Stefan , Kiwamu

The following TFs are now being measured.

• PRM
  • M3 L to PY
  • M3 P to PY (automatically starts after the L to PY finishes)
  • M3 Y to PY (automatically starts after the P to PY finishes)
• PR2
  • M3 P to PY
  • M3 Y to PY (automatically starts after the P to PY finishes)

All of them runs on opsws5. They started at 10:20 am local.

Summary: A camera with a flash right beside the lens was used to look for potential backscatter noise sites. Most baffles look good, and there was only one strong backscatter site within the arm cavities: the large gate valve seats by the ITMs.  There were also a few retro-reflective sites outside the arm cavities: for the compensation plates, the HAM3 ISI, and the supports for the elliptical baffles and the TCS mirror 2 were quite retro-reflective. As an aside, I also noticed that the TCS alignment port was partially blocked by a nozzle. In the lower sensitivity input arm, the MCA1 and 2 baffles had bright reflections, as did the HAM3 ISI.

ITMX. In Figure 1, the top image shows approximately what the beam spot on ITMX “sees”. I use these photos to look for potential scattering problems; the camera is placed very close to the center of the optic where the beam spot will be. The flash mimics the wide-angle scattering of interferometer light from the beam spot and lights up regions that will retro-reflect interferometer light back to the beam spot, where it can recombine with the main beam to produce scattering noise. Of course the technique is limited by different angular distributions of scattered IFO light and light from the flash, as well as by color differences, but it gives a rough idea and also shows glints, which are hard to predict. The camera is about 10 cm in front of ITMX, so it sees a little more through the hole in the baffle than the beam spot on the optic will. Nevertheless I expect that the baffle will not block the view of the gate valve seat, the shiny reflecting arc at the right of the view through the baffle aperture. This is the only site found in the high-intensity arm cavities. I think the first step is to double check that the valve seats are actually visible from the ITM beam spots.

The lower image in Figure 1 is the view from the X-manifold spool of ITMX, with the camera located in the IFO beam path (the camera is in the beam path when the flash retro-reflects off of the optic). The arm cavity baffle looks good: the small reflecting rectangle at the bottom center of the baffle is the connection for the safety lanyard and is actually under the bottom side of the baffle and thus should be outside the clear aperture from ETMX. It looks like it is inside the baffle because the far part of the baffle box sags down a little and we are seeing a little of the underside of the baffle.

ITMX RM (compensation plate).Figure 2 shows the view from the beam spot on the compensation plate (the reaction mass). There are strong retro-reflections from the HAM3 ISI. The glints are off of stage 1 of the ISI so there is some isolation of the reflecting surface. There are also glints off of the elliptical baffle, which has one stage of passive isolation like the ISI, and also off of the mount for TCS mirror 2, which is not seismically isolated.

The view in TCS mirror 2 (the copper-colored circle), shows that the TCS alignment port is partially blocked by the nozzle of the port. Thus there is not a complete view of the compensation plate from all parts of the port, which may make alignment more difficult. We also need to watch for backscatter sources on the TCS table.

BS.The first page of views from the beam splitter, Figure 3,  show bright reflections from the frames of the ITMs. I have reported this before (Link) and Mike Smith’s subsequent calculations suggested this would not be a problem, though I don’t think that specular reflection was considered.

Another potential source of retro-reflections to the spot on the BS are the reduction flanges for the tubes holding the gate valves between BSC1 & 8 and BSC3 & 7.

The second page of BS views shows the view back out the input arm. As with the view from the ITMX compensation plate, there are particularly bright glints from the HAM3 ISI (notice the beams of light shining on the floor of the tube), including one from the table edge, just a few centimeters below the path to/from PR3.

PR3. Figure 4; looking toward the BS, there are fairly strong reflections from the electro-polished aluminum baffle, MCA1, as well as from masses on the HAM3 tabletop.

PR2.The worst reflection in Figure 5 seems to be from the edge of the MCA2 baffle.

