Reminder: Morning meetings are now on Monday, Tuesday, and Thursday at 8:30.
SEI:
SUS
CDS
3IFO
Vac
FMCS
OpLev
Tonight I spent some time on ASC during full lock.
In addition to the new and improved dETM pitch loop (LHO#17006), and the existing dETM yaw loop, I was able to close high bandwidth loops for ASB36Q → BS using FM2, FM3, and FM10 in MICH_P and MICH_Y. The gain is 0.1 for MICH_P and 0.3 for MICH_Y. [FM10 is a BS plant inversion which seems to still work pretty well. FM2+FM3 make the loop 1/f everywhere.] The BS yaw loop UGF was >1 Hz (when the gain was turned up to 0.7), and I suspect the pitch loop was similar.
With these high-bandwidth BS loops closed, I then requested the BS SEI guardian to take the ISI to FULLY_ISOLATED. We saw yesterday (LHO#17007) that turning on stage 2 of the BS ISI causes a transient in the BS yaw, thereby breaking DRMI lock. But with a high-bandwidth BS yaw loop closed tonight, the interferometer was able ride out this transient, with no excursion visibile in the BS oplev signals.
Then I turned off the BS oplevs (around 2015-03-02 8:45:30 UTC). This improved the DARM spectrum slightly from 8 Hz to 30 Hz or so.
After that, I moved ETMX in pitch and yaw until the cETM error signals were near their zero crossings. Then I closed the cETM loops as described in LHO#16931, but with gains of -1 for pitch and -0.2 for yaw. The lock broke before I got a chance to estimate the bandwidths. Adjusting cETM (and then closing the loops) brought the interferometer visibility up to 95%. However, the recycling gain remained slightly low, at 26 W/W. So there must be yet more loops to close in order to increase the recycling gain above 30 W/W.
model restarts logged for Sat 28/Feb/2015
no restarts reported. Conlog frequently changing channels report attached.
We made a few attempts to turn on the BS stage 2 loops after DRMI acquired lock this afternoon, both times DRMI became misalinged and we loct the lock. We reset the CPS offsets and saw that the residual was small before turning on the loops, but still things became misalinged when we turned the loops on.
As far as I can tell, this yaw misalignment is a transient which happens when Rz is turned on. In the attachment, you can see that the BS gets misaligned by about 0.3 μrad, and then settles back to its old value after about 30 s. 0.3 µrad is too much misalignment to maintain DRMI lock; probably 0.1 µrad or less is required.
So perhaps we just need to find a gentler way to engage the stage 2 Rz loop.
Turning on x, y, and z of stage 2 seem fine as far as the BS pitch and yaw are concerned.
Alexa, Evan, Gabriele, Sheila
We have closed 6 low bandwidth loops with DRMI locked with arms off resonance today, based on what we learned from talking to LLO yesterday:
INP1: REFLA9I-REFLB9I -> IM4 PIT and YAW
PRC2: REFLA45I-REFLA9I -> PR2 PIT only (YAW signal seems to have an offset)
SRC1: ASB36I-> SRM pit only, although error signal loks OK for Yaw as well
MICH: ASB 36Q -> BS, PIT and YAW
In the past we had phased AS36 to maximize the BS signal in Q, but we noticed today that the Q signal is contaminated by SRM. We rephased AS B 36 to minimize the SRM signal in Q, this reduced the SRM pitch motion seen by AS36 B Q by 40 dB.
We have not attempted to close the AS_C-> SR2 loop, since we are far off center on AS_C. It seems that we will have to check search for the alignment that minimizes clipping on the Faraday and use picomotors to re-center AS_C,; we already know that we are clipping on AS_C when we are well aligned for the OMC PDs. (alog 16831 ). Despite this, it looked like ASB 36 I was a decent signal for SRM in both pitch and Yaw.
Nice progress all around on alignment controls! For AS36, what is the phase difference between maximizing for the BS and minimizing the SRM?
We moved the phase by 15 degrees (we only tuned this to within 5 degrees)
Alexa, Gabriele, Sheila, Evan
We have updated the DHARD P filters so that we have a 3 Hz BW when we are on resonance. When we first engage the WFS at 50pm CARM offset, the loop is stable at 100mHz BW. This loop would also be stable at 3 Hz BW; however, we don't want to have to adjust the loop gain as we reduce the CARM offset, so we have left the loop at low BW at 50pm CARM offset. The DHARD Y filters are installed for a high BW configuration; however, they have not been tested yet.
The old DHARD P configuration was as follows: FM3 (0.1:0), FM4(:0.01), FM7(SB3.8), FM8(invDhP), FM9 (SB9.8), FM10 (ELP10),Gain = 8. Note: this is the inverse plant that Evan measured in LHO#16520.
