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ID Date Authorup Type Category Subject
  14718   Tue Jul 2 12:30:53 2019 gautamUpdateElectronicsAcromag crate switched to Sorensens

[chub, gautam]

We crossed off another couple of bullets today.

It took me ~1 hour to realize that c1susaux requries the running of sudo /sbin/ifup eth0 to be run in order to see the martian network - why???


  1. Stopped the c1susaux machine:
    • Moved alignment sliders of ITMX and ITMY to 0 as a precaution.
    • Shutdown the c1susaux machine so that it doesn't become unhappy with the missing Acromags when we power the unit down.
  2. Dialled down supply voltages on the +/- 15 V and +/- 20 V DC Sorensens. Current draw became 0 A on the front panel indicators.
  3. Chub tapped some new terminal blocks for +15 V DC and +20 V DC
    • This required some additional daisy chaining, which is why we dialled down the Sorensens.
    • New cables were made using the "standard" LIGO color scheme, which isn't really applicable in this case because we are using +15 V DC (orange sheath wire) and + 20 V DC (yellow sheath wire) whereas the closest LIGO standard voltages are +18 V DC and +24 V DC.
    • A test cable, presumably meant to be used in the electronics area (orange for +15 V DC) was destroyed for this work as we opted for speed rather than making a new cable.
  4. Disconnected bench power supplies that were powering the Acromags, and connected the new cables.
    • I opted to use 5 A fuses in the terminal blocks for these supplies as the current draw is pretty significant.
  5. Dialled the Sorensens back up to the nominal voltages:
    • Attachment #1 shows the front panels of the Sorensens before and after this work.
    • The current limit on the +20 V DC Sorensen had to be raised, because the Acromag box draws ~2.3 A on its own, whereas the previous current draw was 2.8 A.
  6. Brought the c1susaux machine back online. Took me a while to get to the bottom of why I wasn't able to see c1susaux on the martian, but eventually, I figured out the whole sbin/ifup thingy. 

I don't understand the exact chain of causation, but during this work, the fast c1sus model crashed. I had to go through a few iterations of the scripted vertex machine rebooting, but things seem to be back in a normal state now, see Attachment #2. Should probably run the IFO test suite to make sure everything is a-okay, but for now, I am able to lock the IMC so I'm moving on.

The main task remaining here is to take new pictures of everything and upload to the wiki. Also, need to update the Sorensen labels to reflect their current values, some of them are outdated.

  • Take photos of the new setup, cabling.
  • Remove the old c1susaux crate from the rack to free up space, possibly put the PSL monitoring acromag chassis there.
  • Test that the OSEM PD whitening switching is working for all 8 vertex optics.(verified as of 5/3/19 5pm)
  • New 15V and 24V power cables with standard LIGO connectors need to be run from the Sorensenn supplies in 1X5. The chassis is currently powered by bench supplies sitting on a cart behind the rack.
  • All 24 new DB-37 signal cables need to be labeled.
  • New 96-pin DIN connectors need to be put on two ribbon cables (1Y5_80 B, 1Y5_81) in the 1X4 rack. We had to break these connectors to remove them from the back of the eurcrates.
  • General cleanup of any cables, etc. left around the rack. We cleaned up most things this evening.
  • Rename the host computer c1susaux2 --> c1susaux, and update the DNS lookup tables on chiara.
Attachment 1: 1X5Sorensens.pdf
Attachment 2: CDS_20190702.png
  14719   Tue Jul 2 16:57:09 2019 gautamUpdateCDSc1sus is flaky

Since the work earlier this morning, the fast c1sus model has crashed ~5 times. Tried rebooting vertex FEs using the reboot script a few times, but the problem is persisting. I'm opting to do the full hard reboot of the 3 vertex FEs to resolve this problem.

Judging by Attachment #1, the processes have been stable overnight.

Attachment 1: c1sus_timing.png
  14720   Tue Jul 2 17:34:54 2019 gautamUpdateLSCIrides opened up on EY table

In preparation for the ASS debugging, I decided to check out the beam path on the EY table. In order to be able to do this, I had to setup the POY locking to trigger on AS110 instead of TRY (as is usual for this kind of debugging). Then I could poke an IR card in the beam path without destroying the lock.

There are two irides in the beam path immediately between the vacuum window and the harmonic separator that splits off the IR and green beams. I found that the beam was in fact getting clipped on both of them. It was also somewhat off center on a 2" beamsplitter that sends half of the light to the QPD (currently decommissioned). The purpose of these irides are (I think) to eliminate some ghost reflections of the green beam and also the Oplev beam. I opened up the irides until I felt that there wasn't any more clipping of the IR beam, but the appropriate ghost beams were still getting caught.

I also re-aligned the beam onto the TRY Thorlabs PD so as to better center it on the active area. In summary, the result of this work was that the TRY level went from ~0.6 to ~0.93. There may still be some scope for optimizing this - I tried running the Y-arm ASS scripts, and already, the loops don't run away any more. I'll do the systematic analysis of the servo anyways. But given that the IMC Trans lev el used to be ~15,500 counts and is now ~14,500 counts, I think ~7% drop in TRY level is in line with what we "expect" (assuming the pre-power-degradation TRY level was 1.000).

Note that these irides were installed (I think) by Yuki, and so cannot explain the ASS anomalies of July 2018 (i.e. it does not exonerate in-vacuum clipping of the beam, as Koji had already verified that the in-air path was clean back then).

  14722   Wed Jul 3 11:47:36 2019 gautamUpdateBHDPRC filtering

A question was raised as to how much passive filtering we benefit from if we pick off the local oscillator beam for BHD from the PRC. I did some simplified modeling of this. For the expected range of arm cavity round trip losses (20-50 ppm), I think that the 40m CARM pole will be between 75-85 Hz. The corresponding recycling gain will be 40-50, with the current PRM. I assumed 1000 ppm loss inside the PRC. The net result is that, assuming the single pole coupled cavity response, we will get ~8-9 dB of filtering at ~200 Hz of the intensity noise of the input laser field to the interferometer if we pick the LO beam off from the PRC (e.g. PR2 transmission), instead of picking it off before.

The next questions are: (i) can we do a sufficiently good job of achieving the required RIN stability on the LO field for BHD without relying on the passive filtering action of the PRC? and (ii) is the benefit of the PRC filtering ruined in the process of routing the LO field from wherever the pickoff happens to the BHD setup?

Attachment 1: PRCfiltering.pdf
  14736   Tue Jul 9 08:33:31 2019 gautamSummarySUSETMX PIT bias voltage changed by ~1V

After this activity, the DC bias voltage required on ETMX to restore good X arm cavity alignment has changed by ~1.3 V. Assuming a full actuation range of 30 mrad for +/- 10 V, this implies that the pitch alignment of the stack has changed by ~2 mrad? Or maybe the suspension wires shifted in the standoff grooves by a small amount? This is ~x10 larger than the typical change imparted while working on the table, e.g. during a vent.

Main point is that this kind of range requirement should probably be factored in when thinking about the high-voltage coil driver actuation.


We unstuck ETMX by shaking the stack. Most effective was to apply large periodic human sized force to the north STACIS mounts.

  14738   Tue Jul 9 18:06:05 2019 gautamUpdateLSCY-arm ASS in a workable state

The Y-arm ASS was tuned to be in a workable state. Basically, I followed Koji's recipe.

The SNR of the dither lines in the TRY and YARM control signals were checked - Attachment #1. The dither frequencies are marked with vertical dashed lines (can't figure out how to add 4 cursors in DTT so there's two in each row for a total of 4). A couple of days ago, when I was doing some preliminary checks, I found that the oscillator at 24.91 Hz caused a broadband increase in the TRY noise between DC and ~100 Hz. But today I saw no evidence of such behaviour. So I decided against changing the frequency.

The linearity of the demodulated error signals around the quadratic maxima of the TRY level was checked. I did not, however, investigate in detail the frequency-dependent offset Koji has reported in his elog. 

After this work, the TRY level is at 0.95. This is commensurate with the MC trans level being lower by ~7% relative to July 2018. Furthermore, the ASS servo is able to return to TRY~0.95 with a time-constant of ~5 seconds in response to misalignment of the cavity optics. After I investigate the X-arm ASS, I will reset the normalization for TRX and TRY.

