REFL11 I, as seen in digital land, is connected to the slow output of the CM board. I tuned the demod angle of the REFL11 demodulator board by cable length back in ELOG 9850. It would be good to check that the phase is still good. If the CM board gains are at 0dB, we should be able to used the digital angle adjustment as normal. 

We need to get an interferometric estimation of the SRC length error / SRC sideband splitting, because if the 7.5cm hand-measured error is true, it looks like it might be hard to control the DRMI on 3F. 

I did some DRMI sensing simulations, to get an idea if sensing matrix elements might change as the CARM offset changes. Last night, I tried just going to zero CARM offset on ALS, and was having problems keeping the PRMI locked on REFL33, so I wanted to confirm that it should at least work in theory. 

Thus, I simulated what happens to the sensing matrix element in the vertex DoFs as the CARM offset is reduced, in both the PR and SR cases. I normalized all of the elements to PRCL at zero carm offset, to get an idea of what the good relative gains should be for MICH and SRCL. 

In the end, there don't seem to be significant DC gain changes, or demod angle fluctuations, in either the PRFPMI or DRFPMI case, as the CARM offset changes, which is good.

However, the SRC length as hand-measured, seems to mess up the MICH angle in the DRFPMI case, and really lowers the SRCL signal amplitude. 

To be fair, past efforts of simulating demodulation angles haven't always been borne out on the IFO, so we should still forge ahead experimentally until it becomes apparent that there is a real problem. 

Here are the simulations for the IFO as-is:

(A note on the plots. Though they kind of look like Bodes, they're just the sensing element represented as a complex number in the I-Q plane,I being phase=0 and Q = 90)

All three signals are along the I axis in the DRMI case, which seems like it would be tough to control, since we only have 2 3F diodes... We've been using REFL33Q when PRMIing, which is simulated at around 45 deg; it should be easy to verify this empirically. 

Here are the same plots with the SRC length corrected. Now MICH shows up mostly in the Q phase as desired in the DRMI case. SRCL in REFL165 also wins 20dB of optical gain, as well. 

To drive the point home, here's a simulated scan of AS110 and REFL55 Q to show the effect of the measured length error:

 The PMC wasn't locking very happily after this. I tweaked the pointing onto the PMC REFL diode, to make sure it was centered, and touched the alignment into the PMC. I also reset the FSS Slow output to zero. It took a little while for the laser to settle in, for some reason, but the transmission is up at 0.80 now. 

Tweaked MC2 pointing to get the MC transmission high enough to let WFS kick in, which nicely got the rest of the MC alignment done. After that, I offloaded the WFS into the MC suspensions. 

Lastly, I ran the command that Rana posted in ELOG 10391, to set the FSS input offset (From -0.18 to -0.06)

I have not had any success the past two days in getting an interferometric measurement of the SRC length. 

So, the question posed at today's meeting was: "How precisely do we need to change the SRC length to be able to lock the DRMI on 3F"

The two ways I could think to quantify this are:

• How much MICH -> [S,P]RCL cross coupling is ok?
• How much [S,P]RCL ->  MICH cross coupling is ok?

REFL33 should have its phase set to put PRCL along I, and REFL165 should have SRCL along I, so the simulation result that matters is the angle of MICH in these planes. The cross couplings are then given by the appropriate trigonometric projections. In the following plots, I used 10% as the acceptable cross coupling in either direction. 

Result:

Thus,

• To limit the MICH -> [S,P]RCL coupling to 10%, we must hit the ideal length within +- 1.2cm.
• To limit the SRCL -> MICH coupling to 10%, we must hit the ideal length within +- 2mm.
• It doesn't look like we can get the REFL33 angle totally to 90 degrees, REFL165 looks more promising.

Code (finesse + pykat + ipython notebook) and plots are attached. 

More AO efforts. No huge news. 

Came at AO from each side. For each sign, I lost lock just a few dB from the AO portion of the loop crossing unity gain. Both attempts were about arm powers of 1, which should correspond to ~300pm CARM offset, which I have simulated the crossover as possible with my current loop models (including latest MC loop). The gain steps were usually 6dB in between measurements. 

Positive polarity on CM board screen:

I made it to +5 dB of the last plot here, but the 6th broke it open. Gains on CM In2, CM AO, and MC In2 were -6, -4, -2 on that last, lock breaking, step. 

Negative polarity on CM board screen:

Lost it just 2dB above the last trace. Gains were -6, +1, -2 (So, overall 5dB higher than the other polarization)

Many things happened in between these two lock stretches, but I'm not sure what may or may not have affected things. They include:

• Jenne mentioned PRMI being fussy earlier in the evening. I adjusted REFL33 and POP22 angles during a PRMI lock, while CARM was held away with ALS. My simulations suggest that there are small changes to the 3F sensing when the arms are totally absent, but doing it at a finite CARM offset is closer to where we want it, it seems. 
• I tried using REFL165Q for MICH, since my simulations suggest a better MICH/PRCL angle, which would stave off cross couplings. Lined up excitations, etc., but no luck. 
• I measured the PRMI loops
  • found PRCL to have ~200Hz UGF, 8dB gain peaking. Maybe a little high, but didn't seem terrible. 
  • MICH had UGF of around 20Hz, with the FM gain at 0.8. By the shape of the phase bubble, the loop seems designed for higher bandwidth. I raised the gain to 2.5 for a 70ishHz UGF, and called in FMs 7 and 9 for additional triggered boosts. Things seemed to stay locked pretty well. 
• Lower excitation amplitude the second time around, measuring the AO loop. Looking at the CM output spectra, you can see the excitation wailing away; I wanted to avoid it.

