Summary: in preparation for beam arriving in HAM6 / ISCT6, I wanted to explore the potential for mode mismatch to the OMC, and how it might be corrected.  I found that for essentially any reasonable combination of errors in optic positions and ROCs, the mode matching can be recovered by a small adjustment to SR2.  (Given the way the SRC is designed, I don't think this is surprising to anyone -- it may even be intentional! -- but it was an interesting exercise.)

Details:

At L1 they observe a mode mismatch to the OMC of ~25%, depending on which ITM supplies the bounce.  Lisa found that this could be caused by a small (1.5cm) change to the SR2-SR3 distance, assuming the PRC length is nominal.  At LHO we are a 2-3 weeks away from measuring the beam arriving in HAM6.  In principle, there may be errors in the position of any of the optics on the order of 1cm, and errors to the ROC for the curved mirrors (of order ~few cm?).  The question is, if we are very unlucky and the initial mode matching to the OMC is bad, can we correct it in a simple way?

I used Lisa's script from LLO:8565 as a starting point to estimate the mode mismatch that could occur from small errors in the positions and ROCs for optics in the output path, SR3 to OMC.  At LHO the PRC length has been measured to better than 1mm; it's very close to nominal, so for now I assume the positions of the PRs, the BS, and the ITMs are correct.  That leaves six optical components with un-verified positions: SR3, SR2, SRM, OM1, OM2, and the OMC.  (I fold errors in the position of OM3 into the position of the OMC.)

Modeling a beam subject to small variations in eleven optical parameters is a lot to keep track of in closed-form, so I implemented a Monte Carlo approach: for 10k trials I independently varied the longitudinal position and ROC of the six optics in the output path, and calculated the mode overlap with the OMC waist (w0=490um).

Errors in position were drawn from Gaussian random variables with sigma = 2.0cm; these were applied to SR3, SR2, SRM, OM1, OM2, and the OMC.  Errors in radius of curvature were drawn from a Gaussian distribution with sigma = 5.0cm; these were applied to SR3, SR2, SRM, OM1, and OM2.  I'm not sure if these values are reasonable (2cm in position sounds like a lot), but they seemed like fair conservative guesses, based on the as-built dimensions for L1 in E1200274-v3, compared to the nominal values in T0900043-v11.

For 10k trials, the median overlap with the OMC waist after varying the parameters of the optics was 0.85; the distribution is shown in Fig2.  This median is better than what's observed at L1, which may mean they got unlucky, or the magnitudes of my errors are too small.  (NOTE: for simplicity I am using a single bounce off ITMX with the nominal ROC of 1934m.)

Next, I used a la mode's optimizePath() function to correct the mode mismatch by varying the position of SR2.  Based on table layouts this seemed to be the easiest optic to move.  The range on the optimization of SR2's position was +/-5cm.

The result is that even for very bad mode overlaps, the errors can be compensated by moving SR2.  And, whether or not the overlap can be completely recovered is only a function of how far you can move SR2.  (I.e., if we are terribly unlucky at H1, maybe we can move it by more than 5cm.)  This might be known already to optics experts, but it was surprising to me that even for large errors in optic ROCs the mode can be corrected by changing a single degree of freedom.  I guess this is what you gain when your beam-reducing telescope has a short Rayleigh range?  (Flip side: we're really sensitive to the position of SR2 and SR3.)

In the attached: Fig1 is the distribution of mode overlap to the OMC, for 10k trials with independently varied parameters.  Fig2 is how well you can improve things by moving SR2; the horizontal coordinate is starting (mis)match, and the vertical coordinate is corrected (mis)match, after at most a +/-5cm change to SR2.  Fig3 is a comparison of how much you need to move SR2 vs how much you get back.  The scripts I used are there too.  It's not a very elegant implementation, for 10k trials it takes way too long to finish, something like an hour.



Notes:

 - This is all fine from a mode-matching perspective, but I don't know enough about optical cavities to say whether changing the SRC length by 5cm is okay or a complete disaster.  Also, I think that a la mode's optimization procedure changes only the position of the optic in question, and doesn't take into account the changes to relative lengths.  So, when it moves SR2 by 5cm, a la mode is increasing the distance from SR3 to SR2, and decreasing the distance from SR2 to SRM.  This would be fine if SR2 was a lens, but it's a mirror; if the position changes by 5cm the SR3-SR2 and SR2-SRM distances should change in the same direction.  (I think that since the SR3-SR2 distance is the important one, this is does not change the results, but I haven't checked in detail.)

