In order to better understand how the composite signal would behave in the presence of noise, I decided to do a simple analysis of the cavity signals while sweeping through resonance.

My noise model was to just assume that a given signal has some rms uncertainty (error bars) and use linear error propagation to propagate from simple signals to more complicated ones.

I used the python package uncertainties to do the error propagation.

I assumed that the ALS signal, the cavity transmission, and the cavity PDH error signal all have some constant noise that is independent of the cavity detuning. Below is a sweep through resonance (x axis is cavity detuning in units of radians).

The shaded region represents the error on each signal.

Next I calculated the 'first order' calculated error signals. These being a raw PDH, normalized PDH, an inverse square root trans, and the normal ALS again. I tuned the gains so they match appropriately.

Here, one can see how the error in the trans signal propagates to the normalized and trans signals and becomes large are the fractional error in the trans signal becomes large.

Next I did some optimization of linear combinations of these signals. I told the code to maximize the total signal to noise ratio, while ensuring that the overall signal had positive gain. I did this again as a function of the cavity detuning.

Each curve represents the optimized weight of the corresponding signal as a function of detuning.

So this is roughly doing what we expect, it prefers ALS far from the resonance, and PDH close to the resonance, while smoothly moving into square root trans in the middle.

It's a little fake, but it gives us an idea of what the 'best' we can do is.

Finally I used these weights to recombine the signals into a composite, to get an idea of the noise of the overall signal. At the same time, I plot the weighting proposed by Koji's mathematica notebook (using trans and 1-trans, and a hard switch to ALS).

So as one can see, at least for the noise levels I chose, the koji weighting is not much worse than the 'optimal' weighting. While it is much simpler.

The code for all this is in the svn at 40mSVN/nicolas/workspace/2014-03-06_compositeerror

The ALS error (i.e. phase tracker output) is linear everywhere, but noisy.
The 1/sqrt(TR) is linear and less noisy but is not linear at around the resonance and has no sign.
The PDH signal is linear and further less noisy but the linear range is limited.

Why don't we combine all of these to produce a composite error signal that is linear everywhere and less-noisy at the redsonance?

This concept was confirmed by a simple mathematica calculation:

The following plot shows the raw signals with arbitorary normalizations

1) ALS: (Blue)
2) 1/SQRT(TR): (Purple)
3) PDH: (Yellow)
4) Transmission (Green)

The following plot shows the preprocessed signals for composition

1) ALS: no preprocess (Blue)
2) 1/SQRT(TR): multiply sign(PDH) (Purple)
3) PDH: linarization with the transmission (If TR<0.1, use 0.1 for the normalization). (Yellow)
4) Transmittion (Green)

The composite error signal

1) Use ALS at TR<0.03. Use 1/SQRT(TR)*sign(PDH)*(1-TR) + PDH*TR at TR>0.03
2) Transmittion (Purple)
 

I don't know why, but as you can see in Steve's plot from earlier this morning, the PMC transmission has been going down significantly all weekend.  The PMC refl camera was very bright.  I tweaked up the alignment (mostly pitch), and now we're back to normal. 

The IMC was having trouble staying locked all morning, and I'm hoping that this PMC adjustment will help - the MC already looks better, although it's only been a few minutes.

fb timing was off again.

 Morning seconds without adjustment.

Pd 76 and 77 are compared at 30 days of pumping. We spend 13-14 days at atmosphere  before each.

 Pump down 76 was with leaky ion pump gate valve. The ion pumps are not in use for years so they accumulated some higher pressure  PLUS the valve switching caos at computer reboot most likely

increased the ion pumps pressures to about 10-20 torr

I think one of the ion pump gate valve was not sealing well. This leak was holding back pump down speed at pd76

[EricQ, Manasa]

ALS common locked by actuating on MC2 and ALS Differential locked by actuating on ETMX and ETMY (Stable lock acquired for over an hour).

Common and Differential offsets were swept to obtain IR resonance in both the arms (arms stayed on resonance for over 15 minutes).

Procedure:

1. Configured LSC settings to allow locking using ALS error signals.

2. Locked common and differential using ALS error signals

Aux matrix
              ALSX    ALSY
------------------------------
XARM    1            -1
YARM    1              1
-----------------------------
X arm servo settings:
FIlters: FM1, FM5, FM6, FM7, FM9
Gain = -8.0

Y arm servo settings:
Filters: FM1, FM5, FM6, FM7, FM9
Gain = +8.0

Out matrix
    XARM    YARM
------------------------
ETMX    1    0
ETMY    0    1
------------------------

3. Transitioned CARM control output to actuate on MC2 instead of ETMX

SUS-MC2_LSC servo gain = 1.0
The transition was done in very small steps : actuating on MC2 in -0.01 steps at the outmatrix upto -1.0 while reducing the ETMX actuation to 0 simultaneously.

DARM still stayed locked only with actuation on ETMY.