Update 645pm: In the spirit of general IFO recovery, I re-centered the ITM and ETM oplev spots, and also the IR beam on the IPPOS QPD to mark the new input pointing alignment (the spot is slightly lower on the AS camera than what I remember). I then tweaked the XARM transmission to maximize it, and re-set the TransMon normalization. I edited the normalization script to comment out the normalizing of the TransMon QPD gains as the QPDs are in some kind of indeterminate state now. Attachment #2 shows the current status, you can also see the normalization being reset. LSC mode disabled for overnight.

Once the XARM ASS is also checked out, I propose moving back to locking the DRMI / PRFPMI configs. 

Attachment 1: ditherFreqs.pdf
Attachment 2: transRenorm.png
  14739   Tue Jul 9 18:17:48 2019 gautamUpdateGeneralProjector lightbulb blown out

Last documented replacement in Nov 2018, so ~7 months, which I believe is par for the course. I am disconnecting its power supply cable.

  14740   Tue Jul 9 18:42:15 2019 gautamUpdateALSEX green doubling oven temperature controller power was disconnected

There was no green light even though the EX NPRO was on. I checked the doubling oven temperature controller and found that its power cable was loose on the rear. I reconnected it, and now there is green light again. 

  14742   Wed Jul 10 10:04:09 2019 gautamUpdateSUSTip-Tilt moved from South clean cabinet to bake lab cleanroom

Arnaud and I moved one of the two spare TT suspensions from the south clean cabinet to the bake lab clean room. The main purpose was to inspect the contents of the packaging. According to the label, this suspension was cleaned to Class A standards, so we tried to be clean while handling it (frocks, gloves, masks etc). We found that the foil wrapping contained one suspension cage, with what looked like all the parts in a semi-assembled state. There were no OSEMs or electronics together with the suspension cage. Pictures were taken and uploaded to gPhoto. Arnaud is going to plan his tests, so in the meantime, this unit has been stored in Cabinet #6 in the bake lab cleanroom.

  14745   Wed Jul 10 16:53:22 2019 gautamUpdateSUSPRM watchdog condition modified

[koji, gautam]

We noticed that the PRM watchdog was tripping frequently. This is a period of enhanced seismic activity. The reason PRM in particular trips often is because the SIDE OSEM has 5x increased transimpedance. We implemented a workaround by modifying the watchdog tripping condition to scale the SD channel RMS by a factor of 0.2 (relative to the UL and LL channels). We restarted the modbus process on c1susaux and tested that the new logic works. Here is the relevant snippet of code:

# Disable fast DAC if variation tests too high
# PRM Side is special, see elog 14745
    field(DESC,"Tests whether RMS too high")
    field(SCAN,"1 second")
        field(INPA,"C1:SUS-PRM_ULPD_VAR  NPP  NMS")
        field(INPB,"C1:SUS-PRM_PD_MAX_VAR  NPP  NMS")
        field(INPC,"C1:SUS-PRM_LLPD_VAR  NPP  NMS")
        field(INPD,"C1:SUS-PRM_SDPD_VAR  NPP  NMS")

The db file has a note about this as well so that future debuggers aren't mystified by a factor of 0.2.

  14747   Thu Jul 11 12:42:35 2019 gautamSummaryCDSP2 interface board

I looked into the design of the P2 interface board. The main difficulty here is geometric - we have to somehow accommodate sufficient number of D-sub connectors in the tight space between the two P-type connectors. 

I think the least painful option is to stick with Johannes' design for the P1 connector. For the CM board, the P2 connector only uses 6 pairs of conductors for signals. So we can use a D-15 connector instead of 2 D-37 connectors. Then we can change the PCB shape such that the P1 connector can be accommodated (see Attachment #1). The other alternative would be to have 2 P-type connectors and 3 D-subs on the same PCB, but then we have to be extra careful about the relative positioning of the P-type connectors (otherwise they wont fit onto the Eurocrate). So I opted to still have two separate PCBs.

I took a first pass at the design, the files may be found here. I just auto-routed the connections, this is just an electrical feedthrough so I don't think we need to be too concerned about the PCB trace routing? If this looks okay, we should send out the piece for fab ASAP.

I will work on putting together the EPICS server machine (SuperMicro) this afternoon.


2. D040180 / D1500308 Common Mode Board

CM servo board itself doesn't need any modification. The CM board uses P1 and P2. So we need to manufacture a special connector for CM Board P2. (cf The adapter board for P1 T1800260). See also D1700058.

Attachment 1: IMG_7728.JPG
  14753   Thu Jul 11 17:58:38 2019 gautamUpdateEquipment loanTT suspension --> Downs

Arnaud has taken 1 TT suspension from the 40m clean lab to Downs for modal testing. Estimated time of return is tomorrow evening.

  14754   Thu Jul 11 18:15:22 2019 gautamSummaryElectronicsPSL/IOO rack checkout

I looked at the PSL/IOO racks to check for which boards, if any, require an additional P2 interface, so that we can try and design a generic one for the IMC/CM boards and whatever else may require it. While searching the elog, I saw that Koji and Johannes had already done this, see Koji's elog in this thread. Some remarks:

  1. D990155 seems to be unused in both PSL and IOO racks. The one in the PSL rack has some LEMO cables plugged in to the front panel, but they go nowhere. So I think that both of these are redundant (in the assessment below, only one was marked redundant).
  2. In the PSL rack, the "TTFSS Interface", "PSL PMC SERVO", and "DAQ INTERFACE" (which I think is obsolete) cards all have their P2 connectors daisy chained together, going to a cross-connect. Kruthi and I traced this to be going to a cross connect marked "J23-PSLRACK-CCP". In the PSL wiring diagram of which we have a hardcopy in the control room, it looks like these channels are related to the RefCav? So I think this is not required to be interfaced to our new Acromag DAQ system. 

Conclusion: Only the IMC Servo and CM boards need their P2 connectors connected to Acromag.It would be helpful to remove the TTFSS Interface board and figure out what exactly the pin-mapping for the backplane connectors are, but I didn't do this today because there is a "High Voltage" line going to the Interface Board and I'm not actually sure of the signal chain for the FSS servo.

  14755   Fri Jul 12 07:37:48 2019 gautamUpdateSUSM4.9 EQ in Ridgecrest

All suspension watchdogs were tripped ~90mins ago. I restored the damping. IMC is locked.

ITMX was stuck. I set it free. But notice that the UL Sensor RMS is higher than the other 4? I thought ITMY UL was problematic, but maybe ITMX has also failed, or maybe it's coincidence? Something for IFOtest to figure out I guess. I don't think there is a cable switch between ITMX/ITMY as when I move the ITMX actuators, the ITMX sensors respond and I can also see the optic moving on the camera.

Took me a while to figure out what's going on because we don't have the seis BLRMS - i moved the usual projector striptool traces to the TV screen for better diagnostic ability.

Update 16 July 1515: Even though the RMS is computed from the slow readback channels, for diagnosis, I looked at the spectra of the fast PD monitoring channels (i.e. *_SENSOR_*) for ITMX - looks like the increased UL RMS is coming from enhanced BR-mode coupling and not of any issues with the whitening switching (which seems to work as advertised, see Attachment #3, where the LL traces are meant to be representative of LL, LR, SD and UR channels).

Attachment 1: 56.png
Attachment 2: ITMXunstick.png
Attachment 3: ITMX_UL.pdf
  14762   Mon Jul 15 18:55:05 2019 gautamUpdateIOOMegatron hard-rebooted

[koji, gautam]

In addition to c1psl needing a reboot, megatron was un-ssh-able (although it was responding to ping). Clue was that the NPRO PZT control voltage was drifting a lot on the StripTool trace. Koji hard-rebooted the machine. Now IMC is locked, and FSS slow servo is also running.

  14763   Tue Jul 16 15:00:03 2019 gautamUpdateSUSMultiple small EQs

There were several small/medium earthquakes in Ridgecrest and one medium one in Blackhawk CA at about 2000 UTC (i.e. ~ 2 hours ago), one of which caused BS, ITMY, and ETM watchdogs to trip. I restored the damping just now.

  14765   Tue Jul 16 16:00:01 2019 gautamUpdateCDSc1iscaux Supermicro setup

I worked on preparing for the c1iscaux upgrade a bit today.