  - I belatedly realized that the ROCs for the SR optics have been measured and they're listed on the core optics website (galaxy.ligo.caltech.edu/optics).  So, errors in the ROC of 5cm are probably way too generous.  I'm not sure about the OM1 and OM2 optics.

 - Of course in order to correct something you need to measure it first.  If the mode mismatch is bad we'll have to characterize the beam on ISCT6 with Chris M's beam scan technique or something similar.  It might be worth modeling how accurately we can measure the necessary correction to SR2's position.

J. Kissel, S. Aston, A. Pele, B. Weaver, T. Sadecki

Looking to get a "did the new baffles screw up the suspension?" answer sooner, rather than later, Betsy and Travis unlocked H1 SUS BS and and I ran a full suite of transfer functions. The results looked reasonably clean, except for some reduced Qs on the first L/T/P modes, and an out-standing mode at 1.69 [Hz] in vertical (see first attachment). 

With the "undamped ISI!" bug in my ear from SR3, and the help of the notes in the "plotall" comparison script, 
${SusSVN}/sus/trunk/BSFM/Common/MatlabTools/plotallbsfm_tfs_M1.m
we recalled that we've seen this same feature 1.69 [Hz] before on a BSFM when the SEI system was free, but undamped (see LHO aLOG 7305). Sure enough, the SEI system had been tripped since who-cares-when during the measurement. A follow-up measurement of V to V with the SEI system back online (with HPI "pos" loops ON, and ISI damped), the 1.69 [Hz] mode disappeared (see second attachment), and Qs were restored on the lowest modes (not shown -- I only captured a T to T before being interrupted by Jim who has priority).

Apologies for the errant calibration on the single, good-looking, V to V TF -- I went to fix it after I found the error, but the site has lost connection with it's Matlab license server. #facepalm

We will assess again, officially, after first contact is removed -- but the new baffles are free of the suspension, or vice versa.

Note: I've created a new script,
${SusSVN}/sus/trunk/BSFM/Common/MatlabTools/plotbsfm_dtttfs_M1_singleDOF.m
to create the second attachment, for those times when we only have time for a before-and-after DTT TF in one DOF such as this.

Today's data:

2014-07-23_1841_H1SUSBS_M1_L_WhiteNoise.xml
2014-07-23_1841_H1SUSBS_M1_P_WhiteNoise.xml
2014-07-23_1841_H1SUSBS_M1_R_WhiteNoise.xml
2014-07-23_1841_H1SUSBS_M1_T_WhiteNoise.xml
2014-07-23_1841_H1SUSBS_M1_V_WhiteNoise.xml
2014-07-23_1841_H1SUSBS_M1_Y_WhiteNoise.xml

2014-07-23_2313_H1SUSBS_M1_T_WhiteNoise.xml
2014-07-23_2313_H1SUSBS_M1_V_WhiteNoise.xml

where the latter two files are while the ISI was damped (and the V file is what's used for the second attachment).

(Kate G, Jeremy B, Matt H)

Quick summary alog...more detailed one to come

HAM3

After Stuart gave both suspensions a clean bill of health (so we know that as of this morning they were good)..I locked the face stops of the intermediate and bottom mass so that Jeff B could start cleaning.

HAM2

ALL OPTICS HAVE FIRST CONTACT ON THEM. It was a Herculean effort today......especially by Kate, but we managed to get all four optics in HAM2 first contacted from start to finish today, including outer crusts painted and peek pull tabs. We did have to remove another baffle today (the one attached to the PR3 structure that is used to prevent the wire heating), so not quite ready for SEI to begin balancing yet. I need to put all the baffles, EQ stops, etc that have removed to allow FCing to be done back. But give Jeremy and I 1.5-2 hours to put it all back together and should have it ready.

I dont have the photos/details on particle counts, etc but in the near future hoprfully Kate or I will have some spare time to write about.

After securing doors on HAM4, TFs taken indicated an issue with the actuation for the SR2 M1 LF BOSEM channel (see LHO aLOG entry 12923). Upon investigation this was found to be due to a loose connector on the air side of the chamber flange (see LHO aLOG entry 12942) and must have developed during chamber close-out activities.

