Kiwamu found that MICH feedback signal suddenly becomes quiet about a second before the lock loss of PRMI.

Attached shows that this is due to the output of the M3 ISCINF filter (observed by the input of M3 lock filter, top right) creeping up and hitting the 5e5 count output limit.

Stefan remembers that this limit was necessary for lock acquisition to prevent one of OSEMs from going out of range and causing a bad alignment disturbance. Once the lock is acquired, then, the logical thing is to increase the limit or disable it.

Also, though the LSC feedback goes to the top stage, it seems like no optimization was done, M1 Lock filter only has 0.01 Hz pole. It should be possible to make a better blending to relieve M2 stage.

• Laser Safe (probably stay for most of day)
• HAM5:  SR3  went in yesterday, TODAY:  elec & alignment today, table payload
• TCS:  off table proj yesterday look good;  Hartman today (no Laser Hazard)
• Baffle work possibly going on (issue with possible use of 3IFO parts)
• ESD EY work
• Staging SEI assy/testing ongoing

No restarts reported.

the alingment offsets are off on both TMSs, and Arnaud's measurement is started.

Sheila, Kiwamu,

The goal tonight was to add TOP and UIM of ETMY to the DARM actuator in order to increase the control bandwidth. This worked fine and the UGF was pushed a bit higher and it is now 4 Hz.

As Sheila reported on alog 11787, we prepared ETMY. So we started using ETMY in addition to ETMX. Since ETMY's ESD is not ready yet, we used only TOP and UIM of ETMY. This helped the DAC range of the UIM stage and therefore we could push the UGF a bit higher. At the end, we ended up a UGF of about 4 Hz. The infrared RMS is now about 90 Hz. We didn't redesign the low-frequency boost this time as our target was to have a higher UGF. The attached is the ALS diff spectrum (shown in red), with the spectra from yesterday for comparison. You can see that the noise is suppressed below 4 Hz. Currently the UGF is limited by UIM and TST which saturate at high frequencies.

Arnaud, Sheila, Kiwamu,
We copied the plant inversion filters from ETMX UIM to ETMY, and ran a transfer function to test it.  The results are saved in /ligo/home/sheila.dwyer/ALS/HIFOXY/Y_UIM.xml

I imported the measurement into foton, and compared it to the low pass blend (which was on when I took the measurement) and a pedulum at 1 Hz with a Q of 1, which is what our plant is supposed to be with the inversion.  They match pretty well, screenshot attached.  Since our inversion of the ETMX top mass and the UIm match for the resonances that are common, we just copied the ETMX top mass plant inversion to ETMY and decided to try this out.

Also, we tried using an offset for the ESD drives, which should give us a bit more range.  With the bias at 125000cnts, I added an offset of -51777 counts to each of the quadrants, following the math in T1400321.  At 4 Hz, we measured a factor of 1.77 more gain , at 6 Hz 1.6 more gain. 

This time it was probably our fault, kicking the suspension

We don't know why this tripped, there is a spike in the PEM 1-3Hz FOM. 

Yesterday night, I tried to run SR2 M2-M2 and M3-M3 (lower stages) in chamber transfer functions after the osems were centered on wednesday. Although both M2 and M3 watchdogs tripped during the measurement, so I am running it again tonight. (This time, I decreased the drive and increased the watchdog threshold).

(David H, Thomas V, Greg G, Alasitair H, Matt H)

Well if yesterday was "The Empire strikes back", today was "Return of the Jedi" and the good guys had a win.

You may remember from this mornings alog that we had been having a few troubles with the alignment of TCSx.

After a brainstorming meeting with Aidan the decision was made to ignore the path defined by the flipper mirrors having problems with (what is supposed to be the central heating path) and align what is the annular heating path (which only uses mirrors) to the output beam splitter and through the irises defining the beam path up the periscope, into the chamber and onto the CP. We will then use the central heating mask instead of the annular heating mask (in the location the annular heating mask would be ), and thus temporarily turn the annular heating beam path into the central heating beam path.

The first step we did was to use a HeNe beam to adjust the output beam splitter and the beamsplitter just before the on table power meter so that the front and back reflections were in the same plane (they werent installed that way). We then went all the way back to the first large gold mirror after the polarisers (which are after the beckhoff controlled HWP) and mirror by mirror in the annular (now temporary central heating) beam path made sure that they were set so that the beam was in a plane with the table at a height of 4 inches.

Once the beam got to the output beamsplittler, the beamsplitter and the last gold mirror before the periscope was used to align the beam to the irises that we had defined to put the beam correctly into the chamber. I roughly made sure that the beam transmitted through the output beam splitter was going to the on table power meter, and the beam path that would go to the FLIR camera was beam blocked as I no longer no that the beam path is correct (I removed the lens there so that needs to be reinstalled).

