J. Kissel, M. Evans

Forgive me while I catch you up to where we are.

Here's some data collected over the course of these SUS's lifetimes thus far. An a priori thanks goes to J. Garcia for taking most of this data!

I collect it all in one place, with the data shown in the mindset of the discussion of why there's so much excess motion in Pitch (during ambient times). I'll show more plots later that show that it's actually Longitudinal that's going nuts, but ... we'll get there.

Remember that both ETMY and ITMY have the same exact filters with the same exact gains.


For now: check out the attached. We will find out that (1) is more useful than (2).
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(1) I show a collection of data that is representative of the current situtation, comparing damping loops ON vs. OFF (see allquads_120628_H2SUS_DampingComp_ALLM0_ZOOMED_TFs.pdf). From this plot, we immediately notice the following:

- L is basically undamped for both SUS, especially its low frequency modes (where the dominant RMS motion lies)
- P is totally squashed (over-damped), especially the higher frequency modes
- T, R, V, and Y could maybe use a little more juice, but otherwise look OK -- but even in these DOFs, the lowest frequency modes are poorly damped

These particular filters were designed for the LASTI QUAD, with the gains copied and pasted without really looking at anything more than the ring down time, and (they haven't [changed/been tuned] since Brett's QUAD at LASTI  4 years ago, and therefore what gains were in place in March are still in place now). 

(2) Then, just because cross-coupling came up in conversation, I show the "detail" plots for each of the damped data sets. In particular, take a look at the cross-coupling plots (pgs 7-19) to get a direct measurement of the cross coupling between various degrees of freedom. Note that I've added the Y to L / L to Y plot (pg 13), which is not normally shown because it's not a physically expected cross-coupling. Why? Because we were at one point confused as to whether the excess motion was in Pitch or Yaw. I think, because of the spectra shown yesterday, now we're reasonably convinced that the excess motion during quiescent times is Pitch.

It's admittedly quite difficult to discern and information from these plots, because they're in all sorts of different units... but you can eye-ball it, and see that what cross-coupling does exist is reasonably well below the "diagonal" terms of the transfer function. On the to-do list: make these plots more readable by [converting them into/using] the conversion from rad to m (either modeled or measured).

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I'll post a separate log with what I think is going on, with better data to prove it, but I'll say here just in case people are impatient:

- L is totally undamped, both in L and P. The tons of excess motion seen in P at 0.43 and 1.0 Hz are L modes, that, because of fundamental cross coupling are showing up a lot in P. As of yet, we only have a good measure of the test mass P, since we don't have any cavities to measure the L. 
- Because we're overdamping P so much, when those who saw only pitch increased the P gain, the loop went unstable, so we couldn't solve the problem directly.
- From the looks of the open loop gain plots (which will be shown in a separate log, where I'll spell out the problem and solution in greater detail) my proposed "quick fix" solution:
    Decrease the P gain by 3.
    Increase the L gain by 10.
See if that works / helps.
    

OK. I wanna show the open loop plots, so lemme get this up and out, so I can start working on that aLOG.

Just a heads up: while y'all are asleep, I'muna gunna take some active measurements of ETMY, and perhaps gather some quiescent spectra of the TOP stage of TMSY while those are running. I hope to be done in 2 hours, starting from 9:30a ET, 6:30a PT. I have reserved this amount of time on the CDS reserve systems MEDM as well. Please, don't hesitate to call if you need me (617 452 3605) to stop before hand -- otherwise, consider me to be done at 11:30 ET, or 8:30a PT.

It's a shoddy lock, it only lasts for maybe 0.5 sec or so and unlocks, and after 0.5 sec or so it locks again, and this lock/unlock cycle is perfectly in sync with the alignment fluctuation, but it locks nevertheless!

The alignment is not that great, but when it locks we can see a very weak 00-mode spot on the ETM surface at the center of the mirror. Right before it unlocks, the spot shifts in PIT (so my assessment about YAW being a problem might have been wrong).

The real breakthrough was to lock the PLL. You would think that the PLL doesn't matter that much if you lock the laser to the arm, but in reality the frequency noise of Prometheus is so big that it masks things badly. Higher order mode peaks were there but indistinguishable from each other and the demod signal looked like a hopeless random noise hell masking the peaks. As soon as the Beckhoff model was fixed (I don't know why it broke in the first place) and we locked the PLL, we were able to see multiple resonances clearly.

After Jax and Elli somewhat refined the alignment, we turned the PDH lock loop on, and with some tweaking in the gain and sign I was able to find the beam spot on the ETM.

The DC level of the reflected light on the PDH PD is still fluctuating by a large amount, and we confirmed that the fluctuation is NOT from the clipping on the diode by using a power meter in front of the diode. It's not clear where the clipping is happening, it might be the Faraday, or upstream. I'll measure the power fluctuation in the Hartman sensor path tomorrow.

This is good enough of a victory for today.

(corey, jim)

Dial Indicator Install (this work was on Tues)

Dial Indicators used to monitor the HAM3 ISI/HEPI system are roughly in place.  This hardware should not be touched/bumped as it will be used to monitor and ultimately help position the HAM3 ISI. 

