We manually realigned the BS and PRM optical levers on the optical table.
I have restored the damping of BS and PRM. Today is janitor day. He is shaking things around the lab.
BS & PRM oplev is restored. Note: the F -150 lens was removed right after the first turning mirror from the laser. This helped Rana to get small spot on the qpd.
It also means that the oplev paths are somewhat different now.
Using PRX, I remeasured the relative actuation strengths of the BS and PRM to see if the PRM correction coefficient we're using is good.
My result is that we should be using MICH -> -0.2655 x PRM + 0.5*BS.
This is very close to our current value of -0.2625 x PRM, so I don't think it will really change anything.
The reason that the BS needs to be compensated is that it really just changes the PRM->ITMX distance, lx, while leaving the PRM-ITMY distance, ly, alone. I confirmed this by locking PRY and seeing no effect on the error signal, no matter how hard I drove the BS.
I then locked PRX, and drove an 804Hz oscillation on the BS and PRM in turn, and averaged the resultant peak heights. I then tried to cancel the signal by sending the excitation with opposite signs to each mirror, according to their relative meaured strength.
In this way, I was able to get 23dB of cancellation by driving 1.0 x PRM - 0.9416 * BS.
Now, in the PRMI case, we don't want to fully decouple like this, because this kind of cancellation just leaves lx invarient, when really, we want MICH to move (lx-ly) and PRCL to move (lx+ly). So, we use half of the PRM cancellation to cancel half of the lx motion, and introduce that half motion to ly, making a good MICH signal. Thus, the right ratio is 0.5*(1.0/0.9416) = 0.531. Then, since we use BS x 0.5, we divide by two again to get 0.2655. Et voila.
I tried to reduce BS 3.3 Hz motion with local damping. 3.3 Hz probably comes from the stack, but I want to reduce this because PRMI beam spot is moving in this frequency.
I tried it by putting some resonant gains to oplev servo and OSEM damping servo, but failed.
What I learned:
1. BS OSEM input matrix diagonalization looks impressively good. Below is the spectra of oplev pitch/yaw and OSEM pos/pit/yaw/side comparing with and without damping (REF is without). You can see mechanical resonances are well separated. Also, damping servos don't look like they are adding noise at 3.3 Hz.
2. 3.3 Hz motion is not stationary. Amplitude is sometimes high, but sometimes low. Amplitude changes in few seconds. You can even see 3.3 Hz in the dataviewer, too.
3. I set new oplev gains. I lowered them so that UGFs will be ~ 2.5 Hz. I turned ELP35 on.
C1:SUS-BS_OLPIT_GAIN = 0.2 (was 0.6)
C1:SUS-BS_OLPIT_GAIN = -0.2 (was -0.6)
4. All OSEM sensors feel about the same amount of 3.3 Hz motion.
5. OLPIT and OLYAW reduces if you put 3.3 Hz resonant gain to oplev servo, but it is maybe not true since they are in-loop error signals. You can't see the difference from OSEM sensors. Below is oplev pitch/yaw and OSEM pos/pit/yaw/side comparing with and without 3.3 Hz resonant gain (REF is without).
It is not as dramatic as PRMI, but I could see BS 3.3 Hz motion at AS and REFL when MI is locked at dark fringe.
Below is uncalibrated spectra of REFLDC and ASDC when
Red: MI is locked at dark fringe
Blue: there's no light (PSL shutter closed)
We have to do something to get rid of this.
[Anchal, Paco, Yuta]
I calibrated the BS oplev PIT and YAW error signals as follows:
The numbers are:
BS Pitch 15 / 130 (old/new) urad/counts
BS Yaw 14 / 170 (old/new) urad/counts
I bet the calibration is out of date; probably we replaced the OL laser for the BS and didn't fix the cal numbers. You can use the fringe contrast of the simple Michelson to calibrate the OLs for the ITMs and BS.
The numbers I have from the fitting don't agree very well with the OSEM readouts. Attachment #1 shows the Oplev pitch and yaw channels, and also the OSEM ones, while I swept the ASC_PIT offset. The output matrix is the "naive" one of (+1,+1,-1,-1). SUSPIT_IN1 reports ~30urad of motion, while SUSYAW_IN1 reports ~10urad of motion.
From the fits, the BS calibration factors were ~x8 for pitch and x12 for yaw - so according to the Oplev channels, the applied sweep was ~80urad in pitch, and ~7urad in yaw.
Seems like either (i) neither the Oplev channels nor the OSEMs are well diagonalized and that their calibration is off by a factor of ~3 or (ii) there is some significant imbalance in the actuator gains of the BS coils...
Need to double check against OSEM readout during the sweep.
[Suresh / Kiwamu]
Adjustment of the OSEMs on BS has been done.