The location of the CARM resonance peak lines up with my simulation, which is good, but there appears to be less phase than expected... I tried making sure that we don't have any whitening uncompensated for, but it looked ok. All my AO path loop model contains is the CM board TF (measured and fitted), the IMC seen as an actuator(measured and fitted), and the REFLDC optical TF (simulated in MIST). Maybe the DC path of whatever diode this is coming from needs to be included...

Discontinuities / glitches could be seen in the CM board fast output when MC board gains were changed, which isn't so nice. Incidentally, I notice now that each lock loss corresponded to a step of AO gain on the CM board.

Rather than using a CAD drawing, I used Gabriele's code from ELOG 9590 to try and judge if we could shorten the SRC by the appropriate length, without clipping the SR3-SR2 beam. 

Specifically, I used these lines:

% Move SRM 7.5 towards SR2, parallel to beam

delta=75;

dAS = BS2-AS; % Vector from SRM to SR2

dASmag = sqrt(dAS(1)^2+dAS(2)^2);

dMove = delta*dAS/dASmag; %  delta times unit vector

CS = CS+dMove;

draw_sos(CS, 180/pi*angles)

As a reminder, Gabriele's code used the following logic:

• We know the nominal dimensions of all of the suspensions
• We hand measured various distances between features of the suspension structures. (Corner to corner)
• A global fit, minimizing the maximum error, reconstructed the positions of the suspensions. 
• Beam positions assumed to be ideally aligned. 
• Beam trajectories traced out, and optical path lengths estimated (taking into account changing indices of refraction due to flipped mirrors)

In my opinion, this is the best estimate of beam trajectory that we currently have.

Thus, from looking at the plot above, I claim we can correct the SRC length without clipping the beam by moving the SRM forward by the required 7.5cm.

Although the measured distance may be off on the order of a cm (since our PRC correction had a 0.5cm disagreement between interferometric and hand distance measurements), this will nevertheless markedly improve our 3F DRMI sensing, based on my previous ELOG. 

Hence, given our discussions last week, Jenne and I will proceed to ready the interferometer for venting in the morning, by following the vent checklist.

Our sole objective for this vent is this move of the SRM. 

Steve, please check the jam nuts, and begin the vent when you get in.  Thanks!

Interferometer alignment is restored

ASS has been run on each arm, recycling mirrors were aligned by overlapping on AS camera. 

Notes:

• Mode cleaner alignment took some manual tweaking, locked fine around 1k counts. Still no autolocker.
• At this point, some light was visible on AS and REFL, which was a good sign regarding TTs. 
• Used green light to align ETMs to support a green 00 mode. 
• Ensured no recylcying flashes were taking place on AS camera and PRM face camera.
• Arms were locked using AS55, with the other ITM misalgined, for better SNR than PO[XY]. ASS brought arm powers to ~0.06, which is about what we would expect from 1k MC2 trans instead of 16k.
  • ASS Yarm required debugging, see below.
  • ETMX was getting kicks again. Top Dsub connector on the flange near the ground closer to the end table was a little loose. We should fasten it more securely.
• At this point, michelson alignment was good. Brought in PRM to see PRC flashes, REFL spot was happy. Brought in SRM to AS sppot. 
• Saved all optic positions. 
• Oplevs:
  
  • PRMs new aligned state is falling off the QPD.
  • ETMs and BS oplev centering are fine, rest are less good, but still on the detector.

ASS-RFM issue:

ETMY was not getting its ASC pitch and yaw signals. C1SCY had a red RFM bit (although, it still does now...)

I took a look at the c1rfm simulink diagram and found that C1RFM had an RFM block called C1:RFM-TST_ETMY_[PIT/YAW] and C1SCY had one called C1:TST-SCY_ETMY_[PIT/YAW]. 

It seems that C1TST was illegally being used in a real signal chain, and Jenne's recent work with c1tst broke it. I renamed the channels in C1RFM and C1SCY to C1:RFM-SCY_ETMY_[PIT/YAW], saved, compiled, installed, restarted. All was well.

There are still some  in SCY that have this TST stuff going on, however. They have to do with ALS, it seems, but are SHMEM blocks, not RFM. Namely:

• C1:TST-SCY_TRY
• C1:TST-SCY_GLOBALPOS
• C1:TST-SCY_AMP_CTRL

Ottavia was having some severe interaction latency today. Xorg was taking up >90% of the CPU, just sitting around. The machine was logged in to a desktop session with lots of graphical effects turned on. I changed the system default session to "gnome-fallback" in /etc/lightdm/lightdm.conf, which was already set as the default for controls, but wouldn't get chosen for the autologin that happens on boot. 

Hopefully this helps ottavia stay usable...

I think I found out why rossa was mad. 

An apt-get update on the 18th downloaded kernel 2.6.32-65-generic, so 2.6.32-58-generic, which what was previously chosen as a working kernel, had moved down in the grub ordering.

