I've finished adding yellow boxes around the DC sliders on the IFO_ALIGN SCREEN for all the suspensions to indicate when values are ramping as per Sheila's request. I tested some of it successfully. Please take note of any weirdness and report it to me.
Thanks
Listed below are the past 10 day trends. For further in-depth analysis, please refer to Jason O., Pete K. or Rick S.
Attached are 7 day pitch, yaw, and sum trends for all active H1 optical levers.
Adding AOS and SEI tags.
All look good here, no changes from last week's trends.
H1 status:
- CP3 short is gone, final configuration ongoing
- no crane work in the LVEA scheduled for Tuesday
- beam tube enclosure sealing continues
- staging building alarm is coming in on the fire panel
---feel free to acknowledge, not a fire concern
Tomorrow's Maintenance:
- Richard - ITMs and BS satellite amp upgrades, possibly more
- Richard - CPS timing RF cables at end stations
- JeffB - monthly envi. checks
- Kyle - VEA laser safe for soldering,
- JeffK - commit models to SVN
- Hugh - HAM4 and HAM5 model corrections
- TJ - bounce and roll guardian roll state
- TJ - psl guardian
Still chasing the SRC gouy phase. On Saturday I was looking for the beam reflected back from the SRM through the SRC, transmitted through the ITM towards the ETM. I was trying to see the beams on the ETM baffles. The bottom line is that after trying to move multiple optics including BS, ITMY, SR3, SRM, I was not able to see any beam on the ETM baffle PDs except for the propt reflection from the BS towards ETMY (which doesnt travel through the SRC).
Method:
ITMx, ETMx, ETMy, PRM were misaligned for this measurement. To split the beams travelling through the SRC an optic in the SRC must be misaligned. I could look at the beams on gige cameras ASair and cam17 and the analogue camera looking at Ham 5. I saw no beams on the ETMy gige camera, is this working currently?The baffle Pds are 35cm or 3 beam diameters apart, so was aiming the split the prompt reflection from the BS to ETMy from the beam that travels once through the SRC by at least 1.5 beam diameters.
First tried moving single optic, eg BS or SR3, by applying excitaions of different frequencies in pitch and yaw, and then looking for a signal on the baffle PDs. I saw no signal that was not the prompt reflection, which was present whther or not the SRM was aligned. ThenI tried moving BS to center the prompt reflected beam onto a baffle PD, moving it slightly off to the side and then moving the and moving SRC optics with an excitaion in pitch and yaw, one at a time.
Then tried moving SRC/ITMY optics, with no BS misalignment. I saw no beams on the baffle PDs when moving the SRC optics, anr only the prompt reflection when moving the ITM and the BS.
I could see a beam inside the SRC on the SR3 baffle, which I think was the second trip around the SRC. So I think the first trip around the SRC was making it through the ITM and it wasn't clipped, but I couldn't get it on the ETMy baffle.
As a side note:
Funnily enough, while doing this misalignment business I noticed three beams on the gige camera 'cam_17' on ISCT_6. I think these is the straight shot, the one round-trip and two-round trip beams through the SRC. The angle between these beams also tells us the SRC gouy phase. Stefan and I tried to look at these beams last year on the AS_air camera with no success, and we concluded that we couldn't split these beams without clipping on an optic. But the cam_17 is a new camera in a different part of the AS_air beam waist. And it looks like we are seeing all three beams. Interesting.
One explanation for the lack of a visible beam in the end stations from the reflection of the SRC could be a bad mode matching of the SRC to the arm cavities—which could result in the beam blowing up after 4km of travel. A bad mode matching would also reduced the RSE cavity pole; something we observed.
