A story about minor disasters, and crises averted:
Once upon a time, in a cleanroom not so far away..... there lived an optic. To preserve anonymity, we shall call him "ETMU05". This optic had a rough day. When removing the grippers from the magnet-to-optic fixture, 4 out of 6 magnets broke off the dumbbells (the dumbbells were still securely glued to the optic...these had come out of the same batch that had problems last week, same problem). The remaining 2, LL and LR, were sadly of the same polarity. This is bad, because it means that the "humans" taking care of "ETMU05" didn't check the polarity of the face magnets properly, and ensure that they were laid out in an every-other pattern (LL and UR having the same polarity, and LR and UL having the opposite). So, the humans removed all magnets and dumbbells from ETMU05. All remaining glue was carefully scrubbed off the surfaces of ETMU05 using lens paper and acetone, and the magnets and dumbbells were sonicated in acetone, scrubbed with a lint-free wipe, sonicated again, and then scrubbed again to remove the glue. ETMU05 had a nice cleansing, and was drag wiped on both the AR and HR surfaces with acetone and iso. ETMU05 is now on vacation in a nice little foil hut.
His friend, (let's call him ETMU07) had a set of magnets (with polarities carefully confirmed) glued to him. The cleaned magnets and dumbbells removed from ETMU05 were reglued to their dumbbells, and should be dry by tomorrow.
.....And then they lived happily ever after. The End.
The revised schedule / status table:
ETMU07 had its wire winched to the correct height, was balanced, standoff glued. Can be ready for going into the oven tomorrow, if an oven is available. (One of Bob's ovens has a leak, so he's down an oven, which puts everything behind schedule. We may not be able to get anything into the oven until Monday).
ETMU05 had magnets glued to the optic. Hopefully tomorrow we will winch the wire and balance the optic, and glue the standoff, and be ready to go into the oven on Monday.
The spring plungers were sonicated, but have not yet been baked. I told Daphen that we'd like the optics baked first, so that we can get ETMX in the chamber ASAP, and then the spring plungers as soon as possible so that we can install ETMY and put the OSEMs in.
The updated status table:
We removed ETMU07 from the suspension tower, after confirming that the balance was still good. Bob put it in the oven to bake over the weekend. The spring plungers and our spare magnets are all in there as well.
I tried to remove the grippers from ETMU05, and when I did, both side dumbbells came off of the optic. Unfortunately, I was working on getting channels into the DAQ, so I did not clean and reglue ETMU05 today. However Joe told me that we don't have any ETMY controls as yet, and we're not going to do Yarm locking (probably) in the next week or so, so this doesn't really set any schedules back.
The cleaning of ETMU05 will be tricky. Getting the residual glue off of the optic will be fine, but for the dumbbells, we'd like to clean the glue off of the end of the dumbbells using a lint free wipe soaked in acetone, but we don't want to get any acetone in the magnet-to-dumbbell joint, and we don't want to break the magnet-to-dumbbell joint. So we'll have to be very careful when doing this cleaning.
The Status Table:
ETMU05 : Gluing Side magnets back on to the optic.
The following steps taken in this process:
1) The two magnet+dumbell units which had come loose from the optic needed to be cleaned. A lint free wipe was placed on the table top and a few cc of acetone was poured on to it. The free end of the dumbbell was then scrubbed on this wipe till the surface regained its shine. The dumbell was held at its narrow part with a forceps to avoid any strain on the magnet-dumbbell joint.
2) The optic was then removed from its gluing fixture (by loosening only one of the three retaining screws) and placed in an Al ring. The glue left behind by the side magnets was scrubbed off with a optical tissue wetted with Acetone.
3) The optic was returned to the gluing fixture. The position of the optic was checked by inserting the brass portion of the gripper and making sure that the face magnets are centered in it [Jenne doubled checked to be sure we got everything right].
4) The side magnets were glued on and the optic in the fixture has been placed in the foil-house.
If all goes well we will be able to balance the ETMU05 and give it to Bob for baking.
ETMU07 : It is still in the oven and we need to ask Bob to take out. It will be available for installation in the 40m tomorrow.
Last night I found that the response of ITMX against the angle offsets were strage.
Eventually I found a loose connection at the feedthrough connectors of ITMX chamber.
So I pushed the connector hard, and then ITMX successfully became normal.
It looked like someone had accidentally kicked the cable during some works.
This bad connection had made unacceptable offsets in the OSEM readout, but now they seem fine.
We put ETMX back in its tower, and confirmed its balance. It might be pointing a teensy bit upward, but it is way less than the DC pointing offset we see when we put the OSEMs in the towers (since the PDs and LEDs have some magnetic bits to them).
