My goal was to find out whether or not the RCG upgrade on January 13th has fixed the 18-bit DAC Major Carry Transitions. However, no evidence of DAC glitches found BEFORE OR AFTER the upgrade.

There were loud glitches in SRCL on January 10th but they do not associate with zero-crossing of the SUS MASTER OUT channels. Even if there were any DAC glitches, unfortunately, they would have had hidden below the noise floor (the glitch at LLO here  is seen at 40 counts max after highpass). On January 16th the high SR3 counts (counts = |65535| and above) do not seems to generate any glitches that are significantly louder than the noise floor. I have also picked out some of the time that the glitches in MICH are well above the noise floor and see if they are coincide with the zero-crossing. All the results are attached below. No DAC glitches found. However, that doesn't mean they do not exist....

I used the 4th order 20 Hz highpass on the control signal because it worked well with Livingston glitch data (plot attached).

The glitch time I used for January 10th are [0.3915, 0.5791, 1.127, 4.474, 7.934, 8.265, 10.78, 11.33, 13.45, 18.88], and [1.952, 2.782, 3.401, 4.932, 6.713, 7.916, 9.398, 11.1, 14.68, 15.96, 16.38, 18.23] for January 16th. I used Laura's python script (from alog16354) to identify spots on the SUS data that correspond to the glitches.

Suddenly I found that the EX green beam is not clipped much any more by looking at the QPD spectrum, and it turned out that the green beam was totally misaligned. This happened as the EX green QPD centering servo was turned off yesterday, and eventually TMS drifted away.

Anyway, I turned the QPD centering back on, and the clipping was immediately back.

I adjusted the QPD PIT offsets and found that setting QPDA PIT offset to -0.9-ish while keeping QPDB PIT offset to zero-ish fixes the clipping and keeps both of the QPD NSUMs to be about 1.02 to 1.03 (good).

First attachment shows clipping spectra, the second one is after the big offset was set.

Elli took pictures of the green beam in both of these states, and the beam is at a nice position when being clipped, and the beam moves down below by maybe a couple cm or more when it's not clipping.

Since we cannot move TMS up or down, there's not much hope to unclip the beam without drastically off-center the green beam.

LVEA: Laser Hazard
Observation Bit: Commissioning   

07:15 Karen & Cris – Cleaning in the LVEA
07:50 Sudarshan – Going into the LVEA
08:07 Hugh & Jim – Going to HAM1 to unlock HEPI
08:45 Christina, Karen, Cris – 1st cleaning of cleanroom in LVEA
08:51 Stuart & Jason – B&K hammer testing ITM-X OpLev pier
09:06 Filiberto – In LVEA west bay working on Test Stand racks
09:49 Stuart & Jason – Out of the LVEA
10:05 Students to see Richard on site
10:17 Apollo on site to work on the VPW AC system
13:02 Kyle – At HAM1 working on pumping setup
14:00 Kyle – Out of the LVEA – GV5 and GV7 are open - HAM1 is on ion pump only
15:10 Apollo on site working on the VPW AC system

[Jason O, Stuart A]

Power spectra measurements taken earlier this week (see LHO aLOG entry 16917) suggested we should target the ITMY Oplev for our initial B&K hammer measurements.

Problems with the B&K data acquisition card yesterday prevented us from taking measurements. However, thanks to Calum, who had seen simialr occurrences at Caltech, we were able to get back up and running. Just to note that, the B&K Capabilities Wiki collates relevant documentation, and a Troubleshooting guide has now been added.

We proceeded to take B&K measurements for both the ITMY RX Leaner and TX Large Dwarf OpLev piers. A tri-axial accelerometer was clamped to a cross member near the top of each pier (see images of the set-up below). Measurements were taken using the "Simple Hammer Display 3.pls" template available in T1000697. A hammer trigger threshold of approximately 8N was found to work best. ASCII data has been exported from the B&K Pulse analysis software directly into text files (*.txt) so that it can be plotted using the "BandK_plot.m" script.