All the bad suspensions (#5176) has been adjusted. They are waiting for the matrix inversion test.
The AS spot on the camera was oscillating at ~3 Hz. Looking at the Oplevs, the culprit was the BS PIT DoF. Started about 12 hours ago, not sure what triggered it. I disabled Oplev damping, and waited for the angular motion to settle down a bit, and then re-enabled the servo - damps fine now...
Lately, I have been working on a 3d sketch of the BS OPLEV Table on SolidWorks. This is my progress so far, a few of the components I will have to sketch myself, such as the HeNe laser and photodiodes. This will just be a general layout of the HeNe laser, optics, and photodiodes.
As part of the hunt why the X arm IR transmission RIN is anomalously high, I noticed that the BS Oplev Servo periodically kicks the optic around - the summary pages are the best illustration of this happening. Looking back in time, these seem to have started ~Nov 23 2020. The HeNe power output has been degrading, see Attachment #1, but this is not yet at the point where the head usually needs replacing. The RIN spectrum doesn't look anomalous to me, see Attachment #2 (the whitening situation for the quadrants is different for the BS and the TMs, which explains the HF noise). I also measured the loop UGFs (using swept sine) - seems funky, I can't get the same coherence now (live traces) between 10-30 Hz that I could before (reference traces) with the same drive amplitude, and the TF that I do measure has a weird flattening out at higher frequencies that I can't explain, see Attachment #3.
The excess RIN is almost exactly in the band that we expect our Oplevs to stabilize the angular motion of the optics in, so maybe needs more investigation - I will upload the loop suppression of the error point later. So far, I don't see any clean evidence of the BS Oplev HeNe being the culprit, so I'm a bit hesitant to just swap out the head...
The BS SIDE damping gain seemed too low. The gain had been 5 while the rest of the suspensions had gains of 90-500.
I increased the gain and set it to be 80.
I did the "Q of 5" test by kicking the BS SIDE motion to find the right gain value.
However there was a big cross coupling, which was most likely a coupling from the SIDE actuator to the POS motion.
Due to the cross coupling, the Q of 5 test didn't really show a nice ring down time series. I just put a gain of 80 to let the Q value sort of 5.
I think we should diagonalize the out matrices for all the suspensions at some point.
I have been working on analyzing the seismic data obtained from the 3 seismometers present in the lab. I noticed while looking at the combined time series and the gain plots of the 3 seismometers that there is some error in the calibration of the BS seismometer. The EX and the EY seismometers seem to be well-calibrated as opposed to the BS seismometer.
The calibration factors have been determined to be :
The seismometers each have 3 channels i.e X, Y, and Z for measuring the displacements in all the 3 directions. The X channels of the three seismometers should more or less be coherent in the absence of any seismic excitation with the gain amongst all the similar channels being 1. So is the case with the Y and Z channels. After analyzing multiple datasets, it was observed that the values of all the three channels of the BS seismometer differed very significantly from their corresponding channels in the EX and the EY seismometers and they were not calibrated in the region that they were found to be coherent as well.
Note: All the frequency domain plots that have been calculated are for a sampling rate of 32 Hz. The plots were found to be extremely coherent in a certain frequency range i.e ~0.1 Hz to 2 Hz so this frequency range is used to understand the relative calibration errors. The spread around the function is because of the error caused by coherence values differing from unity and the averages performed for the Welch function. 9 averages have been performed for the following analysis keeping in mind the needed frequency resolution(~0.01Hz) and the accuracy of the power calculated at every frequency.
The gain in the given frequency range is ~3. The phase plotting also shows a 180-degree phase as opposed to 0 so a negative sign would also be required in the calibration factor. Thus the calibration factor for the Y channel of the BS seismometer should be around ~3.
The mean value of the gain in the given frequency range is the desired calibration factor and the error would be the mean of the error for the gain dataset chosen which is caused due to factors mentioned above.
Note: The standard error envelope plotted in the attached graphs is calculated as follows :
1. Divide the data into n segments according to the resolution wanted for the Welch averaging to be performed later.
2. Calculate PSD for every segment (no averaging).
3. Calculate the standard error for every value in the data segment by looking at distribution formed by the n number values we obtain by taking that respective value from every segment.
The BS seismometer is a different model than the EX and the EY seismometers which might be a major cause as to why we need special calibration for the BS seismometer while EX and EY are fine. The sign flip in the BS-Y seismometer may cause a lot of errors in future data acquisitions. The time series plots in Attachment #4 shows an evident DC offset present in the data. All of the information mentioned above indicates that there is some electrical or mechanical defect present in the seismometer and may require a reset. Kindly let me know if and when the seismometer is reset so that I can calibrate it again.