Discussions are ongoing as to where the ETM should sit on its table, but we'll probably toss it into the chamber later this evening.
I took ETMY out of the magnet gluing fixture, and put it in a ring, in the foil house. It is ready to have the wire winched and get balanced at our convenience.
[Kiwamu, Jenne, Koji, Suresh]
The following steps in this process were completed.
1) Secured the current ETMX (Old ETMY) with the earth quake stops.
2) Removed the OSEMs and noted the Sl no. of each and its position
3) Placed four clamps to mark the location of the current ETMX tower (Old ETMY's position on the table)
4) Moved the ETMX (Old ETMY) tower to the clean table flow bench. In the process the tower had to be tilted during removal because it was too tall to pass upright through the vacuum chamber port. It was scary but nothing went wrong.
5) Koji calculated the location of the new ETMX and told us that it should be placed on the north end of the table.
6) Moved the OSEM cables, counter balancing weights and the 'chopper' out of the way. Had to move some of the clamps securing the cables.
7) Moved the ETMU07 tower from the clean room to the ETMX table
8) Positioned the OSEMs as they were placed in the earlier tower and adjusted their position to the middle of the range of their shadow sensors. The four OSEMs on the face did not give us any trouble and were positioned as required. But the side OSEM could not be put in place. The magnet on the left side, which we are constrained to use since the tower is not designed to hold an OSEM on the right side, seems a little too low (by about a mm) and does not interrupt the light beam in the shadow sensor. The possible causes are
a) the optic is rotated. To check this we need to take the tower back to the clean room and check the location of the optic with the traveling microscope. If indeed it is rotated, this is easy to correct.
b) the magnet is not located at the correct place on the optic. This can also be checked on the clean room optical bench but the solution available immediately is to hold the OSEM askew to accommodate the magnet location. If time permits the magnet position can be corrected.
We have postponed the testing of the ETMU07 tower to 1st of Nov Dec.
We finished the installation of ETMX into the chamber.
In order to clear the issue of the side OSEM, we put a spacer such that the OSEM can tilt itself and accommodate the magnet.
Though we still don't fully understand why the side magnet is off from the center.
Anyway we are going to proceed with this ETMX and perform the REAL green locking.
(what we did)
- took the ETM tower out from the chamber, and brought it to the clean room again.
- checked the rotation of the ETM by using a microscope. It was pretty good.
The scribe lines at the both sides are at the same height within the diameter of the scribe line.
- checked the height of the ETM by measuring the vertical distance from the table top to the scribe line. This was also quite good.
The height is correctly 5.5 inch within the diameter of the scribe line.
- checked the magnet positions compared with the OSEM holder holes.
All the face magnets are a little bit off upward (approximately by 1mm or less).
The side magnet is off toward the AR surface by ~ 1-2mm.
(yesterday we thought it was off downward, but actually the height is good.)
- raised the position of the OSEM holder bar in order to correct the miscentering of the face magnets.
Now all the face magnets are well centered.
- brought the tower back to the chamber again
- installed the OSEMs
We put a folded piece of aluminum foil in between the hole and the side OSEM as a spacer.
- leveled the table and set the OSEMs to their mid positions.
- slided the tower to place
ETMU05 (ETMY) had its wire winched to the correct height, was balanced, and had the standoff glued. Since it's kind of like final exam week at Caltech, Suresh had his suspension exam today, and did most of this work himself, with me hanging around and watching.
As you can see in my almost entirely green table, all that is left to do with the whole suspensions project is bake the optic (hopefully Bob has time / space this week), and then stick it in the chamber! Hooray!!! (Can you tell I'm excited to not spend too much more time in the cleanroom?)
The ETMU05 has been removed from the suspension and put into the little foil house.
Before removing it I checked the position and pitch of the optic with reference to the table top.
Using the traveling microscope I checked the height of the scribe lines from the table top. They are at equal heights, centered on 5.5 inches, correct to about a quarter of the width of the scribe line.
The retro-reflection of the He-Ne laser beam is correct to within one diameter of the beam at a distance of about 1.5m. This is the reflection from the rear, AR coated, surface. The reflection from the front, HR coated, surface was down by about two diameters.
Jenne has checked with Bob and agreed on a date for baking the optic.
I am leaving ITMX and ETMX freely swinging, so that later I can take the spectra and diagonalize the input matrices.
Please don't restore the watchdogs until tomorrow morning.
The input matrix of ITMX has been diagonalized.