Plots are available below for the two pier types tested. The frequency of the first resonances observed (X response to X excitation) can be compared to previous measurements made on production units at Caltech, see T1100152, as well as those measured at LLO. The resonance measured at Caltech is denoted by the dashed black line in the plots and was taken when the various structures were bolted and grouted.   

Resonance Summary:

OpLev   Type   Pier Name     DCC#      Caltech   LHO 
ITMY    RX     Leaner        D1001297  34.5 Hz   21 Hz 33 Hz
ITMY    TX     Large Dwarf   D1000452  85.5 Hz   34 Hz

First structural resonances for both ITMY Leaner & Large Dwarf piers appear consistent with similar non-grouted piers measured at LLO. However, the Leaner pier exhibits an extra resonance feature around 34 Hz, which is most likely due to the bolting configuration (n.b. as well as no grout, there are also no vibration absorbers fitted). Interestingly, there is no evidence of the 3.3 Hz or 6.6 Hz features, present in the OpLev Spectra, seen in either pier.

All data and plotting scripts have been committed to the SUS svn:

/ligo/svncommon/SusSVN/sus/trunk/Common/MatlabTools/BandK_plot.m

/ligo/svncommon/SusSVN/sus/trunk/QUAD/H1/ITMY/BandK/
SimpleHammerDisplay3-ITMY-ITMY_OpLev_RX_LPier_T1a-SUSunlocked-ISIunlocked-VAnotfitted-Ximpact.txt
SimpleHammerDisplay3-ITMY-ITMY_OpLev_RX_LPier_T1a-SUSunlocked-ISIunlocked-VAnotfitted-Yimpact.txt
SimpleHammerDisplay3-ITMY-ITMY_OpLev_TX_LDPier_T1a-SUSunlocked-ISIunlocked-VAnotfitted-Ximpact.txt
SimpleHammerDisplay3-ITMY-ITMY_OpLev_TX_LDPier_T1a-SUSunlocked-ISIunlocked-VAnotfitted-Yimpact.txt

n.b. the raw B&K Pulse *.pls file for each measurement was also checked into the svn along with the exported *.txt file.

Summary

Using the swept sine injection that was going on during the last DC readout noise, I tried to estimate the coupling of frequency noise to DARM.

It turned out ot be quite large, at the level of 2e-13 m/Hz above 1 KHz (see first plot). After some discussions and more thinking, we realized that if the IMC longitudinal locking point is not perfectly tuned to the top of the resonance, the IMC will convert frequency noise into intensity noise, and therefore the measure TF is not really the pure coupling of frequency noise to DARM.

Indeed, the swept sine is very well visible in the IMC transmited power (for example in the ISS signals). I could use the TF from frequency noise to RIN (see second plot) to estimate the IMC longitudinal offset. It turned out to be of the orer of 2e-12 m, which is about 0.5% of the IMC linewidth. This seems quite reasonable. We'll have to retune the IMC locking point in the short term.

This IMC locking offset might be the explanation for the high frequency broad band coherence between DARM and PRCL/SRCL signals.

More details - estimation of frequency noise coupling to DARM

We were injecting the sweep sine into the common board correction, and we were reading the cocrrection after the injection. I could measure DARM using the calibrated signal CAL-DELTAL_EXTERNAL_DQ (after applying a dewhitening in the form of 5 zeros at 1 Hz and five poles at 10 Hz, DC gain of 1). I could measure the actual frequency board correction using IMC-F_OUT which is calibrated in kHz. In this way, the transfer function from the common board correction to DARM is a direct measurement of the coupling F of frequency noise to DARM. Unfortunately, I could get coherence only above 1 kHz. I could get better coherence between the common board error signal and DARM above 100 Hz. This transfer function is F/G, where G is the response of REFL_9_I to freqeuncy noise at the IFO input. This is described by the double cavity pole, which is quite well described by 1/(1i*f) at frequencies above 100 Hz. So I can match the high frequency of DARM/IMC-F_OUT and DARM/LSC-REFL_SERVO_ERR (corrected for the pole) to get another estimation of F, valid from 100 Hz and up. I also can get a measurment of G which is 6e8 / (1j*f). The result is shown in the first plot.