Vinny, Brynley Over the past 2 weeks, we used a temporary magnetometer in the CS CER and the EY CER and computer racks. We placed the magnetometer in a range of locations, and created spectra from the magnetometer at each. It had been mentioned that the timing slave card in various chassis might be the cause - as an LED with a 2 second period is fitted on each. To that end, after a first study, our follow up was aimed at those chassis with timing slave cards. The first spectral plot attached shows spectra from the EY CER. All of the traces are near the noise floor because we were not using the typical magnetometer filter box, which applies a gain of 100 above 1 Hz. Despite this the combs are easily and increasingly visible as the magnetometer gets closer to the timing racks. Each trace is made with 170 averages of .1875 Hz resolution FFTs. The second plot shows spectra from the corner station CER. This time we used an SR560 pre-amplifier to get our gain of 100 above 1 Hz. Once again the comb was stronger as the magnetometer got closer to the timing racks. Once again each trace is made from 170 averages of .1875 Hz resolution FFTs. The third figure shows the spectra taken from the CER at EY. We used the SR560 to apply gain of 100 above 1Hz. For this plot, the magnetometer was placed near to a number of instruments, some with timing slave cards, and some without. EY's TCS-1 rack RF oscillator source. The 0.5Hz combs are very strongly visible throughout the signal. The trace is made from 15 minutes of data, with 0.03125Hz resolution The fourth plot is a short segment of the magnetometer's time series associated with the spectrum in the third plot. The magnetometer was placed near to the Timing Slave card on EY's TSC-TRF Oscillator source. The time series shows that on second boundaries, the magnetometer sees a large field, quickly dieing away. No post-processing or filtering has been performed on this time series. There has been no "Observing" data during these investigations, but the detector had "DC Lock" from Feb. 20 04:00 - Feb 20 12:00 . The last image is a oherence plot (between H1:LSC-DARM_IN1_DQ and H1:PEM-CS_ADC_4_28_OUT_DQ) made from those 8 hours of data. 64 second FFTs, 899 averages. The comb is clearly visible, confirming that this is the comb appearing in DARM.
NOTE: To clarify, at EY, we temporarily usurped on the PEM TILT X channel for our magnetometer. The plots which show the TILT are in fact our temporary magnetometer. BP 02/29/2016
I have extended the cross spectrum analysis (see 25009 and its comments) to the entire O1 run.
Preliminary conclusions are that:
I will dig into some interesting days or periods and study how different things were.
[Setting up band limited rms]
To analyze the cross spectrum as a function of time, I decide not to do spectrogram type analysis which may contain too much information. Rather I wanted to study the time evolution of the band limited rms. This approach is very similar to what Gabriele does (e.g. 22514).
I selected eight interesting bands in which I avoided tall peaks in the spectrum because I am not interested in their amplitudes in this study. The attached below shows the eight selected frequency bands.
The frequency bands are chosen as follows, Band 1 = [20 25], Band 2 = [30 35], Band 3 = [50 55], Band 4 = [81 95], Band 5 = [101 110], Band 6 = [121 126], Band 7 = [130 140] and Band 8 =[150 156].
[Time-varying calibration parameters are corrected]
I have corrected for all kappas, the time varying calibration parameters, by applying them to the H1 DARM model of the calibration group. Since one cross spectrum is produced from a twelve minutes integration, kappas are also averaged for twelve minutes. Therefore, the data sets that I analyzed here must be less sensitive to calibration errors due to the time varying parameters which can deviate roughly by 10% from the reference values.
[Glitches and transients are removed]
I have removed data segments that were contaminated by some glitches or transients because I am not interested in their characteristics. This was done by computing an average Rayleigh static over the frequency range from 60 to 100 Hz and rejecting the segment which had a Rayleigh statistic deviating from unity by more than 10%. So the data set I analyze here has more or less good Gaussianity.
[Result 1: time evolution]
The attached plot below shows the band limited rms of the selected eight frequency bands as a function of time in days starting from Sep-01 00:00:00 UTC.