  1. Attachment #1: This shows where the 120 GB solid-state hard-drive and the 2 RAM cards (2GB each) are installed.
    • I found that it required considerable application of force to get the RAM cards into their slots.
    • Note: the 4GB RAM is broken up into two separate physical cards, each 2GB. The labeling is a bit confusing, as each card suggests it is by itself 4GB.
  2. OS install for c1iscaux:
    • I followed Jon's instructions (and added some of mine to the wiki page to hopefully make this process even less thinking-intensive).
    • To be able to use the IP address, removed "bscteststand" from chiara martian.hosts and rev.113.168.192.in-addr.arpa as the last mention I could find of this machine was from 2009 (and I'm pretty sure it isn't an active unit anymore). I then restarted the bind9 process. 
    • The hostname for this machine is currently "c1iscaux3" for testing purposes, I will change it once we do the actual install.
    • There was an error in the installation instructions to allow incoming ssh connections - it is openssh-server that is required, not openssh-client. This has now been fixed on the wiki page instructions.
  3. Acromag static IP assignment:
    • Assigned 2 ADCs (XT1221), 5 DACs (XT1541) and 5 sinking BIO units (XT1111) static IP addresses (and labelled them for easy reference) using the windows laptop and the Acromag IP config utility.
    • I saw no reason not to use the 192.168.114.yyy scheme for the Acromag subnet on this machine, even though c1auxex and c1vac both have subnets with this addressing prefix. For reasons unknown to me, Jon opted to use 192.168.115.yyy for the c1susaux Acromag subnet.
  4. Followed the excellent step-by-step to install EPICS, Modbus and Asyn.
    • This took a while, ~1 hour, dominated by the building of EPICS. The other two took only a couple of minutes each.
    • The same combination suggested on Jon's wiki, of Modbus R2-11, EPICS base-7.0.1 and asyn4-33, are the most current at the time of installation.
    • Couple of typos that prevented straight up copy-pasting were fixed on the wiki.
  5. Playground for testing new database files:
    • made a directory /cvs/cds/caltech/target/c1iscaux3 and copied over the .db files from /cvs/cds/caltech/target/c1iscaux and /cvs/cds/caltech/target/c1iscaux2 over.
    • Johannes said he did not develop any code to automate the process of translating the old .db files into the new ones for the Acromag - I won't invest the time in developing any either as I think just manually editing the files will be faster. 
    • I think I will follow the c1susaux convention of grouping .db files by the physical electronics system where possible (e.g. REFL11 channels in one file, CM channels in one file etc), as I think this makes for easier debugging.
    • There is an old "PZT_AI.db" file which I think consists completely of obsolete channels.
  6. Next steps:
    • Wire up the crate [Chub]
    • Make the database files and modbus files for talking to the Acromags on the internal subnet [Gautam], check the .db files [Koji]
    • Wiring of whitening switching from P1 to P2 connector, Issue #1 in this elog (this will also requrie the installation of the DIN shrouds) [Koji]
    • Soldering of P2 interface boards [Gautam]
    • Bench testing [Gautam, Koji, Chub]
    • Installation and in-situ testing [Gautam, Koji, Chub]

All the required additional parts should be here by the end of the week - I'd like to aim for Wednesday 7/24 for the installation in 1Y3 and in-situ testing. While talking to Rana, I realized that we should also factor in the c1aux slow channels into this acromag crate - there is no need for a separate machine to handle the shutters and illuminators. But let's not worry about that for now, those channels can simply be added later.

Attachment 1: IMG_7769.JPG
  14769   Wed Jul 17 21:22:41 2019 gautamUpdateCDSCM board Latch Enable subtlety

[koji, gautam]

Koji pointed out an important subtlety pertaining to the "LATCH ENABLE" signal line on the CM board. The purpose of this line is to smoothly facilitate the transition of a change in the "multi-bit-binary-outputs", a.k.a. "mbbo", that are controlled by MEDM gain sliders, to the analog electronics on the CM board. Why is this necessary? Imagine changing the gain from 7dB (=0111 in mbbo representation) to 8dB (=1000 in mbbo representation). In order to realize this change, all 4 bits have to change their state. But this almost certainly doesn't happen synchronously, because our EPICS interface isn't synchronous. So at some intermediate times, the mbbo representation could be 0100 (=4dB), or 1111 (=15dB), or many other possible values, which are all significantly different from either the initial value or the desired final state. This is clearly undesirable.

In order to protect against this kind of error, a Latched output part, 74ALS573, is used to buffer the physical digital logic levels from the switches in the analog gain stages. So in the default state, the "LATCH ENABLE" signal line is held "LOW". When a change happens in the EPICS value corresponding to a gain slider, the "LATCH ENABLE" state is quickly toggled to "HIGH", so as to enable the appropriate analog gain stages to be switched, and then again to "LOW", at which point the latch holds its output state. This logic is currently implemented by a piece of code called "latch.o", which is the compiled version of "latch.st", which may be found in /cvs/cds/caltech/target/c1iool0 where it presumably was written for the IMC servo board, but not in /cvs/cds/caltech/target/c1iool0  , which is where the CM board database files reside. The only elog reference I can find pertaining to this particular piece of code is from Alan, and doesn't say anything about the actual logic.

For the new c1iscaux, we need to implement this logic somehow. After discussion between Koji and me, we feel that a piece of python code is sufficient. This would continuously run in the background on the supermicro server machine. The channel hierarchy for each gain channes is as follows (I've taken the example of C1:LSC-CM_REFL1_GAIN):

  • C1:LSC-CM_REFL1_GAIN ------ this is the channel tied to an MEDM slider, and so is a "soft" channel
  • C1:LSC-CM_REFL1_SET ------- this is a "soft" channel that gets converted to an mbbo
  • C1:LSC-CM_REFL1_BITS ------ this is a channel that actually controls (multiple) physical binary outputs on the Acromag

So the logic will be that it continuously scans the EPICS channel C1:LSC-CM_REFL1_GAIN  for a change in set value. When a change is detected, it has to update the C1:LSC-CM_REFL1_SET channel. In the next EPICS refresh cycle, this would result in the mbbo bits, C1:LSC-CM_REFL1_BITS , all changing to the appropriate values. After these changes have happened, we need to toggle the LATCH ENABLE in order to allow the changes to propagate to the analog gain stage switches. Need to think about what's the best way to do this.

  14771   Thu Jul 18 10:46:04 2019 gautamUpdateCDSDatabase files made

I completed the translation of the .db files for the EPICS database records from the VME notation to the Acromag/Modbus/Asyn notation. The channels are now organized into 5 database files, located in /cvs/cds/caltech/target/c1iscaux3/,  for convenience:

  1. C1_ISC-AUX_LSCPDs.db -------- This handles whitening gain, AA enable/bypass, Demodulator FE, and PD Interface Board channels for REFL11, REFL55, REFL33, REFL165, POP22, POP110, POX11, POY11, AS55 and AS110 photodiodes.
  2. C1_ISC-AUX_CM.db -------------- This handles all channels for the CM board. The mbbo addressing notation needs to be checked.
  3. C1_ISC-AUX_QPDs.db ----------- This handles all channels for the IPPOS QPD.
  4. C1_ISC-AUX_ALS.db ------------- This handles all channels for the IR ALS DFD LO and RF power monitoring.
  5. C1_ISC-AUX_SPARE.db ---------- This handles the unused channels for the various whitening, AA and PD interface boards.

For reasons unknown to me, the database files in the other Acromag system target directories (e.g. c1susaux, c1auxex) all had 755 level access permission - maybe this is required for systemctl to handle the EPICS serving? Anyways, I upgraded the permission level of the above 5 files using chmod.

There are almost certainly typos / other errors, and I may have missed copying over some soft/calibrated channels, but I hope that this way of grouping by subsystem will make the debugging less painful. Once Chub connects up the power lines to the Acromags, I will run the soft tests. For this purpose, I've also made a C1_ISC-AUX.cmd file and a C1_ISC-AUX.env file in the above target directory, and also made the modbusIOC.service file in /etc/systemd/system on the supermicro.