More details - estimation of the IMC longitudinal offset

I can estimate the coupling of frequency noise at the IMC input to intensity noise at the IMC output with the transfer function between IMC-F_OUT and PSL-ISS_SECONDLOOP_SUM14_REL_OUT (which is calibrated in RIN). I get something of teh order of 1e-6 1/Hz at high frequency. The TF is not completely flat, but let's ignore this for the moment being.

If the IMC is locked off resonance, I get a direct coupling of frequency noise to intensity noise given by

dP/p = 32 Finesse^2 L_IMC / (lambda * c) * offset * frequency_noise

So I get the estimate of the offset to be of the order of 2e-12 m, to be compared with the linewidth lambda/4/Finesse = 5e-10 m

This morning, before anyone got on site to complain about it, Hugh and I unlocked HEPI on HAM1. We then turned on the isolation loops we installed last night. Everything turned on as (un)expected, we were able to steer then table back close to where it was. In addition, sensor correction in Z from the ground STS2 under HAM2 works as well, meaning we get a little inertial isolation below 1hz, something like a factor of 10 at .2hz. Attached plot shows HEPI L4C spectra of 3 states, blue is locked this morning, green is unlocked/isolated, red is isolated with sensor correction. There is probably some contamination from a few hz to 30 hz from Kyle's pump cart (almost touching one of the piers!) and other activites in the LVEA. Or at least I hope that's what explains the big peak at 2-3 hz.

On Tueday, the End Y HEPI Servo Computer Power Supply was ground bounded, and the Accumulators on the Fluid system were charged, alog 16907.  On Thursday, I removed the ground strap for ~6 hours to understand if the coherence reduction seen was from the Ground bonding or the Accumulator Charging.

Conclusion: the bulk of the improvement comes from the Accumulator charging.

While there is a minor amount of increased coherence seen in Z and HP it isn't near the amount seen before the Tuesday work especially HP--See the reference traces on 16907.  Of course, most of the ultimate noise reduction comes from Jeff's tuning of the controller pushing the ugf down to 10mhz but charging the accumulators and well grounding the servo computer are important too.

The attached plots have the reference traces as post Tuesday work and the current traces are beginning at 1730utc 26 Feb.

Kyle 

HAM1 ion pump OK -> Spun down HAM1 turbo and decoupled pump cart plumbing -> Leaving turbo controller energized and turbo cable connected for now (mag lev rotor levitated and not fully stopped) -> Opened GV5 and GV7 

Utilizing the ion pump at this atypically high pressure will marginally reduce its life but is the safest configuration for the vacuum system and is the least disruptive to commissioning

The plots below are the 24 hour OpLev trends

SudarshanK, GabrieleV, PeterK.

The modifications was made on the ISS second loop power stabilisation board to change the variable gain represented by  H1:PSL-ISS_SECONDLOOP_GAIN form 0 to 40dB to -11 to 31dB. This is on top of the addition 20dB gain that was added and reported in alog 14291, and controlled by H1:PSL-ISS_SECONDLOOP_ADD_GAIN.

We also made some modifications on the Guardian scripts that engages the second loop. Now the second loop can be engaged from the IMC guardian window although some fault checking will need to be implemented.

The in-loop and out-of-loop RPN measurement with the loop closed, gain set at maximum, boost and integrator engaged is attached below. The loop performance looks on-par with our past measurements, about 1E-8 at 10Hz.

For some reason these were not reconnecting, so I removed and readded them. They reconnected immediately after.

