Alexa, Dan, Elli, Evan, Koji, Sheila

• With the youngest parametric instability on the continent tamed by the ring heater, we locked a few times tonight, each time for an hour or more.  At the start of each lock the OMC DCPDs were either saturating or approaching their nonlinear region, due to an excited violin mode harmonic around 1009.62Hz.  We believe this is an ITMY mode but haven't been able to damp it yet.
• A quick transfer function of the OM1 suspension showed that the mode splitting we saw in the yaw d.o.f. last week is no longer there, see the first image attached.  This is good, but it means that this suspension is very close to some kind of mechanical contact that changes the plant.  I have reverted the yaw damping gain to the value from before, and committed new L and Y TFs to the SUS svn.
• The green light transmitted to the corner through the X arm has decreased by ~15% in the past day, see the second plot.  Sheila renormalized the X_TR signal so that the guardian will be satisfied with the X arm alignment.  Changes in the alignment of PR3 didn't recover the power (so we're not misaligned on the PD), and the power level at the endstation hasn't changed.  Baffled.
• We studied the OMC SUS excitation data from last night to measure the scattering noise from the OMC, Sheila will post more information later.  For now, compare the first PDF attached, which shows a spectrogram during the large longitudinal excitation of the OMC SUS from last night, with the second PDF, which is the same plot from tonight with no excitation.  The quiescient motion of the OMC does not appear to generate scattering noise.  There is clear nonstationary noise around 100Hz and also around 40Hz, but this does not have the arch-shaped features from scattering, and isn't correlated to the OMC suspension motion.  There's still a turbo pump running outside of HAM6.

Sheila, Gabriele, Evan, Koji, Dan, Alexa, Elli

Yesterday Koji, Evan and Sheila locked at 15W, and after an hour and a half the lock became unstable and they reduced they power due to suspected PI. A spectrogram ('darmspectrogram3_1.png ') of last night's lock shows a 844Hz line grow in the DARM spectrum (see attached spectrogram from 2015-04-15 09:30:00 UTC).  This corresponds to a PI at frequency 15540Hz, which is the first PI LLO saw (LLO alog 15934).  The line appears about an hour after the 15W lock began and the power was reduced after 1hr25min.  Once the power was reduced to 10W the line got smaller.  

This evening we locked at 15W at 2015-04-15 23:40:00 UTC and we saw the same line grow at 843.4Hz, corresponding to a PI at 15540.6Hz (see spectrogram 'spectrogram16April_843HzPI.png ').  This line grew untill we lost the lock at 1hr55 mins later ~ 2015-04-14 01:35:00 UTC (not due to the PI).  We measured the DARM spectrum around 15.5kHz using the SR785.  Attached is a plot '16AprilDARMSpectrum.jpg ' of the growing 15.54kHz line.

Grabriele saw that the 843Hz line was coherent between between the X-arm ASC QPDs and Darm, so we turned on the ETMx ring heater (see alog 17899).  The ring heater is requesting 1W total, or 0.5W each on the upper and lower segments.  We locked for a second time tonight at 15W at 2015-04-16 05:18:10 UTC. With the ETMX ring heater running, we didn't see any growth in the 15.54kHz line, as measured by the SR785.  See 2nd plot '16AprilDARMSpectrum_withETMXRH.jpg '.

Measurement notes:

-Spectrogram generated at LigoDV https://ldvw.ligo.caltech.edu/ldvw using channel H1:CAL-DELTAL_EXTERNAL_DQ.

-Spectrum meaurement taken with SR785 connected to OMC DCPD readout.  There is a script in /ligo/home/eleanor.king/netgib/SR785/SPSR785omcdcpds.yml that is used to take the spectrum (use the command <    ./SRmeasure SPSR785omcdcpds.yml > to take a measurement).

-Dan points out there are also OMC DCPD 64kHz  testpoints which are channels H1:IOP-LSC0_MADC0_TP_CH12 and H1:IOP-LSC0_MADC0_TP_CH13, which correspond to DCPD_A_INMON and DCPD_B_INMON.

The numbers are relative to the power delivered to HAM6. We still need single bounce OMC lock data in order to infer the OMC throughtput.
Obviously the systematic error was larger than the statistical error noted...

Sheila, Gabriele, Elli

ETMx ring heater turned on at 15:04:16 1:56:00 UTC requesting 0.5 W in upper and lower segments.

The ring heater is on because it looks like we have been watching a parametric instability build up at 15540.5 Hz over the last hour or so of lock.  There is coherence between the X-arm ASC QPDs and Darm at this frequency, which is why we are trying using the ETMX ring heater.  There is a script  in /ligo/home/eleanor.king/netgib/SR785/SPSR785omcdcpds.yml that we have been using to track the amplitude of this mode (use the command <    ./SRmeasure SPSR785omcdcpds.yml > to take a measurement).

For some reason all of the gains on the ETMx upper and lower segments were set to 1, so I have changed them back to what they were in February (which is also what the ITMs are currently set to).

H1:TCS-ETMX_RH_SET UPPER&LOWER DRIVECURRENT_GAIN =12.5

H1:TCS-ETMX_RH_UPPER&LOWER VOLTAGE_GAIN =3.5

H1:TCS-ETMX_RH_UPPER&LOWER PCB_GAIN=3.5

H1:TCS-ETMX_RH_UPPER&LOWER CURRENT_GAIN=-0.08

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.

[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.

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.

Improving intensity noise with MC2_TRANS beam position (failed)

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.

Increasing the IMC angular loop bandwidth

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:

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.

Improving intensity noise with DOF1/2 offsets

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

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

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:

• It seems that the peak at around 250 Hz is related to the OMCR path.  The peak was reduced after the vent and replacement of the BS with a 90/10, and closeing the OMC refl beam diverter reduces it below the DARM noise floor.)
• closing POP and AS air beam diverters didn't seem to have any impact on the spectrum, the DHARD roll offs we added ddin't do much either.  
• We measured fringe wrapping by exciting the OMC and OM1.  Analysis coming tomorow, but at first it looks like the OMC backscatter should not be limiting the sensitivity.  
• We were locked at 15 Watts for a few hours, after this time we saw broadband noise in DARM and tried to use the 785 to check for PI.  We had used the 785 earlier in the lock, but the second time we weren't able to connect to it.  By reducing the power we stayed locked.  (An incorrect calibration around this time lead to a sensmon range of around 40 Mpc)
• ALS scanning is faster this week, since we added a fast scan durring the vent that checks the two most commonly found frequencies.  

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:

• configuration 1 (45 mHz blend, narrow band sensor correction, no BRS) from 23:49:51 April 14th to 0:06:36 Arpril 15th (black traces) (this is the configuration that we have been using as a nominal configuration when the BRS is not working, we know that it is not good when the wind is high)
• configuration 2 (90 mHz blend, narrow band sensor correction, no BRS) from 23:27:30-23:48:51 April 14th UTC (blue traces)
• configuration 3(90 mHz blend, broad band sensor correction, BRS on) from 0:43:43 to 01:08 UTC, a large glitch nearly broke the lock at 0:51:58 (red traces)

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.  

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.