[steve, yuki, gautam]

The plastic tubing/housing for the fiber arrived a couple of days ago. We routed ~40m of fiber through roughly that length of the tubing this morning, using some custom implements Steve sourced. To make sure we didn't damage the fiber during this process, I'm now testing the vertex models with the plastic tubing just routed casually (= illegally) along the floor from 1X4 to 1Y3 (NOTE THAT THE WIKI PAGE DIAGRAM IS OUT OF DATE AND NEEDS TO BE UPDATED), and have plugged in the new fiber to the expansion chassis and the c1lsc front end machine. But I'm seeing a DC error (0x4000), which is indicative of some sort of timing error (Attachment #1) **. Needs more investigation...

Pictures + more procedural details + proper routing of the protected fiber along cable trays after lunch. If this doesn't help the stability problem, we are out of ideas again, so fingers crossed...

** In the past, I have been able to fix the 0x4000 error by manually rebooting fb (simply restarting the daqd processes on fb using sudo systemctl restart daqd_* doesn't seem to fix the problem). Sure enough, seems to have done the job this time as well (Attachment #2). So my initial impression is that the new fiber is functioning alright .

M3.4 Colton shake did not trip sus.

I restarted the LSC models in the usual way via the c1lsc reboot script. After doing this I was able to lock the YARM configuration for more noise coupling scripting.

Yuki Miyazaki received 40m specific basic safety training.

The PMC and IMC were unlocked. Both were re-locked, and alignment of both cavities were adjusted so as to maximize MC2 trans (by hand, input alignment to PMC tweaked on PSL table, IMC alignment tweaked using slow bias voltages). I disabled the inputs to the WFS loops, as it looks like they are not able to deal with the glitching IMC suspensions. c1lsc models have crashed again but I am not worrying about that for now.

9pm: The alignment is wandering all over the place so I'm just closing the PSL shutter for now.

LIGO GC notified us that nodus had SSL2.0 and SSL3.0 enabled. This has been disabled now.
The details are described on 40m wiki.

Gautam and I restarted the models on c1lsc, c1ioo, and c1sus. The LSC system is functioning again. We found that only restarting c1lsc as Rolf had recommended did actually kill the models running on the other two machines. We simply reverted the rebootC1LSC.sh script to its previous form, since that does work. I'll keep using that as required until the ongoing investigations find the source of the problem.

Looks like the ADC was not to blame, same symptoms persist.

Todd E. came by this morning and gave us (i) 1x new ADC card and (ii) 1x roll of 100m (2017 vintage) PCIe fiber. This afternoon, I replaced the old ADC card in the c1lsc expansion chassis, and have returned the old card to Todd. The PCIe fiber replacement is a more involved project (Steve is acquiring some protective tubing to route it from the FE in 1X6 to the expansion chassis in 1Y3), but hopefully the problem was the ADC card with red indicator light, and replacing it has solved the issue. CDS is back to what is now the nominal state (Attachment #1) and Yarm is locked for Jon to work on his IFOcoupling study. We will monitor the stability in the coming days.

Rolf came by today morning. For now, we've restarted the FE machine and the expansion chassis (note that the correct order in which to do this is: turn off computer--->turn off expansion chassis--->turn on expansion chassis--->turn on computer). The debugging measures Rolf suggested are (i) to replace the old generation ADC card in the expansion chassis which has a red indicator light always on and (ii) to replace the PCIe fiber (2010 make) running from the c1lsc front-end machine in 1X6 to the expansion chassis in 1Y3, as the manufacturer has suggested that pre-2012 versions of the fiber are prone to failure. We will do these opportunistically and see if there is any improvement in the situation.

Another tip from Rolf: if the c1lsc FE is responsive but the models have crashed, then doing sudo reboot by ssh-ing into c1lsc should suffice* (i.e. it shouldn't take down the models on the other vertex FEs, although if the FE is unresponsive and you hard reboot it, this may still be a problem). I'll modify I've modified the c1lsc reboot script accordingly.