Typically, the two lowest bands (band 1 and band 2) vary more than the others presumably due to the fact that they can be easily degraded by seismic activities, alignment loop and LSC feedforward. In contrast, the rest of high frequency bands (bands 3 -8) are more stable but still do fluctuate. Notice that the high frequency bands decreased their rms at t = 50 days or so. I believe that this is due to Robert's improvement of reducing the PSL jitter coupling (22497). Also, one can find many interesting periods where one of the bands increased the displacement while the rest stayed unchanged and so on. I will try to check those interesting days later.
The fluctuation of the four highest bands (bands 5 -8) are at 15-20 % level (or 30-40 % in peak to peak) with high sigma data points excluded.
By they way, I forgot to multiply sqrt(df) with df being the frequency resolution to all the band limited rms 
. The frequency resolution df is currently 0.1 and therefore all the data shown in the above plot should be lowered by a factor of sqrt(0.1) = 0.3. This does not change the main conlusions.
[Result 2: behavior of the high frequency bands]
Now, the plot below shows a primitive correlation plot.
where the horizontal axis represents the displacement of band 8 and the vertical axis is for the rest of the bands in order to show correlation with band 8. I have excluded the first 50 days in which the high frequency noise was higher due to the PSL jitter coupling. By the way, the x-axis is in log scale although it may look linear to some people. As seen in the plot, bands 4-7 show a positive correlation with band 8. Also their slopes seem to be identical. These indicate that noise level above 80 Hz fluctuate in such a way that it keeps the same spectral color. As mentioned above, the size of fluctuation is about 15-20% for bands 4-8.
All the data in the above plot should be lowered by a factor of 0.3 for the same reason as the time series plot . This does not change the main conlusions.
A follow up: I have looked into the difference between the data before and after t = 44 days (Oct-13-2015). I still think that it is due to Robert's improvement of reducing PSL periscope jitter coupling.
[DARM and DCPD cross spectra]
Here is what the data says. See the attached below.
Here I plot two different spectra from two different days: a DARM spectrum generated by using the C01 recalibrated frame data and cross spectrum of DCPD A and B calibrated into the displacement for each day.
First of all, the DARM spectrum shows an improvements in the range from 50 Hz to 400 Hz (see cyan and yellow curves). Noise from the later days shows featureless noise in this frequency range. The same improvement is visible in the cross spectra. The PSL periscope jitter peaks in 300-400 Hz had almost gone below some other smooth noise floor and structures in 60 -300 Hz disappeared and left a smooth noise floor. Noise above 400 Hz seems unchanged between two days.
By the way, DARM of Oct-7-2015 showed a wandering peak (?) in 166-176 Hz band which are not visible in the above plot because they are averaged out by the 24 hours integration. Also, the discrepancy below 30 Hz between two days could be due to seismic and alignment, but I have not paid attention to this frequency region. I attach the actual fig file as well.
[Qalitatively same improvement seen in detechar summary page]
Somewhat consistent improvement can been seen in the detchar summary page. I attach a gif animation comparing the spectra from the two days -- one can see the improvements not only at the 300-400Hz peak but also in 50 - 300 Hz.
Note that despite the different GWINC curves and title location, the x and y axes seem to be identical.
Later, it turned out that the optical gain was not compensated in all the above data. See the correction at alog 25918
TITLE: 2/27 eve Shift: 00:00-08:00 UTC (16:00-00:00 PST), all times posted in UTC
STATE of H1: Planned Engineering
INCOMING OPERATOR: None
QUICK SUMMARY: The environment was friendly today, Sheila and Evan are working their magic, and the alarm in the computer users room has only gone off twice since Richard left for the day.
During O1 we had several long lock stretches with all test mass violin mode damping turned off (for all harmonics). The longest stretch that I know of is 35 hours, from 2015–12–19 07:00:00 Z to 2015–12–20 18:00:00 Z.
Here I give the quality factors of the violin mode first harmonics. The test mass identifications are taken from the mode table on the wiki. Of the 32 first harmonics, one was not seen in the data, and a further six do not have clear ringdowns in their envelopes. We had some other locks with no damping, so we should look at these to see if the behavior of these seven modes makes more sense.