The new DHARD P configuration is as follows: FM2(zpk([-1.5+i*4;-1.5-i*4;-3.5+i*1.5;-3.5-i*1.5],[-41+i*70;-41-i*70;-46+i*100;-46-i*100],160000)*gain(2)), FM4(:0.01), FM7(SB3.8), FM9 (SB9.8), Gain = 21. Evidently, we have removed Evan's plant inversion and replaced it with a compensation filter which we designed from Gabriele's model. The attached image shows the difference between the old and new configuration modulo the gains.
At 50pm CARM offset, we were able to close this loop first with a gain of 21 (low BW), and then with a gain of 165 (3 Hz BW). Since the optical gain changes as we reduce the CARM offset, we decided to leave the loop at 50pm CARM offset with a low BW. Once we were on resonance, this loop was stable and gave us a 3 Hz BW as desired. This is in the guardian now.
The old/nominal DHARD Y configuration is as follows: FM3 (0.1:0), FM4(:0.01), FM7(SB3,14), FM8(invDhP), FM9 (SB9.8), FM10 (ELP10),Gain = 8. Note: this is the inverse plant that Evan measured in LHO#16566.
In preperation for a higher BW loop we have installed FM2 (same compenstation as for P), and FM6 (zpk([-0.376+i*15.215;-0.376-i*15.215;0.22+i*19.22;0.22-i*19.22], [-0.405+i*18.071;-0.405-i*18.071;-0.207+i*11.314;-0.207-i*11.314],1)gain(0.488863)). FM6 is designed to compenstate the resonant peaks between 1.5-3Hz in Gabriele's model LHO#17001 (this was confirmed by measurement). The second attached image shows the comparision between the nominal/old configuration and these new filters modulo the gains.
This loop has not been test yet. The guardian currently sets this to the old configuration.
[Alexa, Evan, Sheila, Gabriele]
The attached MATLAB file is a model of how the ITM/ETM plant changes due to radiation pressure. I considered the actuation from the PUM and radiation pressure reaction on the test mass. I used the QUAD model to obtain the mechanical transfer functions I need. I checked that the modeled PUM to test mass transfer functions matches very well a measurement I took this morning. The optical stiffness matrix is computed following Sidles Sigg PLA 354, 167.
The laser input power and recycling gain are parameters of the model.
The first attached plot shows how the ETM actuation transfer function changes when we have 2.8 W in inupt of the IFO. The main low frequency peaks in both pitch and yaw are splitted, but the important thing to note is that the higher frequency features do not change significantly. This is expecially important for yaw: the 2-3 Hz structures don't move. My understanding is that those structures are parallel resonances coming from the upper stages of the QUAD, which are not affected by radiation pressure. It seems therefore that a reasonable strategy to implement larger bandwidth DHARD/CHARD loops is to compensate for the high frequency features, since they shouldn't change significantly with radiation pressure. Then we can develop a controller that works for both pitch and yaw, without a complete plant inversion.
The second attached plot shows the effect of radiation pressure in the hard/soft basis. Peaks move as expected.
Alexa, Evan, Gabrielle, Sheila
Thanks to Keita's work on ETMX Damping (alog 16895) and L2P (16968), we are now locking ALS DIFF with no oplev damping on either ETM. Attached are spectra from all four stages of both quads, in both cases the ETMY oplev damping was off, for ETMX the solid lines are the old configuration with oplev damping on, the dashed lines are the new configuration described in Keita's alog with the OpLev damping off.
The wind gusts are at around 30mph, we could see from the ALS control signals that the arms are moving more than usual, so I changed the end stations to the high blends and we are using BRS sensor correction at end X. (configuration described in alog 16583)
we are back to 45mHz blends, since the wind has died down, but the BRS sensor correction is still on.
S. Dwyer, J. Kissel Speaking with Sheila this morning, the improvement in the ALS performance was "not as clear" as the last time, when the winds were 40 [mph] at EY (i.e. LHO aLOG 16526). This could be that the wind only got to roughly ~30 [mph] during the above configuration switch. Recall that in LHO aLOG 16526, the X-end was *not* changed, and the wind amplitude was large only at the Y-end.
I was checking ISI configurations this morning and found that X&Y sensor correction at EX was actually OFF on the ISI, but it was turned off at a different point in the path than I usually try to steer commissioners and operators toward using.This would have made it look like sensor correction was on, when no STS signal was actually going to the ISI. I hope this explains some of why "the improvement was not as good as before". I've been meaning to make some edits to Hugo's new SensCor MEDM to make this clearer, but haven't gotten around to it. I also found a few other configuration errors, but I didn't bother writing them down. Time to get more serious about SDF's, I guess.
