Rana and I went out to look at the breakout board for setting the gains/whitening for PR3. We found three out of the four segments were set to have one stage of whitening; the fourth had no whitening. Regardless, all four segments had an antiwhitening filter engaged in their filter banks.

We flipped bits on the breakout board as follows: on each segment, bits 2, 3, and 5 are high; all others are low. This gives one stage of whitening, and somewhere between 5000–10000 dc counts on each segment.

JimW HugoP, (Friday Oct 24th)

Fabrice recently pointed out that ETMY-ISI was not performing as well as the other LHO BSC-ISIs.

Jim adjusted his LV3 contollers and we tried them on Friday. Only the Y controller was changed. We looked at the logitudinal motion on ST1 of the ISI, and at the Pitch and Yaw motion seen by the (re-calibrated) oplev. We compared the ASDs, and RMS motions, before and after the adjutments.

Attached plots tend to indicate that Jim's controller adjustement helped reducing the ETMY logitudinal RMS motion. The new controllers were left ON on Friday.

Found that the DRMI was misaligned this afternoon. Trends show that the HAM5 optics moved and started shaking a little around 8 AM.

I'm able to get the ISI into damped mode, but it trips its vertical actuators if I try to transition into any of the 3 isolation modes via its guardian screens.

Similar situation for HAM5-HEPI. It also trips its vertical actuators (but for this one, the 'plot ACT Trip' button fails to produce a plot; it has some NDS or channel name problems in the script).

We are trying to track down what optics have moved, but this is hampered somewhat by the lack of a SUS DRIFT screen here at LHO.

Having this running would make it easier to find what optic has moved when we have these mysterious misalignments.

model restarts logged for Sat 25/Oct/2014
2014_10_25 07:26 h1fw1
2014_10_25 18:42 h1fw0

both unexpected restarts

After the whitening gain tune up for the BS OL QPD this week, we tried using the OL damping, but found that the performance was underwhelming.

Using the HSTS BS SS model from the SUS group in the noise budget directory, I made some filters to give us gain in the 0.1-3 Hz band and some low pass filtering above 10 Hz. Also some notches for the bounce/roll modes, but since I couldn't find the measured frequencies, I just copied from LLO.

The attached Bode plot shows the modeled pitch and yaw loop shapes. The yaw one is a little less stable due to the different yaw eigenfrequencies - I just used simple poles/zeros rather than try plant inversion. Rather than fine tune the OL loops we'd be better off tweaking the BOSEM damping loop for yaw to reduce the 2.1 Hz Q. I also chose to have the lower UGF be above 0.1 Hz to prevent too much interaction with the slow WFS loops. The 0.2 Hz bump in the yaw loop is an optional 'MSboost' filter that I've added to squash a 0.15-0.25 Hz microseismic peak. I would leave it on all the time, but we could have a few of these for different microseismic states. The 4th attachment shows the step and impulses of the loops with MSboost ON. The top left plot shows the step response of the pitch loop. The bottom left the step response of the yaw loop. The plots on the right show the responses of the pitch and yaw loops to step and impulse applied to the M2_L DoF. The impulse amplitude is sized to be close to what the lock acquisition transient is in force, but probably too long in duration.

I will show the before and after spectra, but the winds started audibly shaking the control room an hour ago, making it kind of an unfair comparison.  The 0.1-1 Hz ground noise has not changed much, but the 2-30 Hz noise is up by a factor of ~10.

A piece of good news: the broadband noise seen earlier this week in the yaw error signal is gone. The broadband noise in both pitch and yaw is now 1e-10 rad/rHz above 2 Hz. The huge peak at 20 Hz in the pitch spectrum is probably the flagpole mode of the cerulean pillar.

For all OL, we should add the OL feedback signals (OLDAMP_{P/Y}_OUT)to the DAQ and remove the OLDAMP_IN2 channels (not needed since we already record M3_OPLEV_OUT). 

These will be 256 Hz channels, so impact on frame size is minimal.

After our modifications to the DRMI LSC thresholds and loop gains on Thursday night, we had several short locks. Yesterday, we saw the same good locking behavior again. We found that the reason for the short lock duration was a typo in our trigger matrix: the PRCL boosts weren't getting turned on. After switching those and tweaking some filter shapes, the locking is fast and the locks last a long time.

The first attached plot shows the minute trend of our 4 hour lock last night. The 6 WFS loops are engaged during this time, as well as the DC centering. Near the end of the lock, there is a SRC mode hop and it stays locked like that for 1 hour. There are 20% fluctuations in the SPOP18 and SASY90. The control signal plots in the left hand column are scaled so that the full y-scale is approximately the full suspension DAC range (there is a divide by 4 from the LSC to the SUS DAC outputs). The MICH and PRCL loops are pretty calm, but there are several large transients in the SRCL loop which, I believe, corresponds to the TEM00 -> TEM01/10 mode hop.

