One problem solved, two problems found.

TITLE: 05/15 Day Shift: 1430-2330 UTC (0730-1630 PST), all times posted in UTC
STATE of H1: Planned Engineering
OUTGOING OPERATOR: None
CURRENT ENVIRONMENT:
    SEI_ENV state: MAINTENANCE
    Wind: 6mph Gusts, 3mph 3min avg
    Primary useism: 0.06 μm/s
    Secondary useism: 0.13 μm/s 
QUICK SUMMARY: Work in HAM2 continues today as part of the ISS swap, but not until the Kobelco unit has had some maintenance done this morning. No in-chamber work allowed until that's finished. 31 disconnected channels on the EDC since the corner HEPI pump controller appears to still be down.

In other news, a M6.7 EQ out of Japan is rolling through, and it's a beautiful morning on-site.

Good news is that we're done with the alignment of the ISS path. Pictures and details are to follow.

Then I reinstalled the last IFO REFL baffle right in front of the HAM2-HAM1 septum window. (The baffle was removed after marking the exact position using three temporary dog clamps on the ISI on day 1 because it was in the way, I was supposed to record that in alog 90158 but forgot. I'm absolutely sure that the position of the baffle was restored within 0.1mm of the original position.)

Bad news is the IFO REFL was clipped on that baffle. 00 mode flash isn't clipped that much but horizontal modes certainly are. That was not THAT surprising because the IMC alignment was/is not great (see my comment 90224). This looks to me that the uncontrolled degree of freedom of the IMC is wrong regardless of the reason why a huge alignment change had to be made to center the MC2 TRANS QPD.

Good news is the ISS path alignment is not impacted by that, at least greatly, because we made sure that the beam hit the right location of IM4 TRANS as well as ISS array QPD before we did anything in the ISS path. Note that the baffle clipping the beam is not in the ISS path.

In other words,

• the beam position on MC3 might have been poor but we used IM3 and IM2 to steer the beam INTO the ISS path such that the alignment there is reasonably close to in-vac alignment,
• when the beam coming out of MC3 is brought back to the good position/angle, we can bring the beam back onto IM4 trans using IM3 and IM2,
• if the beam is not found on the ISS QPD at that point, we can scan IM3 (and IM2 if necessary) further to find the beam,
• and use the first pico for the ISS array path to keep the beam on the array QPD while slowly bringing IM3 (and IM2 if that's touched) back to the good angle.

However, since we don't want to revisit HAM2 once we close it, I'd like to understand what's going on for the IMC/IFO alignment. 

To close out the week, we got stops and shroud mounts installed on the 2 CRS today. This is as far as we can go until we can get flexures or start assembling HOQIs, so probably not much more to report until later next week. We've covered the CRS in foil to protect them, and packed up the left over hardware for these 2 sensors. 

TITLE: 05/14 Day Shift: 1430-2330 UTC (0730-1630 PST), all times posted in UTC
STATE of H1: Planned Engineering
INCOMING OPERATOR: None
SHIFT SUMMARY:

Cement truck convoy day for CEBEX today.  Bigger BeamSplitter "captured" in the suspension assy & FARO-ed in the afternoon.  A couple big middle school tours.  ISS Array alignment continued.
LOG:

• 1438 Kim finishing up with garb supply checks.
• 1524 technical cleaning in lvea (kim)
• 1543-1709 Charge Measurements (ryanC)
• 1547-1554 checking on pumps and overall VAC status (jordan)
• 1553 Rebar inspector arrived for CEBEX
• ~1615 LVEA transitioned to SAFE for....
• ~1615-1813 BBSS work (ibrahim,betsy,oli)
• 1640:  susr2 rack work near ham3 (josh)
• 1648:  Cement Truck convoy begins to MY!!
• ~1650 CP1 checks (travis)
• 1713-1723 Finley Middle School Tour (amber)
• 1715-2035 cleaning tests in-chamber....turned ON illuminator in BSC3 (bsc1 & bsc2 is already ON) (robert.tj)
• 1717-1755 Walkabout in lvea (richard)
• 1727-1821 technical cleaning in lvea (kim)
• 1758-1814 Finley Middle School 8th grader tour (maggie)
• 1815-1833 LVEA Transition back to HAZARD (tony)
• 1824- 2137 Corner rga (jordan)
• 1920-1930 checking FARO parts (stephenA)
• 1942-2324 team-ISS Array starting chamber work (keita)
  • 2002-2248 rahul joining
  • 2015 elenna joining
• 1943 -2120 team-BBSS back at it (ibrahim, betsy, randy)
• 1955-2012 Warming up FARO (jason)
• 2013-2225 CRS work in the CRS Lab (jim.shoshanna.michaelR)
• 2015-2158 SPI alignment + possible laser hazard (jeff.josh)
  • 2158 jeff out
  • 2224 josh out
• 2022 Connection alarm for HEPI_PUMPS, not a beckhoff issue, so will need jim to restore (notified Jonathan.patrick/CDS + Jim)
• 2038-2111 MER to check on HEPI cabling (fil)
• 2041-2055 connecting with jordan + betsy (travis)
• 2108-2258 sqzt7 beam profiling, turning sqz laser ON for this work and OFF when done (sheila.ryanS.tony)
• 2109-2328 team FARO getting set up at Test Stand (jason.ryanC)
• 2140 turned BSC123+HAM3 illuminators OFF (corey)
• 2243-2301 Checking out a pelican case (b&k) near HAM6 (tj.jim)
• 2246-2252 corner rga check (jordan)
• 2304 Checking on corner station HEPI Pump Station (jim)
• 2312 More BSC2 cleaning & tests.  Turned BSC123 + H3 illuminators back on (robert w/ Oli-buddy)