It turns out the grub configuration accepts strings, so I changed it to GRUB_DEFAULT="Ubuntu, with Linux 2.6.32-58-generic", ran sudo update-grub, and Rossa now seems to boot happily. 

[q, Jenne, Manasa]

ELOG Outline

• Aligned arms
• Took a bunch of photos of ITMY chamber. 
• Used Crystallaser to reverse trace POY beam path
• Realized real POY flashes were visible
• Tried adjusted POY steering to give us enough room to move SRM forward 3 in
• Not enough steering room
• Placed beam centering targets just before OM3 and after OM4, on far side of BS table
• Twisted SR2 by ~5 degrees
• Moved SRM laterally ~3 inches (beam had been hitting optic center, then suspension cage after SR2 twist)
• Moved SRM foward about 3 inches, adjusted angle for coarse retroreflection
• Measured distances between suspensions
• Tried running Gabriele's distance reconstruction code, results not looking so good; redundancy checks are off by ~1cm
• Started roughly repositioning OM1 and OM2 to get through beam targets
• Closed light doors
• ITMY pointing has gone bad, no green or IR resonance to be seen, still have IR and Green in Xarm, so TTs, BS are ok

I figured out that didn't change the initial guess for the fit routine in Gabriele's code. I also changed the fminsearch criteria to least squares fitting, instead of minimax. The consistency checks now look just as good as the previous time we did these kind of measurements, no disagreements bigger than 1.6mm. 

Thus, the current estimate of the SRC length after yesterday's motions is 5402mm, where we desire 5399mm. So, we will try to move SRM 3mm closer to SR2, after confirming that we are not clipping the POY beam. After all that, we will level the table.

Today so far:

• I moved SRM forward by 3mm
• Then I leveled the ITMY table 
• At this point, bringing the ITMY oplev beam back onto its QPD got me back to green locking and IR flashes 
• AS and POY beams are both making it out to their tables, as seen by IR card. (Though not to their in-air optics)

Here's my quick brain dump of things to do before we can pump down (anyone see anything missing?):

• Check the clearance of the POY beam at the SRM cage
• Re-do distance reconstruction measurements, confirm desired SRC length
• Lock the SRM cage down fully (right now, has 2 clamps on, and one laying unused)
• Align SRM for SRC flashes
• Adjust SRM OSEM positions as needed
• Adjust SRM oplev beam path, measure lever arm for calibration
• Confirm beam spots on output mirrors in ITMY and BS chambers are ok
• Take pictures of ITMY chamber. 
• Closeup checklist

POY has >2 inches of clearance from the SRM cage. 

Distance reconstruction indicates an SRC length of 5399mm, which was exactly our target. 

 [Koji, ericq]

We have completed the above points; the ITMY table is still level.

Despite what the wiki says, the SRM LR OSEM open voltage is ~1.97V instead of ~1.64, so we shot for half of that. 

The in-air steering of the SRM oplev return beam needs adjustment. I'll estimate the beam path length when I'm taking pictures and closing up. 

Left to do:

• Now that AS is back on diode, lock arms and align everything. Confirm everyone's happiness. 
• Take numerous pictures of ITMY chamber.
• Center oplevs
• Put doors on
• Close shutters
• Pump down
• Replace MC refl Y1 with the beamsplitter
• Turn PSL power back up

Related In-Air work:

• Fix POY steering
• Fix SRM oplev return steering

Everything is aligned, AS and POY make it out of vacuum unclipped, OSEM readings look good.

I set up the SRM oplev, centered all oplevs.

Tomorrow, we just have to take pictures of the ITMY chamber before we put the heavy doors on. 

I closed the PSL shutter as we didn't want to burn the mirror surface when we are not working.

Photos have been taken of the ITMY chamber, and uploaded to picasa. Here's a slideshow:

I've installed a new 2pin lemo cable going from the CM servo out to in2 of the MC servo board, and removed the temporary BNC. I used some electrical tape to give the cable some thickness where the lemo head screws on to try to strain relieve the solder joints; hopefully this cable is more robust than the last. 

I put an excitation into the CM board, and saw it come out of MC_F, so I think we're set. 

• Beamsplitter was put into MC refl path.
• HWP was rotated to maximize power into PMC. 
• MC autolocker locked, small alignment tweak led to WFS taking over
• Light present on REFL, AS and POP!
• After small adjustments to TTs and ETMY, locked Yarm with AS55, ran ASS. 
• Adjusted AS camera and RFPD alignment for ASS'd AS beam. 
• Left arm locked on AS55, aligned new POY beam onto POY11. Centered ITMY oplev while I was there. 
• After adjusting digital POY11 demod angle with an excitation into ETMY, arms were POX/POY locked and ASS'ed.
• PRM and SRM eyeball aligned

The IFO is ready for 3F DRMI comissioning 

I haven't been able to lock the DRMI tonight, neither with 1F and no arms nor 3F and arms held off with ALS... I tried previous recipes, and new combinations informed by simulations I've run, to no avail. 

I touched the alignment of the green beat PD on the PSL table, since the X beatnote was rather low, but wasn't able to improve it by much. I never took a spectrum, since it wasn't my main focus tonight, but the low frequency motion of both arms on ALS, as observed by RIN, was good as I've ever seen it. 