  14773   Thu Jul 18 19:58:56 2019 gautamUpdateCDSWork on Acromag chassis

Now that the .db files were prepared, I wanted to test for errors. So I did the following:

  1. Acromags were mounted on the DIN rails. Attachment #1 shows the grouping of ADC, DAC and BIO units. They are labelled with their IP addresses.
  2. Wiring of power:
    • Chub had already prepared the backplane with the power connectors, switches and indicator LEDs.
    • So I just had to daisy chain the +24 V (RED) and GND (BLACK) terminals for all the acromags together, which I did using 24 AWG wire (we may want to use heavier gauge given the current draw).
  3. Ethernet cables were used to daisy chain the network connectivity between the various units.  Attachment #1 shows the current state of the chassis box.
  4. Front panel pieces were attached and labelled, see Attachment #2
    • I found it was sufficient to use the front - we may use the rear panel slots when we want to add connections for controlling the c1aux machine channels.
    • The D15 P2 connector panel for the CM board will arrive tomorrow and will be installed then.
  5. Entire setup was connected to power and ethernet, see Attachment #3
    • As usual, the current draw is significant for the collection of Acromags, I got around this problem by using the bench supply to "Parallel" mode to enhance the current driving capacity.
    • For the ethernet connection, I used the office space port #6, which I connected at the network rack end to the eth1 port of the Supermicro.

All the Acromags are seen on the 192.168.114 subnet on c1iscaux3 yes- however, when I run the modbusIOC process, I see various errors in the logfile no, so more debugging is required. Nevertheless, progress.

Update 2245: Turns out the errors were indeed due to a copy/paste error - I had changed the IP addresses for the ADCs from the .115 subnet c1susaux was using, but forgot to do so for the DACs and BIOs. Now, if I turn off the existing c1iscaux so that there aren't any EPICS clashes, the EPICS server initializes correctly. There are still some errors in the log file - these pertain to (i) the mbbo notation, which I have to figure out, and (ii) the fact that this version of EPICS, 7.0.1, does not support channel descriptions longer than 28 characters (we have several that exceed this threshold). I think the latter isn't a serious problem.

Getting closer... Note that I turned off the c1iscaux VME crate to prevent any EPICS server clashes. I will turn it back on tomorrow.

Attachment 1: IMG_7771.JPG
Attachment 2: IMG_7770.JPG
Attachment 3: IMG_7772.JPG
  14776   Fri Jul 19 12:50:10 2019 gautamUpdateSUSDC bias actuation options for SOS

Rana and I talked about some (genius) options for the large range DC bias actuation on the SOS, which do not require us to supply high-voltage to the OSEMs from outside the vacuum.

What we came up with (these are pretty vague ideas at the moment):

  1. Some kind of thermal actuation.
  2. Some kind of electrical actuation where we supply normal (+/- 10 V) from outside the vacuum, and some mechanism inside the chamber integrates (and hence also low-pass filters) the applied voltage to provide a large DC force without injecting a ton of sensor noise.
  3. Use the blue piers as a DC actuator to correct for the pitch imbalance --- Kruthi and Milind are going to do some experiments to investigate this possibility later today.

For the thermal option, I remembered that (exactly a year ago to the day!) when we were doing cavity mode scans, once the heaters were turned on, I needed to apply significant correction to the DC bias voltage to bring the cavity alignment back to normal. The mechanism of this wasn't exactly clear to me - furthermore, we don't have a FLIRcam picture of where the heater radiation patter was centered prior to my re-centering of it on the optic earlier this year, so we don't know what exactly we were heating. Nevertheless, I decided to look at the trend data from that night's work - see Attachment #1. This is a minute trend of some ETMY channels from 0000 UTC on 18 July 2018, for 24 hours. Some remarks:

  1. We did multiple trials that night, both with the elliptical reflector and the cylindrical setup that Annalisa and Terra implemented. I think the most relevant part of this data is starting at 1500 UTC (i.e. ~8am PDT, which is around when we closed shop and went home). So that's when the heaters were turned off, and the subsequent drift of PIT/YAW are, I claim, due to whatever thermal transients were at play.
  2. Just prior to that time, we were running the heater at close to its maximum rated current - so this relaxation is indicative of the range we can get out of this method of actuation.
  3. I had wrongly claimed in my discussion with Rana this morning that the change in alignment was mostly in pitch - in fact, the data suggests the change is almost equal in the two DoFs. Oplev and OSEMs report different changes though, by almost a factor of 2....
  4. The timescale of the relaxation is ~20 minutes - what part(s) of the suspension take this timescale to heat up/cool down? Unlikely to be the wire/any metal parts because the thermal conductivity is high? 
  5. In the optimistic scenario, let's say we get 100 urad of actuation range - over 40m, this corresponds to a beam spot motion of ~8mm, which isn't a whole lot. Since the mechanism of what is causing this misalignment is unclear, we may end up with significantly less actuation range as well.
  6. I will repeat the test (i.e. drive the heater and look for drift in the suspension alignment using OSEMs/Oplev) in the afternoon - now I claim the radation pattern is better centered on the optic so maybe we will have a better understanding of what mechanisms are at play.

Also see this elog by Terra.

Attachment #2 shows the results from today's heating. I did 4 steps, which are obvious in the data - I=0.6A, I=0.76A, I=0.9A, and I=1.05A.

In science, one usually tries to implement some kind of interpretation. so as to translate the natural world into meaning.

Attachment 1: heaterPitch_2018.pdf
Attachment 2: Screenshot_from_2019-07-19_16-39-21.png
  14777   Fri Jul 19 15:51:55 2019 gautamUpdateGeneralProjector lightbulb blown out

[chub, gautam]

Bulb replaced. Projector is back on.

  14778   Fri Jul 19 15:54:47 2019 gautamUpdateGeneralControl room UPS Batteries need replacement

The control room UPS started making a beeping noise saying batteries need replacement. I hit the "Test" button and the beeping went away. According to the label on it, the batteries were last repalced in March 2016, so maybe it is time for a replacement, @Chub, please look into this.

  14780   Fri Jul 19 17:42:58 2019 gautamUpdateGeneralrossa Xdisp bricked

For some reason, rossa's Xdisplay won't start up anymore. This happened right after the UPS reset. Koji and I tried ~1.5 hours of debugging, got nowhere.

  14781   Fri Jul 19 19:44:03 2019 gautamUpdateCDSDatabase file test


The database files for C1ISCAUX seem to work file - the exception being the mbbo channels for the CM board.


This was just a software test - the actual functionality of the channels will have to be tested once the Acromag crate has been installed in the rack. One change I had to make on the MEDM screen for the LSC PD whitening gains was to get rid of the "NMS" suffix on the EPICS channel names for whitening gain sliders/drop-down-menus. I suspect this has to do with the EPICS version we are using, 7.0.1. Furthermore, AS165 and POP55 no longer exist - I hold off removing them from the MEDM screen for the moment.

Next steps:

From the software point of view, the major steps are:

  1. Fix the mbbo channel notation in the database files
  2. Write and test the latch enabling code
  3. Figure out what scripted tests can be done to test the functionality of the new Acromag box.

I am stopping the EPICS server on the new machine and restarting the old VME crate over the weekend.

Attachment 1: Whitening.png
  14783   Sat Jul 20 01:03:37 2019 gautamUpdate Dataviewer error

What channels are you trying to read?


I'm not able to get trends of the TM adjustment test that Rana had asked us to perform, from the dataviewer. It's throwing the following error:

Connecting to NDS Server fb (TCP port 8088)
Connecting.... done
Server error 7: connect() failed
datasrv: DataWrite failed: daq_send: Resource temporarily unavailable
T0=19-07-20-01-27-39; Length=600 (s)
No data output.

  14784   Sat Jul 20 11:24:04 2019 gautamUpdateGeneralrossa bricked


SnapPy scripts made to work on Pianosa.


Of course rossa was the only machine in the lab that could run the python scripts to interface with the GigE camera. And it is totally bricked now. Lame.

