I made a script that checks the N2 pressure, which will send an email to myself, Jenne, Rana, Koji, and Steve, should the pressure fall below 60psi.
The script checking the N2 pressure is not working. I signed into the foteee account to look at some of the picasa photos, and there are thousands of emails (one every 10 minutes for the past month!) with error messages. Q, can you please make it stop (having errors)?
The error looks like it's mad about a "caget" command. I don't have time to investigate further though.
I ran the "off" script for the Xarm ASS, followed by the "on" script, and now the Xarm ASS doesn't work. Usually we just run the freeze/unfreeze, but I ran the off/on scripts one time.
Koji, if you have some time tomorrow, can you please look at it? I am sorry to ask, but it would be very helpful if I could keep working on other things while the ASS is taken care of.
Steve, can you please find a cable that goes from the LSC rack to the IOO rack (1Y2 to 1X2), or lay a new one? It must be one single long cable, without barrels sticking it together. This will help me actuate on the Marconi using the LSC rack's DAC.
Q: please update this Wiki page with the go-back procedure:
Few 1/4 -20 socket cap head screw with washers were tested for optimum torque.
QJR 117E Snap On torque wrench was used. I found that 40 lb in was enough.
These numbers will varie with washers, material it's going into and so on!
The standard among high-strength fasteners, these screws are stronger than Grade 8 steel screws. They have a minimum tensile strength of 170,000 psi. and a minimum Rockwell hardness of C37. Length is measured from under the head.
Inch screws have a Class 3A thread fit. They meet ASTM A574.
Black Oxide—Screws have been heat-treated for hardness, which results in a dark surface color.
Rana is next to calibrate his feelings and declare the right number.
Than Koji....and so on
Once we a number, than I buy more torque wrenches to fit it.
RFpds box is moved from RF cabinet E4 to clean cabinet S15
Inventory updated at https://wiki-40m.ligo.caltech.edu/RF_Pd_Inventory
Large Area InGaAs PIN Photodiode -- C30642GH 6 pieces in stock
Large Area InGaAs PIN Photodiode with a 2,0 mm active diameter chip in TO-5 package with flat glass window
Large area InGaAs PIN photodiode with useful diameter of 2,0 mm in a T0-5 package with a flat glass window. The C30642GH provides high quantum efficiency from 800nm to 1700nm. It features high responsivity, high shunt resistance, low dark current, low capacitance for fast response time and uniformity within 2% across the detector active area.
Just randomly found this old entry from 3 years ago. We should never have installed a GAP 2000 - they are an inferior type of InGaAs diode. We should add to our list replacing these with a 2 mm EG&G diode.
How many 2 mm EG&G InGaAs diodes do we have Steve? Can you please find a good clean diode case so that we can store them in the optics cabinet on the south arm?
We replaced the dead photodiode on MC REFL PD with a new one (GAP 2000). We measured the frequency response of the PD and tuned the resonant frequency using inductor L5 (in the circuit diagram) to be 29.575MHz - over an average of 10 measurements.
Since the bandwidth of the fiber PD is ~ 1GHz, we could design the frequency discriminator to have a wider bandwidth (~ 500MHz). The output from the frequency discriminator could then be used to define the range setting of the frequency counter for readout or may be even error signal to the PID loop.
A test run for the analog DFD with cable length difference of 27cm gave a linear output signal with zero-crossing at ~206MHz.
Detailed schematic of the setup and plot (voltage vs frequency) will be updated shortly.
Since the Frequency counters have not been a reliable error signal for FOL PID loop, we will put together an analog delay line frequency dicriminator as an alternative method to obtain the beat frequency.
The configuration will be similar to what was done in elog 4254 in the first place.
For a delay line frequency dicriminator, the output at the mixer is proportional to where
L - cable length asymmetry, fb - beat frequency and v - velocity of light in the cable.