The second PDF shows the error and control signal spectra for the DRMI LSC loops during a non-hopping epoch from last night.

PRCL: The error signal is white, so not much to be gained by changing the loop shape. The control signal is dominated by 0.05 - 0.5 Hz as is expected from the ISI performance.

MICH: The error signal is dominated by sub-Hz stuff, so we could squash it better with a 1:0.1 zero:pole stage if we found it necessary. The MICH control signal is dominated more by the sub 0.1 Hz motion than anythin else in the DRMI.  Usually we think this is the seismic amplification produced by the seismic isolation system.

SRCL: Similar story to PRCL, but more noise from <0.1 Hz than 0.1-0.5 Hz.

In all spectra, the large line at 131 Hz is a calibration line used for making sensing matrix and demod phase measurements.

After the lock loss, it never got it itself together. The ASC loops stayed railed and kept it from being aligned enough to lock. 
Also, the Guardian had a filter writing problem and so it stopped restoring the correct IFO state after the DOWN state 
(it was trying to set a filter which was under the control of the LSC filter module trigger logic and stopped because it didn't 
get the correct readback. This fault condition should be added to Guardian to make the log file more informative and we 
should fix this conflict in the LSC state defs). 
After clearing all of that stuff and bypassing the Guardian temporarily, the Michelson, PRMI and DRMI all locked fine.

model restarts logged for Fri 24/Oct/2014
2014_10_24 01:43 h1fw0
2014_10_24 21:43 h1fw0

both unexpected restarts

As reported in the previous alog (alog 14602), I analyzed several locking events in which the LSC controllers attempted to lock the DRMI.

All the data were taken before we made the improvement (alog 14602) in order to study how to make locking faster. The idea was to collect many cases such that we can try to understand what is going on in lock acquisition. 

In summary:

• I picked up 44 locking events between 0:06:00 to 1:06:00 in Oct-23 2014 UTC (see attachement 1)
• 22 events were categoryzed to be distinct events that were close to catch the DRMI. I call them class 1. (see attachement 2)
  • =>Out of 22, there were 2 events in which  we suceeded in locking DRMI. Each lasted for roughly 15 min or so.
• The rest of 22 events were determined to be events where the SRCL was too far in its displacement so that the SRCL control went in vain. I call them class 2. (see attachment 3)

• Effectively, the downtime was about 30 min or so in this specific period of time.
  • => this means that there were roughly one or two times of class 1 events per 2 min. But, success probability for each event was as low as 10 % which could make the downtime as long as order of 10 min.
• A reason why it was not locking in class 1 was that the duration when SRCL was within the linear range was too short.
  • => this may be improved by reviewing the SRCL loop design such that the loop reacts more quickly with less saturation in the DACs.

Analysis of class 1 events

Class 1 events were defined to be the ones which showed high POP RF18 vaules (> 100 uW) for more than 0.2 sec and showed high AS RF90 values of more than 2000 counts when POP RF18 was also high.

The plot shown below is a x-y projectin of POP18 and AS90 to show how these events evolved in this 2-D space:

Each event has different color from some others. As shown, a typical tack of class 1 events is to go down toward lower right in the plot and then jump up to upper right relatively quickly. This means SRCL is the last degree of freedom which comes into the linear range. 

Also I attach a collection of some relavent LSC signals in time series as attachement 4. As seen in the plot, the SRCL feedback saturate most of the time at the SRM DAC. This should be mitigated by some means in order to do an efficient SRCL control for locking. Also the upper right panel of the plot shows how long time SRCL stayed within the linear range. As shown, the staying time is typically order of 10 msec which is faster than the time scale of the SRCL control (~ 50 msec for the typical UGF of 20 Hz) or comparable. So this is not great.

Interestingly, most of the events showed a dip in the POPRF18 signal (upper left panel) roughly 10 msec after POP18 rose up. This may indicate some kind of misalignment as the LSC controller push the optics.

Class 2 events

They are the events in which we were not lucky enough to have the SRCL in the vicinity of the linear range. The plot below is the 2-D representation of how they evolve:

The typical track looks different from that of class 1. They stay in the lower right part of the plot most of the time.