In our WFS work earlier today, Koji and I reset the WFS offsets, and it actually seems to have helped a good deal, in terms of the "fuzz" of MC REFL on the wall striptool. I had previously presumed this to be due to excess angular motion, but perhaps it is more accurately described as an alignment offset that let the nominal angular motion couple into the RIN more. 

Yesterday, Koji and I measured the transfer function of pitch and yaw excitations of each MC mirror, directly to each quadrant of each WFS QPD. 

When I last touched the WFS settings, I only used MC2 excitations to set the individual quadrant demodulation phases, but Koji pointed out that this could be incomplete, since motion of the curved MC2 mirror is qualitatively different than motion of the flat 1&3. 

We set up a DTT file with twenty TFs (the excitation to I & Q of each WFS quadrant, and the MC2 trans quadrants), and then used some perl find and replace magic to create an xml file for each excitation. These are the files called by the measurement script Koji wrote. 

I then wrote a MATLAB script that uses the magical new dttData function Koji and Nic have created, to extract the TF data at the excitation frequency, and build up the sensing elements. I broke the measurements down by detector and excitation coordinate (pitch or yaw).

The amplitudes of the sensing elements in the following plots are normalized to the single largest response of any of the QPD's quadrants to an excitation in the given coordinate, the angles are unchanged. From this, we should be able to read off the proper digital demodulation angles for each segment, confirm the signs of their combinations for pitch and yaw, and construct the sensing matrix elements of the properly rotated signals. 

The axes of each quadrant look consistent across mirrors, which is good, as it nails down the proper demod angle. 

The xml files and matlab script used to generate these plots is attached. (It requires the dttData functions however, which are in the svn (and the dttData functions require a MATLAB newer than 2012b))

I brought back the PMC, MC and Arms.

PMC:

• Same as when we replaced the busted sorensen, the kepco regulators in 1X1 (which power the FSS HV amp, PMC PZT and WFS) needed to be brought back up in the proper order. (Middle two are  + and - for the FSS, need to be rolled up in unison). Also the same as that occasion, sticky sliders prevented the full voltage range on the PMC PZT from being accessible. I touched every button on the PMC and FSS screens, which seemed to fix it. 
• I then realigned the PMC to ~0.80 transmission

MC:

• Needed to do some hand alignment to get a lock
• Measured spot positions, they were all under 2mm
• Despite centering the beams on the WFS and setting the offsets, WFS would not turn on successfully
• Also, the autolocker on megatron isn't doing anything but blinking
• Also also, MC2 is exhibiting some intermittent alignment wandering. The SUSDOF traces look like flat ramps lasting a few minutes. 

Arms:

• No green was evident anywhere, but it didn't take to much alignment tweaking to get IR flashes
• No signals were evident on RFPDs, confirmed light on PDs and power to demod boards. 
• Turned out the 11MHz Marconi was not doing anything, and needed to be reset to the modulation frequency in ELOG 10314 (which reminds me that I need to update the sticker on the marconi)
• Locked arms, ASS'ed, oplev spots were acceptable. 

The autolocker is now working, but I didn't change anything to make it so. I was just putting in some echo statements, to see where it was getting hung up, and it started working... This isn't the first time I've had this experience. 

It turns out IOO had a bad BURT restore. I restored from 5AM this morning, the WFS are ok now. 

We're back! It was entirely my fault.

Some months ago I wrote a script that chiara calls every night, that rsyncs its hard drive to an external drive. With the power outage yesterday, the external drive didn't automatically mount, and thus chiara tried to rsync its disk to the mount point, which was at the time just a local folder, which made it go splat. 

I'm fixing the backup script to only run if the destination of the rsync job is not a local volume. 

I've changed the LSC rack wiring a little bit, to give us some flexibility when it comes to REFL11. 

Previous, the REFL11 demod I output was fed straight to the CM servo board, and the slow CM board output was hooked up to the REFL11I ADC channel. Thus, it wasn't really practical to ever even look at sensing angles in REFL11, since the I and Q inputs were subject to different signal paths/gains. (Also, doing LSC offsets would do wonky things to refl11 depending on the state of the switches on the CM board screen.)

Thus, I've hooked up the CM board slow output into the the previously existing, aptly named, CM_SLOW channel. The REFL11 demod board I output is split to IN1 of the CM board, and the REFL11 I ADC channel. 

So, there is no longer hidden behavior in behind the REFL11 input filters, channels are what they claim to be, and the CM board output is just as easily accessible to the LSC filters as before. 

 [ericq, Jenne]

We attempted some of the same old CARM offset reduction tonight, but from the other direction. (We have no direct knowledge of which is the spring and which is the anti-spring side)

We we able to get to, and sit at, arm powers on the order of 5. Really, we kind of wanted just to push things to try and inform our current ideas of what our limiting factor is, so as to appropriately expend our efforts. 

