I added one additional ADC to the x1lsc0 and x1oaf0 chassis. This completes the 3IFO IO-Chassis inventory.
Following up on the IMC alignment improvement described earlier, I took a look at the residual fluctuations in the IMC transmitted RIN. Indeed, the RIN is much better on average when the correct IMC alignment offsets are used, but there are still quite large fluctuations. These are very well correlated to the residual angular motion, as visible in the IMC ASC error signals.
To quantify this phenomenon, I computed the band limited RMS of the ISS signal in the 100-400 Hz band and computed my usual linear regression analysis using all the IMC WFS and QPD signals. The first attachment shows that all the residual RIN fluctuations are predictable based on angular motion. The most relevant signal is WFS_B_I_YAW (see second attachment). Looking at the spectrum of the signal, it is quite clear that the low frequencies are dominated by a wide and smooth shoulder, likely due to input beam jitter created by air currents in the PSL room.
If this hypothesis is correct, we could implement an additional control loop, that servos the input beam to WFS_B. Since the DC of the input beam is already servoed to MC2_TRANS and since the DC of WFS_B is already used in DOF1 and DOF2, this additional loop must be AC coupled.
Another attempt today to run the HAM6 system with only the 500 l/s "main" ion pump (valved out the turbo pump), but once again the controller was not able to keep up with the load.
We are back to pumping with the turbo/ion pumps in parallel.
Note: The turbo pump was valved out today at a pressure of 4.0x10^-07 torr.
Yesterday the turbo was valved out at a pressure of 5.3x10^-07 torr.
[Alastair]
I'm turning the Y-arm CO2 laser on to test a new script that sets the rotation stage position. There is a beam dump in place on the table, so the output will not reach the CP.
Laser turned off at 17:07 local time.
Testing of script:
Power request Measured power
300mW 0.3009W
400mW 0.3996W
200mW 0.1991W
600mW 0.5996W
[Koji Sheila]
The OMCR QPD sleds are finely aligned using picos.
The incident beam alignment was controlled by SRC2, BC servos (DC3/DC4), and OMC ASC.
OMCR QPDA was centered by "OMCR QPD Centering B" picomotor (upstream steering mirror in the OMCR path).
Then OMCR QPDB was centered by "OMCR QPD Centering A" picomotor (downstream steering mirror in the OMCR path)
Repeated these steps until we have the beams at the center of the QPDs.
After the pico action, the beam alignment on the ISCT6 was revirewed. There was visible misalignment as expected and
this was adjusted by the bottom periscope mirror.
LVEA: Laser Hazard Observation Bit: Commissioning 07:00 Karen & Cris – Cleaning in the LVEA 08:05 Richard – LVEA Looking at racks 08:10 Robert – In the LVEA 08:10 Hugh – Running transfer functions on ITMX & BS 08:15 Robert – At End-X making magnet field measurements 08:20 Richard – Out of LVEA 09:17 Peter & Rick – Finished in the PSL 09:48 Christina – Finished at End-X and End-Y 09:49 Robert – Back from End-X 09:50 Robert – Going to LVEA to run acoustic injections 11:19 Dick – Going to ISC racks near PSL 11:29 Dick out of LVEA 11:45 Gerardo – Valving out the HAM6 turbo pump 11:49 Gerardo – Out of LVEA 14:34 Elli – At HAM6 working on signal analyzer 14:45 Elli – Out of LVEA 15:04 Gerardo – Valve in HAM6 turbo pump 15:10 Gerardo – Out of LVEA 16:03 Koji – Going into the LVEA to check spot 16:15 Koji – Out of the LVEA
I've taken Amplitude Spectral Density measurements on all of the suspension coil drivers that utilize the quad monitor bd. Below are screenshots of the data from the ones that I think may require some investigation. This data will be commited to SVN.