PRM.  Figure 6 shows a fairly bright reflection from the MCA1 baffle, a wide-angle reflection from the circular baffle, and reflections from objects on the HAM3 table.

MC1 & 3. Figure 7 shows that the MCA1 baffle again seems quite reflective and that there are also reflections from objects on the HAM3 table.

MC2. The reflection from the MCA1 electro-polished surface in Figure 8 does not appear as bad from this side, possibly because of the greater distance.

When I came in today, the arm was unlocked. For some reason the tidal relieve to HPI ETMX was still integrating. When I cleared its history, all watchdogs on ETMX, its ISI and HPI tripped. 

HPI and SUS were easy to recover. When trying to re-engage state 1 for ISI stage 1 though, the ISI consistently tripped when trying to move it to the final alignment biases.

Daniel, Stefan

With the PLL running reliably, I successfully handed off the mode cleaner control to the ALS COMM signal.

 - I copied all old HIFOY scripts in /als/h1/scripts/ into /als/h1/scripts/HIFOY_safe
 - I updated the CARM_down script and started working on the CARM_handoff script.
 - The initial part of the CARM_handoff script ran fine, and I was able to turn off the MC feed-back to MC2.
 - The CARM loop before engaging the AO path has a UGF of 20Hz - rather low, and the phase margin is questionable (0deg margin at 100Hz)
 - Then I noticed that CARM FM6 was an outdated filter, which needed to be updated for the new PLL. I added FM10 "shape", which is a z1.4:p1000 with the gain matching the previous filters FM6 and FM7.
   This effectively got rid of a p40:z7k - a filter that we now have in analog in the PLL. With that I increased the UGF to 90Hz.
 - I tried ramping up the AO path, but always lost it before I was able to measure the OLG. More work to be done there.



Updates to the CARM_down and CARM_handoff scripts:
 - The MC2_M3_ISCINF_L FM6 used to be a z150:p500 lead filter for extending the actuation lead to 500Hz. I restored it.
 - We are now using H1:SUS-MC2_M3_LOCK_L FM9 instead of FM8. I adapted the scripts
 - Use CARM FM10 instead of FM6 and FM7.
 - I took all ARM HEPI feed-back engaging out of the script - that is handled by the ALS at the end station.
 - I took any reference to RFAIR_9 out of the down script.

Sheila, Daniel, Stefan

I tuned up the beat note alignment this morning. 

With the arm locked we have 88uW total on the COMM_A_LF detector, 42uW from the arm and 47uW from the SHG.  This gives us a beatnote of 28mV pp, with the PFD RF power readback saying -35dBm. 

The Comm PLL locks for a few seconds and runs out of range (due to fluctuations at the microseism frequency).  One solution would be to feedback to the ETM  from the green laser at the microseim frequency ( right now we only have very low frequency feedback to HEPI), this would probably be nice in the end, because the PLL would lock nicely and we need to figure out out how to do this for HIFOXY anyway.  Another solution would be to engage COMM with the PLL partially locking, which does still give a useable error signal, which would be quicker to implement.

[Koji Yuta]

On Friday afternoon, an RF amplifier unit with 3f (27/135MHz) diplexer (D1300989) and a 4ch demodulator unit
with 2f (18/90MHz) diplexer mod (E1300899) were installed to R2U27 and R3U8, respectively.

- The RF diplexer amplifier D1300989 S1400079

The module was fixed at U27 of the R2 rack and cabled up. Test signals were applied from an RF signal source via the installed TNC-N cable.
Quick check of the 3f chain has been done:
1) Applied a -40dBm  (6.3mVpp) signal at ~27.5MHz to the input cable => obtained the output of 2.5Hz with the amplitude of ~1200Vpp (attachment 1)
2) Applied a -50dBm  (2.0mVpp) signal at ~136.5MHz to the input cable => obtained the output of 270Hz with the amplitude of ~11500Vpp (attachment 2)

There could have been the whitening filters turned on. So the response should be done again with more careful tuning of the input frequency.