Rana pointed out some rookie mistakes in the filter banks for the QPD centering in HAM6 (AS WFS and OMC QPDs).  We changed the DC3_P,Y loop and the OMC ASC loops to fix the following:

• The filter to provide 1/f loop shaping, a 1.4:1000, has been changed to match the observed resonance frequency of the HTTS and also to lower the high-frequency pole.  The ASC model runs at 2048Hz, and a pole nearly at the Nyquist frequency is Bad News.  The OMC model runs at 16384Hz, so the first implementation of these filters wasn't a problem, but anyways it doesn't make sense to have a rolloff frequency that high.  The filters have been changed to 1.6:300 for yaw, and 1.75:300 for pitch.  The resonance frequencies were taken from the Phase3a HTTS TF measurements.
• The integrator was changed to use the measured resonance values for the frequency of the zero.
• The oddly-named ELF100 was replaced by a cheby1 low-pass at 7Hz.  An elliptic bandpass at around 400Hz was removed.  Also, there's a +12dB gain step in front of the integrator for those times when you need, well, 4x more.

A comparison of the old and new filters is attached; the old version is in blue.  We lose phase at 1-10Hz but it shouldn't be a problem for these simple loops.  The DC4_P,Y filters still need to be changed, but the DRMI is under guardian control and sometimes the loops are turning on, so I'll wait for a quiet moment to fix them.  (Also the guardian filter settings are all wrong.)  Need to remember to add a 60Hz comb to these loops, too.

Alexa, Rana, Evan

This afternoon, we spent some time improving the ASC for PRMI.

PRCL (REFL_A_RF9_I→PRM)

We balanced the amplitude response of the segments on REFL_A_RF9. We let PRX swing freely, watched the fringes on each of the four segments, and then adjusted the gains until the responses had more-or-less equal amplitude. This gave a noticeable improvement in the POPAIR_B_RF18 buildup with PRMI locked on 9 MHz.

We wanted to increase the bandwidth of the PRCL loops to about 1 Hz, so that we could then implement MICH loops with a bandwidth of about 100 mHz. To this end, we did the following adjustments:

• We added an f² compensator (two zeros at 1 Hz, two poles at 55 Hz) to the PRM M2 pitch/yaw locking filters in order to undo the effect of the final PRM stage.
• We added a zero/pole pair (zero at 1.5 Hz, pole at 55 Hz) to the ASC-PRC filter bank, FM6. This is in addition to an exsting 1/f shape using FM1 and FM2.
• We increased the damping gain on PRM M1 to –1.5 for yaw and –5 for pitch (they were –1 and –2 before). By doing this, we were able to increase the UGF of the PRCL loops to about 10 mHz, as inferred from step functions delivered to the PRM alignment.

MICH (AS_A_RF36_Q→BS)

We then balanced the amplitude response of the segments on AS_A_RF36, usig a similar method with free-swinging SRY (and we double-checked using free-swinging Michelson).

With the PRCL loops active, we engaged the MICH loops. Everything seems to work fine for about 1 minutes, until the MICH error signals started to run away.

IMPORTANT: for both MICH and PRCL ASC loops, we now feedback to M2 stage instead of M1.

Guardian

We updated the ISC_CONFIGS guardian script to include a PRMI ASC state. This handles the ASC in/output matrix, the ASC filter, and the suspension feedback to the M2 stage instead of M1. The DOWN state, restores the suspension feedback to M1. Right now, I have also copied and pasted this to the DRMI ASCs, since we expect to use something similar. The old code is commented so we can always revert. 

Times

PRMI was locked on the SB with both MICH and PRCL ASC loops turned on from October 25th 2014 00:54:10 to 0:55:30 UTC.

Next

We should measure the full sensing matrix between REFL/AS and PRM/BS, and use it to decouple these loops. Then apply this to DRMI. For DRMI we should include a SRCL loop, and possibly also feedback PRCL to PR2.

Gains (for reference)

ASC-MICH_Y_GAIN = 0.003, ASC-MICH_P_GAIN = 0.003, ASC-PRC1_P_GAIN = -0.03, ASC-PRC1_Y_GAIN = 0.1

8:00 LVEA is LASER HAZARD with Limited Access
8:20 ISS Diffracted Power was set to the proper values range.
9:00 Quick visit to the LVEA (with commissioner’s authorization)- Hugh/Mitchell.
9:10 Back from LVEA – Hugh/Mitchell
9:30 Testing PCAL channels at EndX VEA – Patrick/Shivaraj
9:35 Optics alignment on ISCT1 table by HAM1 – Kiwamu
9:44 Heading to EndY – Kyle
10:05 Returned from the LVEA – Kiwamu
11:09 Back from EndX – Patrick,Shivaraj
11:42 Kyle is back from EndY
11:45 Heading into the LVEA (checked with commissioners) – Betsy
13:51 Heading into the LVEA (checked with commissioners) – Travis/Krishna
13:58 Back from LVEA – Travis/Krishna

Attached is ASD comparing HEPI L4Cs on ETMY & ETMX.  I'm still working out the calibration but for comparison it is something.  It is pretty subtle mostly but ETMX is quieter than ETMY.  Not so subtle in a few places: 1 hz ...