A HeNe beam was setup to trace through the irises (heading in direction of going towards the periscope). Once the optic beam path had been re-established I swapped out the 1" irises we had (which had clipping on the beam occuring) for 2" irises. We then inserted a 2 inch gold mirror into the path between the 2 irises and sent the HeNe beam down towards HAM5 and the target that we had set up at a distance that mimicks where the CP would be. An "X" was marked on the card and the HeNe aligned to this "X' and the FLIR camera setup so that this spot was centered on the camera.

HeNe beam removed and the CO2 beam projected onto the target. Good to see that the CO2 beam appears to hit exaclty where the HeNe indicated it should (lets out sigh of relief)....so this should mean that the CO2 beam should go into the chamber and onto the CP correctly. Whilst doing the projection we also placed in the central heating mask (it has been rotated 90 degrees so that the rejected beam is directed towards the edge of the table not the center of the table as indicated in the drawing because the beam dump would not fit) and used the projection to help center the mask. Worked well...and success was declared. I dont have the pics of the projection, but pics were taken.

All beams have beam blocked so that if wanted to run the laser around the clock we can (we wont be until given the go ahead by the local LSO). A bugzilla list (Bug 868...https://services.ligo-wa.caltech.edu/integrationissues/show_bug.cgi?id=868) has been made of the tasks that can think of that are still outstanding/need to be done for this table.

One concern: A couple times today we had further issues with the HWP. We would dial up an angle for it to go to, the MEDM screens would indicae that the HWP was at the angle we had requested yet it physically was at a different angle. I have asked Thomas to look into tomorrow as this is a concern.

Pic:

TCScurrentalignmentstanding shows a quick summary of whats aligned and what still needs to be done

J. Kissel, for K. Izumi, and S. Ballmer

Now that Stefan and Kiwamu have the first reasonably successful evening with ALS DIFF (see LHO aLOG 11759), I wanted to make an assessment of how their filter design ended up compared to my original design (see LHO aLOG 11676). I attach the frequency dependence of each stage, divided into the distribution filters, plant inversion filters. Then I attach total path (with gain filters included).

There's still a little bit of confusion about the distribution of over-all gain of the system i.e 
- the ALS DIFF PLL's error signal, which serves as the DIFF sensor, had a some calibration filters turned OFF for some reason, leaving the output in [V] instead of the planned [um]
- converting the overall SUS actuator gain to be [ct_{TST DAC} / um_{ISC IN}] has not yet been installed, leaving the actuator gain still in [ct_{TST DAC} / ct_{ISC IN}]
so it would take some work to understand the over gain of the loop and/or with which UGF Stefan and Kiwamu ended up. 

Contrasting the creation of the super actuator between SB + KI vs. mine:
- They've used the blend filters I've installed identically, so no mystery there.
- For the plant inversion, they've diverted from my design in two ways:
     - A much more accurate inversion of the resonant forest for each stage, resulting in high Q filters with long impulse responses -- the price paid for phase accuracy
     - They've inverted the resonant forest for the TST stage, creating a resultant very high-Q resonant feature in the inversion filter to balance the zero in the TST to TST plant at 0.87 [Hz]. I did not invert the TST stage, and managed to scrounge up enough phase for the *model* to be stable (but this means little compared with reality.)
     - Instead, they've turned the TST (and each subsequent stage above) into a 1 [Hz], Q = 1, single pendulum.

Unfortunately, since the ALS DIFF lock isn't too terribly stable, we can't get more than a few frequency data points to confirm stability, but we'll try again tonight. 

I think the reasons why they were saturating with the overall unity gain frequency only at ~1.2 [Hz] (as opposed to my model of 15 [Hz]) is because of the mystery factor of 4 missing from the TST mass drive (see LHO aLOG 11676), and because we still don't have ETMY up and running because of ESD woes (yet to be aLOGged) -- i.e. a factor of 8 in drive strength that's missing. According to all the modeling done thus far and now a measurement, we really need it!

Next up -- find the factor of four in the ESD and fix it!

-------------------
Relevant Configuration Record (gain = 1.0 if not mentioned):
H1:ALS-C_DIFF_PLL_CTRL
FM3 "antiVCO"
FM4 "cnts2V"
G = 10.0

(LSC Input Matrix element = 1.0)

H1:LSC-DARM_IN
FM1 "ALSDIFF"
FM2 "invPlant"
FM3 "Boost"
G = 10.0

(LSC Output Matrix element = 1.0)

H1:SUS-ETMX_L3_ISCINF_L (these were the extra last minute filters added to try and manipulate the overall super-actuator from saturating)
FM6 "p5z50"
FM7 "p5z50"

H1:SUS-ETMX_M0_LOCK_L
FM1 "invL2L1" (part one of plant inversion filter)
FM2 "invL2L2" (part two of plant inversion filter)
FM3 "top/tst" (gain only filter to compensate for the gain ratio)