* Seems like this can still lead to the other vertex FEs crashing, so I'm leaving the reboot script as is (so all vertex machines are softly rebooted when c1lsc models crash).

c1lsc crashed again. I've contacted Rolf/JHanks for help since I'm out of ideas on what can be done to fix this problem.

Electrician is coming to fix one of the fluorenent light fixture holder in the east arm tomorrow morning at 8am. He will be out by 9am.

The job did not get done. There was no scaffolding or ladder to reach troubled areas.

I freed ITMX and coarsely realigned the IFO using the OPLEVs. All the alignments were a bit off from overnight.

The IFO is still only able to lock in MICH mode currently, which was the situation before the earthquake. This morning I additionally tried restoring the burt state of the four machines that had been rebooted in the last week (c1iscaux, c1aux, c1psl, c1lsc) but that did not solve it.

TP-1 Osaka maglev controller  [  model TCO10M,  ser V3F04J07 ]  needs maintenance. Alarm led  on indicating  that we need Lv2 service.

The turbo and the controller are in good working order.

*****************************

Hi Steve,

Our maintenance level 2 service price is $...... It consists of a complete disassembly of the controller for internal cleaning of all ICB’s, replacement of all main board capacitors, replacement of all internal cooling units, ROM battery replacement, re-assembly, and mandatory final testing to make sure it meets our factory specifications. Turnaround time is approximately 3 weeks.

  RMA 5686 has been assigned to Caltech’s returning TC010M controller. Attached please find our RMA forms. Complete and return them to us via email, along with your PO, prior to shipping the cont

Best regards,

Pedro Gutierrez

Osaka Vacuum USA, Inc.

510-770-0100 x 109

*************************************************

our TP-1 TG390MCAB is 9 years old. What is the life expectancy of this turbo?

                        The Osaka maglev turbopumps are designed with a 100,000 hours(or ~ 10 operating years) life span but as you know most of our end-users are

                        running their Osaka maglev turbopumps in excess of 10+, 15+ years continuously.     The 100,000 hours design value is based upon the AL material being rotated at

                        the given speed.   But the design fudge factor have somehow elongated the practical life span.  

We should have the cost of new maglev & controller in next year budget. I  put the quote into the wiki.

All suspension tripped. Their damping restored. The MC is locked.

ITMX-UL & side magnets are stuck.

I found c1lsc unresponsive again today. Following the procedure in elog #13935, I ran the rebootC1LSC.sh script to perform a soft reboot of c1lsc and restart the epics processes on c1lsc, c1sus, and c1ioo. It worked. I also manually restarted one unresponsive slow machine, c1aux.

After the restarts, the CDS overview page shows the first three models on c1lsc are online (image attached). The above elog references c1oaf having to be restarted manually, so I attempted to do that. I connect via ssh to c1lsc and ran the script startc1oaf. This failed as well, however.

In this state I was able to lock the MICH configuration, which is sufficient for my purposes for now, but I was not able to lock either of the arm cavities. Are some of the still-dead models necessary to lock in resonant configurations?

The rat is cut by mechanical trap and it was removed from ITMX south west location.

A nagy kover patkanyt a fogo elkapta es megolte.

Small earth quakes and suspensions. Which one is the most free and most sensitive: ITMX

The second big glich trips ETMX sus. There were small earth quakes around the glitches. It's damping recovered.

Great, thanks!

I don't know what had been wrong, but I could lock the PMC as usual.
The IMC got relocked by AutoLocker. I checked the LSC and confirmed at least Y arm could be locked just by turning on the LSC servos.

I tried unsuccessfully to relock the MC this afternoon.

I came in to find it in a trouble state with a huge amount of noise on C1:PSL-FSS_PCDRIVE visible on the projector monitor. Light was reaching the MC but it was unable to lock.