So I installed several packages. The key was to install pypylon - if you go to the basler webpage, pypylon1.4.0 does not offer python2.7 support for x86_64 architecture, so I installed pypylon1.3.0. Here are the relevant lines from the changelog:

gstreamer-plugins-bad-0.10.23-5.el7.x86_64    Sat 20 Jul 2019 11:22:21 AM PDT
gstreamer-plugins-good-0.10.31-13.el7.x86_64  Sat 20 Jul 2019 11:22:11 AM PDT
gstreamer-plugins-ugly-0.10.19-31.el7.x86_64  Sat 20 Jul 2019 11:20:08 AM PDT
gstreamer-python-devel-0.10.22-6.el7.x86_64   Sat 20 Jul 2019 10:34:35 AM PDT
pygtk2-devel-2.24.0-9.el7.x86_64              Sat 20 Jul 2019 10:34:34 AM PDT
pygobject2-devel-2.28.6-11.el7.x86_64         Sat 20 Jul 2019 10:34:33 AM PDT
pygobject2-codegen-2.28.6-11.el7.x86_64       Sat 20 Jul 2019 10:34:33 AM PDT
gstreamer-devel-0.10.36-7.el7.x86_64          Sat 20 Jul 2019 10:34:32 AM PDT
gstreamer-python-0.10.22-6.el7.x86_64         Sat 20 Jul 2019 10:34:31 AM PDT
gtk2-devel-2.24.31-1.el7.x86_64               Sat 20 Jul 2019 10:34:30 AM PDT
libXrandr-devel-1.5.1-2.el7.x86_64            Sat 20 Jul 2019 10:34:28 AM PDT
pango-devel-1.42.4-1.el7.x86_64               Sat 20 Jul 2019 10:34:27 AM PDT
harfbuzz-devel-1.7.5-2.el7.x86_64             Sat 20 Jul 2019 10:34:26 AM PDT
graphite2-devel-1.3.10-1.el7_3.x86_64         Sat 20 Jul 2019 10:34:26 AM PDT
pycairo-devel-1.8.10-8.el7.x86_64             Sat 20 Jul 2019 10:34:25 AM PDT
cairo-devel-1.15.12-3.el7.x86_64              Sat 20 Jul 2019 10:34:25 AM PDT
mesa-libEGL-devel-18.0.5-3.el7.x86_64         Sat 20 Jul 2019 10:34:24 AM PDT
libXi-devel-1.7.9-1.el7.x86_64                Sat 20 Jul 2019 10:34:24 AM PDT
pygtk2-doc-2.24.0-9.el7.noarch                Sat 20 Jul 2019 10:34:23 AM PDT
atk-devel-2.28.1-1.el7.x86_64                 Sat 20 Jul 2019 10:34:21 AM PDT
libXcursor-devel-1.1.15-1.el7.x86_64          Sat 20 Jul 2019 10:34:20 AM PDT
fribidi-devel-1.0.2-1.el7.x86_64              Sat 20 Jul 2019 10:34:20 AM PDT
pixman-devel-0.34.0-1.el7.x86_64              Sat 20 Jul 2019 10:34:19 AM PDT
libXinerama-devel-1.1.3-2.1.el7.x86_64        Sat 20 Jul 2019 10:34:19 AM PDT
libXcomposite-devel-0.4.4-4.1.el7.x86_64      Sat 20 Jul 2019 10:34:19 AM PDT
libicu-devel-50.1.2-15.el7.x86_64             Sat 20 Jul 2019 10:34:18 AM PDT
gdk-pixbuf2-devel-2.36.12-3.el7.x86_64        Sat 20 Jul 2019 10:34:17 AM PDT
pygobject2-doc-2.28.6-11.el7.x86_64           Sat 20 Jul 2019 10:34:16 AM PDT
pygtk2-codegen-2.24.0-9.el7.x86_64            Sat 20 Jul 2019 10:34:15 AM PDT

Camera server is running on a tmux session on pianosa. But it keeps throwing up some gstreamer warnings/errors, and periodically (~every 20 mins) crashes. Kruthi tells me that this behavior was seen on Rossa as well, so whatever the problem is, doesn't seem to be because I missed out on installing some packages on pianosa. Moreover, if the server is in fact running, I am able to take a snapshot - but the camera client does not run.

  14785   Sat Jul 20 11:57:39 2019 gautamSummaryCDSP2 interface board

The boards arrived. I soldered on a DIN96 connector, and tested that the goemetry will work. It does yes. The only constraint is that the P2 interface board has to be installed before the P1 interface is installed. Next step is to confirm that the pin-mapping is correct. The pin mapping from the DIN96 connector to the DB15 was also verified.

*Maybe it isn't obvious from the picture, but there shouldn't be any space constraint even with the DB37/DB15 cables connected to the respective adapter boards.

Attachment 1: IMG_7773.JPG
  14786   Sat Jul 20 12:16:39 2019 gautamUpdateCamerasCNNs for beam tracking || Analysis of results
  1. Make the MSE a subplot on the same axes as the time series for easier interpretation.
  2. Describe the training dataset - what is the pk-to-pk amplitude of the beam spot motion you are using for training in physical units? What was the frequency of the dither applied? Is this using a zoomed-in view of the spot or a zoomed out one with the OSEMs in it? If the excursion is large, and you are moving the spot by dithering MC2, the WFS servos may not have time to adjust the cavity alignment to the nominal maximum value.
  3. What is the minimum detectable motion given the CCD resolution?
  4. Please upload a cartoon of the network architecture for easier visualization. What is the algorithm we are using? Is the approach the same as using the bright point scatterers to signal the beam spot motion that Gabriele demonstrated successfully?
  5. What is the significance of Attachment #6? I think the x-axis of that plot should also be log-scaled.
  6. Is the performance of the network still good if you feed it a time-shuffled test dataset? i.e. you have (pictures,Xcoord,Ycoord) tuples, which don't necessarily have to be given to the network in a time-ordered sequence in order to predict the beam spot position (unless the network is somehow using the past beam position to predict the new beam position).
  7. Is the time-sync problem Koji raised limiting this approach?
  14789   Sun Jul 21 12:54:18 2019 gautamUpdateLoss MeasurementMC2 loss map

Can you please be more specific about what the error is? Is this the usual instability with the camera server code? Or was it something new?


The camera server is throwing an error and is not grabbing snapshots :(

  14790   Sun Jul 21 12:55:38 2019 gautamUpdateCDSCM board Latch Enable test script

DATED, SEE ELOG14941 for the most up-to-date info on latch.py.

I wrote (/cvs/cds/caltech/target/c1iscaux3/latch.py) and tested the logic illustrated in Attachment #1. Results of a test are shown in Attachment #2, the various channels change as expected. Note that for negative values of the gain channel, the corresponding "BITS" channel will take on values like 65536 - this is because the mbboDirect data type is a 16 bit data type, and presumably the MSB is the sign bit. A bit mask is applied to this channel before the actual BIO unit bits are set - we should verify that the correct behavior happens, but I don't immediately see any problems.

To me, this is a robust logic, but it will benefit from more sets of eyes giving it a look over. The idea is to run this continuously on the Supermicro machine.

Apart from this, I also fixed some errors in the mbboDirect record syntax - so now I am able to start up the EPICS server without it throwing any error messages. It remains to verify that changing an EPICS gain slider results in the appropriate gain bits being flipped in the correct way (on the hardware side, I think the correct behavior is happening on the software end). For this testing, I turned off the old c1iscaux crate at ~10am, and started up the server on c1iscaux3. I am reverting to the nominal config now (~1pm).

Further testing will require the wiring inside the Acromag chassis to be completed. This should be the priority task for next week.

*Update 1130 22 July 2019: I've now installed the required dependencies on c1iscaux3 and setup the latch.py script to run as a systemctl process dependent on modbusIOC.service.

Attachment 1: LatchLogic.pdf
Attachment 2: LatchLogicTest.png
  14795   Mon Jul 22 07:21:13 2019 gautamUpdateCDSpainosa messed with

Somebody changed the settings on painosa without elogging anything about it. Why does this keep happening? I thought the point of the elog was to communicate. I think there are sufficient number of problems in the lab without me having to manually reset the control room workstation settings every week. Please make an elog if you change something.

  14800   Mon Jul 22 23:53:16 2019 gautamUpdateALSIR ALS locking attempt


My goal tonight was to lock the PSL frequency to be resonant in the XARM cavity, using the PSL+EX beat as the error signal. I was not successful - mainly, I was plagued by huge BR mode coupling in the error signal, and I could not enable the BR notch filter in the control loop without breaking the lock. Need to think about next steps.