The lowest Q observed was 0.2×109.
| Freq. [Hz] | TM | Q (×109) | Notes |
|---|---|---|---|
| 500.054 | IX | 2.0 | |
| 500.212 | IX | 1.7 | |
| 501.092 | IX | 1.8 | |
| 501.208 | IX | 1.1 | |
| 501.256 | IX | — | Did not ring down |
| 501.452 | IX | 1.3 | |
| 502.621 | IX | 1.8 | |
| 502.744 | IX | — | Did not ring down |
| 501.608 | IY | 1.7 | |
| 501.682 | IY | — |
Did not ring down
Did not ring down
Did not ring down
|
| 501.749 | IY | 1.1 | |
| 501.811 | IY | 1.6 | |
| 503.007 | IY | 1.9 | |
| 503.119 | IY | 1.9 | |
| 504.805 | IY | 1.7 | |
| 504.872 | IY | 2 | |
| 505.587 | EX | 0.7 | Middling quality data |
| 505.707 | EX | — | Not seen |
| 505.710 | EX | — | Did not ring down |
| 505.805 | EX | 1.6 | |
| 506.922 | EX | 1.1 | |
| 507.159 | EX | 1.2 | |
| 507.194 | EX | 1.7 | |
| 507.391 | EX | 1.3 | |
| 507.992 | EY | 1.6 | |
| 508.010 | EY | — | Did not ring down |
| 508.146 | EY | 0.3 | Middling quality data |
| 508.206 | EY | 0.2 | Middling quality data |
| 508.220 | EY | 1.9 | |
| 508.289 | EY | 1.3 | |
| 508.585 | EY | 0.7 | |
| 508.661 | EY | — | Did not ring down |
The program which decrements the open reservations was on a machine which was recently decommissioned. It is now running on script0 as user controls under a screen environment.
[Kiwamu, Elli, Nutsinee, Cao]
We attempted to align the SLED beam onto the Y-arm HWS today. We scanned the SR3 in both pitch and yaw and identify three beam spots. Two spots could be obseved while scanning in yaw and in pitch. One of them was a common spot. The two spots were separated by 800 micro-radians.
PITCH: To identify two spots in PITCH, use wedge angle of ITMY: vertical wedge with angle of .07 degrees. Thus ITMy causes beams to separate in vertical direction
Increasing pitch of ITMY leads to moving both vertically separtated spots move upward, which implies that the beam reflected off the HR surface is vertically below the beam reflected off the R surface.
This was re-confirmed by scanning the SR3. We noticed that the beam identified as the HR beam occurs consistently at 800 mico-radians below the AR beam.
YAW: To identify two spots in YAW, we turned the CO2 lasr on and apply 4W power to observe change in spherical power measured by the HWS. The spherical power only changes for the beam spot at lower SR3 yaw value. The only issue theat occurs was that when compared to simulation, the changes is in the opposite sign. But we are sure that this the right beam spot, which is surpringly the beam spot at the beginning
We then walk the SR3 to nominal value and performed fine adjustment of the picometer to centre the beam spot on the y-arm HWS.
We then check the X-arm HWS, this is where new problem arises. After scaning the SR3 both in pitch and yaw, we optimise to centre the X SLED beam on the HWS. Despite this, the image streamed from the X-HWS shows a beam with lower intensity, as compared to Y arm HWS beam. The Gaussian beam profile is also not clearly visible. We performed a CO2 laser test again and observed spherical power measured by the X-HWS. The results shows that the spherical power value is very noisy and doesn't have an apparent trend hat it is supposed to have as the CO2 laser is on.
Per work permit 5741, continued with the modification of the SUS SAT Amps. All units for EX, EY and HAM4 were completed today. See LHO aLOG 25685 for status of corner station.