- The RF diplexer amplifier D1300899

The demodulator was modified by Dick and tested by Yuta. The test proceduer is here. E1400033

The module is installed to the R3U8 for AS18 and AS90. There are LO signals labeled Ch1/2/3.
However, the diplexer channels for 9/18MHz are CH3 and CH4. So we need to confirm what the
correct channel assignment should be. This will affect the ADC channel assignment.

Transfer functions on HAM4 didn't go as well as hoped. There are some issues starting around .5 hz, that are only visible on the GS13s, then more around 3hz, still mostly visible only on GS13s. I don't know what to make of it, as the CPS's don't seem off in the same areas (see attached pdf's). I tried taking several DTT tf's over the same region (0.1 - 5hz in the attached png image), and they don't look as bad the matlab tf's. Everything else on the ISI looks good.

Tried a few things such as 250mHz blends on Stage1 & 2 for all dofs, w & w/o notches, tried notch on T240 (not helpful.)

Noise of Stage2 CPSX & GS13X blend In1 was higher generally between .5 & 1 hz with the 250 vs 750 blend, that seemed strange.

.5hz peak appears on St1 CPSX when switched to T100.44Notch on Stg1X from 750mHz, that too seemed strange to me.

Left ITMx in same configuration I found it this morning: 750mHz blends everywhere except St1 Y has T100mHz_NO.44 and Stage2 X & Y has Narrow_Notch added.

No alignment changes.

The cables H1: ISC 414 and 416 have a problem with either pin 3 or 16 or both.  These are the pins used for the input offset adjust for the PLL boards.  I used the tester at the etherCAT chassis and saw the offset adjust fine, then used the tester at the rack end of the cable and I don't see it.  This is D19 on the schematic D1300812

Other things are working, like the gains and the OK status. 

Kiwamu, Stefan

- Fitted the  BS M2 L2P drivealign - we get about the same performance for isolation
- Tried to fit the BS M2 L2Y drivealign - the result was worse than the previous filter, so I just left the old filter in.
- Kiwamu fitted the PRM M2 L2P drivealign - we get a decent decoupling - more than 3 around the peak at 0.75ish Hz

- Started the PRM M2 P2Y measurement.

We've been seing a 0.5Hz resonance (plus harmonics) on BSC-ITMX (this Jeff's summary here). We investigated more on that today.

This half hertz:

- appears on ALL the sensors of the ISI on X,Y and RZ

- appears on ALL the sensors of the ISI on H1,H2 and H3 (which makes sense according to the previous statement)

- doesn't appear on HEPI

- appears on M0 Longitudinal, but with a much smaller amplitude

We've tried different configurations. We first noticed this issue with HEPI position controlled and ISI fully controlled (Ctrl lvl1 on ST1+ST2, T100mHz blend filters on ST1-X and ST1-Y, 750mHz blend elsewhere).

- It disappears when the ISI is under damping only.

- It reappears when only ST1 is controlled.

Weird thing: it doesn't appear when only ST1-X controller is ON, but it DOES appear when only ST1-Y controller is ON.

Also, to be sure that the issue wasn't coming from the actuators, I drove a white noise on ST1-X and ST1-Y (damping only). It didn't appear.

At this point, I would guess we're having a CPS/ground issue again, with no conviction. We'll try to monk with the electronics Monday.

To finish, I just want to remind that we have a temporary solution, which is putting a narrow notch at this frequency into ST2-CPS blend filters. With this temporary fix, we are pretty happy about the ISI performance.

S. Biscans, H. Radkins, J. Warner, J. Kissel

[[Belated entry from last night]]

In order to investigate the recently found oscillations and/or frequency combs in ISI ITMX that has been troubling the Green Team (see LHO aLOG 9494), we explored a few different configurations of the corner station BSC-ISIs. This aLOG covers the first three configurations we tested. Since these initial tests, Seb, Jim and Hugh have explored more configurations (see LHO aLOG 9537). This serves as the record for the temporary temporary solution which got the performance needed to satisfy the Green Team (see LHO aLOG 9518) -- the addition of a high-Q notch in the ISI-ITMX displacement sensor blend filters on both both stages.