Phase 3a TF measurements have been retaken for all stages of the SR2 suspension as follows:-  

- SR2 M1-M1 undamped (2014-07-23_1300_H1SUSSR2_M1_ALL_TFs.pdf)
- SR2 M2-M2 undamped (2014-07-23_1500_H1SUSSR2_M2_ALL_TFs.pdf)
- SR2 M3-M3 undamped (2014-07-23_1600_H1SUSSR2_M3_ALL_TFs.pdf)

HAM4 ISI Status: ISI unlocked, no damping or isolation loops running.

SR2 alignment: No offset was applied during this measurement.

SR2 undamped measurements for each stage have been compared with other H1 HSTS suspensions at Phase 3a of testing (allhstss_2014-07-23_Phase3a_H1SR2_*_ALL_ZOOMED_TFs.pdf).

Summary: 

M1-M1 TFs verify that the actuation problem has been solved, with L & Y DOFs now exhibiting expected performance, and raise no new concerns.
 
M2-M2 TFs, show good agreement with the model and are consistent with other H1 HSTS suspensions.

M3-M3 TFs, while noisy, again, thees show good agreement with the model and are consistent with other H1 HSTS suspensions.

All data, scripts and plots have been committed to the sus svn as of this entry.

   Did a vacuum and wipe down cleaning in HAM3. The visual inspection with the flashlight array did not show large amounts of contamination inside the chamber. There were many large pieces of metal in the wells underneath the support tubes. After removing this debris, wiping did not show additional metal on the Alpha wipe. 

   Particle counts were somewhat high during most of the cleaning, due to the disturbance of vacuuming and wiping. The counts spiked when Betsy & Travis entered BSC1, but they dropped back to “normal” background levels in a few minutes. What seemed to lower the particle counts significantly was having the top half of the soft cover open. One data point does not make a trend, but this is something to keep an eye on.

Location				                 0.3	0.5	1.0
West side cleanroom cover on		14	4	2
In chamber Cover on			202	96	16
In chamber cover on +5 minutes	88	40	13
In chamber cover top half open	3	1	1
After vacuum cover on			339	182	36

East side cleanroom cover on		0	0	0
In chamber cover on			222	126	22
B&T in BSC1 cover on HAM3		668	435	101
In chamber cover on +5 minutes	286	161	29
In chamber cover top half open	17	13	9
After vacuum cover on			74	42	17
After wipe down cover on             	421	216	47

West side cleanroom cover on		32	19	3
In chamber cover on			251	143	37
In chamber cover top half open	37	16	6
   Betsy & Travis exit BSC1 during the west side wipe down
After wipe down cover on	         	340	182	34
After wipe down cover on + 10 min  115	70	16

From one of the ops workstations in the back of the control room. Should finish about the time of the morning meeting. No touching, please.

Betsy, Travis

As Jeff mentioned in his log below, this afternoon we payloaded the ITMy SUS with:

- Sleeve

- Wedges

- Cross braces

- Vibration absorbers

- All trays, shields, and TFE support pieces removed

- We have 3 3/4" screws and 1 wafer holder to add, but these will be quick.

This involved the usual removal of 3 flooring panels to get the sleeve on, and their subsequent replacement.

Counts in the chamber before starting the work just after lunch were:

0.3um  60

0.5um  40

1.0um  20

An hour later during the high-traffic period of all of the above by just Travis and I, the counts were:

0.3um  1000

0.5um  550

1.0um  320

And then 20 mins later:

0.3um  540

0.5um  320

1.0um  120

Note, during the elevated counts Jeff had HAM3 soft covers open and was crawling around that table cleaning.  More likely the higher counts were us with the heavy lifting and numerous screw attachments.

DarkhanT, MikeV, Shivarajk, ForrestS, TravisS

We have completed our alignments and measurements at Xend.

The Pcal transmitter and receiver modules are installed, bellows are in place, and viewport protector gates are removed.

The key for the power supply that energizes the laser has been removed.

The Xend VEA is now in Laser Safe (at least that is how we left it an hour ago).

More to follow regarding ETM reflectivity and optical efficiency measurements.

The unstable Ry HEPI Dof suggested we check for rubbing from stops.  Ran Range of Motion & Linearity tests this morning.  The ROM is good to 0.7mm and the linearity results look fine too.

