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. 

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. 

Alexa, Gabriele, Sheila, Evan

Summary

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.

Details for Pitch

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.

Details for Yaw

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)

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 = 10); it's possible that the init and locked gain set for 5 W is not correct. This is something we new was not ideal, and we will correct. If you are having trouble locking the MC and the alignment looks good, I would suggest requesting the input power to 2.8 W and see if that works.  

model restarts logged for Thu 26/Feb/2015
2015_02_26 02:46 h1fw0
2015_02_26 10:55 h1pemey
2015_02_26 12:16 h1pemey
2015_02_26 15:29 h1fw1
2015_02_26 15:38 h1broadcast0
2015_02_26 15:38 h1dc0
2015_02_26 15:38 h1fw0
2015_02_26 15:38 h1fw1
2015_02_26 15:38 h1nds0
2015_02_26 15:38 h1nds1
2015_02_26 15:39 h1nds1
2015_02_26 20:40 h1fw0

Three unexpected restarts. Thursday maintenance: h1pemey modified as part of RFM investigation (was reverted). DAQ restart to acquire new HAM1 vacuum gauge.

model restarts logged for Fri 27/Feb/2015
2015_02_27 12:01 h1fw0

One unexpected restart.

Elli, Dave, Evan

Summary

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.

Details

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:

• The sweeps for the negative detuning have much broader peaks than the sweeps for the positive detuning.
• The positive-detuning sweeps have two peaks per FSR, regardless of whether the PD is clipped or not. There also is not much difference between the clipped and unclipped data (by eye, anyway).

Also, some useful numbers:

• The as-built SRC length is (as far as I know) nominally 56.008 m, as given in D0902838, so we expect an FSR of 2.68 MHz.
• The SRM transmissivity is supposed to be 37%, so the finesse of the SRC at zero detuning is 13.5. [Although I am somewhat confused here: Kiwamu claims that the installed optic is SRM-w14, but galaxy lists SRM-05 (with 20% transmissivity) as "H1 install".]
• The above two numbers give the SRC HWHM as 99 kHz.
• With an as-built SRC Gouy phase of 19°, we expect a transverse mode spacing of 141 kHz.

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.

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.