In list form, these are the suspects: ETMX L2 UR -- (State 1 too large) BS M2 UL, UR -- (State 1 & 2 too large on UL, No change in noise between states for UR) ETMY L1 UL, LL, LR (No change in noise between states) PR3 M3 LR -- (No change in noise between states) PRM M3 LR -- (No change in noise between states) SRM M3 UL, LL, LR -- (No change in noise between states) SR3 M2 UL, UR, LR -- (UL close to ADC noise, UR, LR no change in noise between states) SR3 M3 UR, LR -- (No change in noise between states) Ed didn't mention, but these measurements are not calibrated, i.e. they're in units of ADC counts of monitor board voltage (hence the comparison between ADC noise in counts). To calibrate into current across the coils, one needs to invert (divide by) the response of the noise monitor circuit (D070480), zpk([0,0,0,0],[5,5,5,5,4.8e3,4.8e3],196) which takes you to, Vout, the voltage across the differential legs of the output op-amps, before the output impedance network of each driver, then you need to divide Vout by the output impedance network and the coil, to get the current across the coil, Ic, Ic = Vout / (2*coilDriver.Zout + osemCoil.Zc). Note that these are suspects because we've simply played the "this performance doesn't look like the others" game. As the list of suspects is smaller than "all of the noise monitors," we can now focus our attention here so it's less overwhelming to get answers to questions like - is it right? - why doesn't it look like the others? - is it the driver response itself or the monitor? etc.
I made another study regarding the low DARM cavity pole issue (alog 17863). This time, I studied effect of losses in the arm cavities and SRC to see how they behave.
A conclusion is that we need a relatively large loss of approximately 7% in SRC in order to explain a DARM cavity pole of 290 Hz.
(The DARM cavity pole model)
I approximated the system to a three-mirror-coupled-cavity so that it has SRM, ITM and ETM in series. I assumed no DARM offset for simplicity. Doing some algebra, one can get a set of cavity equations and therefore the DARM cavity pole as well. In an analytic form, one can write the DARM cavity pole as
f_cavp = C / (4 * pi * L_arm) * abs( log( (re*ri - re*rs) / (1 - ri*rs) ) ).
To derive the above equation, I neglected loss in ITM (so that ri^2+ti^2 = 1) and also the phase rotation of the audio sidebands in SRC as usual. Since the system is compactified to the three-mirror configuration, it does not allow one to add differential arm losses (unless you do something tricky).
(The effect of losses)
I added loss on ETM (which is equivalent to common loss in the arm cavities in reality) and SRM (which should be equivalent to a SRC loss). The attached plot below shows the frequency of the DARM cavity pole as a function of either arm loss or SRC loss.
The blue curve is the cavity pole frequency as a function of arm loss with zero SRC loss. The green curve is the one without arm loss but with loss in SRC. As seen in the plot, adding loss in the arm cavities increases the cavity pole frequency. This is intuitively correct as the arm cavity itself is now becoming low-Q and hence wider linewidth. On the other hand adding loss in SRC decreases the cavity pole because adding loss essentially diminishes the signal-recycling effect so that the DARM cavity pole tends to go back to its nominal single arm cavity pole which is at 42 Hz.
In order to get a cavity pole of 290 Hz (which is drawn as a dashed red line in the plot), we need a large loss of about 7% in SRC. Since SRC is formed by a low reflective SRM (T = 37%), one needs a loss comparable to the transmissivity of SRM in order to significantly change the property of the SR cavity.
The python script for making the plot is also attached.
This morning and early afternoon I worked on the IMC alignment. My goal was to reduce the coupling of input beam jitter to intensity noise in transmission of the IMC. In brief, I dithered the input beam with the PZT at 80 Hz in pitch (amplitude of 3 cts.) and at 110 Hz in yaw (amplitude of 2 cts.) and looked at the ISS second loop power. I wrote a python script to demodulate the ISS second loop signal at tghose two frequencies, so that I could produce two error signals. They turned out to be very sensitive to the IMC alignment.