9:15- Heading into the LVEA (HAM 2) to apply First Contact – Matt/ Kate/Jeremy 
9:19- 9:30 Quick Trip to the LVEA (Mike V)
10:15- PCAL work at End X – Mike V/Rick S/Student/
10:31- 11:48 Going into the LVEA for HAM 3 cleaning – Jeff B.
10:37- 12:22 Work on BSC2/BSC1 – Betsy/Travis
10:40 - Work on Optics Lab/Laser ON – Nathan
10:44- 12:00 Heading into the LVEA to work on SR2(Testing) – Stuart
10:58- ITMY Alignment in the LVEA – Jason
12:41- Back to HAM3 – Jeff B.
13:00-15:48-Back to work on  BSC2 
14:11-Back to HAM2- Matt/Kate
14:43- Heading into the LVEA to run some tests (Electrical Field Measurement) with Electrometer – Mike/Gerardo
15:20- Doing some work outside by the beam tube – Robert & students

J. Kissel

Betsy, Travis, and Jason have finished initial alignment of the Reaction Chain on H1 SUS ITMY. Over lunch, I've run a set of DTT transfer functions to confirm we're not rubbing in a way that would affect the IAS assessment. The TFs reveal the chain is free as a bird, so the IAS numbers are legit. Nice work, team!

They're beginning to "payload" the SUS now (add the stiffening sleeve, vibration absorbers, etc.), and we'll take a full set of TFs again tonight, including the Main Chain to confirm all is well.

All scripts and data have been committed to the svn.

[Stuart Hugh Arnaud]

Following on alogs 12929 and 12902, an other test was carried out on SR3 giving a bettter understanding of why its first vertical mode was damped. The same V2V tf was taken with the ISI damped, and interestingly enough the Q of this mode gets higher when the ISI is damped, cf attached screenshot.

It appears that the rotational modes of this HAM are also around 1Hz (looking at Rx Ry TF from an ISI measurement taken in May cf attachment), mode that we were certainly exciting when driving the suspension along the vertical axis with the ISI undamped.

At first we were wondering why some previous vertical measurements were showing high Q resonances, but quickly realized that those were taken with the ISI either locked or half locked (from July 15th ISI was locked, from yesterday when doors were off, Matt half locked the ISI to back off the EQ stops).

Manual DTT transfer functions are now running on SR2 for the next few hours.

Measurements made yesterday indicated a problem on the SR2 (HSTS) M1 LF BOSEM channel (see LHO aLOG entry 12923), they also suggested it was an actuation issue and not sensing. This was confirmed this morning by applying offsets to each M1 channel in-turn and monitoring the sensor response (see SR2_M1_Offsets.png below).

Therefore, I've been further investigating this problem in the LVEA, first by using a break-out board at the Satellite Box (field cable H1:SUS_HAM4-10), to measure DC coil resistances as follows:-

T1 Pins = 10-23, R = 40.6 Ohm
T2 Pins = 7-20,  R = 40.1 Ohm
T3 Pins = 4-17,  R = 39.6 Ohm
LF Pins = 1-14,  R = Open Circuit

Thus verifying the issue was down-stream, i.e. either with the field cable or in-chamber.

I then repeated the same DC coil resistance measurements at the other end of the field cable i.e. the air side of the vacuum flange (HAM4-D6):-

T1 Pins = 10-23, R = 38.9 Ohm
T2 Pins = 7-20,  R = 38.4 Ohm
T3 Pins = 4-17,  R = 37.8 Ohm
LF Pins = 1-14,  R = 38.4 Ohm

Confirming that the issue resided with the in-air side of the flange with the field cable. I re-seated and tightened the connector at the flange and this rectified the problem.

Applying an offset to the M1 LF channel now exhibits the expected behavior (see SR2_M1_LF_Offset.png below).

A full set of TFs will now need to be taken to ensure there are no further issues with this suspension.

n.b. this issue is essentially identical to the loose cable connection at the air-side of the flange that was recently reported for H1 ITMX (see LHO aLOG entry 12544).