4. Transitioned DARM control to ETMX and ETMY.

Used ezcastep to step up DARM control (Y arm output) actuation on ETMX and step down the actuation on ETMY.

Final output matrix
    Xarm    Yarm
-----------------------
ETMX      0    -0.5
ETMY      0     0.5
MC2    -1.0      0
-----------------------

Noise plot in attachment.

5. Finding arm resonance

Used ezcastep to gradually build up offsets in CARM (LSC-XARM_OFS) to find IR resoance in one arm (Y arm).
Introducing a small (order of 0.5) DARM offset (LSC-YARM_OFS) shifted the Y arm off-resonance.
Used CARM offset to get back the Y arm to resonance.
Changing CARM and DARM offsets alternately while tracking the Y arm resonance got us to a point where we had both the arms resonating for IR.

6. At this point the MC decided to give up and we lost lock.

Notes:
1. We found that the WFS2 YAW output filterbank had the output switched OFF (probably accidentally by one of us). This was reenabled. Please be careful while manually turning ON and OFF the MC WFS servos.

MC remained locked with WFS enabled all through last night and this morning. Koji dropped by and looked at the MC. The MC WFS servo, though stable, was at the edge of becoming unstable. This was because I did not touch the WFS pointing on the QPDs yesterday after realigning. So I recentered the WFS, reset the WFS filterbank offsets and reenabled the servo.

I measured the spot positions on MC mirrors for reference.

Spot positions in mm (MC1,2,3 pit MC1,2,3 yaw): [1.405767579680834, 0.79369009503571208, 1.3220430681427462, -1.2937873599406551, -1.1704264340968924, -1.2518046122798692]

 In addition, we have to make sure to not let the suspension DACs saturate and make sure that the impulse response time of the OL servo is short; otherwise the lock acquisition kicks or bumps can make it wiggle for too long.

CMG-40T handheld controller unit is missing its power supply. In order to zero the instrument one has to apply plus and minus DC voltage.

The wiring on this 10 pin Amphenol PT02E-12-10P is shown.

You don't need to make transition from ALS X/Y to ALS C/D. Just stabilize the arms with ALS C/D from the beginning.

I locked the arms using ALS error signals and the LSC filter modules. But when I try to acquire CARM and DARM using ALS, the arms lose lock when the matrix elements ALSX to Yarm and ALSY to X arm reach -/+0.9

What I did:

1. ALS locking of arms
(i) Found arm beat notes
(ii) Input matrix POX and POY elements set to '0'
(iii) Aux matrix elements ALSX to Xarm and ALSY to Y arm set to '1'
(iv) Power normalization matrix elements for TRX and TRY set to '0'
(v) Triggers for arm lock over ridden and the FM triggers were set to 'manual'
(vi) Arm servo gains set to '0'
(vii) All but FM5 were disabled
(viii) Phase tracker history reset and servo actuation set to ETMs
(ix) Servo gain increased in steps (+/-10 for the arms)
(x) FM1, FM6, FM7 enabled (see note 1 below)
(xi) FM9 enabled

Arms were locked with ~2000Hz rms

2. CARM and DARM locking
(i) Scanned the arms for IR resonance
(ii) Moved off-resonance (Stepped arm servo offsets by 30 counts)
(iiI) Stepped matrix elements ALSY to X arm and ALSX to Y arm ezcastep C1:LSC-PD_DOF_MTRX_6_29 +-0.1 C1:LSC-PD_DOF_MTRX_7_28 +0.1

Whenever the matrix elements reached -/+0.9, the arms were kicked out of lock. I don't see anything obvious as to why this is happening even after nearly 10+times of redoing.

Notes:
1. I found the filters for the arm servos different for X and Y. FM1 and FM8 were missing in one of the filter modules. Jenne remembered Rana modifying and removing the unnecessary filters in one arm. We put back FM1 (low pass filter) which might not be necessary for PDH lock but is necessary for ALS. FM8 is now added to FM7.
2. To self : Check ALS Y arm power outlets (60Hz frequency comb seen in the error signal)

The IMC has not been behaving well since this morning and totally not happy when Q was finishing his measurements. The WFS servo had large offsets in pitch. Looking back at the trend and using ezcaservo to restore the suspensions did not help.

I realigned the IMC and brought TRANS SUM to ~18000 and MCREFL to < 0.5. The spot positions are not very good; nearly 2 mm off in pitch on MC1 and MC3. But after the alignment of MC, the WFS servo offsets were below +/-20.

The MC has been locked stably with WFS servo ON for the last few hours.

P.S. I did not touch the WFS pointing or reset the WFS offsets.