The response of the BS actuator in a low frequency regime has been measured.
+ With free swinging MICH, the sensor (AS55_Q) was calibrated into counts/m.
=> The peak-peak counts was about 110 counts. So the sensor response is about 6.5x108 counts/m
+ Locked Michelson with AS55_Q and the signal was fedback to BS.
+ Set the UGF high enough so that the open loop gain below 10 Hz is greater than 1.
+ With DDT's swept sine measurement, C1:LSC-MICH_EXC was excited with a big amplitude of 40 counts.
+ Took a transfer function from C1:LSC-MICH_OUT to C1:LSC-MICH_EXC.
+ Calibrated the transfer function into m/counts by dividing it with the sensor response.
This seems like an error prone method for DC responses due to the loop gain uncertainty. Better may be to use the fringe hopping method (c.f. Luca Matone) or the fringe counting method
An update on calibration of the BS actuator : A fitting has been done.
Q and I aligned the BS such that we were hitting the center of ETMX. The ETMX cage does not have OSEM setscrew holes on the front, so it is not possible to put the targets that Steve made on this optic. So, I put the freestanding ruler in front of the optic, with the edge of the ruler at the center (as viewed from above) of the optic. Then Eric steered the BS until we were hitting the 5.5" mark, and roughly half of the beam was obscured by the ruler.
We then aligned ITMX such that the prompt reflection was colinear with the incoming beam.
I checked the 2 spots through the BS, heading to the AS port. (2 spots since MICH hasn't been locked / finely aligned yet). They were being clipped on the 2nd output PZT. I adjusted the knobs of the first output PZT to center the spots on the 2nd PZT. Note that the output PZTs' power is still off, and has been off for some unknown length of time. I had found them off when prepping for the vent a week or two ago. So the current alignment depends on them staying off. We don't really need them on until we're ready to employ our OMC.
The beams now look nicely unclipped on the AS camera, and we're aligning MICH.
I've measured seismic and acoustic noise on BS and AS tables. It seems that horizontal motion of BS table is ~1.5-2 times more then AS table in the frequency range 5-50 Hz.
This seismic measurement is for BS and AS tables.
This was in response to my suggestion to move the REFL beam path to the table containing the BS/PRM Oplevs. From this seismic data it is clear that the BS table is no worse than the AS table, so we should plan to make the layout change during the next vent.
[Koji, Steve, Jamie, Jenne, Yuta]
We opened BS and ITMX chambers, took lots of photos, and closed them with heavy doors.
I turned off high voltage power supplies for PZTs and blocked PSL beam. We are ready for the pumping tomorrow.
Important photos we took:
- positions of green optics at BS chamber, which was moved on the vent on Aug 2011
- positions of PZT mirrors and cable connectors at BS chamber, which will be replaced with tip-tilts on the next vent
- arrow on PR2 pointing HR (it was correct)
- tried to take photos of clipping IR beam at BS OSEM holder from ITMX chamber
We also took bunch of other photos.
Beam dump needed at BS chamber:
We also checked some un-dumped beams at BS chamber. We need dumps;
- behind MMT1, for unwanted transmitted beam
- behind IPPOSSM3, for unwanted transmitted beam (IPPOSSM3 is the last mirror in BS chamber for IPPOS)
Steve and Eric
Placed pick up mirror for BS face and PRM back. I will ask Jamie to clamp it.
There will be an other camera set up to view the face of PRM
Today at 11:13 AM the stack of invacuum BS table was kicked and IFO misaligned. We adjusted PZT2 voltage by ~20 V in yaw such that IPPOS was restored. Then we could lock arms.
For those of you who like to do work on the interferometer without reporting it in the elog because you think that what you did doesn't affect anything, this is your example of how our time can be wasted by such laziness.
BS chamber seemed to be kicked again around 10:00 am today.
I moved PZT mainly in YAW and locked both arms. I adjusted the beam to be almost on the center of both ETM by sights.
Bob, Steve, and Koji
We opened North heavy door of the BS chamber in the afternoon.
In the evening, Koji worked on the PRM/SRM removal.
- Cleaned up the OPLEV mirrors to create some spaces near the door.
- Clamped PRM/SRM.
- Removed OSEMs. Made a record of the OSEMs. The record is on the wiki (http://lhocds.ligo-wa.caltech.edu:8000/40m/Upgrade_09/Suspensions)
- Found the SOSs are quite easy to remove from the table as they are shorter than the MOSs.
- Put a new Al sheet on a wagon. Put the SOSs on it. Wrapped them by the Al foils.
- Carried it to the clean room. They are on the right flow bench. Confirmed the wires are still fine.
- Closed up the chamber putting a light door.