• I checked the status of the fast machines on the CDS>FE STATUS page. All up.
• Then I checked the slow machine status. c1iscaux and c1psl were both down. I manually reset both machines. The large noise visible on C1:PSL-FSS_PCDRIVE disappeared.
• After the reset, light was no longer reaching the MC, which I take to mean the PMC was not locked. On the PSL>PMC page, I blanked the control signal, reenabled it, and attempted to relock by adjusting the servo gain as Gautam had showed me before. The PMC locks were unstable, with each one lasting only a second or so.
• Next I tried restoring the burt states for c1iscaux and c1psl from a snapshot taken earlier today, before the machine reboots. That did not solve the problem either.

Glitch, small amplitude, 350 counts  &  no trip.

I think we don't need to keep Crystal Ref: we can change this into a regular Wenzel box with no outside control or monitoring.

6.2M Bandon, OR did not trip any sus

[Johannes, Koji]

We went around the LSC, PSL, IOO, and SUS racks to check how many dual backplane interfaces will be required.

Euro card modules are connected to the backplane with two DIN 41612 connectors (as you know). The backplane connectors provide DC supplies and GND connections.
In addition, they are also used for the input and output connections with the fast and slow machines.

According to the past inspection by Johannes, most of the modules just use the upper DIN41612 connector (called P1). But there are some modules exhibited the possibility of the additional use of the other connector (P2).

Tuesday afternoon Johannes and I made the list of the modules with the possible dual use. And I took a time to check the modules with DCC, Jay's schematics, and the visual inspection of the actual modules.

LSC Rack

• Common mode servo (D040180 Rev B)
  • Schematic source D040180 Rev B D1500308
  • Assesment: Both P1 and P2 are to be connected to Acromag, but there are only a few channels on P2
  • P1: 1A-32A Digital In
  • P2: 1A-3A Analog Out (D32/33/34, SLOW MON and spare?)
          9A Digital Out for D35 (Limitter)
          10A-15A Spare
          16A Digital In (Latch Enable/Disable)
          25A, 25C  Differential Analog in (Differential offset input, indicated as "BIAS") 
• PD Interface (D990543 Rev B)
  • Schematic source D990543 RevB
  • Assesment: No connection necessary. We don't monitor/control anything of any LSC PDs from Acromag.

PSL Rack

• Generic DAQ Interface (D990155) - This is a DAC interface.
  • Schematic source: Jay's page D990155 Rev.B All the lines between P2 and P3 are connected.
  • Assesment: Only P2 is to be connected to Acromag.
  • P1 DAC mon -> not necessary
  • P2 A1-A16, Connected to DAC in P2-P3
• PMC Servo
  • Schematic source: LIGO DCC D980352
  • Assesment: Only P1 (1A-9A) is to be connected to Acromag. (Just one DSub is sufficient)
  • P1 1A-9A
• Crystal Ref (D980353)
  • Schematic source: LIGO DCC D980353
  • Assesment: Only P1 (1A-4A) is to be connected to Acromag. (Just one DSub is sufficient)
  • P1 1A-4A
• TTFSS REV A
  • Schematic source: PNot found
  • Assesment: Probably Only P1 is sufficient. We need to analyze the board to figure out the channel assignment.

IOO Rack

• PD Interface (D990543 Rev B)
  • Schematic source D990543 RevB
  • Assesment: Only P1 connection is sufficient.
• Generic DAQ Interface (D990155)
  • Assesment: Remove the module. We already have the same module in PSL Rack. This is redundant.
• Common mode servo (D040180 Rev B)
  • See above
• Pentek Generic Input Board D020432
  • Schematic source Jay's page D020432-A
  • Assesment: No connection. There is no signal on the backplane.

SUS Rack

• SUS Dewhitening
  • Schematic source: Jay's page D000316-A
  • Assesment: No connection.
  • We can omit Mon CHs.
  • Bypass/Inputs are already connected to the fast channels.

I've taken a PI Piezo Actuator (P-810.10) from the 40m collection. I forgot to note it on the equipment checklist by the door, will do so when I next drop by.