 I have modified the script ALSchangeOffsets.py (in ..../scripts/ALS/) to also handle a "CARM" situation.  There is a new button for this on the ALS in LSC screen.  This script takes the desired offset, and puts half in the ALSX offset, and half in the ALSY offset.  Whatever offset you ask for is given the sign of the input matrix element in the ALS->CARM row of the input matrix.  For example, if you ask for a CARM offset of 1, and the matrix elements are ALSX->CARM=+1 and ALSY->CARM=-1 (because your beatnotes are on opposite sides of the PSL), you will get an offset of +0.5 in ALSX and -0.5 in ALSY, which should be a pure CARM offset. The offsets get set as expected, but I haven't had a chance to test it live while the arms are locked. 

I also want to write a script that will average the IN1 of the 1/sqrt(TR) signals, and put that number into the 1/sqrt(TR) offsets.  If this is run when we are at about half fringe, this will set the zero point of the 1/sqrt(TR) signals to the half fringe (or where ever we are).  Then, we need a script similar to the ALS CARM one, to put offsets into the CARM combination of 1/sqrt(TR)s. 

I think that putting the offsets in before the servo filters will mean that the signals coming out of the input matrices will already be at their zero points, so we won't have as much trouble shifting from ALS to IR.

At today's meeting, it was suspected that these noise levels were far too low. (ELOG 9660)

I've attached the math I did to get the conversions, as well as the dark noise SQRTINV spectra at various imitated transmission values and the python script that does the converting. 

I've gone over my calculations, and think they're self-consistent. However, a potential source of misestimation is the treatment of the Lorentzian profile simply existing with the coupled arm line width (38pm). The conversion to m/rtHz is directly proportional to the line width of the transmission peak, so if it is much broader in practice (because of imperfect PRC buildup or something), the noise will be that much worse.

I'm open to any other feedback about what I may have done wrong!

I measured the arm cavity losses as Kiwamu did way back in ELOG 5074.

I used the same logic as the ../scripts/LSC/armloss script, but did it manually. This meant:

1. Lock and ASS-Align both arms. 
2. Misalign the ITM of the arm that I'm not measuring, to get its spot off of AS
3. Take 10 seconds of ASDC_OUT data while the arm is locked. 
4. Unlock, misalign ETM of arm of interest, take another 10 seconds of ASDC_OUT
5. Relock, run ASS, goto #3

Analysis was done similar to ../scripts/LSC/armloss.m. This uses the nominal T values (.014 and 15e-6) to estimate the input power from the unlocked ASDC data, and the cavity reflectivity from the locked ASDC / input power. Then, loss is calculated by:

• Pin = ASDC(unlocked) / R1
• Rc = ASDC(locked) / Pin
• rc=sqrt(Rc), etc.
• Loss = 1 - (( 1 / r1r2)) * ( 1 - t1^2 r2 / (r1 - rc)) ^2

I did this for pairs of locked / unlocked data stretches. (Subsequent pairs maybe have slightly different things going on, but each pair was taken within a minute or so of each other)

Unfortunately, during the X Arm measurements, the MC was misbehaving with large REFL fluctuations, so I don't have confidence the results.

The Y Arm data seems fine, however. 

The Y arm loss is 123.91 +/- 10.47 ppm 

(Trial-to-Trial fluctuations dominate the fluctuations within each trial by far, and their standard deviation is what I report as the random error above)

This seems roughly in agreement with old values I've seen in the ELOG. I'll remeasure the x arm tomorrow during the day. Here's a plot showing the ASDC values of the Y Arm measurements. 

Step by step description of transition from 2arm ALS to Common/Differential LSC for FPMI

- Step 0: Place the frequencies of the arm green beams at the opposite side of the carrier green.

- Step 1: Activate stablization loops for ALSX and ALSY simultaneously.
  (Use LSC filter modules for the control. This still requires correct handling of the servo and filter module triggers)

- Step 2: Activate stablization loops for ALS Common and Differential by actuating ETMX and ETMY

- Step 2 (advanced): Activate stabilization loops for ALS Common by actuating MC2 and ALS Differential by ETMX and ETMY

- Step 3: Transition from ALS Common to 1/SQRT(TRX)+1/SQRT(TRY). Make sure that the calibration of TRX and TRY are matched.
  The current understanding is that the offset for 1/SQRT(TRX)+1/SQRT(TRY) can't be provided at the servo filter. Figure out
  what is the correct way to give the offsets to the TR signals.

- Step 4: Lock Michelson with AS55Q and then POP55Q (PD not available yet) or any other PD, while the arms are kept off-resonant using ALS.

- Step 5: Reduce the TR offsets. Transition to RF CARM signals obtained from POP55I or REFL11I in the digital land.

- Step 5 (advanced): Same as test6 but involve the analog common mode servo too.

- Step 6: Transition from ALS Differential to AS55Q

Independent test: One arm ALS (To be done everyday)

- ALS resonance scan

- Measurement of out-of-loop displacement (or frequency) stability 

- Check openloop transer function

Independent test: Common Mode servo for one arm

- Reproduce Decmber CM servo result of transition from one arm ALS to CM servo
  Insert 1/sqrt(TRY) servo in between?

