Jenne, Lisa, Stefan,
Still running at 40W, for 2h.
Tried to damp some PIs and go to low-noise.
- We successfully damped 15009Hz (ETMY) and 15542Hz (ETMY) (damp settings picture attached.)
- 15541Hz (ETMX) was ringing up.So we tried switching to ETMY and transition the ETMX coil driver to low noise.
- We successfully switch the coil drivers, but...
- We switched to ETMY, low noise, held lock for a while, but saturated the ETMY ESD with 20Hz noise from the ASC, as well as a 532.77Hz line, that we don't know the origin off. (PI?) (picture)
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Also, we realized that DTT is a bit too smart: The 64kHz channel H1:OMC-PI_DCPD_64KHZ_A_DQ can in principle look at PIs above the Nyquest through aliasing. However, since DTT only alows you to select a freqency about 10% below the Nyquist frequency, there is an effecive dead band where DTT cannot see PIs between ~29500Hz and ~36036Hz. The MATLAB script below produces a spectrum up to the Nyquist. Indeed, we found an elevated mode at 30018.3Hz, although it was not quite saturating.
MATLAB code to get spectrum up to Nyquist frequency:
addpath /ligo/svncommon/NbSVN/aligonoisebudget/trunk/Externals/SimulinkNb/Utils/
gwd = GWData();
gwd.make_kerberos_ready;
gwd.site_info(2).port = 31200;
gwd.site_info(2).server = 'nds.ligo-wa.caltech.edu';
H1.channels = {'H1:OMC-PI_DCPD_64KHZ_A_DQ'};
time_fetch = tconvert('26 Jun 2016 01:15:00');
[data, t, ~] = gwd.fetch(time_fetch, 1000, H1.channels);
Fs=4*16384;
pwelch(data,[],[],[],Fs)
[Lisa]
Attached is Jenne's PI knowledge, she also updated the PI wiki page.
This last 40W lock ended at June 26, 2.11 UTC while trying transitioning to low noise to damp the 15541 Hz ETMX PI.
The 532.7Hz matches the beat frequency between the 15541.9Hz ETMY and 15009.2Hz ETMY modes that were at very elevated amplitudes during this lock. 15541.9Hz appears to have been unstable ringing up with a time constant of 190 seconds, damping was engaged with a gain of 1000, so it may have been PI or being driven up, while the 15009Hz damped over the duration of the lock with someone actively changing the control gain. See the figures of 15540Hz and 15kHz mode group amplitudes over the last half hour.
There were two peaks ringing up in the unmonitorred region between 29000Hz and 32768Hz, one appearing in the OMC DCPD signals at 30551.09 and another at 31083.90. See third figure. The beat note between these two peaks is also around 532.7Hz. The connection can be seen in the fourth figure when the beginning of lock spectrum (green) is compared to the end of lock spectrum (blue). The largest green peak is the sensing harmonic of the 15009Hz mode. The largest blue peak is the first sensing harmonic of the 15541Hz mode. These mixing with the 532.7 produce the center frequency and the 31620Hz peak. There appears to be something else producing messy ~480Hz 'sidebands' on some of these peaks.