I expanded the previous panels to 6U height for the new DAQ chassis we're buying for the upgrade. I figure it's best if we stick to the modular design, so I'm showing a panel for 8 BNC connectors as an example. The front panel has 12 slots, the back has 10 plus power connectors, switches, and the ethernet plug.

I moved the power switch to the rear because it's a waste of space to put it in the front, and it's not like we're power cycling this thing all the time. Note that the unit only requires +24V (for general operation, +20V also does the trick, as is the situation for ETMX) and +15V (excitation field for the binary I/O modules). While these could fit into a single CONEC power connector, it's probably for the better if we don't make a version that supplies a large positive voltage where negative is expected, so I put in two CONEC plugs for +/- 15 and +/- 24.

I want to order 5-6 of these as soon as possible, so if anyone wants anything changed or sees a problem, please do tell!

When I came in this morning no light was reaching the MC. One fast machine was dead, c1lsc, and a number of the slow machines: c1susaux, c1iool0, c1auxex, c1auxey, c1iscaux. Gautam walked me through reseting the slow machines manually and the fast machines via the reboot script. The computers are all back online and the MC is again able to lock.

EDIT: After discussing with Koji and checking the existing M2ISS PDs I put the two C30642G back and took two C30665GH (active diameter: 3mm) diodes. Only one of this type remains in storage.

I removed two C30642G photodiodes from the stash for the new M2ISS hardware and updated the wiki page accordingly.

I had a very fruitful discussion with Rich about this circuit today. He agreed with the overall architecture, but made the following suggestions (Attachment #1 shows the circuit with these suggestions incorporated):

1. Use an Op27 instead of LT1128, as it is a more friendly part especially in these composite amplifier topologies. I confirmed that this doesn't affect the output voltage noise at 100 Hz, we will still limited by Johnson noise of the 15kohm series resistor.
2. Take care of voltage distribution in the HV feedback path
   • I overlooked the fact that the passive filtering stage means that the DC current we can drive in the configuration I posted earlier is 150V / 25kohm = 6mA, whereas we'd like to be able to drive at least 10 mA, and probably want the ability to do 12 mA to leave some headroom.
   • At the same time, the feedback resistance shouldn't be too small such that the PA91 has to drive a significant current in the feedback path (we'd like to save that for the coil).
   • Changing the supply voltage of the PA91 from 150 V to 320 V, and changing the gain to x30 instead of x15 (by changing the feedback resistor from 14kohm to 29kohm), we can still drive 12 mA through the 25 kohms of series resistance. This will require getting new HV power supplies, as the KEPCO ones we have cannot handle these numbers.
   • The current limiting resistor is chosen to be 25ohms such that the PA91 is limited to ~26 mA. Of this, 300V / 30kohm ~ 10 mA will flow in the feedback path, which means under normal operation, 12 mA can safely flow through the coils.
   • Rich recommended using metal film resistors in the high voltage feedback path. However, these have a power rating, and also a voltage rating. By using 6x 5kohm resistors, the max power dissipated in each resistor is 50^2 / 5000 ~ 0.5 W, so we can get 0.6 W (or 1W?)  rated resistors which should do the job. I think the S102K or S104K series will do the job.
3. Add a voltage monitoring capability.
   • This is implemented via a resistive voltage divider at the output of the PA91.
   • We can use an amplifier stage with whitening if necessary, but I think simply reading off the voltage across the terminating resistor in the ladder will be sufficient since this circuit will only have DC authority.
4. Make a Spice model instead of LISO, to simulate transient effects.
   • I've made the model, investigating transients now.
5. High voltage precautions:
   • When doing PCB layout, ensure the HV points have more than the default clearance. Rich recommends 100 mils.
   • Use a dual-diode (Schottky) as input protection for the Op27 (not yet implemented in Spice model).
   • Use a TVS diode for the moniotring circuit (not yet implemented in Spice model).
   • Make sure resistors and capacitors that see high voltage are rated with some safety margin.
6. Consider using the PA95 (which Rich has tested and approves of) instead of the PA91. Does anyone have any opinions on this?