- How can we realize smooth transition from ALS to POY11?

Not a whiteboard, but here's a cartoon of my oplev cost function cartoon.  For the "maximize this area" and "minimize this area", I plan to use ratios between the curves, and then give those ratios to a sigmoid function.

 Keven, Steve

1X6, 1X7 and 1X9 instrument racks floor space were cleaned today

 I was getting the Y Arm ready for Eric Q's loss measurements and so I looked at the noise and loop shape. The loop shape was strange:

You can see that the gain margin is too low at high frequencies. That's why we have >15 dB of gain peaking. Way too much! I think this is from Masayuki and Manasa increasing the phase margin at some point in the past. I lowered the gain by 3 dB from 0.1 to 0.07 and now the awful gain peaking is less. But what about the low frequency gain? Is there enough?

I calibrated the OUT channel with 14 nm/count (1/f^2) with a Q = 10 pole pair at 1 Hz. The error signal is done to cross over at 180 Hz. It looks like the resonant gain at 25 Hz is a little too much and the in-loop RMS is 10 pm. Jenne says the linewidth is ~1 nm, so this seems sort of OK. Except that the LIGO-I DARM RMS had to be <0.1 pm for ~the same linewidth. Do we need to do better before trying to bring the arms into resonance?

I've remove FM1 and FM8. I put the RollRG of FM8 into the BounceRG and renamed it BounceRoll. Also changed the Y-arm restore so that RollRG and the 5,5:0,0 are no longer triggered automatically since the double integrator was overkill and we already have a 1:0 in FM2. I also lowered the peak gain for the roll mode RG from 30 to 10 dB because it was also overkill. We've gained a few more degrees at the UGF.

Successful PRMIsb locking with REFL165I/Q

My previous entry suggested that somehow the REFL165 signals show reasonable separation between PRCL and MICH, contrary to our previous observation.
I don't know what is the difference now. But anyway I took this advantage and tried to lock sideband resonant PRMI.

REFL165I was adjusted so that the signal is only sensitive to PRCL. Then REFL165I and Q were mixed so that the resulting signal shows.
(Next time, we should try to optimize the Q phase to eliminate PRCL and just use the I phase for PRCL.

At first, I used AS55Q for lock acquisition and then switched the MICH input matrix to REFL165.
Later I found that I can acquire PRMI just turning on AS55Q without turning off REFL165.

The REFL165 MICH signal had an offset of 15cnt. The lock was more robust and the dark port was darker once the MICH input offset was correctly set.

MICH OFS = 0
Turn on AS55Q only / or AS55Q + REFL156I/Q
Once it is locked and all of the FMs are activated, give -15.0OFS to MICH.
Turn off AS55Q.

Input ports:
AS55       WHTN: 21dB  demod phase -5.5deg
REFL165 WHTN: 45dB demod phase -156.13deg

Input matrix:
AS55Q x1.00 MICH
REFL165I x-0.035 + REFL165Q -0.050 MICH

REL165Q x+0.14

Triggers:
MICH POP110I 100up/10down / FM Trig FM2/3/6/7/9 35up 2down 5sec delay
PRCL POP110I 100up/10down / FM Trig FM2/3/6/9 35up 2down 0.5sec delay

Servo:
MICH OFS -15.0 / Gain -10 / Limitter ON
PRCL OFS 0 / Gain -0.02 / Limitter ON

Output matrix:
MICH ITMX -1.0 / ITMY +1.0
PRCL PRM 1.0

I have installed Dropbox on the 40m workstations, using the foteee account. 

I put it in /users/Dropbox.

As a side note, I did the install while sitting on Pianosa, but since I put the folder on the mounted hard drive, I think we should be able to use it from any workstation, although I have not yet confirmed this.

I wanted to check how the refl signals looked like.
I decided to measure the demod phase where PRCL and MICH appear, one by one.

The method I used is to actuate PRCL or MICH at a fixed frequency and rotate the demod phase such that
the signal at the actuating frequency disappears.

For the PRCL actuation, PRM was actuated by the lock-in oscillator with the amplitude of 100cnt.
For MICH, the ITMX and ITMY was actuate at the amplitude of 1000cnt and 1015cnt respectively.

The script I used was something like this

ezcaread C1:LSC-REFL11_PHASE_R
ezcaservo -r C1:CAL-SENSMAT_CARM_REFL11_Q_I_OUTPUT C1:LSC-REFL11_PHASE_R -g 100 -t 60
ezcaread C1:LSC-REFL11_PHASE_R

"11" should be changed according to the PD you want to test.
"Q" should be changed to "I" depending on form which quadrature you want to eliminate the signal

The option "-g" specifies the servo gain. This specifies which slope (up or down) of the sinusoidal curve the signal is locked.
Therefore, it is important to flip the signal angle 180degree if a negative gain is used.