Gabriele, Alexa
Gabriele had accidently unlocked the MC this morning, and had trouble relocking it. I know people had trouble with the MC yesterday morning, but there was no alog about this ... :(
The input power this morning was set to 5 W. When MC would try to acquire lock, the MC2 M3 LOCK L would reach the limit. I adjusted the input power to 2.8W and we locked immediatly. The IMC "DOWN" guardian adjusts the MC common mode board input gain depending on the input power (Power <4, 4
On the bottom left of the LSC overview you can set the power scaling for the LSC (channel H1:PSL-POWER_SCALE_OFFSET). I think in order for the MC to lock, this power scaling needs to match tyhe PSL power. So an alternative to aleways locking the MC at 2.8W is to change this power scaling in the LSC screen.
I had confirmed that the power normalization in the LSC was the same as the input power, so it seems we had different problems.
Elli, Dave, Evan
After today's work to get SRMI locked (LHO#16993), we were able to take some preliminary measurements of the SRC using the aux laser. More work will be necessary before quoting any numbers about the length or Gouy phase.
A brief description of the setup: on IOT2R, there is an auxiliary NPRO (Lightwave) which shoots into the back of IM4 and thereby probes the corner optics. Some of the light is reflected back onto IOT2R (along with some PSL light). An NF1611 is used to read out the beat of the PSL and the aux laser. On ISCT6, there is a second NF1611 which probes OMC REFL (which also contains a beat of the PSL and the aux laser, after these beams have been through the corner optics).
For this measurement, we detuned the aux laser by about 200 MHz relative to the PSL. We then locked the IOT2R beat frequency to the LO of a network analyzer (actuating on the aux NPRO PZT). While Elli kept SRMI locked, we swept the analyzer's LO by about 10 MHz. We recorded the transfer function (ISCT6 beat) / (analyzer LO).
Then Dave clipped beam in front of the ISCT6 PD, and we took another TF. This should in theory allow modes of odd order to contribute more strongly to the ISCT6 beat note.
Then Dave unclipped the beam again, and we took another TF with a −200 MHz detuning.
We're still trying to make sense of the data, but here are some initial impressions:
Also, some useful numbers:
The data are attached. 02 is at positive detuning, no clipping; 03 is at positive detuning, clipping; and 04 is at negative detuning, no clipping.
Reploted the sweep 02 with the linear phase term removed. Markers are at 192.67 MHz (blue), 193.40 MHz (green) and 195.35 MHz (orange).
The marker offset between blue and green is 0.73 MHz, whereas between blue and orange it is 2.68 MHz.
If the large peaks are the 45.5 MHz sidebands and the carrier, the 9.1 MHz sidebands would be expected at an offset of 1.07 MHz.
Attached is a diagram of the electrical part of the measurement.
I can't remember what the first amplifier on the AS port 1611 is, so I'll fill it in later. Also, I think the next amplifier (ZFL-2500-VH) is only good down to 500 MHz, so we should replace it if we're going to do measurements at 200 MHz.
Here is the same plot for the negative frequency sweep. The markers are at -195.05 MHz and -197.65 MHz.
Notice, there is a sign flip in the phase—indicating that a dark or bright fringe is located between the two measurement regions.
I calculated the auto-correlation by patching the data of the two regions together and filling in a constant value. In case of the magnitude I used -38.3 dB and zero for the phase.
The first plot shows the auto-correlation of the phase in the frequency range from 380 MHz to 400 MHz. The blue data points are the data. The red curve is a fit of a cosine function with a gaussian amplitude profile. The orange makers indicate the region included in the fit. The center green marker is the fitted value for the minimum of the auto-correlation function. Its neighboring green markers are calculated by assuming the minimum corresponds to the 146th free-spectral-range. The purple marker are the predicted values from the as-built SRC length.
The second plot is the same for the magnitude.
The fitted values for the phase and magnitude auto-correlation extrema are 390.579 MHz and 390.504 MHz, respectively. Again, assuming 146 FSR, this corresponds to cavity lengths of 56.032 m and 56.043 m. The achieved accuracy seems to be around 1 cm—hinting that the SRC could be 3 cm long. Not sure I believe it without some further tests.
Jim, Krishna, Ryan, Jeff, Sheila, Alexa, Evan, everyone
We have been having trouble keeping the Y arm locked with green, due to cavity motion of about 10 um in about 10 seconds. The winds at end Y are approaching 40 mph, and have been climbing for an hour and a half. We have copied the 90mHz blends for X and Y from the ETMX ISI into ETMY and blending high has allowed us to lock ALS for now.
The attached screen shot shows the Y arm control signal (from the end station PDH with no slow feedback on) in beige, and the X arm in yellow. The blends were switchd at about -21 minutes.
Here are a few more PEM screenshots of the wind and what it has been doing.
J. Kissel, S. Dwyer For the record, Sheila only remembers changing the blend configuration for ISI ETMY, which is why only the brown trace (ALS-Y_REFL_CTRL) gets visibly better in the StripTool.