[Arnaud P, Stuart A]

Following doors being re-hung on the HAM5 chamber earlier today (see LHO aLOG entry 12915), Phase 3a DTT TF measurements have been taken this afternoon for SR3 (HLTS) suspension as follows:-  

- SR3 M1-M1 undamped results (2014_07_22_1200_H1SUSSR3_M1_ALL_TFs.pdf)

HAM5 ISI Status: ISI unlocked, no damping or isolation loops running.

SR3 alignment: No offset was applied during this measurement.

SR3 undamped measurements from above have been compared with previous measurements for H1 SR3 at Phase 3a of testing (allhltss_2014-07-22_Phase3a_H1SR3_UnDamp_ALL_ZOOMED_TFs.pdf). The plot key is as follows:-

Blue Trace = Model (hltsopt_metal)
Orange Trace = H1 SR3 M1 (2014−07−15_1089513028), (in-chamber, doors open)
Black Trace = H1 SR3 M1 (2014−07−21_1090036316), (in-chamber, doors hung)
Magenta Trace = H1 SR3 M1 (2014_07_22_1200), (in-chamber, doors hung)

It can be seen that despite having gone in-chamber to improve the M3 alignment and attempt to mitigate any sources of rubbing (which we thought we had) the peculiar damping of the first vertical mode persists. Furthermore, comparing before (Black trace) and after (Magenta trace) there appears to be no improvement.

Somewhat frustratingly, before closing up the chamber, higher resolution measurements of the vertical DOF TF had indicated that the potential rubbing issue had been alleviated (see SR3_V2V_Doors_Open_vs_Closed.png).

We had considered the possibility of hanging the door may have changed the air flow due to purge air, so we carried out a measurement both with purge air on and off (SR3_V2V_PurgeAir_Off_vs_On.png), but again this failed to improve the Q of the first vertical peak.

Finally, a measurement was made with damping loops on for comparison (see SR3_V2V_Damping_On_vs_Off.png), which seems stable.

Also, last night Arnaud repeated the vertical TF while applying +/- biases to various degrees of freedom to try and check in which way SR3 could have been hung up, but to no avail.

Attached below is a log of particle counts taken during the HAM5 work covering the duration 1035 to 1126 (local).

All data, scripts and plots have been committed to the sus svn as of this entry.

(lots and lots of people)....and I want to thank ALL these people for all their help today. Everybody was willing to pitch in and help, and was fantastic that that happened.

Its been another long day and I am tired so this will be quick (more detailed report to come)....also apoogies if this alog makes no sense. My mind is mush now.

HAM5 was closed up today. ISI balance was rechecked and slightly altered, clean of chamber  happened, had also to pause for some time where we had to wait until particle counts dropped to level happy to peel FC off SR3 but eventually got both doors on. We did notice that when FC pulled immediately it looked awesome, and then in the time before door went on, started to see small amounts of particulate already coming back. After doing some quick TFs in a couple DOF's it was given the okay to put doors on and they were put on as quickly as we could. We did learn various things on how to speed up, etc.

Rough timeline: 1st contant removed 11.20am 1" optic. 11.44am first contact removed from SR3 optic. North door on ~12.37pm, South door on ~13.14pm.

Changed up the order for HAM4 door and ISI was half unlocked and North door went on before started anything (discovered after door went on that first contact is still on the inside of the viewports :-(...after discussion with Mike L we will pull off the viewports at a later date to remove). From that we had to wait an awful long time trying to wait for particle counts to drop out of the hundreds. Things learned is we found counts spike when door gets put on, couldnt have the BSC chamber cross flow on as would make counts in the hundreds in HAM4, same with people trying to work in BC1, or even lifting a cover elsewhere. Eventually counts went down and we pulled FC on SR2. Unfortunately right at the end of the pull the gas bottle ran dry on the top gun :-( :-(. And immediately looking at the SR2 optic it looked bad...as if we had never used FC. After a bit of back and forth and a round table discussion it was decided we would try to first contact again with everything its its present state. That is to try to re-spray FC using the hold on cone and if that didnt work to paint on FC after first trying blow off anything that we could. We found the cone didnt work (wouldnt fit) and so we painted. Was a pain as coulndt really see it, but we got it done in the end (well done Kate and Rich for staying behind with me to get this done..your help is appreciated more than can express). So will try to pull FC again in the morning and we will see what we see.

Hopefully others will make alogs regarding particle counts, etc. ...and I may try to write a more detaield report at a later date with some photos etc depending on if they turned out when look at.