Note: Original phase settings before touching them

REFL11  - 19.2
REFL33   135.4
REFL55    48.0
RELF165 -118.5

Here in the measurement PRMI was locked with AS55Q (MICH) and REFL55I (PRCL)


Without no serious reason I injected a peak at 503.1Hz. This peak is not notched out by the servo. There may have been
some residual effect of the feedback loops.

PRCL: By elliminating the peak from the Q quadrature, we optimize the I phase for PRCL.

REFL11,   minimize PRCL in "Q", gain, -1, -19.3659 deg
REFL33,   minimize PRCL in "Q", gain, -1, 132.813 deg
REFL55,   minimize PRCL in "Q", gain, -1, 20.9747 deg
REFL165, minimize PRCL in "Q", gain, -1, -119.004 deg

MICH: By elliminating the peak from the I quadrature, we optimize the Q phase for MICH.
If PRCL and MICH appears at the same phase, the resulting angles shows an identical number.

REFL11,   minimize PRCL in "I", gain, -1, -28.4526 deg
REFL33,   minimize PRCL in "I", gain, -1, 65.9148 deg
REFL55,   minimize PRCL in "I", gain, -1, 12.4051 deg
REFL165, minimize PRCL in "I", gain, -0.1, -143.75 deg

Then, the signal frequency was changed to 675Hz where the notch filters in the servo is active.

PRCL: By elliminating the peak from the Q quadrature, we optimize the I phase for PRCL.

REFL11,   minimize PRCL in "Q", gain, 1, -19.5224 deg
REFL33,   minimize PRCL in "Q", gain, -1, 135.868 deg
REFL55,   minimize PRCL in "Q", gain, 1, 48.5716 deg
REFL165, minimize PRCL in "Q", gain, 1, -122.398 deg

MICH: By elliminating the peak from the I quadrature, we optimize the Q phase for MICH.
If PRCL and MICH appears at the same phase, the resulting angles shows an identical number.

REFL11,   minimize PRCL in "I", gain, -10, -73.7153 deg
REFL33,   minimize PRCL in "I", gain, -10, 135.5 deg
REFL55,   minimize PRCL in "I", gain, 10, -2.55868 deg
REFL165, minimize PRCL in "I", gain, -5, -156.135 deg

This is just a test of the REFL channels for the arms signals. ETMX or ETMY were actuated.

YARM

REFL11, minimize ETMY in "Q", gain 100 => C1:LSC-REFL11_PHASE_R = 145.694
REFL55, minimize ETMY in "Q", gain 100 => C1:LSC-REFL11_PHASE_R = -60.1512

XARM

REFL11, minimize ETMX in "Q", gain 100 => C1:LSC-REFL11_PHASE_R = 142.365
REFL55, minimize ETMX in "Q", gain 100 => C1:LSC-REFL55_PHASE_R = -68.6521

We need to correctly setup crontab or rc.local for the frontend machines.

...yet again.

lsc and sus needed mxstream restarts after I restarted the ntp on fb.

  in order to Win in Loop Tuning, you must draw a cartoon of the cost function on the whiteboard before starting. Some qualitative considerations from our Workshop:

1. We want to use the oplev servo to reduce the motion of the mirror in the frequency band where the Oplev is quieter than the mirror, w.r.t. inertial space.
2. We can estimate the true mirror motion by some simple stack / pendulum model and compare it to the Oplev noise (not the dark noise). There are several contributions to the mirror angular motion due to the cross-coupling in the stacks and pendula.
3. Below ~0.2 Hz, we think that the oplev is not the right reference, but this is not quantitative yet.
4. The high frequency noise in the OPLEV ERROR is definitely electronics + shot noise.
5. We cannot increase the gain of the loop without posting some loop measurements (Bode + steps). Also have to post estimates of how much PRCL noise is being introduced by the Oplev feedback. Oplev feedback should make less length noise than what we have from seismic.

Give us a cost function in the elog and then keep tuning.

 Linus-1, Nodus and others  ac cords can be moved over to new blank yellow extension cord with multiple recepticals.

 Remove two red extension cords going to Smart UPS

[Jenne, Vivien]

We had an oplev tuning party this afternoon.  What we have learned is that we don't have a lot of intuition yet on tuning loops.  But, that was part of the point - to build some intuition. 

I took responsibility for the PRM, and Vivien took ITMX.  I think, in the end, all changes were reverted on ITMX, however Vivien took some data to try and make a computer-generated controller.  Before we got started, I locked and aligned the PRMI, and we centered the PRMI-relevant oplevs.

I moved my "boost bump" around a bit, to do more at higher frequencies, but had to sacrifice some of the "oomph", since it was starting to eat up too much phase at my UGF of ~8Hz.  I also made the stack resonant gain higher Q and lower height so that it didn't eat so much phase.  In the end, I have 25 degrees of phase margin, which isn't really great, but I do win a factor of 2 around 2 and 3 Hz.  Also, now I'm able to engage the 3.2 resgain at all, whereas with the previous filter shape I was not able to turn it on.