J. Kissel, C. Gray Corey grabbed the belated charge measurements for this week. The results are attached. The message: the bias flip appears to have worked as expected, and the bias voltages are slowly creeping back to zero. This is the first effective bias voltage measurement since both bias flips on Feb 16th (the last measurement was the day before, Feb 15th). Recall after the last flip, the first few measurements we're a good indication of the eventual rate of charge / discharge, so we should continue to get weekly measurements. (And now one *more* operator knows how to do it!) Two bits of sadness: (1) the calibration line amplitude monitors are no longer computed. That means we can't make the continual assessment of the longitudinal actuation strength like we'd done during the run, see e.g. LHO aLOG 24547. I'm gunna ask Greg why, and if we can't restart it. (2) Since the ESD Driver's response has changed with the deployment of ECR E1500341 on Feb 9th (see LHO aLOG 25468), the DARM loop model no longer agrees with reality, as was discovered after the bias flip -- see LHO aLOG 25604. In the rush, we gave up, didn't fix the model, and therefore didn't update the EPICs parameters that are used by the GDS pipeline calculate the time dependent actuation strengths. That means that there is no new reference time, and the pre-O1 reference time of Sept 10 2015 is still being used. Maybe that's good, maybe not. Depends on what questions you want to ask. "Reconciling" these optical lever effective bias voltage measurements with the recent measurements of EY ring heater voltage coupling to charge *on the barrel of test mass* (see LHO aLOG 25655): (1) Measuring the ring heater's coupling to the charge on the barrel of the test mass is *not* necessarily the same charge that the optical lever measures, which is between the gap. See discussion in T1500467). (2) Further, having the bias voltage ON at 400 [V] during the EY measurement (see later comment LHO aLOG 25669) will certainly confuse the results. Changing ring-heater potential (the ~ few [mV] drive at 162 [Hz]) is attracting the reaction mass bias ring instead of the test mass charge along the barrel. With the now-moving reaction mass having charge as well (in between the gap, as measured by the optical levers), then one can imagine a good bit of confusion between all of the different mechanisms for charge to change the actuation strength (again, see discussion in T1500467).
Position update: STS2-B and STS2-C are in the BierGarten. They are about a meter apart. Jim is using STS2-C for all corner station sensor correction. STS2-A was moved to the Yend for buried use but it would not center. Robert replaced it with the PEM unit and I put the STS2-A back in the LVEA near HAM2. It currently does not have the igloo in place.
The lack of thermal isolation is evident in the attached plot where the HAM2 blue traces all have much larger low frequency magnitude. Otherwise, the common factor in the coherence plots suggest that HAM5 STS2 is the only unit running well on all axes.
I have lowered the HAM2 unit just now 2330Z so the igloo would fit. It will be several hours likely before it stabilizes. I'll look again at it Monday.
It took many centering attemps but it looks like the STS2-A at HAM2 is now nicely centered. With the igloo just installed though, it may drift as things warm up in the igloo.
Today Keita and I spent some time thinking about OMC length noise, there will be an update coming soon with more information and a noise projection.
We spent some time looking at some nonlinear behavoir noise in the drive to PZT1. Our dither frequency is 4100 Hz, and looking at the low voltage PZT monitor we can see a small 8 Hz and a larger 16 Hz comb. There is also other non stationary noise in the monitor, and a broad peak at 12.7 kHz. We have moved the dither line frequency to 4100.21 Hz, so if this was the cause of the 16 Hz comb in DARM we would now expect it to be more like a 16.84 Hz comb. Evan Goetz tells us that we need 15 minutes or more of data in low noise to evaluate if this has changed any combs in DARM.
We have just reached nominal low noise at 3:14:34 UTC Feb 25th, although the low frequency noise (below 50 Hz) is worse than normal. I've temporarily changed the dither frequency in the OMC guardian, so if there is a longer lock later tonight it should also have this changed dither frequency. (If anyone wants to double check what the dither frequency is, the channel is H1:OMC-LSC_OSC_FREQ
To quote Bill Murray in Groundhog Day, "Anything different is good." (at least in this context) The 16-Hz comb does indeed appear to have changed into a 16.84-Hz comb. A DARM spectrum from two hours (400-sec coherence time) last night in the 150-250 Hz band is attached, along with one from January on a day when the 16-Hz comb was strong. New lines are seen in this band at 151.56 Hz 168.40 Hz 185.24 Hz 202.08 Hz 218.92 Hz 235.76 Hz Some 1-Hz zooms are shown for a couple of the new lines. So...can we fix this problem?