The evaluation of this diagonalisation will be done tonight by freely swinging ITMX again.
(Somehow I couldn't get any data for ETMX from the DAQ channels. I will try it again tonight.)
For solving the matrix, I used Yuta's python code called inmartixoptimizer.py.
I took the transfer functions of UL->UR, UL->LL and UL->LR as described in this entry.
In the measurement, the frequency bin was set to 0.001 Hz and the data were 50 times averaged on dtt.
Here is the new input matrix.
[[ 0.87059649 1.14491977 1.07992057 0.90456317]
[ 0.64313916 0.55555661 -1.44997325 -1.35133098]
[ 1.13979571 -1.19186285 -0.89606597 0.77227546]]
This matrix should give a better performance than before.
The oplevs have been installed on ITMX and ETMX.
Now the oplev servos are running.
The lock of the green beam became more stable after the oplevs were activated.
(what I did)
- opened the ITMX and ETMX chamber.
- rearranged the oplev mirrors in the vacuum chambers so that we can have the reflected oplev beam coming out from the viewport.
At the ITMX table, I put the oplev mirrors approximately on the designed places.
- aligned the beam on the optical benches
- strung a ribbon cable at the 1X9 rack.
This cable connects the oplev interface board and the ADC blue golden board.
- modified c1scx simulink model.
Since the model didn't have proper connections to the ADC channels, I added four ADC channels and plugged them into oplev servo in the model.
- relaunched the c1scx code after building and installing it.
- activated the oplev servos. Amazingly the default gains did work (i.e. all the gain = 1)
- after aligning X arm to the green beam, I did final centering of oplev beams
- - - - - ADC connection for ETMX oplev signals :
ADC0_24 = segment_1
ADC0_25 = segment_2
ADC0_26 = segment_3
ADC0_27 = segment_4
Tonight, swing again.
Please do not restore the watchdogs until tomorrow (Dec.9) morning.
We measured Open loop TF for oplev pitch on ITMX.
All feed back filter of oplev was on as same as before. Original notch filters which notches above 10Hz resonance should be modified with some measurements of present resonant frequency. Up to 10Hz, a simple f^2 filter is used, so the notch should not affect this measurement.
Measured upper UGF is about 2Hz with gain slider 1, and lower UGF is 1.3Hz. Phase margin is 40 degree, so it is not a good idea to increase the gain drastically.
I have measured the coherence also but I could not find a way to put it on this picture. Anyway coherence below 0.6Hz was not so good like ~0.95. This can be improved if larger excitation is used next time.
During this measurement around 0.2-0.3Hz, small earthquake happened but seemed OK for the control.
We will measure the other TF, yaw, ETMX or somthing, maybe tomorrow, due to free swinging ITMX and ETMX tonight.
After Kiwamu had set the free swinging mode for ITMX and ETMX, I found a big jump of ITMX pitch and yaw. This jump is shown on oplev and OSEM plots.
I talked with Kiwamu on the phone that a shutdown of suspensions does not add a big offset, and so that it should not make a big jump.
We were not sure that this jump was due to the shutdown or drift or something else. Anyway I put ITMY oplev on center again at 0;57am.
In this morning, the same thing happened but to opposit direction when Kiwamu activated ITMX and ETMX. Then it turned out that 1000ct offset was existing on pit of ITMX. Erasing the offset fixed ITMX to normal position.
However a big drift exists in 11hours plot on ITMX 0.1->-0.25 at OLPIT, -580->-605 at SUSPIT and 0.08->0.15 at OLYAW, no significan drift at SUSYAW. On the other hand, ETMX has no big drift but has 10-30minites order fluctuations.
After 6am both the drift and the fluctuation became, roughly saying, 10 times larger, probably due to the human activity.
[Koji, Osamu and Kiwamu]
We found that the ETMX free swinging spectra showed a strange resonant frequencies.
We are going to inspect the suspension today.
In a ideal case the SOS (Small Optic Suspension) is supposed to have the following resonant frequecies.
(Although we didn't carefully identify which corresponds to which)
f_POS ~ 0.98 Hz
f_PITCH ~ 0.66 Hz
f_YAW ~ 0.8 Hz
f_SIDE ~ 0.99 Hz
However ETMX showed the following resonant frequencies.
f_POS ~ 0.91 Hz
f_PITCH ~ 0.7 Hz
f_YAW ~ 0.93 Hz
f_SIDE ~ 1.0 Hz
Especially f_YAW looks pretty high. Also the others are not at the right frequencies.
So we are suspicious that something wrong is happening on the ETMX suspension.