Maybe it's because I really want it to have helped, but I feel like the POP spot isn't moving as much when I'm locked on PRMI sidebands as it was earlier (we were seeing a lot of low frequency (few Hz) motion).  So, I think I did something good.

....fb timing issue happened again.

I thought that it was the thing that Koji and I saw the other day, where it was individual front end computers that had lost ntp sync, since it wasn't every core on every computer that was red, but reconnecting to the ntp server on c1lsc didn't do anything.  I then tried reconnecting to the ntp server on fb, and that fixed things right up.  Annoying.

 The MC is happy (but only for this tiny snapshot in time and most probably will go dysfunctional again as it has been for several months, as of this writing)

I've asked Manasa and Q to have a look at the MC in the morning.  Rana and I have found it to be slightly uncooperative in relocking after a lockloss.

We have found that just letting the autolocker go doesn't seem to work very well, and sometimes the MC just doesn't want to re-lock.  Closing the PSL shutter or disabling the autolocker for a few minutes (5ish) doesn't do anything, but leaving it closed for a long time (30 ish minutes) helps a lot.  The MC  will relock immediately after a nice long break. 

I have measured the sensing matrix at a variety of PRCL offset values.

During this each measurement, I also took a 20 second average of the POP 2f signals and the ASDC signal:

All of this data was taken during a single lock stretch. 

If / when I do this again, I want to go out to larger offsets.  I won't take as many points, but I do want to see how far I can go before I lose lock, and what the phase separation looks like at larger offset values (this time, I stopped at +700 counts which is about 0.7nm, to start checking the negative values. MC has been unhappy, so I wasn't able to take very many negative offset values.) 

I conclude that these sensing matrix measurements do see changes in the phase separation with PRCL length offset (what we saw / said yesterday), but that they do not line up with Q's simulation from this afternoon in elog 9671.

The simulation says that we shouldn't be seeing large phase changes until we get out to several nanometers, however the measurement is showing that we get large phase chnages with picometer scale offsets.  Yesterday, Rana and I said that the offsets due to RAM were small (of order picometer), and that they were therefore likely not important (elog 9668).  However, now it seems that the RAM is causing significant length offsets which then cause poor MICH/PRCL phase separation.

To Do List:

* Confirm MIST simulation with Optickle.

* Look at sensing matrix data pre-lockins (in the raw sensors).

* Check that there is no clipping anywhere in the REFL path (at least out of vacuum), and that the beam is sufficiently small on all 4 REFL diodes.

* Calculate the new PRC g-factor with the new length.

Last night we noticed an excess in the GUR1Z seis BLRMS on the StripTool. It was in the 0.1 - 0.3 Hz band. The rumor in the control room was that "this kind of noise has been showing up at night recently".

AS it turns out, this was not some environmental noise around the 40m at night, but instead its some internal servo oscillation in the GUR1 Z channel. In the Guralp seismometers, each channel is a different mechanical sensor (unlike the STS or T240), so when a single channel gets noisy it doesn't always implicate the others.

My guess is that the oscillation came from the Z channel needing to be recentered. I power cycled the interface box just now. The oscillation had already gone away, but I thought this might reduce the excess noise. Maybe it did, but the effect is tiny. You can see in the oscillation reference that the low frequency noise is high, but in the new trace its still kind of high. Needs to be re-centered correctly with the paddle. Or add a centering button to the interface box.

A new violin mode at 1303 Hz was ringing up this afternoon.  Rana and I added a notch for this.

RXA: while the mode at 1303.6 Hz was ringing down, I used the narrowband DTT technique to measure the Q (after turning on the notch in SUS-PRM_LSC). So its another frequency in the PRM (not the BS).

The time that it takes for 2 -foldings is 652 s, which implies that Q = pi*f*tau = 1.3e6. This seems too high by a factor of ~10, so my guess is that there is still some feedback path happening. The previous bandstop filter was centered around 1285 Hz and seems also weird that the PRM would have 2 violin modes with such different frequencies. Is the mirror rotated around the optic axis such that the standoffs are not at the same height?

I have recalibrated the REFL signals.

I first adjusted the demod phases until the I-signals lined up with the I-phase in the sensing matrix plot:

I then balanced the ITM drives by pushing on -1*ITMX and +1.015*ITMY, and seeing a minimum of MICH actuation in the I-phase of REFL55 (the PD I was locking with).

I then took a nice long measurement with DTT, and measured the peak heights in I and Q for each REFL diode.  I was driving PRM with 100 cts at 675.1Hz, and ITMX with 1000 cts at 452.1 Hz (and matching ITMY drive, to make pure MICH).  Knowing these numbers, and the actuator calibrations (PRM elog 8255, ITMs elog 8242), I know that I was driving PRCL by ~4.3 pm, and MICH by ~23 pm. 