[Paco, Yehonathan, Chub]
The BS chamber 10" flange with 4 DSUB-25 feedthroughs has been installed with the cables connected at the in-vac side. This is the second of two flanges, and includes 4 cables ordered vertically in stacks of 2 & 2 for [[LO2-1, LO2-2, PR3-1, PR3-2]] respectively.
Sendhil and I installed the S polarized BS on the ITMY table to steer the NPRO beam through the AR wedge and align it to the POY beam.
We took a shutter from the BSPRM table (which was not used) and a beam dump from the AS table (which was used by the auxiliary laser already removed and installed on the ITMY).
To do: do better alignment of the NPRO beam, maybe installing some iris after the BS and before the AS wedge, phase lock the two beams.
Re: POY beam reduction.
We are able to lock the Yarm with the beam / gain as it is. I had thought we might need to increase the DC gain in the whitening board by a factor of 2, but so far it's fine.
The BS was showing some excess motion. I think I've fixed it. Order of operations:
I'm not sure how this might have gotten switched on...
I've applied LQR feedback technique to BS oplev in pitch. I think the most inconvenient thing in using LQR controller is the amount of additional states created during cost function shaping. It requires 1 filter bank for each state. To avoid this I wrote state estimation code so all states are calculated inside one function.
On the plots below cost function and oplev feedback controller performance are shown.
The BS oplev has been misbehaving and kicking the optic from time to time since noon. The kicks are not strong enough to trip the watchdogs (current watchdog max counts for the sensors is 135).
I took a look at the spectrum of the BS oplev error in pit and yaw with both loops enabled while the optic was stable. There is nothing alarmingly big except for some additional noise above 4Hz.
I have turned the BS oplev servo OFF for now.
I saw this kicking before
I think that this happens when the beam gets too close to the edge of the QPD. We see this regularly in the ETMs, if they've been kicked a bit, but not enough to trip the watchdogs. I think it might be the step/impulse response of the RES3.3 filter, which rings for almost 20 seconds.
Anyhow, I've just recentered the BS oplev. It was at -21urad in pitch, and had more than 400 counts on the top two quadrants, but only about 100 counts on the bottom two. Now it's around 300 counts on all 4 quadrants.
As a totally unrelated aside, I have installed texlive on Donatella, so that I could run pdflatex.
The BS oplev servo was kicking up the BS. It was turned off
Healthy BS oplev
I repeated the BS oplev spectrum today and I do not understand why it does look different. I did it as Kiwamu describes it in entry#4948 The oplev servo was left ON!
It is working today! Finally I repeated the BS spectra, that we did with Kiwamu last week
Kiwamu and Steve,
The He/Ne oplev shows no coherece so relative intensity noise is not limiting factor for the oplev servo
Yesterday I inspected this BS oplev viewport. The heavy connector tube was shorting to table so It was moved back towards the chamber. The connection is air tight with kapton tape temporarly.
The beam paths are well centered. The viewport is dusty on the inside.
The motivation was to improve the oplev noise.
After aligning IFO and putting the access connector on, we also centered IPANG/IPPOS and all oplevs (except SRM).
To avoid clipping of PRM/BS oplevs, we re-arranged oplev steering mirrors on BS table.
What we did:
1. Checked IPANG comes out unclipped after putting on the access connector.
2. Centered IPANG on its QPD.
3. Checked oplevs beams for ITMX/ITMY centered on in-vac mirrors, and centered them on their QPDs.
4. Checked IPPOS beam is centered on the mirrors inside BS chamber, and centered IPPOS on its QPD.
5. Tweaked oplev mirrors on BS chamber to make PRM/BS oplev beam unclipped and centered on mirrors, and centered them on their QPDs. To avoid clipping of oplev beams in BS table, we re-arranged oplev steering mirrors on BS table (outside the vaccum).
QPD values, IFO_ALIGN/MC_ALIGN screens, OSEM values attached.
- IR incident beam and IFO aligned
- X/Y end green coming out to PSL table (in higher order modes)
- IPANG/IPPOS available
- All oplevs available
- AS/REFL/POP cameras ready
- access connector, ETMX/ETMY heavy doors on
- ITMX/ITMX/BS heavy doors are not on
- AS/REFL/POP PDs not centered
- POX/POY/TRX/TRY not aligned
- AS beam coming out of the OMC chamber low by ~ 1 beam diameter (my bad)
- Align AS/REFL/POP PD and lock PRMI
- Take pictures of ITMX/ITMY/BS stacks
- Put heavy doors on ITMX/ITMY/BS chambers
- Start pumping down
Please confirm the SRM OL beam is not too bad and also find where the mis-aligned SRM puts its beam. WE want to be sure that there is not too much unwanted scattering from SRM into the PRFPMI.