Keita, Sheila
So that we can keep the OMC dither small while driving a reasonable level of counts out of the DAC, we added a voltage divider (somewhat creatively built) to the D-sub from the DAC to the driver chassis. This is a 11k/110 Ohm divider on pins 1 +6. We have increased the dither amplitude from 6 cnts to 600 cnts, so the round off errors will now be 100 times smaller compared to our signal.
The attached screenshots show the PZT1 AC monitor before and after this change. The lines below 1 kHz are always there, (even when there is 0 coming out of the DAC) and are not present on the analog signal coming into the driver chassis for the monitor.
We have reverted the frequency to 4100 Hz. If we get a long enough low noise lock tonight we can hope that the 16 Hz comb will be better. If things look good we should upgrade our voltage divider.
Thing is, our dither line used to be 12 counts pk-pk, so the rounding error was actually significant (signal/error ratio is something like 10 in RMS), and the error showed up as lots of lines because we're sending in only one sinusoidal signal. These lines actually drive the PZT length.
Making the dither bigger, the round off error RMS doesn't change much so RIN will become smaller.
We inserted two sets of 11k-110 Ohm resistive divider, one each for positive and negative input of the low voltage pzt driver input because it was easy. This is a temporary non-solution. A permanent solution is TBD.
The first attachment shows the spectrum of the DAC IOP channel for the dither, i.e. the very last stage of the digital, before we increased the amplitude. RMS of the forest of lines is about a factor of 10 below the RMS of the dither.
The second plot is after increasing the amplitude by a factor of 100, the rounding error RMS is still at the same level though you cannot tell from the plot, the dither to error RMS ratio should be more like 1000 now.
Three large lines in the second plot are not round off errors but imaging peaks that were previously buried in the round off errors: 12283.8kHz=16384-4100.2Hz, 20484.2Hz=16384+4100.2Hz, and 28667.8=32768-4100.2Hz.
Actually, the dither line is still at 4100.21 Hz for tonight, (I had forgotten that I put this into the guardian). We will revert it tomorow.
Splendid -- no 16-Hz or 16.84-Hz comb seen in a 2-hour stretch from last night! See attached spectrum 150-250 Hz spectrum for comparison with above plots, along with 0-1000 Hz spectra from last night and from the night before, with the 16.84-comb present. Many thanks from the CW group as we look ahead to O2.
Sheila pointed out that the noise floor for the 2nd spectrum is considerably higher than for the 1st and could be hiding residual lines due to the dither. So I tried shifting the 2-hour time window a half hour earlier, to avoid the hellacious glitch seen in the inspiral range (see 1st figure) near the end of the original Feb 26 interval. The 2nd figure shows the resulting spectrum with a noise floor closer to that on Feb 25. The 16.84-Hz comb still does not appear. So I think it's safe to say that the 100 times multiplication / divide trick did indeed suppress the 16.84 Hz (originally 16 Hz) comb a great deal, but of course, we will need long coherence times and long integrations to see if what's left causes residual trouble for CW searches.
Den, Kiwamu, Evan
We continued investigations into locking robustness and low-frequency noise.
Notes on robustness:
>> Engaging the soft loops is still painful, particularly in yaw. When the loops are ramped up to their nominal gains (a few tens of millihertz bandwidth), the SRM yaw loop misaligns the SRM in yaw, which causes POP90 to rise and causes lockloss after about 1 minute. If the SRM yaw loop is turned off, this misalignment does not occur. So far, the most reliable way to engage the ASC is to (1) engage the soft loops with the −20 dB filters, and let them run for a few minutes, (2) turn off the SRM yaw loop, (3) turn off the −20 dB filters in the soft loops, and then (4) once the soft loop error points have reached 0, turn the SRM yaw loop back on. This has not been added to the guardian.