The linear output signal canbe obtained for
For our purpose in FOL, if we would like to measure beat frequency over a bandwidth of 200MHz, this would correspond to a cable length difference of 0.5 m (assuming the speed of light in the coaxial cable is ~ 2x108m/s.
ETMX sus damping restored.
BS & PRM oplev is restored. Note: the F -150 lens was removed right after the first turning mirror from the laser. This helped Rana to get small spot on the qpd.
It also means that the oplev paths are somewhat different now.
To test what the inherent angular noise of the HeNe 1103P laser is, we're testing it on a table pointing into the BS OL QPD with only a few steering mirrors.
From the setup that I found today, I've removed the lens nearest to the laser (which was used for the BS and PRM) as well as the ND filter (what was this for?) and the lens placed just before the BS QPD.
With the ND filter removed, the quadrant signals are now ~15000 if we misalign it and ~9000 each with the beam centered.
In order to calibrate the OLPIT_IN1 and OLYAW_IN1 signals into mm of beam motion, I misaligned the mirror just before the QPD. The knobs on there actuate the 100 TPI screws and the knurling on the knob itself has 10 ridges, so that's 36 deg per bump.
PIT cal ~ 1.55 (knob deg / count) -->> 10 microns / count --->>> 10 urad / count
YAW cal ~ 1 (knob deg / count) -->> 6.5 microns / count --->>> 6.5 urad / count
Distance from the 45 deg turning mirror to the QPD silicon surface is 23 cm. Distance between knob tip and fixed pivot point is ~4 cm. 1 knob turn = 0.01" = 0.254 mm = 0.254/40 radians of mirror angle.
So 360 deg of knob gives 2*0.254/40 = 0.012 radians of beam angle = 0.012 * 230 mm ~2.3 mm of beam spot motion. Or 6.4 microns of translation / deg of knob.
The distance from the face of the laser to the QPD is 96 cm.
The punchline is that the laser shows a level of noise which has a similar shape to what's seen at LLO, but 10x lower.
The noise at 0.05 - 0.2 Hz is ~2-3x worse than the PR3 at LLO. Not sure if this is inherent to the HeNe or the wind in our setup.
It doesn't work with the lens in there, but it seems pretty close. Please leave it as is and I'll play with it after 5 today.
Manasa and Steve,
Is this what you want? Dashed lines are dark.
BS and PRM oplevs are blocked for this measurement. I will restore to normal operation at 4pm today.
Going back to Wiener filtering for a moment, I took a look at what the T-240 noise level looks like in terms of pitch motion on one of our SOS optics (eg. PRM).
The self-noise of the T-240 (PSD, in dB referenced to 1m^2/s^4/Hz) was taken by pulling numbers from the Users Guide. This is the ideal noise floor, if our installation was perfect. I'm not sure where Kissel got the numbers from, but on page 13 of G1200556 he shows higher "measured" noise values for a T-240, although his numbers are already transformed to m/rtHz.
To get the noise numbers to meters, I use: . The top of that fraction is (a) getting to magnitude from power-dB and (b) getting to asd units from psd units. The bottom of the fraction is getting rid of the extra 1/s^2.
Next I propagate this seismometer noise (in units of m/rtHz) to effective pendulum pitch motion, by propagating through the stacks and the transfer function for pos motion at the anchor point of the pendulum to pitch motion of the mirror (see eq 63 of T000134 for the calculation of this TF). This gives me radians/rtHz of mirror motion, caused by the ground motion:
I have not actually calibrated the POP QPD, so I will need to do that in order to compare this seismometer noise to my Wiener filter results.
+1 to both Evan and Zach for prompt info and +2 to you for getting more stuff than you started looking for. -2 karma to whomever had swiped them and hoarded without signing. You should put a 40m sticker on both of them. Make sure to check / use fresh batteries. The Busby box is BJT based and works on low impedance sources, the Rai box works on anything, but (I am guessing) has less CMRR.