Summary of results: 

• The rate of transient motion in the ground is about four times as high during windy time (~30MPH wind) versus quiet time (~3MPH wind) 
• But the rate of transient motion in the isolated stages is significantly more increased (in the worst case, ETMX ISI ST2 is about 13 times as glitchy during high wind) 
• The amplitude of transients with a peak frequency below ~30Hz was significantly increased during the windy time, but the ampltiude of events above ~30Hz appeared about the same as during relatively quiet time. 
• A summary of plots for ETMX is attached, and the complete study is here on the DetChar wiki

Details:

In response to Sheila's alog 14416 indicating high winds, DetChar looked at the transient motion behavior of ETMX and ITMY during high local wind speeds and compared it to quieter night time (low wind speed and BLRMS motion) from two days before. 

The ETG (Event Trigger Generator, or single-ifo burst pipeline) Omicron was run on a two hour stretch of both windy and quiet times for a subset of DOFs on all stages (ground motion, HEPI, ISI ST1, ISI ST2). Omicron searched for transients (bursts of excess signal power, distinct in time and frequency) between 0.1 and 64 Hz. 

Take away: If we find the transient motion events in optic table motion associated with high wind speeds couple to DARM, feed forward may be a good option to mitigate this effect. 

Kiwamu, Alexa,

This morning, we moved IM4, PR2 and PR3 in order to reduce the amount of the clipping that Keita found the other day (alog 14567).

I moved PR2 and PR3 approximately by +150 and +15 urad horizontally which are the angles that we tried the day before yesterday. As a result, this increased the recycling gain for the 45 MHz sidebands from 21 (alog 14532) to 25.

We may want to go further in these angles for more improvements, but first I need to go through some careful analysis to see if all the observed numbers makes sense.

(some details)

Before starting the project, we realigned the X arm using the green light. The idea is to use the X arm as a reference for recovering good alignment for the infrared light around the corner station. Also we checked the location of the ALS X green light in the GigE camera which can serve as a reference when we touch a picomotor. According to the centroid fitting, the ALS X beam was at (X.Y) = (406.5 pix, 239.7 pix).

After moving PR2 and PR3 to 784 and -162 urad respectivly in the YAW bias sliders, as had been observed, we lost the POP beam at ISCT1. So we moved the picomorot in HAM3 by (dX, dY) = (900, 0) counts using the ALS X green light as a guidance. After picomotoring, we confirmed that there was no clipping according to the camera images. Note that it seemed that this operation somehow introduced vertical displacement slightly in the POP and ALS paths. We did not correct the vertical displacement as it was not considerably large. We locked the infrared laser to the X arm in order to automatically fine-tune the angle of IM4 and PR2 using the REFL WFSs. At this point, we went to ISCT1 and realigned the POP path. In addition to the YAW displacement that we had to correct on ISCT1, the bottom periscope mirror of the POP beam was clipping the beam a little bit. So we steered the top periscope mirror to correct it. Note that the spot position on the top periscope mirror seemed fine and therefore we did not have to move the location of it. We did not correct the ALS path, but it looks like at least the X green light can hit the TRX diode.

We did an OMC scan to measure the power recycling gain. I repeated the same process as we did on this past Monday (alog 14532). The highest DCSUM I obtained for the 45 MHz sidebands was about 7.5 mA when the PRMI was locked. Note that the PRMI alignment was optimized by maximizing POPAIR_RF18 manually. A single shot measurement for the 45 MHz sidebands gave us DCSUM of 0.27 mA. Using the equation in alog 14532, we estimated the recycling gain to be 25.

After moving IM4, PR2 and PR3, the PRC build-up observed by POP18 increased roughly from 170 to 200 uW. Good.

(How much did we shift the beam on PR2 ?)

Actually, this is unclear to me at the moment. I need to look into this issue more carefully. Basically, we seem to have a contradiction between two expected shifts, one is a value derived from the IM4 angle and the other from the PR2 angle.

If we believe that the IM4 bias is accurate, we must have moved its angle by more than +500 urad. This means that the spot positin on PR2 must have moved by ~ 2 x 500 urad x 15 meter = 15 mm toward the positive y-direction, which sounds too large. On the other hand, if we use the PR2 angle instead, my ABCD analysis suggests an expected shift of 0.5 mm on PR2 toward the positive y-direction. So they don't match up at all. Something is wrong. Since both expected shifts are based on the suspension biases, we probably should check the accuracy of them.