Candidates include:

• ALS noise causing excess DARM motion
  • Means we need to DRMI to widen DARM linewidth, avoid sign flip in AS55, IR lock DARM sooner
• Intolerable sensor noise makes CARM wander too much, changing our plant more than our loops can handle
  • We should work on having live calibrated CARM spectra during lock attempts, to compare with Jenne's noise estimates, and see where/how/why we exceed it. 
• detuned CARM pole causes loop instability
  • Maybe some sort of notching can get us by
  • AO path could extend bandwidth, getting the pole into the control band 
• SqrtInv signals losing low frequency sensitivity due to radiation pressure, or DC sensitivity due to transmission curve flattening out
  • Bring in AO path for supplementary bandwidth, which lets us turn up loop gain / engage big boosts
  • Or, switch to REFLDC in digital land, which is nontrivial, due to different optical plant shapes.

We took many digital CARM OLTFs at different offsets; it never really looked like a burgeoning pole was about to make things unstable. The low frequency OLTF data had bad SNR, so it wasn't clear if we were losing gain there. We weren't at arm powers where we would expect the DC transmission curve to flatten out yet, from simulations (which is above a few tens).

My impression from at least our last lock loss was a DARM excursion. However, using the DRMI won't get rid of the second two points.

In my previous simulation results, I've always plotted W/m, which isn't exactly straightforward. We often think about the displacement that a given mirror actuator output will induce, but when we're locking the full IFO, radiation pressure effects modify the mechanical response depending on the current detuning, making the meaning of W/m transfer functions a little fuzzy.

So, I've redone my MIST simulations to report Watts of signal response due to actual actuator newtons, which is what we actually control with the digital system. Note, however, that these Watts are those that would be sensed by a detector directly at the given port, and doesn't take into account the power reduction from in-air beamsplitters, etc.

As an example, here are the SqrtInv and REFLDC CARM TFs for the anti-spring case:

The units of the SqrtInv plot are maybe a little weird, these TFs are the exact shape of the TRX W/N TFs with the DC value adjusted by the ratio of the DC sweep derivatives of TRX and SqrtInv. 

All of the results live in /svn/trunk/modeling/PRFPMI_radpressure/

I touched up the PMC alignment. 

While bringing back the MC, I realized IOO got a really old BURT restore again... Restored from midnight last night. WFS still working.

Now aligning IFO for tonight's work

 I made some measurements to try and see if any difference could be seen with different CARM offset signs. 

Specifically, at various offsets, I used a spare DAC channel to drive IN1 of the CM board, as an "AO Exciter." I used CM_SLOW to monitor the signal that was actually on the board. I used the CARM_IN1 error signal to see how the optical plant responded to the AO excitation. Rather than a swept sine, I used a noise injection kind of TF measurement. 

Here are plots of CARM_IN1 / CM_SLOW at different CARM FM offsets; I chose to plot this in an attempt to divide out some of the common things like AA and delays and make the detuned CARM pole more evident). The offsets chosen correspond roughly to powers of 2, 2.5, and 3. I tried to go higher than that, but didn't remain locked for long enough to measure the TF. 

By eye, I don't see much of a difference. We can zpk fit the data, and see what happens. 

 I went back into the DQ channels to look at the TF from AO injection to REFLDC (which is easy to do with this kind of noise injection TF).  

I fear that REFL does not seem to have as much phase under the resonance as we have modeled, lacking about 10-20 degrees. This could result from the zero in the REFL DC response that we've modeled at ~200ish Hz is actually higher. I'll look into what affects the frequency of that feature. 

It is, of course, possible, that this measurement doesn't properly cancel out the various digital effects, but the REFLDC phase curves do seem to settle to (+/-) 90 after the pole as expected. 

DTT XML file is attached. 

This CPU load may have been me deleting some old frame files, to see if that would allow daqd to come back to life. 

Daqd was segfaulting, and behaving in a manner similar to what is described here: (stack exchange link). However, I couldn't kill or revive daqd, so I rebooted the FB. 

Things seem ok for now...

When I came in, Rossa was booted to Ubuntu 10. I tried rebooting to select 12, but couldn't ever successfully boot again. Since Diego was setting up Allegra from scratch, I've wiped and done the same with Rossa. 

I've done some preliminary modeling to see if there is a good candidate for an IR DARM control signal that is available before the AS55 sign flip. From a DC sweep point of view, ASDC/(TRX+TRY) may be a candidate for further exploration. 

As a reminder, both Finesse and MIST predict a sign flip in the AS55 Q control signal for DARM in the PRFPMI configuration, at a CARM offset of around 118pm.

The CARM offset where this sign flip occurs isn't too far off of where we're currently losing lock, so we have not had the opportunity to switch DARM control off of ALS and over to the quieter IR RF signal of AS55. 

Here are simulated DC DARM sweep plots of our current PRFPMI configuration, with a whole bunch of potential signals that struck me. 

Although the units of most traces are arbitrary in each plot (to fit on the same scale), each plot uses the same arbitrary units (if that makes any sense) so slopes and ratios of values can be read off. 

In the 300 and 120pm plot, you can see that the zero crossing of AS55 is at some considerable DARM offset, and normalizing by TRX doesn't change much about that. "Hold on a second," I hear you say. "Your first plots said that the sign flip happens at around 120pm, so why does the AS55 profile still look bad at 50pm?!" My guess is that, probably due to a combination of Schnupp and arm length asymmetry, CARM offsets move where the peak power is in the DARM coordinate. This picture makes what I mean more clear, perhaps:

Thus, once we're on the other side of the sign flip, I'm confident that we can use AS55 Q without much problem. 

