Recall that we started writing the IFO ALignment slider values to an hourly burt such that we can easily grab-n-restore best alignment values - see alog 18799 from June 2.

The hourly burts are at:

/ligo/cds/lho/h1/burt/2015

under the appropriate date /h1ifoalignepics.snap

'Sorry that no one in the CR recalled this info from last month for you yesterday...

The ESD line is switched back to its original position at 538.1 Hz. SDF table is updated accordingly.

good to hear that the accumulators are holding well. I like your plan
-Brian

Error 4 = The cause was a user-mode read resulting in no page being found (also known as null pointer dereference)

Also added warnings for when the cameras and the frame grabbers are on.

I've commented out the HWS and frame grabber on warnings because we want to use them during commissioning.  We should uncomment this for the science run though.

Just adding some words, parroting what Elli told me: this temperature sensor (RTD) is nominally supposed to be on "the" viewport (HAM4? Some BSC? The Injection port for the laser? Dunno). This sensor is not mounted on the viewport currently, it's mounted on "the" chassis, which (I believe) resides in the TCS remote racks by HAM4. She's seen this in the past: even looking at this sensor wrong (my words, not hers) while you're cabling / electronics-ing near HAM4, this sensor trips. As she says, this was noticed and recovered by her before it became an issue with the IFO because recovery went much slower than anticipated.

If I understand correctly the sensor I think your talking about then yes this should be on the viewport (the BSC viewport which the laser is injected in). The viewport sensor though is an IR sensor, but for some parts of the wiring in the control box (and thus on the MEDM screen) the IR sensor and RTD sensor are wired in together making it hard to know which one caused the trip.  Its supposed to monitor scattered light coming off that viewport. It is very sensitive and can be affected by humans standing near it, light being shown onto it (one of the ways to set the trip level is to hold a lighter up to it ), maybe also heat from electronics, etc. So just sitting in the rack I am not at all surprised that it is tripping all the time and causing grief.

My suggestion is to try to get this installed on the viewport if you can, otherwise if you can’t and it really is causing problems all the time, there is a pot inside the control box which you can alter to change the level at which it trips.

Note that the manual alignment was done after everything was brought back to old numbers (MC1, MC2, MC3 using witness BOSEMs, PZT offset using the output of the PZT before the maintenance). Even though the PZT change was not huge (as seen in the MC REFL position), I cannot claim that the change was nothing.

Also, at first I was confused by the fact that the MC trans camera looks as if the beam is split (01 mode) even though MC is locked to 00. Kiwamu told me that the only way to make sure is to look at IFO cameras like IFO REFL and AS.

PSL FSS oscillation precluding IMC locking

It appears that FSS oscillation was wreaking havoc with the ISS and this was the cause of the IMC not locking.

Reducing the FSS Common gain to zero then bringing it back up to 26 dB stopped the oscillation, as seen on the "PZT  MON (FAST)" trend display on the PSL FSS screen. 

It the display shows a black region (rail to rail oscillation), then the FSS is oscillating.  In the nominal state, it should just show a think black horizontal line.

The FSS was tuned up this morning and is now operating as designed ~ 500 kHz UGF, 60 deg phase margin, no features (peaks) up to 5 MHz.  However, it may not be as robust against kicks from the IMC as it uses the FSS as its frequency actuator.

We did not take time this mornining to investigate the stability of the FAST/Pockels Cell crossover.  I was somewhat surprised to see the FAST gain at 5 dB.  It may be that the crossover is not stable.

We used to run the FAST gain at 15 dB.  Seems that it was turned down to 5 dB on April 15, 2015.

Next opportunity will check the crossover by looking at the mixer monitor noise spectrum in the 1-50 kHz frequency range as we adjust the fast gain - optimize the tradeoff between FAST gain and noise peaking at the crossover.

JimW is generating a request to TJ to add an alarm for the FSS range to the Guardian.

FSS oscillation was fixed while I was tweaking the MC2 trans position. Before that, IMC locked to the correct mode but the IMC WFS ran away. 

