.16, and now it is 0.3). The rms drive on L2 is now more like 30,000 ct rms. L1 is 6000 ct rms, and L3 is 1000 ct rms.