We checked the ETMX suspension and found the UR OSEM was close to the magnet.
So we rotated the UR OSEM so that it won't touch the magnet any more.
We will check the resonant frequencies again by taking the spectra.
In fact the ETMX stacked when we applied a big angular offset to Yaw direction.
This was because that the magnet was actually touching the UR OSEM.
The earthquake stops were fine, they weren't touching the test mass.
Also we looked at the wire and the standoffs, they seemed fine.
We aligned the beam axis pointing down to both X and Y arm.
Now the beams are hitting the centers of both ETMX and ETMY.
Amazingly Osamu made X arm flashing by aligning the cavity.
(what we did)
- opened almost all the chambers except for the MC2 chamber.
- locked and aligned the MC.
We set Marconi to the right frequency, which had been set to the default values, probably due to the power outage in the last weekend.
Also we found a DAC cable disconnected from the IO chassis of c1sus. So we connected it in order to damp the MC suspensions.
- aligned MMT2 and PZT2 in order to let the beam go through the center of PRM.
- checked the beam centering at the two TTs (PR2, PR3).
- rotated PR3 to make the beam go through the centers of both ITMY and BS at the same time.
- tried finding the beam spot at the ETMY chamber, and successfully found it.
To see such faint beam spot, we used an IR viewer.
In addition to that, we put a large piece of aluminum foil as a screen in the chamber.
- aligned the beam to the center of ETMY by tweaking the PZT mirror (SM2).
- aligned the BS so that the reflected beam at the BS goes through the center of ITMX.
- tried finding the beam spot at the X end, and successfully found it hitting the wall in the chamber.
- aligned the BS in order to let the beam hit the center of ETMX.
- tried aligning ETMX and ITMX to the beam.
Eventually we made the X arm flashing.
However the flash was a bit too weak to completely align the cavity.
(plan for tomorrow)
- reinstall some steering mirrors into the BS chamber
- check and neutralize PZT1
- alignment of IP_ANG
Good news. I feel multi-chromatic-locking success is just around the corner.
By the way, there's a new presentation on the DCC from the ANU group where they've locked a short single cavity with both colors - G1000735:
This plot shows ETM oplev and OSEM trend for 10 hours on day before yesterday as almost the same as plot shown this entry. I reported the 10-30minites fluctuations were seen, but I noticed it comes from not suspension but from oplev power fluctuation.
After Kiwamu fixed the ETM OSEM touch yesterday afternoon, still the same trend was seen, so we had thought what we fixed was not enough. This morning I looked at the yesterday's and day before yesterday's trend and noticed the simila trend both the pit and yaw in ETM oplev but not on the OSEM trend. Kiwamu suggested me to put the oplev sum on the same plot. It was!
So, ETMX is not bad, but in fact, still alignment fluctuation exist on the cavity. ITM?
This graph shows 5 hours data in minute trend for ITMX and ETMX from 5am to 10 am today. ITM pitch drift is 3 times lager than ETM pitch if the OSEM sensitivity is assumed to be the same.
This graph is last 1 hour data of above graph in second trend.
It is clealy seen that ITM yaw is jumping between two stages. I guess ITM is something wrong, touching magnets or earthquake stops?
I wish I could use a bigger font for this, but, the suspension work is totally done for the upgrade!!!
Now, nobody break any suspensions, or we're not going to be friends for a while.
Koji and I put ETMY back in its tower, and made sure that both scribe lines are at the correct height. We also confirmed that the balance is good (as Suresh mentioned in a previous elog, since we balanced using the AR surface, the HR surface is pointing downward a little bit, but it's well within the OSEMs ability to correct.
While we were in there, we also looked at Tip Tilt number 002. As mentioned in elog 3645, the pitch pointing was off by a little bit. Since the TTs don't have actuators, the pointing has to be pretty good. We tweaked the balancing, and now the reflected beam goes completely back into the laser aperture, so it's as balanced as it's going to get. This TT is now ready for installation onto the ITMY table as part of the SRC.
Kiwamu confirmed that he's going to install these optics tomorrow, since he's doing some other alignment work today.
Just for good measure, the Table:
I found that a few connections in the simulink model of c1scx was incorrect, so I fixed them correctly.
It had been a mystery why we had to put a funny matrix on ETMX (see this entry).
But now we don't have to do such a voodoo magic because the problem was solved.
Now the damping of ETMX is happily running with an ordinary output matrix.
I looked at the wiring diagram of the ETMX suspension (it's on Ben's web page) and confirmed that the coils are arranged in order of UL, LL, UR, LR.