The Rai box was in the Cryo lab, and the Busby box was in the TCS lab. Neither had been signed out. Lame. Anyhow, thanks to Evan and Zach's memories of having seen them recently, they have been returned to the 40m where they belong. (Also, I grabbed a spare Marconi while I was over there, for the phase noise measurement).
The laser below is dead. JDSU 1103P, SN P845655 lived for 3.5 years.
JDSU 1103P died after 4 years of service. It was replaced with new identical head of 2.9 mW output. The power supply was also changed.
The return spots of 0.04 mW 2.5 mm diameter on qpds are BS 3,700 counts and PRM 4,250 counts.
It was replaced by JDSU P/N 22037130,( It has a new name for 1103P Uniphase ) sn P919639 of mfg date 12-2014
Beam shape at 5 m nicely round. Output power 2.8 mW of 633 nm
BS spot size on qpd ~1 mm & 60 micro W
PRM spot size on qpd ~1 mm & 50 micro W
Does anyone know where the Busby or Rai low noise pre-amp boxes are?
I think I need one in order to measure the noise of the Marconi. Right now, I am trying to measure the amplitude noise, but I'm not seeing anything on the SR785 above the analyzer's noise level.
The IFO_overview of oplevs seems ok, The servos are working fine. The green arms are locked, but master and oplev_summary monitoring screens are not.
I'm proposing to Erick G. to postpone the oplev noise measurement.
Q remotely reverted this change. Scripts seem to work again.
The SUS align/misalign scripts don't work after the new CDS utils upgrade.
I don't know if it's looking for the _SWSTAT channel to confirm that the offset has been turned on/off, or if it is trying to set that channel, to do the switching, but either way, the script is failing. Recall that our version of the RCG still has _SW1R and _SW2R, rather than the newer _SWSTAT for the filter banks.
ezca.ezca.EzcaConnectError: Could not connect to channel (timeout=2s): C1:SUS-PRM_OL_PIT_SWSTAT
Q, can you please (please, please, pretty please) undo this upgrade, and then hold off on any further changes to the system for a few weeks?
The DAC was fine. I realized tonight that the digital filter bank outputs were off, so I wasn't actually sending signals out. Oooops.
CDSutlils has been updated to the newest version, 474; there are some matrix interface methods that will make our locking scripts easier to read, modify, and maintain.
I've tested the ALS and CARM down scripts, and the LSC offsets script, and they all work fine.
I spent some time tonight trying to revive DRMI locking, with the arms held off on ALS. Not much news, I haven't been able to get more than a few short spurts of resonance, using 1F signals.
I did use SRY to measure the BS->SRCL coupling by exciting each mirror and looking at their relative coupling to AS55Q. I found that we should use a value of +0.28 +-0.01 in the MICH->SRM element.
It is here.
The 40m fenced area will start storing this large ~ 8000 lbs chamber on April 14. The asphalt will be cut, jack hammered the next 2-3 days in order to lay concrete.
Their schedule is from 8 to 5 starting tomorrow. We are asking them to work from 6 to 3pm
ETMX is about 12-15 ft away
I've been fiddling with the mode cleaner and green beat box today, to try and get an absolute frequency calibration for MC2 motion. The AC measurements have all turned out weird, I get fractional power laws instead of the 1/f^2 that we expect from the MC2 pendulum. At DC, I get a rough number of 15 green kHz per MC2 count, but this translates to ~7e-10 m/count which is in contrast to the 6e-9 m/count from 2009. I will meditate on this a bit.
In any case, while working at the IOO rack, I tuned the 11MHz modulation frequency, as was done in ELOGs 9324 and 10314, by minimizing one of the beats of the 11MHz and 29.5MHz sidebands.
The new modulation frequency / current IMC FSR is 11.066209 +- 1 Hz, which is a only a few ppm change from the tuning from last July.
This implies a IMC round trip length of 27.090800m +- 2um.
Attached is a plot showing the beat of 55-29.5 going down as I changed the marconi frequency.