Now, back to thoughts about an interim signal:

ASDC by itself does not really have the kind of behavior we want; but the power out of AS as a fraction of the ARM power (i.e. ASDC/TRX in the plot) seems to have a rational shape, that is not too unlike what the REFLDC CARM profile looks like.

Why not use POPDC or REFLDC? Well, at the CARM offsets we're currently at, POPDC is dominated by the PRC resonating sidebands, and REFLDC has barely begun to decline, and at lower CARM offsets, they each flatten out before the peak of the little ASDC hill, and so don't do much to improve the shape. Meanwhile, ASDC/TRX has a smooth response to points within some fraction of the DARM line width in all of the plots. 

Thus, as was discussed at today's meeting, I feel it may be possible to lock DARM on ASDC/(TRX+TRY) with some offset, until AS55 becomes feasible.

(In practice, I figure we would divide by the sum of the powers, to reduce the influence of the DARM component of just TRX; we don't want to have DARM/DARM in the error signal for DARM)

Two caveats are:

• The slope of this signal actually looks more quadratic than linear. Is this ok/manageable?
• I have not yet made any investigation into the frequency dependent behavior of this thing. Transmission in the denominator will have the CARM pole in it, might get complicated. 

[Code and plots live in /svn/trunk/modeling/PRFPMI_radpressure]

I've been trying to figure out why daqd keeps crashing, but nothing is fixed yet. 

I commented out the line in /etc/inittab that runs daqd automatically, so I could run it manually. Each time I run it ( with ./daqd -c ./daqdrc while in c1/target/fb), it churns along fine for a little while, but eventually spits out something like:

Addendum:

On Monday, Jamie suggested checking out the situation with FB's RAID. Searching the elog for "empty blocks in the buffer" also brought up posts that mentioned problems with the RAID. 

I went to the JetStor RAID web interface at http://192.168.113.119, and it reports everything as healthy; no major errors in the log. Looking at the SMART status of a few of the drives shows nothing out of the ordinary. The RAID is not mounted in read-only mode either, as was the problem mentioned in previous elogs. 

I've added (TRX-TRY)/(TRX+TRY) to the DC DARM sweep plots, and it looks like an even better candidate. The slope is closer to linear, and it has a zero crossing within ~10pm of the true DARM zero across the different CARM offsets, so we might not even need to use an intentional DARM offset. 

 I've been able to repeatedly get off of ALS and onto (TRY-TRX)/(TRY+TRX). Nevertheless, lock is lost between arm powers of 10 and 20. 

I do the transition at the same place as the CARM->SqrtInv transition, i.e. arm powers about 1.0 Jenne started a script for the transition, and I've modified it with settings that I found to work, and integrated it into the carm_cm_up script. I've also modified carm_cm_down to zero the DARM normalization elements. 

I was thwarted repeatedly by the frequent crashing of daqd, so I was not able to take OLTFs of CARM or DARM, which would've been nice. As it was, I tuned the DARM gain by looking for gain peaking in the error signal spectrum. I also couldn't really get a good look at the lock loss events. Once the FB is behaving properly, we can learn more. 

Turning over to difference in transmission as an error signal naturally squashes the difference in arm transmissions:

I was able to grab spectra of the error and control signals, though I did not take the time to calibrate them... We can see the high frequency sensing noise for the transmission derived signals fall as the arm power increases. The low frequency mirror motion stays about the same. 

So, it seems that DARM was not the main culprit in breaking lock, but it is still gratifying to get off of ALS completely, given its out-of-loop-noise's strong dependence on PSL-alignment. 

I've taken a first stab at this. Through various means, I've made an estimation of the total noise RMS of each error signal, and plotted a shaded region that shows the range of values the error signal is likely to take, when the IFO is statically sitting at one CARM offset. 

I have not included any effects that would change the RMS of these signals in a CARM-offset dependent way. Since this is just a rough first pass, I didn't want to get carried away just yet. 

For the transmission PDs, I measured the RMS on single arm lock. I also measured the incident power on the QPDs and thorlabs PDs for an estimate of shot noise, but this was ridiculously smaller than the in-loop RIN. I had originally though of just plotting sensing noise for the traces (i.e. dark+shot), because the amount of seismic and frequency noise in the in-loop signal obviously depends on the loop, but this gives a very misleading, tiny value. In reality we have RIN from the PRC due to seismic noise, angular motion of the optics, etc., which I have not quantified at this time. 

So: for this first, rough, pass, I am simply multiplying the single transmission noise RMSs by a factor of 10 for the coupled RMS. If nothing else, this makes the SqrtInv signal look plausible when we actually practically find it to be plausible. 

For the REFL PDs, I misaligned the ITMs for a prompt PRM reflection for a worst-case shot noise situation, and took the RMS of the spectra. (Also wrote down the dark RMSs, which are about a factor of 2 lower). I then also multiplied these by ten, to be consistent with the transmission PDs. In reality, the shot noise component will go down as we approach zero CARM offset, but if other effects dominate, that won't matter. 