Ibrahim, Betsy, Oli

Today, we installed BBS01 into the BBSS successfully. 

BBS01 was on a table. BBSS was on the aluma lift. We picked BBS01 using the ERGO arm and slowly came into the optic. In this process, we:

• Removed the EQ stops and replaced them with the glass tips
• Ensured that the gold wire was held correctly about the lower structure barrell
• Made contact between the gold wire and the grooves of the prisms
• Backed the glass tip EQ stops in to contact, securing and locking the whole suspension (M1 and M2 were already locked)
• Installed the BBSS face shields
• Practiced a lift of how it would go up into the test stand
• Placed teflon pads between the lift arms and the BBSS 45 degree lifting bars - LLO did the same (alog 80802) - this helps with fine structure adjustment when below the ISI
• Covered the BBSS on the lift in prep for test stand install (IAS needs time with the ISI to get exact positions in XY for where BBSS will sit).

On top of pictures below, 2 videos:

• Pushing BBS01 In
• ERGO Arm Sighting and Adjustment

I spun the iNCal (currently installed version) at a low speeds to see if low speed operation shows the same vibrations that high speed operation does (see 67207). Even rotating at 1 Hz shows a large increase in signal in the accelerometer (H1:PEM-EX_ACC_BSC9_ETMX_Z) around 200 Hz. 7 Hz shows an order of magnitude increase between 100-300 Hz. The 0 Hz spectrum is with the iNCal powered but a set speed of 0 Hz. 

The lesson is that the iNCal will inject broad band noise in the strain readout even at very low speed operation.

Following yesterday's alog 90219:

• IM2 and IM3 were reverted back to Monday evening position just using the slider values.
• Using flashes, confirmed that the IM4 trans as well as ISS QPD were roughly at the same position as the Monday evening position.
• Elenna confirmed that ISS OUTER SUM flash peak minus dark offset was 0.031 with 200mW input. (INNER SUM was much smaller.) Back in March it was 0.062 with 2 W input. So somehow the alignment into ISS array used to be REALLY poor.

At this point I and Rahul checked the beam positions in HAM2. Some things to note:

• The beam was uncomfortably close to the holes in the last baffle before the ISS array. It might have been clipped back in March. See ISS_two_hole_baffle.png showing the flash on the right hole. That hole is the "exit" hole for the reflection of the last pico mirror. Left hole is for the incoming beam from the 1" lens (which is right behind the baffle in the picture) but we couldn't take a good photo of the flash in the left hole at the time.
• Once the beam clears the last baffle, the beam is not clipped by the array cover nor the input hole of the array elevator plate.
• IM4 trans beam goes to the first pico mirror cleanly without getting clipped, and it's not clipped at all on the 2" lens.
• IMC trans beam from MC3 hit the IM1 cleanly, clears the baffle after that (IMC_REFL_peri.jpg), and appeared to go to IM2 without getting clipped. Couldn't check IM2->IFI->IM3 but no reason to get suspicious either. 
• IM1 transmission was clearly visible using a card and the IR viewer, it was not clipped by the suspension cage with considerable marging and was hitting the steering mirror behind IM1. 
• IMC REFL comes out of the last (second) IMC REFL periscope cleanly, the beam is well centered on the baffle hole. See IMC_trans_after_IM1.mp4.

We proceeded to swap the ISS array unit.

