Reports until 16:18, Thursday 03 April 2014
H1 SUS
betsy.weaver@LIGO.ORG - posted 16:18, Thursday 03 April 2014 - last comment - 09:10, Friday 04 April 2014(11160)
ITMy fiber welding completed

Travis, Giles, Gary, Jason, Norna, Betsy

This afternoon, Travis, Gary, and Giles finished welding in fibers to the ITMy (ITM011) and it's glass PUM.  At some point during the welding process on Wed a roll of the Test Mass was introduced.  It was noticed this morning before the final destress/annealing took place.  The team attempted a correction to alleviate ~1/2 of the roll error which was somewhat successful.  After reevaluating the tolerance for roll with Dennis and Calum it was decided to leave the roll error as is.  The Test Mass is now hanging from the fibers.

 

Note, the roll error observed this morning was +/- 1.2mm (~7mRad).  We determined that this roll occured between welding the 2 sides of the suspension with the masses locked down the entire time.  The PUM did not show this large roll error.  After correcting and suspending the ITMy, the roll was found to be +/- 0.75mm (~4mRad).  While the roll "tolerance" has never really been set, we attempt to get the roll error within +/- 0.2 mm because that is what we have found we are able to do in all of the previous other monolithic suspensions.

Comments related to this report
betsy.weaver@LIGO.ORG - 16:26, Thursday 03 April 2014 (11162)
Link

Email from Dennis regarding acceptable roll tolerances of an ITM:

Calum,
Using the Zemax model to ray trace, I find that a 7 mrad roll rotation
of the ITM causes only ~0.03 mm radial decentering of the beam at the BS
and a ~0.8 mm radial decentering of the beam at the PRM and at the SRM.
I think that this is acceptable.

Other effects of a DC roll error in the ITM:
- increased coupling of vertical ISI motion to roll motion of the ITM
... but so what?
- slight rotation in the of the phase maps of the ITM ... but so what?
- slight shift in the violin mode frequencies due to the length change
(I think the force in each is not changed due to the roll bias error),
but this is ~1 part in 1000 ... so likely within the violin mode
repeatability anyway?

-- 
Dennis Coyne
giles.hammond@LIGO.ORG - 18:07, Thursday 03 April 2014 (11164)SUS
Link 

Attached are some photos of the welds and the final suspension. As mentioned by Betsy, a +/-1.2mm (~7mRad) roll appeared between welding and with the ITM and PUM locked. As a result, during the destress, the PUM right welds developed a slight necking. The stock still has a large radius at this point and we will run some thermal noise models to verify that no significant change in performance is expected.
Images attached to this comment
mark.barton@LIGO.ORG - 08:58, Friday 04 April 2014 (11169)
Link

To see if the residual roll was problematic, I prepared a case mark.barton/20140304TMproductionTMrollpert of the QuadLite2Lateral model with the latest monolithic parameters but with a perturbation to d4 (the height of the fibre attachment point above the optic COM) at each of the fibres, positive on one side and negative on the other. Even a perturbation of ±1.2 mm (the value reported to me before the extra de-stressing reduced it to 0.75 mm), there was no visible difference in any of the top mass force/torque to optic TFs and especially no extra peaks from cross coupling. This is to be expected because the optic is almost perfectly symmetrical in roll and the compliance of the fibres was not changed (the de-stressing did not touch the central section of the fibres so this was not changed in the model). So the performance of the suspension should not be degraded.

jason.oberling@LIGO.ORG - 09:10, Friday 04 April 2014 (11170)
Link

Final alignment numbers for the monolithic (all directions/rotations reported from the view of the IAS equipment, i.e. looking at the HR face of the ITMy):

  • Pitch measurements
    • PUM: 740 µrad up
    • ITMy: 400 µrad down
    • Differential: 1.14 mrad down
    • Differential Spec: 2.0 mrad
  • Roll
    • PUM: ±0.15 mm CW
    • ITMy: ±0.9 mm CW
    • Differential: ±0.75 mm CW
  • Center of Mass Separation
    • Left: 600.5 mm
    • Right: 602.0 mm
    • Target (for both sides): 602.0 mm