So it seems like the alignment thing was a red herring.

The FSS went into oscillation again, after talking with RIck on the phone we turned the common gain down from 26dB to 23dB.  

We had a spectrum earlier in the night last night that had better low frequency sensitivity. One difference between this and later locks was the BS coil driver switching, the DARM offset could also have been different but I am not sure.  

Sort of unsatisfying (because they're not the real deal, or their incomplete) FEA results for the test mass body modes can be found here:
http://www.ligo.caltech.edu/~coyne/AL/COC/AL_COC.htm (Only for a right cylinder)
and here
T1400738 (only shows the modes which are likely to be parametrically unstable).

A quick glance through the above doesn't show anything at or near that frequency (including abs(16384 - FEA results)). 

I've yet to see FEA analysis of non-test-mass optics, but I've been told that Ed Daw and/or Norna/Calum's summer students on working on it. The best I've seen on that is the ancient 2004 document for the Beam Splitter,
T040232
which is where we colloquialy get the frequency of the beam splitter's butterfly mode, which was done by eyeballing the current beam splitter's parameter location Figure 2. (But, the modeled dimensions are wrong, and the wording is confusing on whether the listed frequencies are from the model with flats or not.)

It appears to be a 10th order violin mode on EY.

It is damped with a 1 Hz wide butterworth (unity gain in the passband), a +100 dB filter, and a gain of -30. No rotation needed.

Jeff

As you notes there is some data in the links you already included and we have started to fill in the blanks. Refer to https://dcc.ligo.org/T1500376-v1. When we talk I (we) can complete.

Calum

For reference, with a combination of Slawek's (T1400738) and Calum's (T1500376) FEA models, and Calum's video of the test mass internal mode shapes (T1500376), we expect to find the drumhead mode around 8029 Hz, the x-polarized butterfly mode around 5821 Hz, and the +-polarized butterfly mode around 5935 Hz (using Slawek's values for the mode frequencies). The next two modes (at 8102 Hz and 8156 Hz) do not involve distortion of the test mass face in the direction of the beamline.

My 24 hours have passed, but the first sentence should read "At some point today the roll mode on EX..."

Suppose that the beam is at (X, Y)=R(cos(theta), sin(theta)) on the mirror where R=0 is the center of roll rotation and theta=0 is the horizontal line crossing the center. Though the COG is somewhat lower than the mirror center due to wedge, R should be more or less equal to the radial distance of the beam from the center of  the mirror.

Mirror thickness at this position is 

T(R, theta) ~ -R*sin(theta)*w + T0

where T0 is the thickness at the center and w is the wedge in radians that is about 0.08deg=1.4mrad for all ITMs and ETMs.

Roll changes the thickness by adding some small angle d_theta to theta: dT=-R*cos(theta)*w*d_theta=-X*w*d_theta.

When the rolling plane is in the middle of the front and the back surface, the light see the half of the total thickness change, so the roll-to-length coupling coefficient should be

length/roll ~ |dT/d_theta /2| = X*w/2

= (X/5mm) * 3.5E-6  [m/rad].

For Matt's estimate of 3E-7 m/rad to hold true, the horizontal centering should be 0.5mm or so, which is pretty good but not outrageously so.

What this probably means is that Matt's estimate about the roll angle was reasonable, as in it cannot be off by that much. A factor of something, not orders of magnitude.

[edit on Jul 15] However, if the roll plane is parallel to the local gravity, the above doesn't hold true.

In this case, w/2 is replaced by the angle between the local gravity and LIGO global vertical: 8urad for LHO EX, 639urad for EY, -619urad for IX and 12urad for IY (https://alog.ligo-wa.caltech.edu/aLOG/index.php?callRep=14876):

 length/roll(EX)~ X*8urad = (X/5mm) * 4e-8 [m/rad],

 length/roll(EY)~ X*619urad = (X/5mm) * 3E-6 [m/rad].

For EX and IY, that's two orders of magnitude smaller than what I showed yesterday, though EY and IX it didn't change.

It seems that we need a suspension model to find out the actual rotation plane.