aLIGO LHO Logbook

H1 ISC

lisa.barsotti@LIGO.ORG - posted 22:56, Monday 03 November 2014 - last comment - 20:47, Tuesday 04 November 2014(14819)

ALS not cooperative tonight

Alexa, Evan, Sheila, Jeff, Nic, Lisa

The plan for tonight was to try again the CARM offset reduction with the DRMI locked on 3f as it was done  a few nights ago . 

However, sadly, we couldn't really stably lock the arms on green by engaging ALS DIFF (feed-back to the ETMs). 

Nothing was (at least intentionally) changed with respect to the "nominal" configuration which has worked in the past. 

In the process of collecting and analyzing several lock losses, we identified the following list of problems/action items:

 * L2P for ETMY is significantly worse than for ETMX, we should fix this: as soon as the differential feed-back to the ETMs is engaged, the ETMY green light fluctuates consistently with PIT fluctuations as seen by the optical lever. This effect was really bad in the afternoon (30% power fluctuations; it got somehow better later in the evening); 

 * ringing up of the 13 Hz ETMY roll mode (again, see Kiwamu's entry): Nic tried to damp this mode by using optical lever PIT as error signal and pushing on L2 PIT, but that didn't work. We will try tomorrow to use the  LLO strategy  by using ALS DIFF;

 * at least once we lose lock because of a 3Hz oscillation in the ESD drive (we should remeasure the cross over L1/L3).

While trying to debug the ALS, we did some work on the DRMI to investigate the tricky demod phase business (see  Evan's entry).

Comments related to this report

alexan.staley@LIGO.ORG - 10:34, Tuesday 04 November 2014 (14829)

Link

We had tried feeding back only to ETMX ESD, to remove the large 13 Hz peak in the ALS DIFF spectra. We had done this in the past, but we could not get it to work. At one point, I also tried adjusting the L3 LOCK L gain in case the ESD charge had changed the crossover. However, not surprisingly this did not make a difference since the ALS DIFF spectra did not show any gain peaking at the crossover frequency.

lisa.barsotti@LIGO.ORG - 20:47, Tuesday 04 November 2014 (14848)ISC, SEI

Link

These are some plots which show the problem described in this entry (13 Hz roll mode oscillation and 3 Hz loop oscillation in bad alignment state, L2P filters worse for ETMY than ETMY). It might be worth checking if the ground / ISI motion was somehow higher than usual last nigh for the arm cavity optics.

P.S.: In the process of doing some lock loss analysis, I realized that our new awesome lock loss tool  didn't like empty lines in the channel configuration file. I think this explains while Sheila et al have been observing unexplained script failures when trying to add more channels (by the way, the max number of channel per file is 20). Nic fixed this problem in this way, now it works well.


def load_channel_list(path):
    channels = []
    with sys.stdin if path == '-' else open(path, 'r') as f:
        for line in f:
            # skip empty lines
            if line.isspace():
                continue
            channels.append(line.strip())
    return channels

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