Cabling (this work started Wed)

In-Vac Cabling for HAM3ISI is mapped out according to D1002874.  Since Septum work finished up this afternoon, I started running Corner-1 cables to their feed through.  I was able to get all cables to the feedthrough (but opting NOT to screw down to feed-thru), EXCEPT for the H1 Actuator (it's 70" long cable was a foot or so too short!).  At any rate, I only ran cables for Corner-1.  I went to the other side of the chamber and separated Corner-3 cables from Corner-2 (since they're going to opposite sides of the Chamber).  Corner-3 looks like it will be the tough one to work on (due to feed-thru in middle of Chamber).

I labeled the dirty side of feedthroughs.

The dust monitor at location 15 in the LVEA was moved into the clean room over HAM 3 at around noon today. It is labeled 'R'. It seems to occasionally lose communication for a cycle or so. I'm not sure of the cause of this.

Greg, Jim, Hugo,

One could hear/feel both of the top mases resonate when being hit. We moved both masses and set them on a different set of washers (we used the same kind of washer as for the previous units). We adjusted the masses/wahsers position util we could not hear/feel the masses resonate anymore.

TF are running overnight. Hopefully, the unwanted resonances that were recorded in HF are now gone.

(corey, greg, jim)

Spring Pull Down Assys were removed

Actuators were installed; serial numbers noted here.

Payload was put on the Stage-1

• Keel with D071200:  (3)Type-6, (3)Type-4, & (6)Type-5
• 35kg put everywhere a GS13 will go except V1 (it's the only one we have and can install)
• A 600lb & 200 lb Leg Element mass on the Optics Table

Also started some cabling.

(On HAMISI#6, we helped Hugo, as needed)

M. Evans, P. Fritschel, J. Kissel ... I think even R. Weiss (call it the B Team)

In order to make some more quantitative statements about how much the test masses are moving, given that The A Team suggests that the test masses are "wobbling too much at about 1Hz," preventing cavity flashes, the B Team took some spectra of the top stage of each of the QUADs. Attached at the results.

There was some discussion that the excess motion was primarily in YAW, but the attached measurements (taken at 2012-06-27 2:00 UTC, which is late at night at LHO when no one was working) show that the most motion is in Pitch. That being said, there are times when Yaw is the larger motion -- we took an ETMY spectra (which we didn't capture because we were so freaked out by it) that we believed to be over today's local lunch time, and saw much more yaw, with resonances at almost exactly 0.4, 0.5, 0.6, and 0.7 Hz. We figured it was some sort of excitation; either an active measurement or outside-of-chamber excitations.

The RMS Pitch motion for both test masses at this time is roughly 0.5-0.7 microradians at 2012-06-27 2:00 UTC.

Remember, this is a measure of the motion at the TOP mass, and NOT a direct measure of test mass motion...

We can't yet make any further statements about the *source* of this excess motion (i.e. why is Pitch so much larger than Yaw). Stay tuned.

Details
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The xmls (of the same name) can be found here:
SusSVN = /ligo/svncommon/SusSVN/sus/trunk/;
${SusSVN}/QUAD/H2/?TMY/SAGM0/Data/

The calibration used for each of the channels is the same (thanks to dividing the rotation degrees of freedom by the lever arm, which is encoded into the OSEM2EUL matrix):

calibration = 1 / (BOSEM sensitivity [A/m] * SatAmp Transimpedance [V/A] * ADC calibration [ct/V])
            = 1 / (65e-3 [A/m] * 240e3 [V/A] * 2^16/40 [ct/V]) 
            = 3.9e-8 [m/ct]

Greg, Hugo

HAM-ISI horizontal GS13 Pod #68 was shiped to us dirty. It was opened here at LHO so the Pod could be cleaned. Once the pod was cleaned, the instrument was set back in the pod and tested this morning. HAM-ISI horizontal GS13 Pod #68 is still functional (Huddle test attached).

Next step, leak checking.

Preparation of Xend for install work continued yesterday. The retrofit of the iLIGO cleanroom was completed. Gerardo check on the remaining OpLev Pylon near BSC9. 

John, Hugh, Bubba and I agreed on path toward installation of the SEI support tubes, bellows and table. Please see list below. 

1. Remove septum at HAM3/Inspect for identified leak/-Apollo-Cleanroom in place/Kyle worked on this yesterday
2. Test septum at HAM5/6-Kyle-Cleanroom in place
3. Move ion pump from HAM5 to HAM6-Kyle-Cleanroom in place/Kyle worked on this yesterday
4. Install all possible feedthroughs on BSC1/2/3 and HAM4/5/6; blank off as needed-Apollo-Appropriate purge needed/Hugh is working on this	
5. Install support tubes, support table and bellows per E980268 at HAM6-SEI/Apollo-Cleanroom in place
6. Pump down and leak check volume-Kyle/Gerardo/John-No cleanroom needed

Summary:

The beam was likely very close to the right edge of ETMY since Friday, and this was due to the fact that we were only using TMS angle for the input beam pointing. We fixed this problem by using QPD servo and started over from scratch.