My first attempt was to move the beam on MC2_TRANS QPD in order to minimize the jitter to RIN coupling. Practicallt, I moved the QPD offsets to zero the error signal produced as explained above. The script I wrote implemented a slow servo to do this automatically. As shown in the first plot, this worked fine: this is a comparison of the RIN before and after the adjustment of the beam position. RIN is a factor 10 lower than before almost everywhere below 200 Hz.
Unfortunately, on a long timescale the offset servo is diverging, as shown in the second loop. The reason seems to be some interaction with the IMC ASC loops: moving the beam on MC2_TRANS adds offsets on the WFS, and then the IMC ASC loops respond slowly. The result is somehow drifting away in DC. So this is not a good soluition.
Duiring my previous attemps I found out that the IMC alignment was responding incredibly slowly to my action. Therefore I estimated the loop bandwidths by measuring their step response time constants:
| Pitch | Yaw | |
|---|---|---|
| DOF1 | 40 s | 80 s |
| DOF2 | 5 min | 4 min |
| DOF3 | 30 min | 30 min |
Clearly they were too slow, so I increased all gains to have a bandwidth of about 50 mHz for all of them. To doi this while the loops were closed, I changed the input matrices, as shown in the third attachment. I checked that after this modification all loops have indeed a step response of the order of 20 seconds. There is however a very larg cross coupling of all loops, confirming the result explained in the previous section.
Although this is a less clean solution, I tried to minimze the intensity noise by acting on the DOF_1 and DOF_2 offsets, or in other words of the WFS_A/B offsets. It turned out that the best choice is to act on DOF_1_Y and DOF_2_P, since this is the combination that effectively zero the error signals without affecting significantly the IMC transmitted power. I adapted my script to servo those two offsets to move the error signals to zero. The result is shown in the fourth attachment.
You can use the attached script, provided that you first switch on the two following dither lines:
H1:IMC-PZT_PIT_EXC ampl. 3 frequency 80 Hz
H1:IMC-PZT_YAW_EXC ampl. 3 frequency 110 Hz
The coupling is still fluctuating quite a lot, expecially for the yaw degree of freedom.
I left some offsets in the two degrees of freedom, as found by the script servo: DOF_2_P = 135.9, DOF_1_Y = 47.5
Isn't the bandwidth f_BW = 1/(2pi tau)? Meaning, more like 10mHz with a 20sec response time.
Continuing on from yesterday's TTFSS work. All notches were removed, and the transfer function was measured (see NONOTCHS.tif). The peak at ~760 kHz is of no big concern. However the peaks at around 1.77 MHz are. These were notched out with C50 (1-65 pF) and series with L2 (220uH). C50 was adjusted to suppress the two peaks. The transfer function was re-measured (see OLTF.tif). The unity gain frequency is around 450 kHz. Currently the common gain is set to 27 dB and the fast gain to 5 dB. Should the loop break out into oscillation, reduce the fast gain to 0 dB, wait until the oscillation stops and then increase it back to 5 dB. Rick, Peter
I looked at the FITS estimate for the optocoupler. The demonstrated FITs for the part is < 5555. Which if I understand things equates to a mean time to failure (MTTF) of just over 20 years. In a nutshell, I do not know why the part failed. Let alone two of them.
Because this looks to be the "final" configuration for a while, I again post an annotated version of the open loop gain transfer function for the PSL's (table top) FSS. In summary, - The unity gain frequency is 449 [kHz], with a phase margin of 58 [deg]. - The feature at 1.8 [MHz] (believed to be a resonance in the EOM) has been notched out, but with a pretty skinny / high-Q notch. - This [creates a new / pushes up the] feature a little higher in frequency, but the gain margin appears to be OK for now. - The 770 [kHz] feature is one of those "lucky" resonances where the zero is before the pole in frequency, so we win phase instead of losing it. So, there's no need to compensate for it, there's plenty of phase margin, and we aren't going to do anything about it. - In the future, we'll install a lower Q / wider notch to completely suppress this feature entirely without creating any new features, but at this time that's been deemed of lower priority.
