Jeff K, Betsy

While the SR2 M3 stage coil had previously been balanced using coil sensors, we tried to use the AS_C PD to repeat the measurement.  AS_C is an in-vacuum PD on HAM6 behind SRM.  Keita helped me center the beam on the PD with SR2 bias.  We then used the SR2 LOCK-IN to drive the SR2 in the pringle mode at 5Hz, with 100k aplitude, at varying coil imbalance states.  Unfortunately we could not see much change in the response when the M3 coils were balanced or unbalanced.  Attached shows the unchanged peaks between the 2 states of coil unbalanace.  SR2 pointing was restored to how we found it when we started.

Things to try next:

- Try on SR3

- Try using AS_B PD - a nearby WFS which does not have a lense in front of it - which maybe caused us a problem

GerardoM and RickS

GUIDANCE FOR A SYSTEM THAT IS ALREADY LOCKED

On the PSL_ISS.adl MEDM screen (see attached image), look at the strip chart in the top-right corner.
The diffracted power level should be about 7%. 
A few percent more or less is OK, but I suggest setting to near 7% at least once per week, say Tuesday during the maintenance period.

To change the diffracted light power, one adjusts the “REFSIGNAL” field in the lower left corner. 
A change in this parameter of 0.01 changes the diffracted power by about 1%, so make small changes.
A larger negative number (say going from -2.00 to -2.01) will decrease the diffracted light level.

This REFSIGNAL field is the DC laser power level (ignoring the minus sign) that the servo compares with
the “Output AC” level on the PD that is selected in the middle-left portion of the screen.

Note that in the screen snapshot the REFSIGNAL is at -2.03 and the PD A Output AC signal is at 2.03.
This indicates that the loop is operating properly; the loop tries to make the PD output be equal to the
reference level (without the minute sign, of course).

Notice that the diffracted light level is varying a bit but is close to 7% on the strip chart. 
At the middle-right edge of the screen the Diffracted Power field indicates 7.38%.  This is the field that is plotted in the strip chart.

GUIDANCE FOR WHEN THE SYSTEM IS NOT LOCKED

In the case that the ISS servo is not locked and you are having difficulty locking it, I suggest the following:

With the loop unlocked (Autolock OFF), observe the PD A AC output level. This may be a bit hard to do if the value is swinging a lot quickly.  
Set the REFSIGNAL level to about ten percent below this observed mean value.
Close the loop (Autolock ON) and observe the diffracted light time series in the strip chart.

If the diffracted light level increases and goes off screen at the top, then your REFSIGNAL setting is too low (absolute value is too small)
so you are not requesting enough light and the servo is trying to diffract a lot of light to give you the low level you requested.
Increase the (absolute value) of the REFSIGNAL field.

If the diffracted light level decreases and goes off screen at the bottom, then your REFSIGNAL setting is too high (absolute value too large)
and you are requesting more light than the servo can give you and still maintain some diffracted light headroom.
Decrease the (absolute value) of the REFSIGNAL field.

Once the system stabilizes, set the diffracted light level to be close to 7% by making small adjustments to the REFSIGNAL value.
Be patient, the time constant is pretty long and small changes make a big difference (on order one or two percent per 0.01 increments in the REFSIGNAL value).

Once the diffracted light level is near 7%, observe a few minutes of the strip chart data. 
The variations should be on the order of what is shown in the attached screenshot.

If all else fails, feel free to call me (Rick) at any hour, any day, and I will try to help over the phone.  My numbers are in the site directory.

Connected photodiode readouts from BSC1 Flange F1-3C1 to Baffle Photodiode Amplifier D1301017 Chassis (SN S1400065) in rack SUS-R5.

Updated the IMC guardian node:

• renamed to IMC_LOCK, in a move towards a more standardized naming scheme.
• specified that a NOMINAL state of LOCKED.
• added indices for all states:

jameson.rollins@operator1:~ 0$ guardutil states IMC_LOCK
100 LOCKED *
20 DOWN *
0 INIT
40 BOOST
30 ACQUIRE
10 FAULT

Screens and links were updated where appropriate (GUARD_OVERVIEW, IMC_CUST_OVERVIEW).

As reported before, ITMY OL is making a huge fake triangular wave motion of 10 minutes period mainly in YAW (CH1).

We know that the optic itself is not moving because we cannot see this anywhere else, e.g. look at CH7 (AS_C QPD) and CH8 (L2 stage OSEM of ITMY).

We know that this is not the intensity noise. The RIN of OL SUM (CH6) for this 10min thing is about 0.3% pk-pk while each quadrant (CH2-CH5) sees two orders of magnitude larger signal. In addition, the phase of SEG1 and SEG4 are the opposite of SEG2 and SEG3.

It appears that  either the OL laser or the receiver or both are moving in YAW (unless the electronics of all four channels are conspiring together, which is very unlikely).

We could not find any apparent correlation between this fake OL motion and various FMCS and PEM channels. AOS people, please investigate.