With the 0.5 [Hz] notch on both stages, we're able to reduce the RMS optic pitch motion from 160 [nrad] to 80 [nrad].

Attachment 1: performance of ST2, as measured by the ST2 GS13s (stage 2 inertial censors) in three different configurations:
(1) Initial measurement in the current best configuration,  Level 1 isolation filters, with "T100mHz_N0.44" blends on ST1 XY and "750mHz" on ST1 ZRXRYRX and all of ST2.
(2) Exact same configuration of ISI-ITMX, but with the ISI-ITMY CPS turned off at the racks in the high-back (via the independent rocker switches on the back panel).
(3) With ISI-ITMY's CPS still off, similar control loop and blend filter configuration of ISI-ITMX except with a 0.5 [Hz] notch filter  in the X and Y degrees of freedom of both stages.

Attachment 2: A comparison between blend filters used in the current best configuration, with and without the 0.5 [Hz] notch filter. Note that this an export from the filters *actually installed* in foton, so the blend filters include the sensor response inversion, so they're not just the complementary blend shape (which is why the 750 mHz filters look screwy upon first glance). 

Remember, this notch is a temporary temporary solution. We're continuing to investigate the source of the problem, and we look forward to both the temporary (see LLO aLOG 10584) and permanent hardware / analog electronics solution (still under development) to the CPS oscillators beating against each other. However, while it's obvious the beating oscillators cured *some* of the frequency comb (comparing Initial Measurement against ISI-ITMY CPS OFF) we're not convinced the beating oscillators is the source of the exactly-0.5[Hz]-line.

For the record, 
- The foton design is notch(0.5,20,20) for a frequency of 0.5 [Hz] a Q of 20 and a depth of 20 dB. It also has a ramp time of 10 sec on the output.
- The notch lives in a separate filter module (FM5, called "notch_narrow") in the CPS blend filter banks (e.g. ITMX_ST1_BLND_X_CPS_CUR)
- You cannot access/turn ON/OFF from the main blend filter screen -- you have to open the "CURR" CPS sub-screen

The PSL shut down because the chiller had a flow sensor 1 error.  Reseting the status then restarting the chiller cleared the error.  The PSL is back on now. 

Travis/Betsy

This morning, we staged to put the ETMy QUAD monolithic structure back together.  We vacuumed as much of the structures as we could.  I re-first-contact-cleaned the ERM-front surface since it had been exposed to the elements since the last vent and showed much particulate dispite blowing it with N2.  The FC cleaning worked and the surface looked improved.  We then removed the ETMy test mass HR First contact (which has been on since it left CIT) and attached the 2 lower structures.  Using the Genie, w transfered the completed lower structure to the silver pallet jack + 5-axis lift table.  We then maneuvered the LS into place and attached it to the upper structure already on the ISI table.  We removed all of the lifting EQ from the QUAD and stowed everything in the unused welding cleanroom.  All went well.  We did not suspend the QUAD - we'll start that on Monday.

Green team-

The arm cavity is finally locking stably, thanks to the work of Sebastian, Hugh, Jeff and company to reduce our pitch fluctuations.  Now we have about 5% fluctuations in the transmitted power that comes from pitch fluctuations, much better than the 50% we had this morning, and the cavity has been locked at least for 10s of minutes.  The slow feedback is now on, controlled by the autolocker. 

We get a max transmission of about 740 counts on ALS-C_COMM_LF, while the single shot beam stayed at 45 counts, which means that the on resonance/single shot resonance is 16.1, so we are getting 74% of the power that we would expect and probably have 26% of our power in higher order modes ( improved from 45% this morning).  This may have been due to Alexa and I moving the EOM in our effort to reduce the RF AM.  Maybe it is worth tweaking the EOM alingment when the cavity is locked to see if this is the sourcce of our mode mismatch. 

I will leave the cavity locking with the autolocker on, until the red team wants to misaling it.