ER-7 is scheduled for mid-June. There will be a short “annealing” run just before the ER-7 run. Seismic: Running TFs on BS and ITMX. BRS: Software crashes about every two weeks. Ops will check the BRS status daily. CDS: Finished connecting the Dew Point sensors for the 3IFO storage containers. VAC/FMC: HAM6 is still pumping. Hope to transition Ion pump today. Beam Tube cleaning of the X-Arm is 25% complete. There will be a safety meeting at 15:00 in the LSB auditorium. There will be painters on site working in the VPW, LSB, and OSB. PSL: Work continues on the FSS. Comm: Tuning and alignment work on the Mode Cleaner and the HWS.
Koji, Evan, Sheila
Tonight we saw the shelf from 50 up to 100 Hz, however we are back to a range of around 35 Mpc. We saw this last week and hoped that it was related to the HAM6 cleanroom. We have done several things:
The first plot was measured with the injection of 20000cnt@0.2Hz to H1:SUS-OMC_M1_TEST_L_EXC.
The second plot was measured with the injection of 10000cnt@0.2Hz to H1:SUS-OM1_M1_TEST_L_EXC.
Jeff, Sheila
This afternoon during an hour of winds consistently between 20-35 mph, we got a chance to use the three configurations Jeff described in 17729. We hoped to get be able to make a clear statement about whether or not the BRS is helping us on windy days to reduce the motion of the optic, we see a modest improvement with the BRS on, which could also be due to reduced ground motion.
We got at least 15 minutes of data with ALS COMM locked and common tidal runnng to ETMX (ugf set to 0.1 Hz) with three seismic configurations:
The IMC F signal, calibrated in kHz, is a readback of the X arm motion above 0.1 Hz in this configuration, with possible contamination from angular fluctuations. The best performance was measured with the BRS on, where the rms is about 67% of the rms measured with the 90 mHz blends and narrow band sensor correction. From the second screenshot, you can see that the ground motion also dropped when we switched to the BRS sensor correction, the rms of the ground is also about 62% lower for the red traces. The third plot shows X direction GS13s for the three configurations.
The last two attachements are the wind direction ( in degrees from north, this is mostly wind along the Y direction) and speed, and the seismic FOM for today.
What was the status of ITMX? It looks like the rms is limited by the bump at ~50 mHz in figure 1. It is possible that this bump in the ALS signal is coming from the 45 mHz blends at ITMX, though a similar bump in the ETMX GS 13 is also visible, which is a bit odd. With 90 mHz blends, one would expect that the gain peaking would be happenning near 90 mHz.
ITMX was indeed in the nominal configuration, with 45 [mHz] blends and narrow-band, 0.43 [Hz] sensor correction. We'd performed one test once that gave us the superstition that moving blend frequency up on the ITMs made ALS performance worse. I don't think this one test was documented.
Evan, Kiwamu,
We had a difficulty in locking the IMC in this afternoon after the FSS activity (see alog 17875). It turned out that the signal in the IMC trans PD was too low to trigger the IMC-MCL filter. Note that the upper and lower thresholds have been set to 100 and 90 cnts respectively for the nominal 3 W operation. We could have simply increased the output digital gain of this path, but at the same time we noticed that the analog signal was pretty low to begin with. It was about 20 cnts at the ADC when the IMC was locked on a 00-mode. We went to the IOT2L table and checked whether there is a clipping or some stupid things, but we did not find anything obvious. Since I did not like an analog signal to be as low as several counts at the ADC, I decided to crank up the analog gain of the PD (PDA100A) from 0 to 30 dB. Now it detects more than 200 cnts when the IMC is locked on 3 W. Evan then adjusted the digital gain such that it keeps the same conversion. We did not get a chance to subtract the dark offset yet, but the IMC is now locking fine.
Note that it seems that the trans PD has been in this low-ADC counts situation since approximately Feb-25 at which point the signal in IMC-TRANS decreased dramatically for some reason. See the attached trend. Could this be due to the LSC/OMC model split (alog 16893) ????