But then I realized that in our simulink model they had been arranged in order of UL, UR, LL, LR.
So UR and LL had been swapped incorrectly !
So I just disconnected and plugged them into the right outputs in the simulink model.
I rebooted c1iscex in order to reactivate c1scx front end code.
After rebooting it, I changed the output matrix to the usual one, then everything looked okay.
(actually it's been okay because of the combination of the wrong connections and the funny matrix).
The alignment of the ITMs and the PRM has been done.
As a result their reflections now come out at the REFL port successfully.
The vacuum work is going on well as we scheduled at the last meeting.
(plan for tomorrow)
- installation of ETMY
- installation of OSEMs on ETMY
- alignment of the beam to the center of ETMY
- alignment of the ETMY to the beam
- final alignment of IP_ANG
- setting up the oplev for ETMY
- replace one of the steering mirrors at the RFEL path by a 0 deg mirror (see here).
- setting up POX/POY (if there are time)
- aligned the PRM tower such that the reflected beam goes back to exactly the same path as that of the incoming beam.
- leveled the ITMY table because the OSEMs of ITMY had been completely out of range.
- aligned the ITMY and ITMX in order to let the reflections back to REFL.
- with a help from Osamu, we put a CCD camera, which actually had been used as OMC_T, just after the view port on the AP table.
- looking at the CCD monitor we were able to see the reflected lights from the ITMs. (In fact sensor cards didn't help looking for the lights.)
- playing with the alignment of the ITMs, we easily obtained Michelson fringes, which were also visible on the CCD monitor.
[Zach and Kiwamu]
We installed the new ETMY tower and successfully aligned the beam to the center of ETMY.
Also we finished the final alignment of IP_ANG.
(what we did)
- took the old ETM out from the chamber and put it on the flow bench at the X end.
- with a help from Joe and Osamu, we brought the new ETM and put it roughly on place.
- did a fine positioning of ETMY.
- covered the ETM tower with a large peace of aluminum foil in order to see the spot on a video monitor.
- stoled a compact video monitor that was sitting on the PSL table since we don't have any monitors at the Y end.
- made a ~1cm hole on the foil as a target for the beam.
- steered PZT1 in order to correct the beam position on ETMY. This is done by looking at the spot on the video monitor.
- steered IPANG_SM1 to let the beam hit a steering mirror in the ETMY chamber which Koji installed recently.
Now we have IP_ANG coming out from the viewport of the ETMY chamber.
[Koji, Oasmu and Kiwamu]
We made the following progresses :
(1) installation of the last TT called SR2.
(2) fixing an earthquake stop issue on the BS
(3) fixing a clipping of beams at the dark port
(earthquake stops on the BS)
- When we were aligning the BS, we found that the BS showed funny behaviors.
For example a kick on LR didn't shake LRSEN, and a big DC angular offset (~ 8 in the medm screen ) was needed to keep a horizontal beam axis in the reflection.
We checked all the earthquake stops and found two suspicious earthquake stops at right bottom side.
They looked like slightly touching the BS. So we moved them further away from the BS.
Then the problem had gone. We doublechecked the health by kicking, applying an angular offset and so on.
We found transmitted/reflected beams from the BS to the dark port was clipped at the BS tower.
We moved the BS tower by ~1cm and realigned the rotation of the BS tower.
We also found the beam spots on the two TTs, PR2 and PR3, were offcentered. Especially the beam spot on PR3 was almost on the edge of the mirror.
Probably this was because we touched PZT1 when aligning the beam to the Y end.
So it means, it is not a good idea to align the beam to the end only by steering PZT1. We should use PR2 and PR3 as well when we align the beam to the Y end.
We realigned them such that the beam hits the center of PR2, PR3 and ETMY.
We worked on some more vacuum businesses. Today we finished did the following works:
- alignment of the POX mirrors
- alignment of the POP1 and POP2 mirrors
- installation of OSEMs onto SRM
- alignment of the SRM tower
(alignment of POP mirrors)
Since a beam on the POP path was quite too weak to see even by IR viewers, we used a He-Ne laser to imitate the real beam instead.
We injected the He-Ne beam from an optical bench to the chamber, and made it go through the PRM and PR2 by using some steering mirrors.
The pin assignment was flipped in a way of mirror image due to the extension cables which cause a mirroring.
So we made mirroring connectors to flipp them back to the correct pin assignment, and plugged the mirroring connectors in between the feedthrough of the BS chamber and the SRM satellite box.
This is a picture showing how they are connected now.
The sole thing that has been deviated from the optical layout was that the SRM returning beam had to be reroute
as the SRM has better reflectivity on the AR surface in stead of the HR one.