>> Den retuned the PR2 actuator feedforward which decouples MICH from PRCL, but this has not been added to the guardian yet.
Notes on noise:
>> Similar to yesterday's frequency noise test, we injected high-frequency noise into the ISS first-loop error point. We drove several volts (both sine waves and broadband noise) up to 10 MHz, but we did not see any nonlinear coupling.
>> As noted previously, the input jitter coupling into DARM is worse than before, particularly in pitch. Den opened the SRM angular loops and moved SRM to minimize the coupling. However, this seemed to make the noise worse in other places. In particular, the region from 35 Hz to 70 Hz swas dominated by some kind of nonstationary excess (perhaps scattering in HAM6). Also, there appeared to be a slight excess frequency noise above 5 kHz.
>> We drove the ITM ring heaters (upper and lower) in common-mode in order to measure the voltage-to-displacement coupling in DARM. By driving a few lines at 250 mVpk between 80 and 160 Hz, we could see that the coupling goes like 1/f2. The levels at 160 Hz are as follows:
| Upper (m/V) | Lower (m/V) | |
| IX | 2.1×10−17 | 4.6×10−17 |
| IY | 0.27×10−17 | 1.0×10−17 |
>> We flipped the sign of the DARM offset. Normally we run with the X arm shorter than the Y arm (i.e., a positive offset is applied at the DARM error point, and DARM is Lx − Ly); so here we are running with X arm longer than Y arm. This is achieved with the ISC_LOCK paramter lscparams.omc_sign that is applied at the appropriate points during the dc readout handoff. The sign of the SRCL feedforward also has to be flipped, and the SRCL FF filters that we normally use cause some 1 Hz instability that unlocks the interferometer. We installed a more aggressive AC coupling filter (FM8), and this solved the issue. DARM has a small amount of excess noise with this new offset, but the SRCL coherence does not seemed to have changed much after FF retuning. Good time to look at is 2016-02-21 21:44:40 (bruco).
Measured coupling of ETM ring heater potential to DARM at 162Hz
| Upper (m/V) | Lower (m/V) | |
| EX | 2.0 ×10-17 | 2.2 ×10-17 |
| EY | 2.1 ×10-16 | 2.3×10-16 |
This measurement shows that EX potential coupling to DARM is similar to IX and IY. However, EY coupling is higher by a factor of 10.
One interesting conclusion is that the coupling of EY potential is similar to LLO (alog 16619) before this TM was discharged. At the same time oplev measurements show small charge on the surface.
Attached plot shows reduction of PRCL control signal when MICH feedforward is running. We actuate on PR2 M2 with gain of 0.24 and assume that BS and PR2 actuators have the same frequency response above 5Hz.
Attached plot shows reduction of input jitter noise seen in DARM after SRC alignment.
We drove IM4 and SRM in angle and measured first and second harmonics of the drive in arm transmission power, POP_DC, AS_DC and OMC_DC. This measurement has shown that PRC and arm misalignment is small (2.3e-3 of divergence angle) and SRC for sideband is also good (0.06 and 0.1 of divergence angle for yaw and pitch), but can be better. Since we could clearly see some misalignment on the camera, we opened SRC1 loop and moved SRM manually by 10urad. SASY90 has increased by 3% and jitter coupling has reduced by a factor of 5. We also noticed that for particular SRM alignments DARM noise increases by a factor of 2-3 in the frequency range 40-80Hz.
Tomorrow we plan to continue investigations on alignment and on potential coupling to DARM.
Higher coupling of ETMY RH potential to DARM is not surpring since ESD bias was equal to 400V during the measurement.
The attachment shows the DARM offset flip test with SRCL control noise removed. It seems that the positive sign is still slightly worse than the usual negative sign.