For the I-phase calibrations, I find the peak height at the PRCL drive frequency, and divide 4.3 pm by that height.  For the Q-phase calibrations, I find the peak height at the MICH drive frequency, and divide 23 pm by that height.

This gives me the following calibrations:

 My calibrated REFL spectra then looks like:

 We had our annual safety inspection today.  Our SOPs are outdated. The full list of needed correction will be posted tomorrow.

The most useful found was that the ITMX-ISCT ac power is coming  from 1Y1 rack. This should actually go to 1Y2 LSC rack ?

 Please test this so we do not create more ground loops.

 And glossing over the MICH offset, here's the PRC offset plots in displacement, rather than radians.

The simulation is actually slightly different now. I now use nominal ITM T values (T=.014) instead of the random R=.99 I had in place. 

(correction: Field Power should be Field Amplitude in the first plot)

After speaking with Jenne and Gabriele, I did a little bit of simulating based on my earlier code that looked at the angle of MICH vs. PRCL, just with cavity detuning instead of macroscopic length change.

The zero point in the following plots is with the PRC locked on the sideband. The PRC detuning was done by changing the PRM-BS microscopic length (in terms of phase), and the MICH detuning was done by adding half of the detuning to the BS-ITMY distance, and subtracting half of it from the BS-ITMX distance. 

This plot is in terms of radians, so to roughly relate it to line width, here's a plot of the POP powers as a function of the PRC detuning. 

[Jenne, Rana]

We put offsets in the PRCL and MICH loops, and measured sensing matrices for each condition. 

What we found was that PRCL offsets of order 1/20th a linewidth (calibration to be checked tomorrow) would give significant changes in the angles of the REFL signal sensing matrix elements.  We broke MICH lock before we were able to put in a significant enough offset to see the demod phases change.

Because there are so many plots, I've put them together in a pdf. Each page has a set of radar plots for sensing matrix elements.  On the bottom of each page I note what our MICH and PRCL offset values were, and where the data is saved (in the 40m scripts directory). To see the differences, make sure your pdf viewer is set to single-page, not scrolling.

One major thing that we noted was that putting in a PRCL offset also changed the MICH offset.  When we increased the PRCL offset, we saw the AS port get brighter (but not as bright as when we were putting in large MICH offsets). 

Tomorrow, I need to check the calibrations we were using, to see how many meters we were moving the optics.  Also, Q, Gabriele and I need to meditate and do some modelling to figure out why the length offset could be affecting the degeneracy so strongly. 

We're exploring some effects which may give some funny macroscopic detuning and cause a near phase degeneracy in the REFL RF signals (see radar plot from Jenne below).

1) Alignment: we centered the oplevs to reduce fluctuations and then tweaked the BS and PRM alignment to build up the power. No significant change in the RF phases of the DOFs.

2) Measuring RAM: we set the dark offsets (by hand since the Masayuki script doesn't really work well anymore) to with 1 counts. We then locked the MC, misaligned the ITMs, and looked at the REFLOUT16 channels using the following command line:

z avg 12 C1:LSC-REFL11_I_OUT16 C1:LSC-REFL11_Q_OUT16 C1:LSC-REFL33_I_OUT16 C1:LSC-REFL33_Q_OUT16 C1:LSC-REFL55_I_OUT16 C1:LSC-REFL55_Q_OUT16 C1:LSC-REFL165_I_OUT16 C1:LSC-REFL165_Q_OUT16

C1:LSC-REFL11_I_OUT16     -12.04
C1:LSC-REFL11_Q_OUT16     -14.34
C1:LSC-REFL33_I_OUT16       0.43
C1:LSC-REFL33_Q_OUT16      -0.28
C1:LSC-REFL55_I_OUT16       2.84
C1:LSC-REFL55_Q_OUT16       5.64
C1:LSC-REFL165_I_OUT16      4.40
C1:LSC-REFL165_Q_OUT16      0.10

So these offsets are small in counts. In meters this corresponds to....less than 3 pm for any of the I signals.

Refl11I = 2.06e-12 meters

Refl11Q = 2.94e-10 meters

Refl33I = 5.28e-13 meters

Refl33Q = 1.07e-11 meters

Refl55I = 2.71e-12 meters

Refl55Q = 3.55e-11 meters

Refl165I = 3.07e-13 meters

Refl165Q = 8.63e-14 meters

3) Next we want to put large offsets into the error points of the loops

4) Change modulation depth

5) Check IMC length (todo for Q/Manasa for Tuesday - Wednesday)

1) Fixup REFL165: remove ND filters, get box for PD, dump diode reflections, put less light on diode, change DC transimpedance (?), max power dissipation on BBPD < 0.5 W w/ 25 V bias. Perhaps replace OP27 with TLE2027.

2) Make plan for fixing fiber layout up and down the arms. Need tubing for the whole run. Don't make it cheesy. Two fibers per arm.