I suppose that if we were really clever we would intentionally choose either the AR or HR surface so as to minimize the effect of the thermal lensing and/or thermal expansion from the locked interferometer absorption.
[Kiwamu, Jenne, Koji, Osamu]
We have mostly prepared the IFO for pump down.
After lunch [Steve, Bob, Koji, Kiwamu, Jenne, Joe, Joon Ho, Vladimir, Osamu] put the access connector back in place. Hooray! Steve still has to check the Jam Nuts before we pump down. Kiwamu checked the leveling of the IOO table, and fixed all of the weights to the table.
For all 4 test masses, bars (upside-down dog clamps) were placed to mark the alignment of 2 sides of the suspension tower. All test mass tables were re-leveled, and the weights fixed to the tables.
For ETMY, PRM, BS, SRM, we confirmed that the OSEMs were close to their half-range. ETMX was already fine. ITMY (the screens and the optics wiki are still old-convention, so this is listed as ITMX! No good!) OSEMs are pretty much fine, but ITMX desperately needs to be adjusted. Unfortunately, no one can find the standard screwdriver (looks like a minus), to adjust the ITM OSEMs. All the other towers had hex-key set screws, but the ITMs need a screwdriver. We will ask Bob to sonicate a screwdriver in the morning.
Yesterday, a sequence of force and gain measurement was made to determine the imbalance in the
quadrant, magnetic-levitation prototype. This was the reason why it failed to achieve a stable levitation.
The configuration is shown schematically by the figure below:
Specifically, the following measurements have been made:
(1) DC force measurement among four pairs of magnets at fixed distance with current of the coils on and off
From this measurement, the DC force between pair of magnets is determined and is around 1.6 N at with a
separation of 1 cm. This measurement also lets us know the gain from voltage to force near the working point.
The force between pair "2" is about 13% stronger than other pairs which are nearly identical. The force by the
coil is around 0.017 N per Volt (levitation of 5 g per 3 Volt); therefore, we need around 12 volt DC compensation
of pair "2" in order to counterbalance such an imbalance. Given the resistence of the coil equal to 26 Om, this
requires almost 500 mA DC compensation. Koji suggested that we need a high-current buffer, instead of what
has been used now.
(2) DC force measurement among four pairs of magnets (with current of the coils off) as a function of distance
From this measurement, we can determine the stiffness of the system. In this case, the stiffness or the
effective spring constant is negative, and we need to compensate it by using a feedback control. This is
one of the most important parameters for designing the feedback control. The data is still in processing.
(3) Gain measurement of the OSEM from the displacement to voltage.
This measurement is a little bit tricky due to the difficulty to determine the displacement of the flag.
After several measurements, it gave approximately 2 V/cm.
Plan for the next few days:
From the those measurements, all the parameters for the plant and sensor that need to determine the
feedback control are known. They should be plugged into the simulink model and to see whether the
old design is appropriate or not. Concerning the experimental part, we will first try to levitate the configuration
with 2 pairs of magnets, instead of 4 pairs, as the first step, which is easier to control but still interesting.
The crontab for op340m which runs various IFO maintenance activities has been set to the wrong path for the watchdog rampdown script since the CDS changeover.
This is a dangerous situation. With the watchdog thresholds set as high as 1000, the magnets can be broken if the new CDS has some mental problems. This kind of thing happened before at LHO (which is why Stan invented the watchdogs). Please try to make sure that the watchdog thresholds are not set that way - its our only defense against bad CDS.
I've now corrected the crontab. The watchdog thresholds are being stepped down every 30 minutes as before.
However, out test points are gone again, so who knows how things are behaving.
I have put an offset of 1000 counts to C1:SUS-ETMX_ALS_OFFSET. This actually misalign the mirror a lot.
While the offset is applied. I adjusted the balance of the coil matrix.
UL 1.580 UR 0.620
LL 0.420 LR 1.380
> ezcaread C1:SUS-ETMX_TO_COIL_0_0_GAIN
C1:SUS-ETMX_TO_COIL_0_0_GAIN = 1.58
> ezcaread C1:SUS-ETMX_TO_COIL_0_1_GAIN
C1:SUS-ETMX_TO_COIL_0_1_GAIN = 0.62
> ezcaread C1:SUS-ETMX_TO_COIL_0_2_GAIN
C1:SUS-ETMX_TO_COIL_0_2_GAIN = 0.42
> ezcaread C1:SUS-ETMX_TO_COIL_0_3_GAIN
C1:SUS-ETMX_TO_COIL_0_3_GAIN = 1.38
Now, we can keep TEM00 for green with +/-1000counts of push although the fast step of the offset make the lock lost.