If all this sounds okay, I'd like to start making the PCB layout (with 5 such channels) so we can get a couple of trial boards and try this out in a couple of weeks. Per the current threat matrix and noises calculated, coil driver noise is still projected to be the main technical noise contribution in the 40m PonderSqueeze NB (more on this in a separate elog).

Basic Pump Throughput Concepts

What is Pump Throughput?

The manufacturer of a vacuum pump supplies a chart for each pump showing pumping speed (volume in unit time) vs pressure. The example, for a fictitious pump, shows the pumping speed is substantially constant over a large pressure range.

By multiplying pumping speed by pressure at which that pumping speed occurs, we get a measure called pump throughput. We can tabulate those results, as shown in the table below, or plot them as a graph of pressure vs pump throughput. As is clear from the chart,  pump throughput (which might also be called mass flow) decreases proportionally with PRESSURE, at least over the pressure range where pumping speed is constant.

The roughing pump speed actually will reach 0 l/s  at it's ultimate pressure performance.

Our roughing pump  pumping speed will slowly drop  as chamber pressure drops. Below 10 Torr this decrease is accelerated and bottoms out. This where the Root pump can help. See NASA evaluation of dry rough pumps...What is a root pump 

We have been operating succsessfully with a narrow margin. The danger is that the Maglev forline peaks at 4 Torr. This puts load on the small turbo TP2, TP3 &  large TP1

The temperature of these TP2 & 3  70 l/s drag turbos go up to 38 C and their  rotation speed slow to 45K rpm from 50K rpm because of the large volume 33,000 liters

Either high temp or low rotation speed of drag turbo or long time of overloading  can shut down the small turbo pumps......meaning: stop pumping, wait till they cool down

The manual gate valve installed helped to lower peak temp to 32C It just took too long.

We have been running with 2 external fans [one on TP1 & one on TP3]  for cooling and one aux drypump to help lowering the foreline pressure of TP2 & 3

The vacuum control upgrade should include adding root pump into the zero pumping speed range.

Atm1,   Pump speed chart:   TP1  turbo -red, root pump -blue and mechanical pump green. Note green color here representing an oily rotory pump. Our small drypumps [SH-100] typically run above 100 mTorr

                                           They are the forepump of TP2 & 3     Our pumpdown procedure: Oily Leybold rotory pumps ( with safety orifice 350 mT to atm ) rough to 500 mTorr

                                                                                                 Here we switch over to TP2 & 3 running at 50k RPM with drypumps SH-100 plus Aux Triscroll

                                                                                                 TP1- Maglev rotating full speed when V1 is opened at full volume at 500 mTorr 

                         History: the original design of the early 1990s had no dry scroll pumps. Oil free dry scrools replaced the oily forepumps of TP2 & TP3 in ~2002  at the cost of degrading the forline pressure somewhat.

                                     We had 2 temperature related Maglev failers in 2005 Aug 8 and 2006 April 5  Osaka advised us to use AUX fan to cool TP1  This helped. 

Atm2,   Wanted Root pump - Leybold EcoDry 65 plus  

Atm3,   Typical 8 hrs pumpdown from 2007 with TP2 & 3 

Atm4,   Last pumpdown zoomed in from 400 mT to 1mT with throttled gate  valve took 9 hrs  The foreline pressure of TP1 peaked at 290 mT, TP3 temperature peaked at 32C

            This technic is workable, but 9 hrs is too long.