In an effort to increase the unity gain frequency of the TTFSS, I had tried a higher resonant frequency but
broader notch filter comprising of a 30 uH inductor for L2 and a 1500 pF capacitor for C16. After re-installing
the TTFSS, I found that the frequency no longer locked. Thinking that it was my circuit modification that was
the root cause, I reversed the changes and found that the frequency servo still did not lock.
The error signal was present when the cavity was swept. Each time the servo was engaged it did not lock
as the slow actuator ramp passed the resonance, which to me indicated that there was no feedback. The
problem was traced to the loop switch not engaging, this in turn was a faulty opto-coupler in the FSS fieldbox.
Coincidentally, the same one that Evan and I had switched the other day. Replacing both opto-couplers and
re-engaging the loop switch, the frequency servo locked.
The file M10P5.tif shows the open loop transfer function with the common gain set to -10 dB and the fast gain
set to +5 dB. The presence of the peaks at ~770 kHz and ~1.8 MHz suggest I did not correctly solder in the
two notches.
At the moment the common gain is set to -10 dB and the fast gain to +6 dB. If the loop starts oscillating -
indicated by a wildly oscillating reference cavity transmission of the PZT monitor plot on the MEDM screen
being a solid black, the fast gain needs to be reduced until the oscillation stops and then slowly restored.
The reference cavity transmission was ~1.45 V.
Peter, Rick
I spoke with Evan just to make sure I understood the conversation and implications of this log, and in doing so I've annotated the plot that Peter attached. Hope this helps! The problem is that this 1.8 [MHz] feature has left the FSS is only marginally stable (it works, but it's unclear whether IFO or IMC lock-losses cause (more) oscillations (than usual)). Peter will attack again in the morning.
J. Kissel, J. Warner We noticed that the wind / tilt at EX was so large that the peak-to-peak amplitude of tilt as measured by the BRS was surpassing the level at which the BRS's gravitational damper turns on. Since we're trying to get data in these high wind conditions, we've gone to the X end and and turned OFF the gravitational damper from the laptop software. Will turn on again some time soon when it's less windy.
Just a reminder (mostly to myself) -- turning off the gravitational damper, by commenting out its drive signal computation in the laptop's software and then restarting the software, renders the BRS useless for an hour or more because of impulse response of the 1 [mHz] high-pass that's applied to the analog signal. I.e. If you're trying to use the BRS quickly after a software restart -- don't count on it! Post email checking edit: Krishna reminds me that one can reduce the impulse by setting the DC offset compensation to the value record just before killing the software. We (Jim and I) consciously decided that the offset was too small to need updating in the software. We were wrong!
This seismometer has given us problems for some time: alogs 15510, 14482, 9727. JeffK may point to others too.
On the attached four plots, there are four successive days, Saturday thru Tuesday at 0100pdt. The lower left panels are the Coherences between the HAM2 & HAM5 (STS-A & C) and the ITMY (STS2.) The Upper Left, Upper Right, and Lower Right panels are the ASDs of the X Y & Z DOFs respectively of STS2 A B & C.
The take away is that in general the character of the ITMY (STS2-B) ground seismometer doesn't change like the other two instruments below 100mhz while the HAM2 & HAM5 instruments change more day to day and mostly look like each other.
Details: The Z DOF is most obvious in that below 50 or 80 mhz, ITMY trends up steeply while the A & C seismos do not. For the Y DOF, the HAM2 (STS2-B) signal seems to be the outlier but the day to day doesn't follow a patten between the instruments so I ... The X DOF is pretty good with the A & C instruments tracking each other pretty closely while the B sensor kinda stays at the same power level, mostly. So, like I say, a Case, maybe.
If I remember right, it sits on some kind of thin plastic or rubber mat, while the others sit directly on the concrete. If possible, it might be useful to make it contact the the concrete floor directly by carving out three holes on the mat.