(Borja)

It has taken me a bit longer than I thought to write back here the final results to proof that the ion pumps are the main chargers of the ETMX and ETMY masses at LHO.

But finally here is the proof. This entry completes my previous entry here. In that entry we saw that when closing the ion pump gate valve at ETMY the charge values for all the quadrants and both orientations (pitch and yaw) became stable. The next obvious question was; what would happen when the ion pump gate valve was opened again?

The answer, shown next, is that the charge in all quadrants begin to vary again as you would expect if the ion pump was the main charger.

The next plots are a summary of all measurements I took at ETMY. The first set of 2 plots is Veff values in pitch and yaw and the second set of 2 plots is the slopes in pitch and yaw respectively. In pink are the set of measurements when the ion pump gate valve was closed (see the stability of the charge for nearly 6 days!) and in red are the measurements when the gate valve was reopened. It took almost a day of having the gate valve open to be able to see charge variations in all quadrants but these changes are considerable. In particular notice the quadrants UR and LL which changed charge from -140 to nearly discharge values. Remember that the labelling of the quadrants in these plots corresponds to the quadrant labelling on the CDS models which does not correspond with the real quadrants being driven. In particular the quadrant labelled LL is actually the driven quadrant UL. Which means that the quadrants suffering higher charge differences when opening the ion pump gate valve are the upper quadrants of the ETMY mass.

The question now is; How can the ion pump have such a quick charging effect in ETMY but we observed no charging effect at ETMX? Again I have the answer here: because we did not wait long enough at ETMX to see the charging effect. Fortunately despite not observing a charging effect in ETMX I did keep taking regular charging measurements on that mass with the ion pump gate valve open for 6 days. Next I plot the summary of all my measurements at ETMX (like I did above for ETMY). The area in pink shows all the measurements with the ion pump gate valve open. It is obvious the charge variations in comparison with all previous measurements at End-X with the ion pump gate valve close. In particular, for the first time at ETMX, we observe negative charges in some quadrants during the time in which the ion pump gate valve was opened.

I have attached to this aLog a compilation of the Veff and slope values for both pitch and yaw of all the measurements I did at End-X and End-Y and the time of those measurements. These data is given as a word file and as a Matlab file for easy operation. I also have included the Matlab figure versions of the above summary plots.

And finally for completeness I have also attached the pdf files with the last set of measurements both at ETMY and ETMX.

I have re-attached the LVEA test stand switches* to their respective H1 networks so that the front-ends may be used again.  This involved re-patching in the MSR (links via the H2B), and re-enabling the trunk ports on the MSR FE and DAQ switches (sw-msr-h1fe, sw-msr-h1daq).

*( sw-lvea-h2fe, sw-lvea-h2daq - for historical reasons)

• Jim W. ITMX ISI testing ongoing.
• Hugh, HAM4 Optical lever -> SUS -> Code.  Optical lever is on the works.
  • HAM4, ISI TF investigation.
  • HAM5, ISI TF ongoing.
• Richard, continue with chassis builds, look into seting up camers/illuminators.
• Gerardo, FC applied to test ITM for electrometer measurements today.
• John reported a chiller triped at the corner station, temperature in the VEA went up, but should be under control soon.

JeffK suggess that the changes in this TF may be due to the unlocked HEPI reducing the frequency and Q of these HEPI modes in the ISI.  I can only find HEPI unlocked but with no fluid flowing for HAM3.  In this attached plot, the modes in question (between 10 & 40 hz) have not changed.  Maybe the fluid needs to be flowing, maybe the loops need to be closed as well.  This is why we need to collect lots of data still.

(Alexa, Kimwau)

Yesterday we noticed that we actually had 14W going into the IFO. I adjusted the rotation stage, so that now we have 10W. Kiwamu locked the rotation stage

The ISS gain slider was adjusted from 8 dB to 10 dB.  Any higher results in a number of peaks present in the power noise spectrum.

The file spectrum2.png was taken with the gain slider at 11 dB.  The file spectrum1.png was taken with the gain slider at 10 dB.

Still processing the TFs but likely okay.  Put the HEPI back to cartesian alignment with the Iso offsets.  The hysteresis of HEPI is evident as I had to change the offsets to get back to position.  So if commissioners lose the HAM5 HEPI they may need to again adjust these offsets.  I've got the Rot DoFs to +-500nrads and the Tran DoFs to +-40umeters.

no restarts reported

Follow up analysis of the OMC scan by Dan (ALOG entry13660)

I believe this was done with a single bounce of ITMX.
ITMY had an oplev issue at the time as you can seen in https://alog.ligo-wa.caltech.edu/aLOG/index.php?callRep=13654

Frequency calibration

Calibratre data points using 0th- to 3rd-order carrier resonances and 0th- and 2nd-order sideband resonances as a frequency reference

Interpolate the frequency calibration by 11th order polynomials (see attachment "OMC_mode_scan_freq_calib.pdf")

Mode identification

Once the frequency is calibrated, the modes can be identified. As the beam is not filtered, it contains all of the sidebands and the sidebands of the sidebands including their higher-order spatial modes. (Attachment "OMC_modes.png" or "OMC_modes.pdf")

In the figure "USB/LSBn" indicates nth-order higher-order mode for upper or lower sidebands for 45MHz modulation.
"usb/lsb" indicates upper or lower sidebands for 9MHz modulation.
"2xUSB0" and "2xUSB0" means 2nd-order modulation sidebands for the 45MHz modulation (i.e. 90MHz sidebands).