H1:GRD-IMC_LOCK_LOGLEVEL
H1:GRD-IMC_LOCK_MODE
H1:GRD-IMC_LOCK_NOMINAL_S
H1:GRD-IMC_LOCK_REQUEST
H1:GRD-IMC_LOCK_REQUEST_S
H1:GRD-IMC_LOCK_STATE_S
H1:GRD-IMC_LOCK_STATUS
H1:GRD-IMC_LOCK_TARGET_S

HAM1 ion pump pumping in parallel with turbo pump for the time being -> My plan is to demonstrate that the ion pump can pump solo for 2 hours at the current pressure (3.5 x 10-6 torr) then to consult with Daniel S. about the cost/benefit of the various options for the weekend

Well, unlike at EndY, the pump station maintenance did not pay off as well.  Bottom line: remaining coherences seen in the Z and HP dofs are not reduced as much as they are at EndY after the maintenance.  Possible reason--while I found lots of Accumulators that needed charging (just like at EndY,) the explicit grounding of the power supply common legs did not make the Pressure Sensing noise better.  In fact something in this process has made the sensor noise worse; but it was't the adding of the ground.

Details:  First I added the explicit jumper from the common legs on the power supply to the supply ground plug but this had no observable affect on the striptool I was watching.  I figured it was doing no harm.  After Guardian brought ISI/HPI down to OFFLINE, I ramped the pressure down with the servo.  Then the motor was greased and Accumulators were charged: most Accumulator were essentially uncharged and two on the pump station were leaking.  I was able to play with the Schaeder Valve and stop the leaks (may be iffy.)  After the Accumulators were charged, the system was brought back online and Guardian reisolated with no problems.

See the first attachment for the second trends where the system was down and then back on.  This is where I first saw that the noise on the pressure sensor channel more than doubled.  What happened to cause the noise to change like this?  I plugged the ground wire in before bring the pump down and didn't see an noise increase.  Is the power supply flaky?  I did have to move the servo box around to access the Accumulators...

It is clear this is bad when you look at the second attachment with the Pump Pressure ASD: it is a few to several factors worse than Sunday(Reference traces.)  The remaining attachments are the coherences between the Pump Pressure and the HEPI L4C & ISI T240s.  The coherences have improved suggesting the Accumulator serve us well.  But the improvements are not as good as seen at EndY where the Pump Pressure Noise dropped  5 to x10.

This morning, Stuart and I used the SDF front end to take new SAFE.SNAP snapshots of the balance of the suspensions - recall, he had done the BS previously, see alog 16896.

Repeating his alog instructions on how to perform this:

- Transition the Suspension to a SAFE state via Guardian
- On the SDF_RESTORE MEDM screen available via the Suspension GDS_TP screen select FILE TYPE as "EPICS DB AS SDF" & FILE OPTIONS as "OVERWRITE" then click "SDF SAVE FILE" button to push a SDF snap shot to the target area (which is soft-linked to userapps).
- This safe SDF snapshot was then checked into the userapps svn:
/opt/rtcds/userapps/release/sus/h1/burtfiles/
M        h1susbs_safe.snap

Note, please don't use the BURT interface to take SAFE.SNAP snapshots anymore, as the SDF monitoring will become disabled.  All other snapshots are free to be taken via BURT, however.

Also, we found many alignment values not saved on IFO_ALIGN which, after confirming with commiss, we saved.

Altough the high frequency is kind of screwed up by the wandering line, we can get some interesting information about the lower frequencies.

The full report can be found at the following address:

https://ldas-jobs.ligo.caltech.edu/~gabriele.vajente/bruco_1108981336/

The most interesting coherence is with SUS-BS_M1_ISIWIT_PIT_DQ, which seems enough to explain most of the noise up to 100 Hz. This is consistent with what Sheila told me, i.e. that we're not fully using BS ISI.

For those interested in the BruCo details, I managed to reduce a lot the time needed to analyze the data, basically with the following modifications: split coherence computation into the single FFT computations, to reduce redundancy; parallelize the computation and expcially the disk access using all available processors. This brought down the typical execution time to analyze 10 minutes of data from 8 hours to about 20-30 minutes. The new code is attached. 