FM5 "blend LP"

H1:SUS-ETMX_L1_LOCK_L
FM6 "invL2LNEW" (part one of plant inversion filter)
FM7 "patch" (part two of plant inversion filter)
FM8 "LISOfit" (part three of plant inversion filter)
FM9 "uim/tst" (gain only filter to compensate for the gain ratio)

FM3 "blendHP" (UIM-TOP HP complement)
FM4 "blendLP" (UIM-TST LP complement)

H1:SUS-ETMX_L3_LOCK_L
FM6 "MatchedinvL2L" (part one of plant inversion filter)
FM7 "patch" (part two of plant inversion filter)

FM4 "blendHP-M0" (TST-TOP HP complement)
FM5 "blendHP-L1" (TST-UIM HP complement)

H1:SUS-ETMX_L3_LOCK_BIAS_INMON = 125000 [cts]
No linearization algorithm installed.

Stefan, Kiwamu,

We spent this afternoon to continue working on the PRMI lock. After an adjustment of the MICH gain, it became able to reliably lock.

Even though it stays locked for typically 2 minutes or so, it looses the lock for unknown reason.

(The gain adjustment)

To get the PRMI stably locked, the MICH gain had to be significantly reduced. The original gain setting by guardian was 16, but this was too big to have a UGF at around 10 Hz. At the end of the exercise, the gain ended up to be 2. I don't understand why it needs to be such low. Anyway, once the gain was adjusted, it locked repeatedly and no gain peaking or saturation were found. Good. I didn't change the PRCL gain at all -- it was fine with the original gain of 1.4. The attached is a screen shot of the PRMI buildup in striptool. The power build up observed by POP18 was 70 at highest and typically between 40 and 60. This is almost the same as before (see alog 10472). This corresponds to a power recycling gain of approximately 6.

(Lock losses)

For some reason, it typically unlocks after a couple of minutes. According to the feedback as well as error signals, it is not due to servo instability. Also I didn't see a sign of saturation in PRM, PR2 or BS. A funny thing is that the MICH loop acts odd before it looses lock. The attached below is time series of various feedback signals when the PRMI lost lock. It unlocked at t=29 sec. As clearly seen in the plot, the MICH feedback suddenly became quiet at t=28sec -- it seems as if a low-pass filter was enabled. I looked into two lock loss events and both events exhibited the same behavior. I believe that this is the last obstacle which prevents us from robust lock. This needs to be fixed.

There are currently 364 unmonitored conlog channels after I updated the list this afternoon. These are all ASC channels and appear to be due to the fact that a make install has been done without a restart. Since we expect a restart soon, I will leave the conlog channel list as is.

(Alexa, Daniel)

Continuing yesterdays work we locked on PRX and installed the beampspitter in the POP path in front of POPAIR_A. The beam was very weak and we had some fun aligning it. We needed an additional lens (ROC 500mm) to keep the beam small. After the beam combiner we measured 170nW of power. Another short focal length lens was installed after the combiner to focus the beam down. We are still missing a photodetector.

Re-did measurements from yesterday.  Daniel brought up point about green light leaking into IR measurements and vice versa.  So addressed this.

IR Laser Light:  Look At filters to attenuate IR

Here we wanted to see which filter was best for viewing the GREEN light, so we wanted the filter which passed green & cut out IR.  With the Prometheus laser we used its IR light.  To make sure there was no Green light, we dropped in a Hoya R72 filter (to remove any Green light from laser).  Then we looked at the filters I bought .  So this is what we had:

• IR light from laser ONLY = 420mW
• Hoya R72 in path = 414mW
• BP550 (+ Hoya) = 3.11mW---best filter for viewing GREEN light
• lp550 (+ Hoya) = 423mW
• lp920 (+ Hoya) = 431mW
• bn532 (+ Hoya) = 167mW

The BP550 is OK, but Daniel says the OD of this filter may be low and we should look for a Schott glass filter (order of 4mm thick, similar to our old iLIGO glasses).  Either that or we can see what a couple of the BP 550s filters look like in series.

GREEN Laser Light:  Look At filters to attenuate Green

Here we want to see which filter is best for viewing IR light, so we want a filter which passes IR & attenuates Green.  With the Prometheus laser we had green light.  To make sure there is no IR light leaking in, we dropped an iLIGO goggle in the beam path as a filter.

• Only Green light = 20.2 mW
• iLIGO Glasses in path = 13.18 mW
• iLIGO + Hoya R72 = less than 5nW
• LP550 (+iLIGO glass) = 39.3 uW
• LP920 (+iLIGO glass) = less than 5nW
• BN532 (+iLIGO glass) = 7.45 mW
• BP550(+iLIGO glass) =8.03 mW

LP 920 may be good...maybe have two in series?