Atm5,   The lowest pressure achived in  the 40m Vacuum Envelope 5e-7 Torr with pumps Maglev  ~300 l/s,  Cryo 1500 l/s  and 3 ion pumps of 500 l/s      [ in April 2002 at pumpdown 53 day 7 ] with annuloses at ~ 10 mTorr

Atm6,  Osaka TG390MCAB Throughput with screen ~300 L/s at 12 cfm backing pump

Starting c1cal now, let's see if the other c1lsc FE models are affected at all... Moreover, since MC1 seems to be well-behaved, I'm going to restore the nominal eurocrate configuration (sans extender board) tomorrow.

I took another pass at this. Here is what I have now:

Attachment #1: Composite amplifier design to suppress voltage noise of PA91 at low frequencies.

Attachment #2: Transfer function from input to output.

Attachment #3: Top 5 voltage noise contributions for this topology.

Attachment #4: Current noises for this topology, comparison to current noise from fast path and slow DAC noise.

Attachment #5: LISO file for this topology.

Looks like this will do the job. I'm going to run this by Rich and get his input on whether this will work (this design has a few differences from Rich's design), and also on how to best protect from HV incidents.

Summary:

It looks like we can have a stable SRC of length 4.044 m without getting any new mirrors, so this is an option to consider in the short-term.

Details:

• The detailed calculations are in the git repo. 
• The optical configuration is:
  • A single folding mirror approximately at the current SR3 location.
  • An SRM that is ~1.5m away from the above folding mirror. Which table the SRM goes on is still an open question, per the previous elog in this thread. 
• The SRC length is chosen to be 4.044 m, which is what the modeling tells us we need for operating in the SR tuning instead of RSE.
• Using this macroscopic length, I found that we could use a single folding mirror in the SRC, and that the existing (convex) G&H folding mirrors, which have a curvature of -700m, happily combine with our existing SRM (concave with a curvature of 142m) to give reasonable TMS and mode-matching to the arm cavity.
• The existing SRM transmission of 10% may not be optimal but Kevin's calculations say we should still be able to see some squeezing (~0.8 dB) with this SRM.
• Attachment #1 - corner plot of the distribution of TMS for the vertical and horizontal modes, as well as the mode-matching (averaged between the two modes) between the SRC and arm cavity.
• Attachment #2 - histograms of the distributions of RoCs and lengths used to generate Attachment #1. The distributions were drawn from i.i.d Gaussian pdfs.

gautam 245pm: Koji pointed out that the G&H mirrors are coated for normal incidence, but looking at the measurement, it looks like the optic has T~75ppm at 45 degree incidence, which is maybe still okay. Alternatively, we could use the -600m SR3 as the single folding mirror in the SRC, at the expense of slightly reduced mode-matching between the arm cavity and SRC.

I made a script to scan the OMC length at each setpoint for the two TTs steering into the OMC. It is currently located on nodus at /users/aaron/OMC/scripts/OMC_lockScan.py.

I haven't tested it and used some ez.write syntax that I hadn't used before, so I'll have to double check it.

My other qualm is that I start with all PZTs set at 0, and step around alternative +/- values on each PZT at the same magnitude (for example, at some value of PZT1_PIT, PZT1_YAW, PZT2_PIT, I'll scan PZT2_YAW=1, then PZT2_YAW=-1, then PZT2_YAW=2). If there's strong hysteresis in the PZTs, this might be a problem.

After tweaking the AS55 demod phase, SRM alignment, triggering settings, I got a few brief DRMI locks in tonight, I'm calling it a success (though this isn't really robust yet). The main things to do now are:

• turn on all the boosts on the LSC loops - today I only managed to trigger the PRCL boost filters successfully without blowing up the lock.
• measure all 3 loops, tweak gain as necessary.
• Run some sensing lines, tune the demod phase.
• The SRCL triggering is strange to me - SRCL loop is currently triggered on POP22_I, but the 2f1 buildup in the symmetric side does not say anything about the linearity of the SRCL error signal? Or are we just hoping the SRM is in the correct place and engaging the servo? Anyway, this setting seems to work but perhaps once the locking is more robust the triggering can be fixed.
• do a quick NB - I expect the main change to be that the AS55_Q dark noise contribution would have gone up on account on the reduced amount of light at this port.