Enough blathering, here's the plot:

Now, in addition to the region of linearity/validity of the different signals, we can hopefully see the amount of error relative to the desired CARM offset. (Or, at least, how that error qualitatively changes over the range of offsets)

This suggests that we MAY be able to hop over to a normalized RF signal; but this is a pretty big maybe. This signal has the response of the quotient of two nontrivial optical plants, which I have not yet given much thought to; it is probably the right time to do so...

After the second of the two recent power outages, the outlet powering Chiara's external drive for local backups didn't come back. The modification to the backup script I made correctly identified that the drive wasn't mounted, and happily logged its absence and didn't try to stuff the internal drive with a copy of itself. However, I hadn't checked the logs to see if the backups were proceeding until today... maybe I should set up an email alert for these, too. 

I plugged the external drive into a live outlet, and mounted the 40mBackup drive with: sudo udisks --mount /dev/sdc1, which is a helpful command that puts the drive at /media/40mBackup as it should be, based on the drive label. 

The /cvs/cds backup is now proceeding, to make up for lost time. 

I spent some time trying to debug our inability to get MICH onto REFL165Q while the arms are held off with ALS, to no real success. 

I set up our usual repeatable situation of PRMI on 33 I&Q, arms held off with ALS. I figured that it may help to first sideband lock on REFL55, since 165 is looking for the f2 sidebands and maybe there is some odd offset between the locking points for f1 and f2 or other weirdness. 

REFL 55 settings:

Demod angle 98->126 (was previously set for PRY locking)

PRCL = 0.5 * REFL55 I (UGF of ~200 Hz) (FM gain unchanged from REFL33 situation of -0.02)

MICH = 0.125 * REFL55 Q (UGF of ~60Hz) (same FM gain as 33)

Some REFL55 offset adjusting had to be done in order to not disturb the 33-initiated lock when handing off. 

I also adjusted POP110 phase to zero the Q when locked, and switched the triggering over to 110I

The PRMI can acquire lock like this with arms held off with ALS, no problem. 

Here, I tried to hop over to 165. PRCL was no problem, needing a +1 on 165I. However, I had no success in handing off MICH.   I twiddled many knobs, but none that provably helped. 

I saw indications that the sensing angle in 165 is small (~20deg), which is not consistent with current knowledge of the cavity lengths. We last interferometrically measured the PRC length by letting the PRMI swing and looking at sideband splitting in POP110. At LLO, they did a length measurement by looking at demod angle differences in PRMI carrier vs. sideband locking. (alog8562) This might be worth checking out...

 I took some spectra of the error signals and MC2 Trans RIN with the loops off (blue) and on (red) during the current conditions of daytime seismic noise.

Short report: Further frustrated by 165 tonight. The weird thing is, the procedure I'm trying with the arms held off on ALS (i.e. excitation line in MICH and PRCL, adjust relative gains to make the signs and magnitudes mach, ezcastep over) works flawlessly with the ETMs misaligned. One can even acquire SB PRMI lock on 165 I&Q, with 80-90 degrees of demod angle between MICH and PRCL. The only real difference in REFL55 settings for misaligned vs. ALS-offset arms is an extra factor of two in the FM gains to maintain the same UGF, so I hoped that the matrix elements for 165 with misaligned arms would hold for ALS-offset arms. 

Alas, no such fortune. I still have no clear explanation for why we can't get MICH on 165Q with the arms held off on ALS. 

I also gave a quick try to measuring the PRCL->REFL55 demod phase difference between carrier and sideband lock (with arms misaligned), and got something on the order of 55 degrees, which really just makes me think I wasn't well set up / aligned, rather than actually conveying information about the PRC length...

Cdsutils r361 installed, for the "avg" updates. aLOG  

Earlier today, I did some simulations that suggested that PRC lengths on the order of a cm from our current estimated one could result in degenerate PRCL and MICH signals in REFL165 at 3nm CARM offset. I attempted more demod-angle derived cavity PRC length measurements with REFL11 and REFL55, but they weren't consistent with each other...

In any case, adding dual recycling, even with a SRC length off by 1cm in either direction, doesn't seem to exhibit the same possibility, so I spent some time tonight seeing if I could make any progress towards DRMI locking. 

I was able to lock SRY using AS55 in a very similar manner to PRY, after adjusting the AS55 demod angle to get the error signal entirely in I. I used this configuration to align the SRM to the previously aligned BS and ITMY. Oddly, I was not able to do anything with SRX as I had hoped; the error signal looks very strange, looking more like abs(error signal). 

I then was able to lock the SRMI on AS55 I & Q, the settings have been saved in the IFO configure screen.  I've used AS55Q for PRMI locking with a gain of -0.2, so I started with that; the final gain ended up being -0.6. PRMI/PRY gain for prcl is something like 0.01, so since I used a gain of 2 for locking SRX, I started the SRCL gain around 0.02, the final gain ended up being -0.03. I basically just guessed a sign for AS110 triggering. Once I lucked upon a rough lock, I excited the PRM to tune the AS55 angle a few degrees; it was luckily quite close already from the SRY adjustment. AS110 needed a bigger adjustment to get the power into I. (AS55: -40.25->-82.25, AS110: 145->58, but I put AS55 back for PRMI)

I briefly tried locking the DRMI, but I was really just shooting in the dark. I went back and measured various sensing amplitudes/angles in SRMI and PRMI configurations; I'm hoping that I may be able to simulate the right gains/angles for eventual DRMI locking.