I didn't verify that the loop gain was low enough at the excitation frequencies.
I put a 1kHz ELP in both arm servos, and got cleaner data for both. The ETM numbers are pretty much consistent with the previously posted ones, and the MC2 data now is consistent across frequencies. However, the MC2 numbers derived from each arm are not consistent.
With the data from ELOG 8242, this implies:
I did a quick measurement get an idea of the ETM actuator calibration, relative to the ITMs. This will still hold if/when we revisit the ITM calibration via the Michelson.
For the test masses, I locked the arms individually using MC2 as the actuator, and took transfer functions from the SUS-[OPTIC]_LSC_EXC point to the PO[X/Y]_I_ERR error signals. There were two points with coherence less than 99% that I threw away. I then took the fraction at each point, and am using the standard deviation of those fractions as the reported random error, since the coherence was super high for all points, making the error of each point negligible relative to their spread.
With the data from ELOG 8242, this implies:
MC2 data was taken with the arms locked with the ETMs. The results are not so clean, the fractions don't line up; there is some trend with excitation frequency... The ratio is around the same as the ETMs, but I'm not going to quote any sort of precision, since I don't fully understand what's happening. Kind of a bummer, because it struck me that we could get an idea of the arm length mismatch by the difference in IMC frequency / arm FSR. I'll think about this some more...
At the very end, the last 10 seconds or so, the POP110 power goes down, and sits at about half it's maximum value. POP22 isn't quite as bad, in that it still touches the max, but the RIN is about 50%. The carrier DC signals (TRX, TRY, POPDC) don't see this huge jump. I don't think I was touching anything the last few tens of seconds. I'm not sure yet how I can so significantly lose sideband power, without losing a similar amount of carrier power.
I saw this same kind of behavior in my locklosses on Wednesday night; we should check out the 165 data, and see if the 3f PRCL error signal shows some drift away from zero.
Also, it's odd that CARM_IN1 and REFL11_I_ERR have different low frequency behavior in the plot you posted. I guess they have some difference in demodulation phase. REFL11_I's bump at -40sec coincides with the dip in arm power and a rise in REFLDC, but ASDC seems pretty smooth, so maybe it is a real CARM fluctuation.
I set the REFL11 analog demodulation angle (via cable length) about a year ago (ELOG 9850), with some assumption about PRCL having the same demod angle as CARM, but this was probably set with the arms misaligned. We should recheck this; maybe we're coupling some other junk into CARM.
Small steps tonight, but all in the forward direction.
On one of my better locks, I saw a kind of weird phenomenon with the PRMI sideband powers versus the carrier powers:
For the last 100 seconds of this plot, I'm all 1f. Alignment is being handled mostly by Q's DC coupled ITM oplevs, and the transmission QPD ASC loops, although I was trying to adjust the offsets in the ASC loops to improve transmission for a bit.
The ring-ups at about -70sec in the CARM and DARM outs are the bounce mode.
I tried looking at 2D histograms of different combinations of channels, for the time around -30 seconds where things looked pretty clean. It looks like the offsets that Q put in last night (+1 for MICH_B and -3 for PRCL_B) are still about right. The PRCL_IN1 and MICH_IN1 were centered around zero at the maximum power points. CARM and DARM had small offsets, which I put into the DARM_B and CARM_B filter banks (0.0066 for DARM_B, and 0.027 for CARM_B), although these are small enough that I don't know that they really do anything.
As a break from locking for a little while, I tried to see if I could get the TT3 and TT4 DAC channels to work for me. I had hoped it would be a quick and easy task, but I'm not seeing signal out. Since it wasn't working, I decided to go back to locking for the night, and look into the DAC in the daytime. I want to use one channel as the IN2 input of the CM board, and another as the external modulation input to the Marconi for transfer functions, so I need them to work.