I think the main IFO characterization remaining to be done to determine the status of the IFO post vent is to measure the losses of the arm cavities. IMO, we will need to certainly fix the clipping at ETMY before we attempt some serious locking.

While working on the single arm alignment, I noticed that today, i was able to get the X arm transmission back to ~1.22, and the GTRX to 0.52. These are closer to the values I remember from prior to the vent. Running the dither alignment promptly degrades both the green and IR transmissions. Since the pianosa SL7 upgrade, I can't use the sensoray to capture images, but to me, the spot looks a little off-center in Yaw on ETMX in this configuration, I've tried to show this in the phone grab (Atm #2). Maybe indicative of clipping somewhere upstream of ITMX?

Anyways, I'm pushing onwards for now, something to check out in the daytime.

In preparation for attempting some DRMI locking, I did the following:

• Slow machine reboots for unresponsive c1psl, c1susaux and c1iscaux. The latter requried a manual burtrestore to recover the usual LSC PD whitening settings.
• Shuttered AUX laser (which was on Standby anyways) - we should really install a remotely controllable shutter for this on the AS table.
• Re-aligned PMC (half turn of knob in yaw, full turn in pitch) - IMC transmission 15,000cts ---> 15,600cts.
• Squished sat. box cables at ITMX and ETMX.

Not related to this work, but I turned the Agilent NA off since we aren't using it immediately.

[aaron, gautam]

We finished up making the new c1omc model  (screenshot attached).

The new channels are only four DAC for ASC into the OMC, and one DAC for the OMC length:

I've attached the diagram of what I mean.

There are a couple caveats and changes that would have to be made that are not included in this diagram, because they would be made on different tables.

1. I moved MMT2, which means the other MMT optics would have to be adjusted to accomodate this. I checked out the configuration on the BS table and this seems doable with a small rotation of MMT1 and maybe PJ2.
2. I don't know the best way to get the OMC REFL beam out... thoughts?
3. This diagram is kind of crappy after my edits, someone should tell me how to avoid collapsing all layers when I open these layout diagrams in inkscape, because I ended up editing the layout in Acrobat instead, where the lack of object grouping caused a bunch of the optics to lose one or two lines along the way.
4. I didn't include all beam paths explicitly but can if this looks like a good configuration.
5. The optic that picks off the transmission through MMT2 will need to move a bit, but there was a clamp in the way; this should be a minor change.
6. The optic just before the OMC needs to be moved up a bit.
7. The optic after the signal OMMT should be changed to a PBS and translated a bit; this is where the LO and signal beams will combine

Gautam also had some questions about the BHD/OMC timeline and plan. I feel somewhat on shaky ground with the answers, but figured I'd post them so I can be corrected once and for all.

1. Is the plan really to use the current OMC setup to make a homodyne measurement? 
   1. ​I'm not sure where on the timeline the new OMC and BHD switchover are relative to each other. I have been imagining doing the swap to BHD before having a new OMC.
2. I thought the current OMC resurrection plan was to do DC readout and not homodyne?
   1. ​I think the OMC resurrection plan is leading to DC readout, but when we switch over to BHD we'll be able to operate at the dark fringe. Is that right?
3. Is it really possible to use our single OMC to clean both the LO and dark port beams? Isn't this the whole raging debate for A+?
   1. ​My understanding is yes, with the LO and DP in orthogonal polarizations. It's not clear to me why we expect to be able to do this while there is a debate for A+, perhaps our requirements are weaker. It is something I should calculate, I'll talk to Koji.
4. A layout diagram would be really useful.
   1. ​Attached now.
5. Where in the priority list does this come in?
   1. ​I am a leaf in the wind. I think this comes well after we have the OMC resurrected, we just want to get a sense for what parts we need so we can order them before the fiscal year closes.