It turned out that the step longitudinal input temporary misalign the mirror in pitch because the length and pitch are coupled.
I guess that we don't excite pitch if we push the mirror slowly. Eventually, we need f2p transfer function adjusted in the output matrix.
I sat down in the control room to find that ETMX and PRM's watchdogs had been tripped. I don't know how long they've been crazy, but there was a big something that showed up in the seismometers around 16:30UTC, or ~11:30 this morning. I don't find any significant earthquakes on the USGS site for that time though, so it might be more local, i.e. work next door or trucks or whatever.
I take back the suggestion that it was that seismic event. Clearly the PRM and the ETMX were kicked at different times, neither of which is the same as the seismic action. Mystery. You can see they have been ringing down for a while though, which is neat.
All of the SUS used to have only 1 filter module for SIDE. They now have 3 filter modules for SIDE just like the other DOFs.
Today I moved the filters around so that the sensor filters are in SDSEN, the servo filters are in SUSSIDE, and the dewhitening for the coil is in SDCOIL.
I noticed along the way that the bounce/roll mode notches for all of the suspensions are still set for the frequencies of the previous suspensions. Suresh has 'volunteered' to find the new frequencies and make the new bandstop filters by looking up the seminal work on this by Dan Busby / Sam Waldman.
The f2p measurements are done on ETMX and ITMX with the real time lockin systems.
The f2p measurements are done on ETMX and ITMX with the real time lockin systems.
I don't explain what is the f2p measurement in this entry, but people who are interested in it can find some details on an old elog entry here or somewhere on DCC.
So far the resultant filters looked reasonable compared with the previous SRM f2p filters.
- backgrounds -
Some times ago I found that the coils on ETMX had not been nicely balanced, and it made a POS to angle coupling when I tried green locking (see here).
In addition to that, accuracy of A2L kind of measurement including the dithering techniques depend on how well the coils are balanced. Therefore we need to balance the coils basically at all the suspended optics.
There used to be a script for this particular purpose, called f2praio.sh. This script does measure the imbalances and then balance the coils.
However this time I used the realtime lockin system to measure the imbalances instead of using the old f2p script.
One of the reasons using the real time system is that, some of the ezca and tds commands for the old script don't work for some reasons.
Therefore we decided to move on to the real time system like Yuta did for the A2L measurement a couple of months ago.
The f2p measurement finally gives us parameters to generate a proper set of filters for POS and also the coil gains. We apply those filters and the gains in order to eliminate the POS to angle coupling and to balance the coils.
- results -
The followers are the resultant filters and coil gains.
The plots below show new f2p filters according to the measurement.
ITMX (assuming pendulum POS has f0 = 1 Hz and Q = 1)
ULPOS fz = 1.009612 Qz = 1.009612
URPOS fz = 1.125965 Qz = 1.125965
LLPOS fz = 0.873725 Qz = 0.873725
LRPOS fz = 0.974418 Qz = 0.974418
ETMX (assuming pendulum POS has f0 = 1 Hz and Q = 1)
ULPOS fz = 1.055445 Qz = 1.055445
URPOS fz = 1.052735 Qz = 1.052735
LLPOS fz = 0.944023 Qz = 0.944023
LRPOS fz = 0.941600 Qz = 0.941600
C1:SUS-ETMX_LLCOIL_GAIN = 1.07233
The precision of the coil gains looked something like 1% because every time I ran the measurement script, the measured imbalances fluctuated at this level.
The precision of the filter gain at DC (0.01 Hz) could be worse, because the integration cycles for the measurement are fewer than that of the coil gains done at high frequency (8.5 Hz).
Of course we can make the precisions by increasing the integration cycles and the excitation amplitudes, if we want to.
The plot below shows how the f2p filters work.
At -2 min I turned on the f2p filters.
Cheater cables for SRM sus tied up. They were dangling aimlessly on the floor.
As a part of the DRMI preparation,
I leave all the suspensions free from the watchdogs for 5 hours from now.
Please DO NOT touch them.
I will check the spectra and the mechanical resonant frequencies on Monday.
Also I will renew all the input matrices of the local dampings based on these free swinging spectra.
There is a useful script for this particular job : shutting down all the suspensions and bringing it back to operation after 5 hrs.
It is called opticshudown, which resides in /cvs/cds/rtcds/caltech/c1/scripts/SUS/.
Also I added this script on the list in the wiki where all the scripts will be listed.