As a side note on the input to the Marconi situation, it occurred to me that instead of laying a new cable, I can borrow the POP55 heliax. We don't have a POP55 diode right now, and the other end comes out across the hall from the Marconi, so it would be pretty easy to have a medium-length cable go from ITMX table to the Marconi. Objections to this?
There was a period of short unexpected jackhammering this morning. I asked them to stop.
The good mood of GTRX was not changed.
blarg. Chrome ate my elog.
112607010 is the start of five minutes on all whitened 1F PDs. REFL55 has more low frequency noise than REFL165, I think we may need more CARM supression (i.e. we need to think about the required gain). This is also supported by the difference in shape of these two histograms, taken at the same time in 3f full lock. The CARM fluctuations seem to spread REFL55 out much more.
I made some filters and scripts to do DC coupling of the ITM oplevs. This makes maintaining stable alignment in full lock much easier.
I had a few 15+ minute locks on 3f, that only broke because I did something to break it.
Here's one of the few "quick" locklosses I had. I think it really is CARM/AO action, since the IMC sees it right away, but I don't see anything ringing up; just a spontaneous freakout.
I was poking around with the PDFR hardware today.
I moved the Agilent which had its screen projected on the monitor. I have put it back...but please verify the settings before using it for tonight.
As the POP55 demod board is actually demodulating the REFL55 signal, I have connected its outputs to the REFL55 ADC inputs. Now, we can go back to using the REFL55 input matrix elements, and the data will be recorded.
I have changed the relevant lines in the locking script to reflect this change.
It was only a mediocre locking night. I was foiled for a long time by 2 things, both of which are now taken care of in the scripts, so I don't waste so much time again.
Scripts are checked into the svn.
I used Q's handy-dandy 2D histogram plotter (..../scripts/general/dataHist, which I have taken the liberty of adding to the svn) to set the PRCL offset when I was locked on REFL165. Here is a version of the plot, when I had an offset of +10 in the PRCL filter bank. There was so much noise on the PRCL input that I quit bothering to try and put in an excitation or ramp the offset value. Note that I have since moved this offset to PRCL_A's offset instead, so taking this plot again should have PRCL_IN1 centered around zero.
I had trouble doing something similar for PRCL when I was locked on REFL55. At first, the offset was so poor that POP110 was only about half the value it was when locked on REFL165, and it had a huge amount of RIN. I tried just doing a z avg of the PRCL_B_IN1 (REFL55I) while locked on REFL165, and that said that REFL55I had an offset of +33.8 counts, so I tried an offset of -33.8 counts to get to zero. But, that was still terrible for POP110 power. As I increased the offset, eventually up to +30 counts, POP110 kept getting better and better. I lost lock at that point (while trying to get 10 sec of histogram data), so I'm not sure that +30 is the final value. I want to also get equivalent histograms with POP22 and POPDC (and maybe arm transmissions?) as the X-axis on these plots. There's no excitation, so all of these can be collected at once.
By babysitting the ITM alignment (looking at the rough DC values of the optical lever error siganls), and doing a little adjustment of the ASC differential offset, I was able to keep lock a few times for more than 2 or 3 minutes while all 1f. Not a whole lot longer than that though, even if I wasn't "poking" the interferometer other than maintaining alignment.
Alignment is making it tough for locks to last more than 10 minutes. Many (but not all) locklosses correlate with some optic drifting away, and taking all of the light with it. The other locklosses are the quick ones that seem to pop up out of nowhere; we haven't made any headway on these. We wanted to get to a state where we could just let the interferometer sit for some minutes, to explore the data, but got caught up with alignment and PRMI things.
We're finding that both ITMs experience some DC force when entering full PRFPMI lock. I will calculate the torque expected from radiation pressure + offset beam spot, especially for ITMX, where we choose the spot position to be uncontrolled by ASS.
I set up the QPD ASC servos to act in a common/differential way on the ETMs. The C1:ASC-XARM_[PIT/YAW] filter modules act on the common alignment, whereas the C1:ASC-YARM_[PIT/YAW] filter modules act on the differential alignment. This can soon be cleaned up with some model renaming to reduce confusion.