  • POX and POY locking was easily restored.
  • EX green alignment was tweaked at the end-table. A large YAW correction was required, which I opted to apply on the mechanical mirror mounts rather than the PZTs. GTRX ~0.4 was recovered.
  • The arm cavity length was first locked using POX as an error signal 
    • Then I looked at the out-of-loop ALS noise, trusting the DFD's V/Hz calibration (red-trace in Attachment #1).
    • I judged it to be close enough to the benchmark reference (green-trace in Attachment #1), and so decided that I could go ahead and try locking.
  • A modified version of the script /opt/rtcds/caltech/c1/scripts/XARM/Lock_ALS_XARM.py was used to transition control from POX to the ALS error signal
    • I found that I had to change the sign of the CARM loop gain for the servo to remain stable (in this config, CARM-->MC2 length, thereby modifying the IMC frequency to keep the PSL resonant in the XARM cavity).
    • I don't know why this sign change was required - we are still sticking to the same convention that the beat frequency increases when the temperature slider for the EX laser is incremented in counts.
    • The script failed multiple times at the BOOST/BR notch filter enabling step.
    • Doing these steps manually, I found that turning the BR notch, FM6, ON destroyed the lock immediately.
    • Motivated by this observation, I looked at the in-loop error signal spectrum, see Attachment #2. Here, the PSL frequency is servoed by the ALS error signal, but the BR notch filter isn't enabled.
    • The Bounce-mode peak is huge - where is this coming from? It is absent in the ALS spectrum when the XARM is locked with POX. So it is somehow connected with actuating on the MC2 suspension? Or is it that the FM6=BounceRoll filter of the XARM loop is squishing the noise when looking at the ALS spectrum in POX lock, i.e. Attachment #1? In which case, why can't I engage FM6 for the CARM loop???

Anyway, now that I have a workable set of settings that gets me close to the ALS lock of the XARM, I expect debugging to proceed faster.

Update 2019 July 23: I looked at the control loop shape today, see Attachment #3. I'm not sure I understand why the "BounceRoll" filter  in this filter bank looks like a resonant gain rather than a notch, as it does for the Oplev or SUSPOS loops for example - don't we want to not actuate at these frequencies because the reason the signal exists is because of the imperfect OSEM/magnet positioning? This does not explain the spectrum shown in Attachment #2 however, as that filter was disabled.

Attachment 1: ALS_X_outOfLoopnoise.pdf
Attachment 2: ALS_X_inLoopnoise.pdf
Attachment 3: CARM_loopShape.pdf
  14802   Wed Jul 24 00:22:24 2019 gautamUpdateALSPSL frequency locked to XARM length using ALS


I succeeded in locking the PSL frequency to the XARM cavity length, with 9 pm RMS (Attachment #1) motion below 1 kHz, by actuating on MC2 to change the IMC length. The locks were pretty stable (~20 minutes) - the dominant cause of lockloss was the infamous ETMX drifting problem.


  1. I did not need to do anything to fix the anomalosly high BR mode coupling I reported yesterday surprise.
    • To test where this could be coming from - I looked at the ALS spectrum again with the XARM length locked to the PSL frequency using POX.
    • Then I compared the spectra with the BR filter in the XARM servo enabled/disabled, see Attachment #2
    • There bounce/roll peak heights even with the BR filter disabled is ~x100 smaller than what I reported yesterday (it remained the case today, because without enabling the BR filter in the CARM servo bank, the TRX level was fluctuating wildly at ~16 Hz). 
  2. The CARM loop (which is what the PSL frequency was slaved to) had ~150 Hz UGF with ~40 degrees phase margin, see Attachment #3.
  3. The quoted RMS sensing noise is if we trust the old POX calibration - may be off by a factor of a few, but probably not an order of magnitude. I'll recalibrate using the free-swinging Michelson technique in the coming days.
  4. The two broad humps in Attachment #1, centered at ~180 Hz and ~300 Hz, are present in the XARM lock as well - so it is somehow imprinted on the arm cavity length. Fixing that will improve the RMS noise performance significantly.

My main motivation here is to make some measurements and investigate the SoCal idea using a toy system, i.e. a single arm cavity controlled using ALS, so that's what Craig and I will attempt next.

Attachment 1: ALS_X_noise_POX.pdf
Attachment 2: BR_comparison.pdf
Attachment 3: ALS_CARM_OLG.pdf
  14808   Wed Jul 24 20:23:52 2019 gautamUpdateCamerasUpgraded Pylon from 5.0.12 to 5.2.0

Since there are multiple SURF projects that rely on the cameras:

  1. I moved the new installs Jon made to "new_pylon5" and "new_pypylon". The old installs were moved back to be the default directories.
  2. The bashrc alias for pylon was updated to allow the recording of videos (i.e. it calls the PylonViewerApp from new_pypylon).
  3. There is a script that can grab images at multiple exposures and save 12-bit data as uint16 numpy arrays to an HDF5 file. Right now, it is located at /users/kruthi/scripts/grabHDR.py. We can move this to a better place later, and also improve the script for auto adjusting the exposure time to avoid saturations.

My changes were necessary because the grabHDR.py script was throwing python exceptions, whereas it was running just fine before Jon's changes. We can move the "new_*" dirs to the default once the SURFs are gone.

Let's freeze the camera software config in this state until next week.

  14811   Thu Jul 25 12:25:56 2019 gautamUpdateALSIR ALSX noise


  1. There are some broad peaks in the ALS out-of-loop noise, centered at ~145 Hz, ~245 Hz and ~570 Hz which are absent in both the POX in-lock error signal and in the green PDH error signals (see Attachment #1). So I conclude they originate in the IR ALS beat chain somewhere. Needs more investigation, in the general quest to improve the ALS noise.
  2. This measurement also shows that the ALS noise is limited by unsuppressed EX green PDH frequency noise above ~400 Hz (100 Hz if you ignore the unexplained broad humps).

These spectra were taken with the arm cavity length locked to the PSL frequency using POX as an error signal, and the EX laser frequency locked to the XARM cavity length by the analog PDH servo at EX, so there is no feedback control with the ALS beat signal as an error signal.

Other details:

  • The transition of arm resonance control from POX to ALS error signal is more robust now - I am able to do this during daytime, and also maintain the lock for >20 minutes at a time.
  • Rana encouraged me not to spend too much time on this - so my next goal here will be to get the Y arm IR ALS working, and then we can control the two arms using ALS error signals in the CARM/DARM basis instead of the X/Y basis.
  • I still think it's worth getting the ALS good enough that the locking becomes repeatable and reliable.
    • The main task here is going to be re-doing the EY green layout to match the EX layout, get good MM into the cavity etc.
    • The IR light also has to be coupled into the fiber at EY.
Attachment 1: ALS_broadPeaks.pdf
  14812   Thu Jul 25 14:28:03 2019 gautamConfigurationComputersfirewalld disabled for EPICS CA

I think rana did some more changes to this workstation to make it useful for commissioning activities - but the MEDM screens were still white blanks. The problem was that the firewalld wasn't disabled (last two steps of the KThorne setup wiki). I disabled it. Now donatella can run MEDM, ndscope and StripTool. DTT doesn't work to get online data because of a "Synchronization Error", I'm not bothering with this for now. I think Kruthi successfully demonstrated the fetching of offline data with DTT.

Attachment 1: donatellaCommissioning.png
  14813   Thu Jul 25 20:08:36 2019 gautamUpdateComputersSolidworks machine

I brought one CPU (Dell T3500) and one 28" monitor from Mike Pedraza's office in Downs to the 40m. It is on Steve's desk right now, pending setup. The machine already has Solidworks and Altium installed on it, so we can set it up at our leisure. The login credentials are pasted on the CPU with a post-it should anyone wish to set it up.