3) Fix LSC model to allow user switching of whitening. Get back to working on AutoLock scripts (not Guardian).

4) Manasa, Q, Jenne, tune Oplev servos Tuesday morning/afternoon.

5) Reconnect the other seismometers (Steve, Jenne). For real.

6) Balance PRMI coils at high frequency.

 Demod boards should be at 90 deg, not 82.7 or 12 or yellow or ****. We should re-inject the RF and then set the D Phase in the filter module to make the signals orthogonal. 165 is a challenging one to get right, but its worth it since the signals are close to degenerate already.

 The X -arm fiber is in the high cable tray and it has has  coupler mounts.

 The Y -arm fiber is in the low cable tray and it has no coupler mounts.

 The fibers are only protected at entering and exiting the trays.

 We have only 68 ft spare 1.5"  ID protective plastic tubing.

[Koji, Jenne]

Koji noticed that the time on the front-end detail screens was not correct, and that the GPS time was not matching up between different models.  Koji ran the following on all front-end machines, and on nodus:

sudo ntpdate -b -s -u pool.ntp.org

Now, everything is fine, and every status light on the cds overview screen is green.

The LSC machine isn't any better, and now c1sus is showing the same symptoms.  Lame.

The link lights on the c1lsc I/O chassis and on the fiber timing system are the same as all other systems.  On the timing card in the chassis, the light above the fibers was solid-on, and the light below blinks at 1pps. 

Koji and I power-cycled both the lsc I/O chassis, and the computer, including removing the power cables (after softly shutting down) so there was seriously no power.  Upon plugging back in and turning everything on, no change to the timing status.  It was after this reboot that the c1sus machine also started exhibiting symptoms. 

I noticed that the fb lights on all of the models on the c1lsc machine are red, and that even though the MC was locked, there was no light flashing in the IFO. Also, all of the EPICS values on the LSC screen were frozen.

I tried restarting the ntp server on the frame builder, as in elog 9567, but that didn't fix things.  (I realized later that the symptom there was a red light on every machine, while I'm just seeing problems with c1lsc. 

I did an mxstream restart, as a harmless thing that had some small hope of helping (it didn't). 

I logged on to c1lsc, and restarted all of the models (rtcds restart all), which stops all of the models (IOP last), and then restarts them (IOP first).  This did not change the status of the lights on the status screen, but it did change the positioning of some optics (I suspect the tip tilts) significantly, and I was again seeing flashes in the arms.  The LSC master enable switch was off, so I don't think that it was trying to send any signals out to the suspensions.  The ASS model, which sends signals out to the input pointing tip tilts runs on c1lsc, and it was about when the ass model was restarted that the beam came back.  Also, there are no jumps in any of the SOS OSEM sensors in the last few hours, except me misaligning and restoring the optics.  I we don't have sensors on the tip tilts, so I can't show a jump in their positioning, but I suspect them.

I called Jamie, and he suggested restarting the machine, which I did.  (Once again, the beam went somewhere, and I saw it scattering big-time off of something in the BS chamber, as viewed on the PRM-face camera).  This made the oaf and cal models run (I think they were running before I did the restart all, but they didn't come back after that.  Now, they're running again).  Anyhow, that did not fix the problem.  For kicks, I re-ran mxstream restart, and diag reset, to no avail.  I also tried running the sudo /etc/init.d/ntp-client restart command on just the lsc machine, but it doesn't know the command 'ntp-client'. 

Jamie suggested looking at the timing card in the chassis, to ensure all of the link lights are on, etc.  I will do this next.


I measured the REFL 165 demod board's I/Q separation. 

Our 11MHz signal is currently 11.066092 MHz, so I put a signal to the RF input of the REFL165 demod board at 165.992380 MHz (15*11 MHz + 1kHz), with a signal of -13 dBm.

I then used the SR785 to measure the transfer function between the I and Q output channels. 

I got 82.7 degrees, at -0.64 dB. (I don't remember now if I had I/Q, or Q/I, not that it really matters). So, it seems that the REFL165 demod board has good separation, and at least isn't totally broken.

EQ UPDATE: Measured it wrong the first time, fixed now.

I measured the spectra of the SQRTINV channels from dark QPDs, with offsets adjusted to imitate various transmission levels. (While the dark noise stays constant in terms of, say, TRX counts, 1/sqrt(TRX) isn't linear, and so the noise coupling depends on the TRX offset). 

I did some calculations to turn this into the equivalent displacement noise when using SQRTINV as an error signal. This depends on where on the fringe you are locking, since the slope of SQRTINV vs. position is not constant, and can only really be treated as linear down to about 1/3 of a line width away from full resonance. In my calculations, I assumed a coupled arm line width of 38pm, and a full transmission of 700 counts in TRX/Y. 

The QPD dark noise RMS when two line widths away (TR = 40) is about 5fm, and only goes down from there.