Using DC oplev values as a guide, we are hand tuning ITM alignment once the AO path is engaged and we see the DC drift occurring. Then, we set the QPD servo offsets and engage them.
In this manner, we were able to lock the interferometer at:
We made the PRMI transition to 1f numerous times, but found that the sideband power fluctuations would get significantly worse after the transition.
We found that the gains that were previously used were too small by a factor of a few. There is a DC change visible in REFL165 before and after the transition (Also POP55, aka REFL55, is not DQ'd ). Really, it isn't certain that we've zero'd the offset in the CARM board either, so REFL55's zero crossing isn't necessarily more trustworthy that REFL165's. We can go back in the data and do some 2D histograming to see where in the error signal space the sideband power is maximized.
Q is writing the locking elog for the night, but just to reply to this thread: The IFO worked well tonight, so things are at least not broken.
Unfortunately, this kind of trend plot is not detailed enough to know if something has gone bad in a quantitative way. But at least we can tell that the suspension wire didn't break.
The 40m fenced area will start storing this large chamber on April 14. The asphalt will be cut, jack hammered the next 2-3 days in order to lay concrete.
Jackhammering was happening around 7:30am
It looks like it did no harm. It is too early to say what may have moved. Rana's worrisome email was late.
The ground preparation is completed.
This is a very cool result. I'm surprised that it can work so good. Please post what frequency dependent weighting you used on the target before running the Wiener code.
I think its important to tune it to keep the low frequencies from getting amplified by a factor of 10 (as they are in your plots). The seismometers are all just noise acting like thermometers and tilt sensors below 0.1 Hz. Temperature and tilt do not couple to our interferometer very much.
It also seems weird that you would need 20th order filters to make it work good. In any case, you can always split the SOS up into pieces before making the digital filters. For LLO, we used 3 buttons in some cases.
Before locking for the evening, I wanted to try again implementing the Wiener filters that I had designed back in Jaunary (elog 10959).
I think that this happens when the beam gets too close to the edge of the QPD. We see this regularly in the ETMs, if they've been kicked a bit, but not enough to trip the watchdogs. I think it might be the step/impulse response of the RES3.3 filter, which rings for almost 20 seconds.
Anyhow, I've just recentered the BS oplev. It was at -21urad in pitch, and had more than 400 counts on the top two quadrants, but only about 100 counts on the bottom two. Now it's around 300 counts on all 4 quadrants.
As a totally unrelated aside, I have installed texlive on Donatella, so that I could run pdflatex.
I saw this kicking before
The BS oplev has been misbehaving and kicking the optic from time to time since noon. The kicks are not strong enough to trip the watchdogs (current watchdog max counts for the sensors is 135).
I took a look at the spectrum of the BS oplev error in pit and yaw with both loops enabled while the optic was stable. There is nothing alarmingly big except for some additional noise above 4Hz.
I have turned the BS oplev servo OFF for now.
ITMX, ETMY, BS and SRM are oscillating ?
I have 12 tick marks for times I got all the way to 1f for all 4 degrees of freedom in the PRFPMI. The CARM / DARM transitions now succeed more than they fail, which is nice.
At Q's suggestion, I am turning off all the violin filters in the MC2 path during the CARM transition. This also means that I don't need any of the notches that Den and I put into the CARM_A and CARM_B filter banks last week, which were right at the edges of the violin notches. Anyhow, this seems to make the transition much more likely to succeed. I don't ever use the CM_SLOW FM10 "crossover helper" that Q had to use last night. The violin filters are turned back on after the CARM transition is complete. We don't ever need those other notches.
I checked the REFL165 vs. REFL55 transfer functions for PRCL and MICH, and they are mostly flat. REFL55 seems like it'll give us extra phase for some reason.