Peak fitting

Peak heights of most of the modes are fitted (by hand). (Attachment "OMC_scan_LHO.pdf")

The decomposition of the modes are listed at the end of this entry

Mode matching

From the mode decomposition, the mode matching of the carrier is 0.86 +/- 0.01

Modulation depth

From the ratio of the sideband photocurrent and the carrier photocurrent, the modulation depth for each modulation was estimated

Modulation depth for f1 (9MHz): 0.198+/- 0.006

Modulation depth for f2 (45MHz): 0.305+/-0.003
 

Wiggling some RF cables for the ASAIR_A_RF45 demodulation, I found a bad SMA connector that was for the LO signal at the fied rack. Depending on stress on the connector, it could rotate the phase by about 90 deg. I attempted to fix it, but I could not find the crimping tool kit in the EE lab. We will do it tomorrow once the tools are found. The RF cable is currently disconnected.

I measured the spot position on PRM by using the usual angular dither technique (see for example LLO alog 5010) with PRY locked. It turned out to be pretty good.

• measured vertical off-centering = too low by 2.0 mm
• measured horizontal off-centering = off toward PR3 by 1.0 mm

(some settings):

• ITMX and SRM are intentionally misaligned.
• PRY is locked on the carrier light by REFL_A_RF45_I with a demod phase of 6.9 deg
• No whitening gain, but whitening stage 1 and 2 are engaged to obtain better signal-to-noise ratio.
• Feedback on PRM and PR2 as usual
• servo gain in LSC = -50 which should give a UGF of 30-60 Hz.
• Excitation in SUS-PRM_LOCK_P(Y) with an amplitude of 1000 counts at 10.1 Hz
• I used dtt to take a transfer function of (REFL_A_RF45_I) / (PRM_LOCK_P(Y)) 
• Before the measurement, PRM was tweaked to maximize the intracavity power

(results)

See the plot below.

(some notes)

• At the beginning of the measurement, the beam on REFL_A was at the edge of REFL_A. This resulted in bogus data because it introduced some kind of wave-front-sensing effect as the PRM angle was modulated.
  • This was fixed by moving the tip-tilt mirrors in HAM1, namely RM1 and RM2.
• I used a conversion factor of 42.2 mm for converting the imbalance alpha (see 40m elog 2863 for the definition) into the position of the rotational nodes.
  • According to D1101377-v2,  I used the following numbers to derive the conversion factor:
    • radius of the mirror: R = 75 mm
    • mirror thickness: L = 75 mm
    • magnet separation D = 95.45 mm

Please don't disturb the Matlab session.  -Hugh

(Alexa, Sheila, Keita)

• X-arm locked on green (see Keita's alog 13740 for more detail on alighment).
• We had to realign Green REFL B on ISCTEX.
• We plugged the 24.407079 MHz RF oscillator source back to the RF Amp, with the demod phase at 120.6deg. The ifr was set to some wrong value, and we didn't bother resetting it for now. For reference, the HIFOX configurartion was Mod Freq: 24.407363 MHz, Demod phase: 120.7 deg (alog 10227).
• COMM beat note was well aligned on ISCT1, we measured 1.5Vppk.
• DIFF and COMM demod controls cable was plugged into the wrong slot in the back of the concentrator. (We moved from slot 3 to slot 1).  This is now consistent with the pull list.
• There is a LO mon error for COMM demod. Will investigate tomorrow.

[Dan, Nic, Koji]

After we tamed the OMC QPD spot motions by the alignment servo, we turned on the high voltage supply
as the vacuum pressure allowed to do that.

Then we did notice that the OMC is already locked. WHAT? Did we miss the most exciting moment!?
Well, it was okay. It was a higher order mode. We shifted the PZT offset and locked at the highest peak that gave
us about 13mA total current.

We went down to LVEA and checked the mode shape. Yes. It was TEM00.

Statement: The OMC was locked

The position of the OMC trans spot was checked at ISCT6. Unfortunately the spot was hitting a pillar of the ISCT6 enclosure.
It is not nice to make a hole on the pillar. We probably need to move the table and think carefully how to connect the tube
to the table enclosure...

The OMC REFL with the best alignment looked a bull's eye as we suspected (attached photo #1). Dan is now measuring the mode scan for the mode matching ratio.

For the celebration, Nic cut open an OMC locking cantaloupe. Thanks Gerardo!