Now we're back to the point where we see some interference, and the good news is that the demod signal is much bigger than before (1V pp). Also we're seeing some change in the reflected DC power due to interference, unlike yesterday.

We still seem to be getting ultra higher order modes all over the place, and we don't see anything on the camera, so we need to refine alignment tomorrow.

The ETM and ITM are wobbling too much at about 1Hz, though. Due to this, the reflected beam seems to be clipped by either the Faraday aperture or the PDH diode aperture, and as a result the DC level of the PDH diode is changing by 30 to 50% constantly. This is not an interference effect (it changes even if you misalign ITM).

Also today the CM board A was not working at all. No output, fast and slow, regardless of the Beckhoff setting.

Alignment details:

When we started playing around with the alignment today, the demod output was the biggest when some light blob was hitting the right cage  bar of ETMY.  We tried many things but we always got back to this position. The likely cause of this is the fact that we only used TMS for initial pointing.

Since we initially only used the TMS angle to point the injection to the center of ITMY without using the PZTs on the ALS table, and since we needed to rotate the TMS so much, actually the ALS beam was falling off of one of the green QPDs. This means that there was a very high chance that the beam is not going through the center of the TMS primary.

Elli and I finished the QPD servo (a servo that uses PZT-driven steering mirrors so the beam from the ALS table is centered on two in-vac QPDs on the TMS) quickly so we didn't have to worry about QPDs. See Elli's alog entry.

After this, of course the pointing of TMS changed, so we started over by first aligning the TMS (with QPD servo on) to the center of the ITMY using baffle diodes, then aligning ITMY to the center of the ETMY using cage bars, then aligning ETMY to center the second beam on ITMY using baffle diodes.

Now we're getting much larger demod signal than before, and we can see that something is going on in the DC level (that is different from the clipping). And we don't see any light blob on the cage bars, so we know that the thing is not close to the edge any more. That's as far as we got today.

(corey, greg, jim)

HAM7ISI Springs have been installed, pulled-down, and Spring Safety hardware is in place.  Did a first run through on the Optics Table to pull out any broken/loose tangs.  The Optics Table can be installed tomorrow.  At this point, I was able to note quite a few serial numbers (s/n) while they were easily viewable.  Here are some of them:

Springs

(where the Tip is associated with each Corner;  i.e. a Spring which is bolted down to a Spring Post of Corner-3 actually has its Tip in the Corner-1 area)

• 1:  030
• 2: 041
• 3:  045

Spring Posts

• 1:  031
• 2:  017
• 3:  032

Flexures

• 1:  041
• 2:  046
• 3:  040

Stage0:  014

Stage1:  010

Optics Table:  009

[Stuart A, Mark B, Jeff B, Vern S]

Whilst last visiting LHO I was able to quickly make some open-light and one dimensional responsivity measurements using three dirty AOSEMs and a test-jig kindly loaned from Mark. The test-jig has previously been used for characterising BOSEMs, and so had to be reconfigured to accommodate the smaller AOSEM coilformer. More importantly, rather than using the rectangular flag employed for the BOSEM, a ~1" long x ~2 mm diameter cylindrical flag was provided by Jeff B.

A UK production Satellite Box (D0901284) was connected up to the AOSEM under test using a dirty in-vacuum quadrapuss harness (D1000234). The Satellite Box was provided with it's required supply lines via a Satellite Box Testing Board (courtesy of Filiberto). For electronics set-up please see image 504 below. A DVM was used to read-out the amplified voltage signal via the diagnostics port (J4) on the Satellite Box (Pins 9 and 28). Note that, the production Satellite Boxes have a input gain of 242k V/A or 0.242 µA/V (double-ended).

Image 506 (below) shows the opto-mechanical set-up for the reconfigured test-jig, including the translation stages and flag assembly. For these tests, only the responsivity is sought, and therefore a one-dimensional characterisation along the sensitive axis is adequate.

When connected up to the Satellite Box, each of the AOSEMs had the following open-light differential voltage measurements:-

- Unit #1, open-light = 14.75 V (i.e. an open-light photo-current of ~61 µA). Corresponds to ~24k counts
- Unit #2, open-light = 10.14 V (i.e. an open-light photo-current of ~42 µA). Corresponds to ~17k counts
- Unit #3, open-light = 12.19 V (i.e. an open-light photo-current of ~50 µA). Corresponds to ~20k counts

Over a ~0.7 mm operating range, these AOSEMs were found to have the following responsivity (see plot below):-

- Unit #1, responsivity = 18784 V/m (i.e. 78 mA/m).
- Unit #2, responsivity = 13028 V/m (i.e. 54 mA/m).
- Unit #3, responsivity = 15721 V/m (i.e. 65 mA/m).

These responsivity results can be compared with the default value we have previously assumed of ~80 mA/m (see LLO aLog entry 2715).

To summarise, these measurements can be used to validate our assumption of using the AOSEM calibration factor of, 1/(80e-3 [A/m] * 240e3 [V/A] * (2^16)/40 [cts/V]) = 3.2e-8 [ct/m], is consistent for units with open-light counts above Jeff K's goal of 25k.