Something to note, as we have the IMC angular controls under consideration:

Jenne has the DRMI locked right now. I took a look at the coherence between the POP QPD and MC2 transmission QPDs. (Since she's using ASC, I also included those control signals. The coherences are about the same, unsurprisingly)

Based on the observed coherences, from about 1 to 6Hz, IMC motion is responsible for a fair amount of the DRMI angular motion. Also, PIT and YAW couple differently. 

I've fallen down the rabbit hole of trying to reconcile our desire for newer versions of the Numpy and Scipy python packages with the use of our handy cdsutils tools. 

I've set up an installation of Anaconda python in /ligo/apps/anaconda. Installing pyepics, nds2, and cdsutils was straightforward, but there were a myriad of odd python packages that cdsutils depends on, that are typically installed at the OS level (python-gst, gobject, glib) which I just manually copied over to the anaconda directories. Also, the version of readline that anaconda ships with is somewhat borked (dark voodoo fix was found here: github link. The issue mentioned there wasn't why I needed the fix. Somehow libreadline was causing pyepics initialization to fail). 

I was initially hoping this kind of exercise would be useful, as having a separate python environment that we control buffers us from the system installation and allows us to use whatever version of packages we want, but the amount of hackery I did to get to get cdsutils to work probably didn't result in the most robust solution. (Maybe there was a better way!)

In any case, I have not changed any of our machines' default paths or environment variables. Instead, I have simply created an alias that points to Anaconda python: "apython"

Example:

Thus, Diego should now be able to complete his script that needs the newer Scipy, as well as CDSutils. 

Final note: I've tested z (read|write|avg) with $PATH modified to have /ligo/apps/anaconda/bin at the start, and they seem to work. If things seem to hold up, maybe we can replace the default command-line python, but its not strictly necessary. 

Given the checkout of the aLIGO BBPDs happening (aLOG link), wherein the PDs were acting funny, and Koji has made some measurements determining that intermodulation/nonlinearity of circuitry can corrupt 3F signals, I've made a similar measurement of the RF spectra of REFL165 when we're locked on DRMI using 1F signals. Maybe this could give us insight to our bad luck using REFL165...

In essence, I plugged the RF output of the PD into an AG4395, through a 10dB attenuator and downloaded the spectrum. I also did REFL33 as a possible comparison and because why not. The attached plots have the 10dB accounted for; the text files do not. 

REFL165 (Exposed PCB BBPD):

(What is all that crap between 8 and 9 fmod?)

REFL33 (Gold Box resonant RFPD):

Green beatnotes recovered.

It was just a matter of aligning the arm greens and PSL greens on the PSL table. I suppose something knocked the PSL alignment out of whack... I was also able to simultaneously see the green beatnote and IR beatnote respond to Yend laser temperature. 

Locked arms on POX/POY, checked RMS of ALS-BEAT[X/Y]_FINE_PHASE_OUT_HZ channels. 

• ALSY: 300Hz RMS
• ALSX: 700Hz RMS

These seem fine. Locked CARM and DARM on ALS, found IR resonances. 

ALS is back in business 

Now that I have followed the chain, the PD signal is indeed being amplified at the LSC rack. It goes into a ZFL-1000LN+ amplifier (~23dB gain at 165MHz and 15V supply), followed by a SHP-100 high pass filter, and then enters the RF IN of the demod board. 

I repeated the measurement in two spots.

First, I took a spectrum of the RF MON of the REFL165 demod board during DRMI lock; this was input-referred by adding 20dBm. 

Second, I inserted a ZFDC-10-5 coupler between the high pass and the RF input of the demod board. This was input-referred by adding 10dBm. 

My calibration isn't perfect; the peaks above the high pass corner seem to be different by a consistent amount, but within a few dBm. 

Thus, it looks like the demod board is getting a little under -40dBm of 165MHz signal at its input. 

 The "coupled" port of the coupler went to the AG4395 input, the output of the Highpass is connected to the "IN", and the "OUT" goes to the demod board. 

After some enlightening conversation with Koji, we figured that the RF amplifier in the REFL165 chain is probably being saturated (the amp's 1dB compression is at +3dBm, has 23dB gain, and there are multiple lines above -20dBm coming out of the PD). I took a few more spectrum measurements to quantify the consequences, as well as a test with the highpass connected directly to the PD output, that should reduce the power into the amplifier. However, I am leaving everything hooked back up in its original state (and have removed all couplers and analyzers...)

I also took some DRMI sensing measurements. In the simple Michelson configuration, I took TFs of each ITMs motion to AS55Q to make sure the drives were well balanced. They were. Then, in the DRMI, I took swept sine TFs of PRCL, SRCL and differential ITM MICH motion to the Is and Qs of AS55 and all of the REFLs. I constrained the sweeps to 300Hz->2kHz; the loops have some amount of coupling so I wanted to stay out of their bandwidth. I also took a TF of the pure BS motion and BS-PRM MICH to the PDs. From these and future measurements, I hope to pursue better estimates of the sensing matrix elements of the DRMI DoFs, and perhaps the coefficients for compensating both SRCL and PRCL out of BS motion. 

I'm leaving analysis and interpretation for the daytime, and handing the IFO back to Diego...