• Rahul went inside HAM2 and disconnected the QPD and array PDs after powering down the transimpedance amplifiers. Note that ISS QPD TIA shares the chassis with the IM4 trans, so IM4 trans went dark for some time too. 
• The old array assy was separated from the ISS array spacer. The latter remained in the chamber, only the top assy was swapped, as was explained in alog 90158.
• The new array assy SN1202965 (S1202965) was put on top of the array spacer. We took time to double check that the bias voltage for QPD comes to the expected pin on the QPD connector before making connection because the connector could be rotated by 90, 180, or 270 degrees and we can ruin some quadrants. Array PD cables were straightforward, it went as planned in alog 90158.
• TIAs were turned on.

At this point we saw flashes on QPDs as well as array PDs right away. INNER as well as OUTER SUM flashes were both about 0.06 (in the old unit it was 0.03 for OUTER but INNER was much smaller).

We started trying to center the QPD using the first pico mirror. Since pico driver is temporary unavailable (IOT2L is moved away) Rahul turned the pico manually while Elena looked at the laptop screen to monitor flashes in the individual segments. We managed an OK job (arrayqpd_centered.jpg) and checked the beam spots again.

• The beam was very high on the left hole of the two-hole baffle (Rahul has a good pic), high on the right hole (right_hole_after_new_array_QPD_centered.mp4), and OK on the input hold of the array (array_input_after_new_array_QPD_centered.mp4).

The baffle height might not be the same as the lens height and/or the ISS array input hole height, but otherwise it seems that we're shooting down the beam from the 1" lens to the ISS array. We'll check if the lens, baffle and the array are all at the same height or not, and decide how to proceed.

We started with yesterday's alignment. I checked flashes in ISS array PDs and didn't like that the balances between them were very much different from how they were when IMC was locked back in March.

Then we started changing IM2 and IM3 to see if we can get back, but I was appalled that the flashes became stronger and stronger on array PDs as we aligned, which probably means that the beam was almost falling off of the PDs when we started. 

That shouldn't have stopped us because we don't know where the beam was on the array PDs when MC was locked (people gave up optimizing that path because things didn't make sense), it could have been falling off of the diode (because each diode is 2mm,  QPD is 3mm, the beam size is ~250um or so, and the beam was almost in one quadrant of the QPD). But I started thinking about many what-ifs and wasted time.

After all, since IM4 TRANS and ISS array QPD are both reasonably close to March 2026 position, we know that the beam position as well as angle of the beam injected into ISS path from IM4 are already close to those when IMC was good in vacuum.

What we should do is this:

• Revert back to Monday IM2/IM3 alignment. Confirm that the IM4 trans position as well as ISS array QPD position are OK.
• Check flashes in 2nd loop inloop and out-of-loop sum. Recheck if at least one of them is comparable to when IMC was locked back in March, taking into account the power difference, even though Sheila checked it yesterday. At this point, we'll have established again that the position and the angle of the beam coming into the ISS path are reasonable.
• Check that the beam in ISS path is nowhere near being clipped by baffles and ISS array cover and the elevator aperture of the ISS array. Don't fix clipping right away, do it after swapping the array because we'll have to move pico mirrors anyway.
• Swap the array. There's no assurance that the beam will be on the QPD right away but that's OK. We can move the unit on the spacer if that helps. Go as close as you can, then start using the two pico steering mirrors. Use the array input aperture to aid the process.
• Once you see the beam on the QPD, continue to center the QPD, fix clipping, not necessarily in this order.
• Check the flash height of array PDs as well as QPD, see if things makes sense.

Other things to note:

This is not required for the alignment but it's helpful to know how much we can move the beam on QPD. In an unlikely event where we somehow lose the beam in vacuum on the array QPD after IMC is locked, we might be able to scan IM3/IM2 to regain the beam on QPD, and slowly move IM3/IM2 back to the nominal position while pico-ing so the beam isn't lost on the QPD. If the beam is not clipped, the beam displacement on the QPD is ~3mm per 1mrad of IM3 rotation using parameters collected from various documents, see attached script.

The same script shows you that the Gouy phase separation between two pico mirrors is 10 degrees (if we use the beam parameter in Matt Heintze's alog 12537, which was probably obtained by the measurement of the bypassed beam) or about 20 degrees (if we use IMC eigenmode parameter propagated to the ISS path using D1200693).

Another thing is, if we believe the design eigenmode number rather than the measured bypassed beam in Matt's alog, the beam waist will be smaller and at about 20cm upstream of the PDs. The beam size on the PDs is about twice as large as it should be (470um rather than 250um). I cannot measure the beamsize of the flashes so we won't do anything, but that's something to remember. If IM3 has enough actuation range, we can later lock the IMC, scan the beam across the PD until the beam falls off, see how sharp the fall-off is, and use the diameter of the PD (3mm) to determine the size of the beam. Maybe a good project for a fellow.