  14815   Mon Jul 29 13:32:56 2019 gautamUpdateLoss MeasurementLoss measurement PD installed in AS path

[yehonathan, gautam]

  • we placed a PDA520 photodiode in the AS beampath, so AS110 and AS55 no longer see any light.
  • ITMX and ETMX were misaligned (since the plan is to measure the Y arm loss).
  • The PDA520 and MC2 transmission are currently going to the Y arm ALS beat channels in the DAQ system. Unfortunately, we have no control over the whitening gains for these channels because of the c1iscaux2 situation.
  14817   Tue Jul 30 09:13:31 2019 gautamUpdatePSLc1psl keyed, Agilent setup cleared
  1. IMC would not lock. c1psl EPICS channels were unresponsive. I keyed the crate and went through the usual burtrestore/PMC-relocking dance.
  2. While at 1X2, I decided to take this opportunity to clean up the AG4395 setup that has been setup there unused for several weeks now.
    • Unplugged the active probe connected via BNC-T connector to the mixer IF output.
    • Noticed that the active probe (S/N 2850J01450) did not have it's power connection connected. According to the manual, this is bad. I don't know if the probe is damaged or not.
    • Moved the AG4395 cart out of the way so that there is a little more room around 1X1/1X2.
  14819   Wed Jul 31 09:41:12 2019 gautamUpdateBHDOMC cavity geometry


We need to determine the geometry (= round-trip length and RoC of curved mirrors) of the OMC cavities for the 40m BHD experiment. Sticking to the aLIGO design of a 4 mirror bowite cavity with 2 flat mirrors and 2 curved mirrors, with a ~4deg angle of incidence, we need to modify the parameters for the 40m slightly on account of our different modulation frequencies. I've setup some infrastructure to do this analytically - even if we end up doing this with Finesse, it is useful to have an analytic calculation to validate against (also not sure if Finesse can calculate HOMs up to order 20 in a reasonable time, I've only seen maxtem 8). 

Attachment #1: Heatmap of the OMC transmission for the following fields:

  • Carrier TEM00 is excluded, but HOMs up to m+n=20 included for both the horizontal and vertical modes of the cavity.
  • f1 and f2 upper and lower sidebands, up to m+n=20 HOMs for both the horizontal and vertical modes of the cavity, including TEM00.
  • Power law decay assumed for the HoM content incident on the OMC - this will need to be refined
  • The white region is where the cavity isn't geometrically stable.
  • Green dashed line indicates a possible operating point, white dashed line indicates the aLIGO OMC operating point. On the basis of this modeling, we would benefit from choosing a better operating point than the aLIGO OMC geometric parameters.


  1. Compute the round-trip Gouy phase, \phi_{\mathrm{gouy}}, for the cavity.
  2. With the carrier TEM00 mode resonant, compute the round-trip propagation phase, \phi_{\mathrm{prop}} = \frac{2 \pi f_{\mathrm{offset}} L_{\mathrm{rt}}}{c}, and the round-trip Gouy phase, \phi_{\mathrm{G}} = (m+n)\phi_{\mathrm{gouy}} for the \mathrm{TEM}_{mn} mode of the field, with f_{\mathrm{offset}} specifying the offset from the carrier frequency (positive for the upper sideband, negative for the lower sideband). For the aLIGO cavity geometry, the 40m modulation sidebands acquire ~20% more propagation phase than the aLIGO modulation sidebands.
  3. Compute the OMC transmission for this round-trip phase (propagation + Gouy).
  4. Multiply the incident mode power (depending on the power law model assumed) by the cavity transmission.
  5. Sum all the fields.

Next steps:

  1. Refine the incident mode content (and power) assumption. Right now, I have not accounted for the fact that the f2 sideband is resonant inside the SRC while the f1 sideband is not. Can we somehow measure this for the 40m? I don't see an easy way as it's probably power dependent?
  2. Make plots for the projection along the slices indicated by the dashed lines - which HOMs are close to resonating? Might give us some insight.
  3. What is the requriement on transmitted power w.r.t. shot noise? i.e. the colorbar needs to be translated to dBVac.
  4. If we were being really fancy, we could simultaneously also optimize for the cavity finesse and angle of incidence as well.
  5. Question for Koji: how is the aLIGO OMC angle of incidence of ~4 degrees chosen? Presumably we want it to be as small as possible to minimize astigmatism, and also, we want the geometric layout on the OMC breadboard to be easy to work with, but was there a quantitative metric? Koji points out that the backscatter is also expected to get worse with smaller angles of incidence.

The code used for the ABCD matrix calcs have been uploaded to the BHD modeling GIT (but not the one for making this plot, yet, I need to clean it up a bit). Some design considerations have also been added to our laundry list on the 40m wiki.

Attachment 1: paramSpaceHeatMap.pdf
  14820   Wed Jul 31 14:44:11 2019 gautamUpdateComputersSupermicro inventory

Chub brought the replacement Supermicro we ordered to the 40m today. I stored it at the SW entrance to the VEA, along with the other Supermicro. At the time of writing, we have, in hand, two (unused) Supermicro machines. One is meant for EY and the other is meant for c1psl/c1iool0. DDR3 RAM and 120 GB SSD drives have also been ordered, but have not yet arrived (I think, Chub, please correct me if I'm wrong).

Update 20190802: The DDR3 RAM and 120 GB SSD drives arrived, and are stored in the FE hardware cabinet along the east arm. So at the time of writing, we have 2 sets of (Supermicro + 120GB HD + 4GB RAM).


We should ask Chub to reorder several more SuperMicro rackmount machines, SSD drives, and DRAM cards. Gautam has the list of parts from Johannes' last order.

  14823   Fri Aug 2 11:37:38 2019 gautamUpdateALSEY IR ALS Assay


I'd like to confirm that the IR ALS scheme will work for locking. The X-arm performance so far has been encouraging. I want to repeat the characterization for the Y arm. So I inspected the layout on the EY table, and made a list of characterization tasks. The current EY beam routing is difficult to work with, and it will definitely benefit from a re-do. However, I don't know how much time I want to spend re-doing it, so for a start, I will just try and couple some amount of light into a fiber and bring it to the PSL table, and see what noise performance I get.


Attachment #1: Photo of the current beam layout. The powers indicated were measured with the Ophir power meter.

  • I measure an SHG conversion efficiency of 0.87 %/W, which is considerably lower than the ~3.7%/W that is theoretically expected, and 1.5%/W that is realized at EX.
  • Of the 0.5 mW of green light that is generated, I measure ~0.375 mW at the viewport into the EY chamber. So there is ~25 % loss in the green beam path on the EY table. Seems high to me.
  • The previous solution of coupling IR light into the fiber realized at EY was to use the SHG leakage IR beam. While there isn't a measurement showing that this dirty beam is noisier than a cleaner pickoff, I'd like to adopt the solution used at EX, which is to use the leakage beam from the first steering mirror in the NPRO beam path. This will allow better mode-matching and polarization control of the beam being coupled into the fiber, which at least in principle, translates to less phase noise.
  • However - the beam layout at the EY table offers much less freedom to work with this idea than EX. A constraint is the clamp that secures the enclosure to the optical table, labelled in the photo. Further behind it, the green steering optics occupy all available space. A more comprehensive photo of the EY table can be found here.
  • Off the top of my head, I don't see any other good open spots on the EY table where we could couple IR light into the fiber. 
  • One other change I'd like to make is to replace the first steering mirror after the NPRO head, which is currently a Y1 HR mirror, with a R=99% BS. This will make it easier to control the amount of power coupled into the fiber, which is something we'd like.

Attachment #2: A candidate mode-matching solution, given the constraints outlined above. It isn't great, with only 85% modematching even theoretically possible. The lenses required are also pretty fast lenses. But I think it's the best possible without a complete overhaul of the EY layout. I'm still waiting for the lens kit to arrive, but as soon as they get here, I will start this work.