For convenience: Evidence for low-frequency broken-ness LHO aLOG 15510 LHO aLOG 14482 LHO aLOG 9727 Factor-of-2 drop in X channel gain LHO aLOG 16208 LHO aLOG 16305
J. Kissel, R. Schofield Trying to convince Robert to let us borrow the newly-returned PEM vault STS-2 (S/N 88921) (see when it was removed in LHO aLOG 12931), I tried to show him in more detail with a little less curves on a plot what was wrong with the ITMY, B, Beer Garden STS-2 (S/N 88941). In the process, we not only rediscovered the problem Hugh shows above -- that the Z DOF on ITMY, below 50 [mHz] is just junk, but we also discovered that the Y DOF on the HAM2, A, Input Arm STS-2 (S/N 89922) is also junk. The attached PDFs show 5 days worth of corner station STS2 ASDs and COHs. For HAM2, check out the Y COH .pdf first. We see surprisingly low coherence between HAM2's Y and the other two, where the other two are perfectly coherent with each other. Looking at the ASD, it also shows the HAM2 spectra are consistently discrepant between 500 [mHz] and 3 [Hz], as well as below 0.1 [Hz]. For ITMY, again, check out the Z ASD first. From there, it's obvious that every day, the motion below 50 [mHz] is just junk. This is confirmed by the coherence, which shows that HAM2 is coherent with HAM5 every day, and ITMY is coherent with neither every day. The fact that ITMY and the HAM5, C, Output Arm STS-2 (S/N 100145) are always coherent between ... nope I can't make a consistent story. DOFs are inconsistently coherent, where they should all be perfectly coherent from 1 [Hz] down to 10 [mHz]. We really just need to huddle test all four of the STSs we have available in the corner, 89921 "PEM" Back from Quanterra 89922 Currently STS A 89941 Currently STS B 100145 Currently STS C and confirm -- once and for all -- which channel of whose is busted. Unfortunately, this means a whole lot of cable lugging around the LVEA -- a pretty hefty Tuesday task. Further -- LHO really needs more low-frequency seismometers -- because (a) We're already "temporarily" using a T240 at EX (S/N 531, borrowed fron the ETF at Stanford, originally installed at LHO in Feb 2014, see LHO aLOG 9758, and D1400077) because the project couldn't find enough STS-2s for us. (b) Even *if* we use all 5 in our possession (we have one at ETMY, S/N 89938), we still wouldn't be able to have one fail without significant down time. The lab's STS2/T240 Inventory, E1200068 hasn't been updated since the last time we churned up this subject in Oct 2014. I'm working on updating it myself by beating the streets; stay tuned for a -v15. Devil's advocate (inspired by Robert): Looking at the X DOF, there are days where all corner STSs are perfectly coherent between 60 [mHz] and ~2 [Hz]. Looking at the Y DOF, there are days where ITMY and HAM5 are perfectly coherent between 60 [mHz] and ~3 [Hz]. Looking at the Z DOF, there are days where all corner STSs are perfectly coherent between 60 [mHz] and ~1 [Hz]. The above implies that the corner station ground motion is perfectly coherent between 60 [mHz] and ~1 [Hz]. This implies we could try using a single STS-2 to run sensor correction for all chambers in the corner station. In order of risk of common-mode rejection being compromised: - For the BSCs, in X&Y, we only need a good signal around the first SUS resonances at ~500 [mHz] for DeRosa's narrow-band filter (See figure 3.32 P1500005). - For the HAMs in X&Y, we only need good coherence down to the bottom (frequency) edge of Hua's polyphase FIR bump, at 50 [mHz] (See pg 4 of attachment to SEI aLOG 594) - For all chambers, in Z, we need good coherence down to 10 [mHz], the lower end of the Mittleman's tilt free filter (See pg 5 of SEI aLOG 594) So, *if* we find an STS we like in which off of it's DOFs are performing perfectly (hopefully, presumably it's the one that just came back from Quanterra, S/N 89921), then we might be able to get away with running the entire VEA off of one STS2 (or T240). Maybe.