Larry W said that some security issues were flagged on nodus. So I ran

on nodus. The exclude flag is because there were some conflicts related to that particular package. Hopefully this has fixed the problem. It's been a while since the last update, which was in January of this year.

Here is an other big one

That seems fine, I wasn't thinking of that beam. in that case could we just have a PBS directly behind MMT2 and send both beams to the same OMMT?

Alternatively we can move OM5 and the beam path OMPO-OMMTSM towards -y, then put the LO-OMMT parallel to the existing OMMT but displaced in +x... we'd have to move the existing OMC and BHD towards +x as well. 

Can we use the leakage beam from MMT2 on the OMC table as the LO beam? I can't find the spec for this optic, but the leakage beam was clearly visible on an IR card even with the IMC locked with 100 mW input power so presumably there's enough light there, and this is a cavity transmission beam which presumably has some HOM content filtered out.

I've started putting together a list of things we'll need to buy to do BHD readout. I'm still messing around with more detailed optics layouts, but wanted to get a list started here so people can let me know if I'm missing any big, obvious categories of goods.

My current plan makes minimal changes to the signal path going to the OMC, and tries to just get the LO beam into the OMC with minimal optics. I'm not thinking of any of the optics as suspended, and it requires several reflections of the LO beam, so probably this is not an excellent configuration, but it's a start for getting the parts list:

1. My current thought is to use the MC reflection, the beam that heads from MC1 to MCR1, as the LO beam
   1. From MCR1, send the LO to a BS that directs it into an MMT, oriented along x (and lets us keep the MC refl PO)
   2. After the two MMT optics, the beam will be traveling along -x, and can be directed to a mirror that sends it towards -y to two steering mirrors that send it along -x then +x near the top of the table (perpendicular to the signal MMT.
   3. Then, send it to a PBS, which replaces the mirror directly after the signal MMT. This is where it combines 
2. Beam is then sent to the steering mirrors to bring it into the OMC
3. In parallel, the signal beam is going through the same path it has now, including the pickoff beam, with the one change that we need a HWP somewhere before the PBS, and the PBS replaces the mirror directly after the MMT (and needs to move a bit closer to have the beam properly directed)

I started making a layout of this scheme, but it's probably not going to work so I'm going to make a quick layout of this more major modification instead:

1. Both the MCR beam and the AS beam come in about parallel. Send each to a PO mirror.
2. The PO mirror directs both beams into parallel MMT aligned along x
3. From the MMT, each is directed to a pair of steering mirrors located where the OMC MMT is located now
4. From the steering mirrors go to the PBS that combines the signal and LO
5. Then to two more steering mirrors to get into the OMC, which may be moved towards +x
6. From the OMC go to the BHD PBS

What we need

Optics

• HWP for just before the LO combines with the signal
• HWP for just before the signal combines with the LO (is this necessary?)
• PBS to replace OM5 (combines the LO and the signal)
• Two MMT optics
• Two piezo-driven TT optics for steering the LO to the PBS
• One additional non-piezo optic for between the LOMMT and the LO-TTs
• One additional BS to get the LO into the MMT (and to let us still have the PO)
• -1 optic—we pick up one mirror that we replace with the PBS

Optomechanics

• 2x HWP mounts
• 1x PBS mount
• 2x mounts for piezo-driven TT
• 2x MMT optic mounts—I didn’t take a close enough look at these during the vent to know what we need here
• 2x mounts for ordinary optics
• 9x clamps for optics mounts (maybe fewer if some are on blocks)
• 9x posts for optics mounts

Electronics

• Additional TT driver
• HV supply for the new TTs
• Are the HWP actively controlled? We might need something to drive those?
• Do we have enough DAC/ADC channels?

Questions

These are mostly just miscellaneous

1. What of these optics need to be suspended? If we need suspensions on all of the LO optics, including the MMT, I’m not sure we’re going to be able to fit all of this on the table as I envision it…..
2. What if anything can we put out of vacuum (HWP for example)?
3. Do we actually need two MMT?