Characterization tasks:

  • Characterize SHG at EY [done 7/28]
  • Characterize gPDH at EY (loop TFs, improve MM, PDH discriminant, check the polarization)
  • Couple IR light into fiber with good MM at EY [done with 36% MM 8/9]
  • Clean fiber at EY, and at the PSL table [done 8/9]
  • Make the PSL + Y IR beat [done 8/9]
  • Noise budget
Attachment 1: IMG_7780.JPG
Attachment 2: Ey_MM_20190802.pdf
  14826   Sun Aug 4 14:39:41 2019 gautamUpdateGeneralsome lab activity
  1. Unresponsive c1psl, c1iool0, c1auxey and c1iscaux VME crates were keyed.
  2. c1psl channels were burt-restored, did a burtrestore, and re-locked the PMC. Tweaked the pointing into the PMC on the PSL table to increase the PMC transmission from ~0.69 to ~0.71.
  3. Re-locked IMC. Ran WFS offset script to relieve the ~100 DAC counts (~10 urad) DC offset from the WFS servos to the IMC suspensions (a serious calibration of this into physical units should be made part of the planned 40m WFS activity). Now that I think about it, since we change the IMC alignment to match the input beam alignment, some post-IMC clipping could modulate the power incident on the ITMs, which is a source of error for the arm cavity loss determination using DC reflection. We need a better normalizing data stream than the IMC transmission.
  4. The IFO_OVEREVIEW medm screen was modified such that the threshold for the PMC transmitted beam to be visible was lowered from 0.7 to 0.6, so that now there is a continuous beam line from the NPRO to the PRM when the IMC is locked even when the PMC transmission degrades by 5% due to thermally driven pointing drifts on the PSL table.
  5. The wmctrl utility on pianosa wasn't working so well, I wasn't able to use my usual locking MEDM autoconfig scripts. Turned out to be due to a zombie MEDM window which I killed with xkill, now it is working okay again.
  6. The misaligned XARM was re-aligned and the loss measuring PDA520 at the AS port was removed from the beam path (mainly to avoid ADC saturations the fringing Michelson will cause).
  7. I noticed that the ETMX Oplev HeNe SUM level has degraded to ~50% of its power level from 200 days ago [Attachment #1], may need a new HeNe here soon. @Chub, do we have spare HeNes in stock?

I want to collect some data with the arms locked to investigate the possibility/usefullness of having seismic feedforward implemented for the arms (it is already known to help the IMC length and PRC angular stability at low frequencies). To facilitate diagnostics I modified the file /users/Templates/Seismic/Seismic_vs_TRXTRYandMC.xml to have the correct channel names in light of Lydia's channel name changes in 2016. Looking at the coherence data, the alignment of the cartesian coordinate system of the Seismometers at the ends and the global interferometer coordinate system can be improved.

I don't know if for the MISO filter design if there is any difference in using TRX/TRY as the target, or the arm length control signal.

Data collection started at 1249018179. I've setup a script running in a tmux shell to turn off the LSC enable in 2 hours.

Attachment 1: ETMX_OL.png
Attachment 2: Seismic_TRXTRYandMC_4Aug2019.pdf
  14829   Mon Aug 5 17:23:26 2019 gautamSummaryComputersWiFi Settings on asia

The VEA laptop asia was configured to be able to connect to too many WiFi networks - it was getting conflicted in its default position at the vertex and trying to hop between networks, for some reason trying to connect to networks that had poor signal strength. I deleted all options from the known networks except 40MARS. Now the network connection seems much more stable and reliable.

  14832   Tue Aug 6 14:55:23 2019 gautamUpdateCDSMaking Matlab R2015b the default

ML2013 is unable to open Simulink on any of the workstations. We decided to make the default version of Matlab R2015b (the default of the version of RCG we are using).

I commenced the procedure of the migration, starting with making a tagged commit of the current running simulink models. A local backup was also made, plus we have the usual chiara-based backup so I think we're in good hands.

Currently the branch and tag are protected - once we verify that everything works as expected post migration, I will open it up. I changed the directory structure of the models, need to confirm that the rtcds compilers don't have any hardcoded paths which may break due to my change.

The symlink to Matlab R2013 was deleted and a new symlink to R2015b was made. I activated the license using the Caltech campus license. Now running matlab from shell starts up R2015b yes. Simulink even works 😲 .

Attachment 1: ML2015b.png
  14833   Tue Aug 6 15:52:06 2019 gautamUpdateBHDPreliminary BHD calculations


The requirement on the phase noise on the direct backscatter from the OMC back into the SRM is that it be less than 10^{-5} \, \mathrm{rad/\sqrt{Hz}} \approx 10^{-12} \, \mathrm{m/\sqrt{Hz}} @ 100 Hz, for a safety factor (arbitrarily chosen) of 10 (= 20dB below unsqueezed vacuum). Assuming 5 optics between the OMC and SRM which contribute incoherently for a factor of sqrt(5), and assuming a total of 1 ppm of the LO power to be backscattered, we need the suspensions to be moving < 5 \times 10^{-13} \, \mathrm{m/\sqrt{Hz}} @ 100 Hz. This seems possible to realize with single stage suspensions - I assume we get f^4 filtering from the pendulum at 100 Hz, and that there is an additional 80 dB attenuation (from the stack) of the assumed 1 micron/rtHz motion at 100 Hz, for an overall 160 dB attenutaiton, yielding 10^-14 m/rtHz at 100 Hz.


This is the same calculation as I had posted a couple of months ago (see elog that this is a reply to), except that Koji pointed out that the LO power is expected to dominate the (carrier) power incident on the OMC cavity(ies). So the more meaningful comparison to make is to have the x-axes of the plots denote the backscatter fraction, \epsilon_{\mathrm{BS}} rather than the LO power. One subtlety is that because the phase of the scattered field is random, the displacement-noise induced phase noise could show up in the amplitude quadrature. I think that in these quadrature field amplitude units, the RIN and phase noise are directly comparable but I might have missed a factor of 2*pi. But in the worst case, if all the phase noise shows up in the amplitude quadrature, we end up being only ~10dB below unsqueezed vacuum (for 1 ppm backscatter). 

For the requirement on the noise in the intensity quadrature - I think this is automatically satisfied because the RIN requirement on the incident LO field is in the mid 10^-9 1/rtHz regime.

Attachment 1: OMCbackscatter.pdf
  14835   Tue Aug 6 23:09:20 2019 gautamUpdateALSEY table work
  • Removed power monitoring PD (It was off anyways)
  • Installed Steering mirror and collimator in K6XS mount (fast axis = p-pol to best effort by eye)
  • Installed lens mounts in approx position
  • Cleaned fiber at EY and connected to the collimator
  • Coupled EY--->PSL and spare PSL-->EY fibers together at the PSL table to facilitate coupling.
  • tbc tomorrow...

Couple IR light into fiber with good MM at EY

  14836   Thu Aug 8 12:01:12 2019 gautamUpdateIOOMC1 suspension oddness

At ~1am PDT today, all the MC1 shadow sensor readbacks (fast CDS channels and Slow Acromag channels, latter not shown here) went to negative values. Of course a negative value makes no sense. After ~3 hours, they came back to positive values again. But since then, the shadow sensor RMS noise has been significantly higher in the >20 Hz band, and there are frequent glitches which kick the suspension. The IMC has been having trouble staying locked. I claim that this has to do with the Satellite box.

No action being taken now while I work on the ALS. In the past the problem has fixed itself.

Attachment 1: MC1_suspension.png
Attachment 2: MC1_suspension.pdf
  14837   Fri Aug 9 08:59:04 2019 gautamUpdateCDSPrep for install of c1iscaux

[chub, gautam]

We scoped out the 1Y3 rack this morning to figure out what needs to be done hardware wise. We did not think about how to power the Acromag crate - the LSC rack electronics are all powered by linear supplies and not Sorensens, and the linear supplies are operating at pretty close to their maximum current-drive. The Acromag box draws ~3A of current from the 20 V supply, not sure what the current draw will be from the 15 V supply. Options:

  1. Since there are sorensens in 1Y2 and 1Y1, do we really care about installing another pair of switching supplies (+20 V DC and +15 V DC) in 1Y3?
    • Contingent on us having two spare Sorensens available in the lab. Chub has already located one.
  2. Use the Sorensens installed already in 1Y1. 
    • Probably the easiest and fastest option.
    • +15 V already available, we'd have to install a +20 V one (or if the +/-5 V or +12 V is unused, reconfigure for +20 V DC).
    • Can argue that "this doesn't make the situation any worse than it already is"
    • Will require the running of some long (~3 m) long cabling to bring the DC power to 1Y3 where it is required. 
  3. Get new linear supplies, and hook them up in parallel with the existing.
    • Need to wait for new linear supply to arrive
    • Probably expensive
    • Questionable benefit to electronics noise given the uncharacterized RF pickup situation at 1Y2

I'm going with option #2 unless anyone has strong objections.

ELOG V3.1.3-