If you find any other useful scripts, please add them on the wiki.
I had a quick look at PRM optical lever.
The He-Ne beam is still successfully coming out from the chamber and I could guide it to the QPD by using steering mirrors.
But the beam size looks too big for the QPD. We should slide the lens which is standing before the injection to get a moderately smaller beam size at the QPD.
- activation of PRM oplev
The returning spot diameter on the qpd ~10 mm. In order to reduce the spot size I moved the f 1145 mm lens toward the PRM ~ 25 cm. The spot size was reduced to ~8 mm, 3200 counts.
I'll try to find an other lens tomorrow.
Here are the free-swinging spectra for the BS, ETMX, ETMY, ITMX, ITMY, MC1, MC2, MC3, and PRM chambers. Kiwamu left the suspensions free for 5 hours this weekend, starting at Sat Apr 30 00:15:26 2011.
This is GPS time 988 182 941. Quick tip: you can do local to GPS time conversions using lalapps_tconvert, which is a lot like tconvert but with special powers. It is installed on pianosa.
$ lalapps_tconvert Sat Apr 30 00:15:26 2011
I generated these figures with the attached Python script, measure.py.
Notice that the C1:SUS-ITMX_SENSOR_UL and C1:SUS-MC3_SENSOR_UL spectra fall as 1/f. Jenne suggested that this might indicate that there is a loose electrical connection.
Also, notice that C1:SUS-ETMY_SENSOR_LR, C1:SUS-ITMY_SENSOR_LL, and C1:SUS-PRM_SENSOR_SIDE are a lot noisier above 10 Hz.
Jenne went through all the suspension racks and pushed all the connectors.
After pushing them, we had a quick look at those spectra and found no funny noise spectrum except for C1:PRM-SENSOR_UL.
We then checked connection around the SCSI cables and eventually found the connection between ADC_card_0 and a SCSI was loose.
We put short standoffs on the ADC card so that the screws from the SCSI can nicely reach to the ADC card. Now everything looks fine.
SUS diagnostic is quite useful !
Atm 1, PRM oplev inward path with 2 lens solution: 14 cm gap between F 1145 and F 1545 mm lenses.
Atm 2, The PRM beam size 3 mm and the beam quality is still bad. The BS path only needed alignment.
[Leo w/ a little help from Kiwamu]
Leo summarized the mechanical resonances of all the suspensions, based on the free-swinging spectra taken on Sat Apr 30.
Since Leo doesn't have the wiki account I helped him putting the information on the wiki.
Good work, Leo !
I am tuning the notch filters for the bounce modes in the suspensions, starting with the ITMs and ETMs. I'll do the MCs, the PRMs, and the SRMs next.
I noticed that the filter for ITMX (in the file C1SUS.txt, the module ITMX_SUSPOS, the selection BounceRoll) that the filter was composed of two bandstops (and a constant gain). It looked like this:
Valera said that one of these was for the roll mode and the other for the bounce mode. However, looking at the spectra that Kiwamu and I made this week, I don't perceive a resonance between 11.4 and 12.2 Hz. So, we're taking a guess that this was for a mode that has moved due to new pendulum designs. For many of the suspensions, in the free swinging test we noticed a line around 23 Hz; we thought we might as well re-use one of these elliptical filters to avoid exciting this line. Of course, if this line does *not* result from excitation of an uncontrolled degree of freedom, this will not help and could be detrimental. When we talk to Valera again, we can review this decision and at that point we might decide just to take out that bandstop.
ITMX is done. I'll continue tomorrow. I've attached closed-loop spectra for before the tuning (itmx-before.pdf) and after (itmx-after.pdf).
(Update: the following day, I took closed loop spectra with (itmx-withbounceroll.pdf) and without (itmx-nobounceroll.pdf) the bandstops. It looks like the bandstops made the bounce mode slightly worse, but the roll mode slightly better.)
I tuned the ITMY bandstops -- 'before' and 'after' spectra attached. Note that the after the tuning, the bounce mode at ~16 Hz is about twice as quiet!
However, notice that in the 'before' plot the roll mode at about 23.5 Hz did not show up at all, whereas it is quite prominent in the 'after' plot. I was concerned that this line could have been a result of placing the bandstop there, so I made another plot with the BounceRoll filter turned off. Sure enough, the 23.5 Hz line is still there. So I'm not crazy: the roll mode did start acting up at some time between my 'before' and 'after' plot, but not as a result of the tuning.
The SRM qpd cable was removed from the BS-table. It's path was changed from 1x4 to ITMY-table following the inner cable tray.