I tried setting offsets for PRMI, but they seem to be strongly dependent on arm alignment. I ended up being pretty confused, and since all the REFL signals are pretty close to zero (when CARM/DARM on RF, PRMI on 3f), I have given up on that avenue for tonight.
I think many of my locklosses tonight (lost from the all 1f state) have been fast things, faster than the ADCs can handle. On the lockloss plots that I've looked at, the FSS PC drive is railed at 10V about 200msec before I lose lock. So, something (presumably in the fast CARM path) is making the MC/FSS loop unhappy. I have plugged in the Agilent to the Out2 of the CM board, so that it looks at REFL11. Unfortunately, this is after the input gain slider, so we don't see much until we're locked, but that seems fine. A video camera is pointed at the screen, so that I get real time spectra. It's hard to watch the TV at the same time as everything else, so I haven't witnessed the moment of lockloss in the fast spectrum yet. Be careful when walking down the Yarm. The tripod is partly in the walkway.
Q, I took a few TFs of the total CARM loop, although none of them are particularly good below a few kHz. I can't push hard enough to get coherence, without blowing the lock. TF data is in /users/jenne/PRFPMI/CM_TFs/CM_TFs_2Apr2015/ .
I was worried for a while that, after I transition PRMI to 1f, I hear lots of low frequency rumbling. However, watching the spectra (relative to references taken with CARM and DARM on RF, but PRMI on 3f), the low frequency error and control signals are staying the same for all 4 DoFs, but the high frequency for PRCL and MICH goes down significantly, so it's probably just that the low frequency stuff sounds more obvious, since it's not drowning in high frequency fuzz.
Whoops, I implemented the IOP downsampling filters wrong. Once I did that, it looked like just delay mismatch, so I added two more computation cycles for a total of four 16k cycles, which is maybe not so justified... Nevertheless, model and measurement now agree much better. Here are the corrected plots.
Here's the comparison of last night's crossover measurement to my loop model. Not stellar, but not totally off base. All of the digital filters are read directly from the foton filter file, and translated from their SOS coefficients, so they should be accurate. I may have tallied together the wrong arrangement of FMs, though. I will recheck.
Although I don't have a measurement to compare it with yet (as I don't know where the crossover was, the filter statesolder, etc. for the older loop measurements), here's what my current CARM loop model looks like, just for kicks. Here, only the first CM board boost is on. If we turn on some super boosting, we can probably ease up on some of the digital boosts, lower the crossover frequency, and put some lowpass that suppress the violin filters' effect on the crossover and reduces digital sensing noise injection.
Lastly, I'll just note that my current MIST model predicts that the CARM cavity pole should be at ~170Hz, and a peak arm transmission of 180 times single arm power. I saw powers of ~120 last night.
A paltry two locks tonight, but not entirely useless. I had some issues keeping the PRMI locked, which some additional boosts helped with. But, my feeling was that our crossover process is not tuned well.
At full lock, both sub-loops have high gain around the crossover region, so the usual DTT loop transfer function measurement produces a meausrement of Gdigital/G_aopath (or minus that. I.e. I'm not currently 100% which is the bad phase in this plot, though it intuitive looks like 0 ). Thus, we can directly look at the crossover frequency and the effect of the different filters there. (I've also been working on an up-to-date CARM loop model today, so this will help inform that).
Below, the black traces are the crossover at the end of the script when using the 120:500 "helper," and purple is without it. As we turn up the AO path gain, the trace "falls" from above, which explains why we can see instabilities around the violin filter.
Having the helper on definitely made the probability of surviving the first overall CARM gain ramp higher, but it's not currently intuitively clear to me why that is the case. Afterwards, we can turn the helper off, to keep the shallower crossover shape. This is what I've put in to the up script for now. I also added a few seconds delay for when the script wants to switch DARM to RF only; I found it was maybe speeding too fast through this point.
DTT xml attached
Have you tried a different set of laser temperatures?
Yep, that is how I got back to stable powers.