I am concluding that the scale factor in the original calibration (alog 16698) was underestimated by a factor of about 2.4 in 2 - 20 Hz frequency band (meaning, the DARM spectra we had collected were too good). This was due to my inaccurate estimation of the ESD actuation response.

For the frequency region above 20 Hz, it has been underestimated by a factor of 3.2 when the PSL power stayed at 2.8 W and the same DARM offset was used. This was due to the inaccuracy in the ESD propagating into the sensing factor and also inaccuracy in the UGF location. I did not try to track how the sensing calibration should have been compensated as a function of the PSL power or the DARM offset (alog 16726).

I have updated the CAL-CS online calibration coefficients accordingly in both the sensing and actuation paths.

Pcal_Y seems to still indicate that the DARM spectrum is consistently too good by 40-65 %.

(ETMX response agreed the sus model by 40 %)

The day before yesterday, I had a chance to repeat the calibration of the ESD response of ETMX by locking the X arm with the IR laser. Comparison with ITMX at 13 Hz gave me an ESD response of 6.32 x 10^-16 m/cnts in ETMX at 13 Hz. This is 1.4 times larger than the expected than the suspension model. Since I used alpha of 2.0 x10^-10 N/V² in the model, the measured response corresponds to a slightly larger alpha of 2.8x10^-10 N/V². With the right force coefficient of -124518.4 cnts applied on ETMX, I tested both the linearized actuation and non-linearized. They showed almost same strength in a frequency band of 10 - 59 Hz as expected but with the linearized version somewhat stronger by 3-ish % (see the attached) presumably due to the charge on the test mass.

Since the change between the linearized and non-linerized actuations is so small, I neglected this effect and kept using the transfer coefficient of the non-linarized version at 13 Hz.

(Estimation of the DARM optical gain)

Using the measured data taken by Alexa (alog 16805), I estimated the optical gain of the DC read out to be 9.09x10^-7 cnts/m. To get this number, I first extrapolated the ESD response to some frequencies at around 20 Hz. Since the loop shape is already known, fitting of the open loop gives me the optical gain. I did eye-fitting this time. The UGF was at around 23 Hz in this particular data.

Since I was able to lock the interferometer at 2.8 W with the DC read out tonight, I cross-checked the DARM open loop. Running a swept sine, I confirmed that it sill kept the same UGF (see the attached below). Good.

(Comparison with Pcal)

First of all, one thing I have to mention is that, in an alog (alog 16781) describing the comparison between LSC-DARM_IN1 and PCAL is not a fair comparison because we know that LSC_DARM_IN1 was not well-calibrated. I checked the CAL-DELTAL_EXTERNAL_DQ at this particular time, but unfortunately the spectrum did not look reasonable probably because I was in the middle of changing some parameters in the CAL-CS. Instead, I looked into a different lock stretch at Feb-02, 5:13:11 UTC with the same IMC incident power of 2.8 W. The Pcal reported greater displacement by a factor of approximately 4.6 (see the attached below).

If I applied the new accurate sensing calibration, the discrepancy would have been a factor of 1.45 or 45% with the Pcal higher than the DARM spectrum.

To double check it, I checked the Pcal again during one of today's lock stretches at Feb-21, 10:04:05 UTC. One thing we have to pay attention is that the Pcal excitation frequency is now shifted to 540.7 Hz (alog 16815). I used the Pcal calibration formula that Sudartian posted in alog 16718 to get the displacement. The ratio between the Pcal and DARM spectrum was about 1.65 or 65% with the Pcal greater than the DARM spectrum. Even though the ratio is slightly different from 8 days ago or so, it still indicates that the DARM calibration is too good by several 10%.

The other excitation at 36.7 Hz (alog 16815) did not have signal-to-noise ratio more than 2 in the DARM spectrum due to high noise in this frequency region and therefore I did not use it this time. Nevertheless, the Pcal at this frequency was also greater as well. So the relation between Pcal and DARM spectrum is qualitatively consistent.