jeffrey.kissel@LIGO.ORG - posted 19:24, Monday 22 May 2017 - last comment - 19:57, Monday 22 May 2017(36335)
H1 SUS ITMX Clear of Rubbing -- even with Large Offsets In Place
J. Kissel
Now the that LVEA temperature is stable and normal, I've gathered transfer functions will all the "nominal" O2 offsets in place:
- Reaction Chain has +150000 V, -5000 P of drive from the test bank, originally installed to alleviate suspected rubbing during our cold January
- Main chain has normal*** P and Y alignment offsets in place.
*** Although the main chain offsets have been used to align the optic to its optical lever reference position prior to the vent, and we suspect that optical lever is a bad reference more on this in a future comment below. However, with this restoration, we're now using up ~85% of the DAC range on the F1 OSEM (where we had been using 35%).
With these offsets in place, preliminary results (i.e. from eyeballing the DTT sessions) show no signs of rubbing.
The data lives here:
/ligo/svncommon/SusSVN/sus/trunk/QUAD/H1/ITMX/SAGM0/Data/
2017-05-22_2056_H1SUSITMX_M0_WhiteNoise_L_0p01to50Hz.xml
2017-05-22_2056_H1SUSITMX_M0_WhiteNoise_P_0p01to50Hz.xml
2017-05-22_2056_H1SUSITMX_M0_WhiteNoise_R_0p01to50Hz.xml
2017-05-22_2056_H1SUSITMX_M0_WhiteNoise_T_0p01to50Hz.xml
2017-05-22_2056_H1SUSITMX_M0_WhiteNoise_V_0p01to50Hz.xml
2017-05-22_2056_H1SUSITMX_M0_WhiteNoise_Y_0p01to50Hz.xml
/ligo/svncommon/SusSVN/sus/trunk/QUAD/H1/ITMX/SAGR0/Data/
2017-05-23_0047_H1SUSITMX_R0_WhiteNoise_L_0p01to50Hz.xml
2017-05-23_0047_H1SUSITMX_R0_WhiteNoise_P_0p01to50Hz.xml
2017-05-23_0047_H1SUSITMX_R0_WhiteNoise_R_0p01to50Hz.xml
2017-05-23_0047_H1SUSITMX_R0_WhiteNoise_T_0p01to50Hz.xml
2017-05-23_0047_H1SUSITMX_R0_WhiteNoise_V_0p01to50Hz.xml
2017-05-23_0047_H1SUSITMX_R0_WhiteNoise_Y_0p01to50Hz.xml
We should consider these offsets a "worst case scenario." I suspect once we get all optics re-aligned to form some sort of Michelson in the corner and/or we open to the arms that we'll find that the optical lever reference was indeed wrong, and we'll end up removing most of the main chain offsets. Plus, I think we now might be able to run with out any reaction chain offsets. Stay tuned for full matlab assessment using the exported data.
On why I think we can't trust the optical lever to restore ITMX alignment. (Even though it's been done a few times.) Attached are 25 day trends of (1) The Pitch of the optic as measured by - the L3 optical lever (in [urad]) - the M0, R0, L1, and L2 OSEMs (in [urad]) - the alignment offset of the M0 stage (in [urad]) compared against the BNS range. (in [Mpc]) This shows that although the optical lever has been restored to a time around 2017-05-07 (just before the vent) none of the OSEMs agree that this is right position (2) The Yaw of the optic as measured by - the L3 optical lever (in [urad]) - the M0, R0, L1, and L2 OSEMs (in [urad]) - the alignment offset of the M0 stage (in [urad]) compared against the BNS range. (in [Mpc]) Similarly show that the OSEMs completely disagree with the optical lever (3) Because the naive always suspect the ISI system, I show the Z, RX, RY, and RZ ST1 position sensors (in [nm] for Z, [nrad] for Rotation), which show > 0.5 [urad] / [um] of position change (4) The amount of F1 (the pitch) OSEM DAC range in use (85% of the range instead of 35%) and the temperature of the optic / suspension measured in vertical displacement of the main and reaction chains (in [um]) and the FMCS temperature channels. Another damning piece of evidence against the optical lever for ITMX -- The MICH fringes are terrible at the moment. This leads me to suspect something when wrong with the alignment restoration done to the lowest stage OSEMs by Vaishali and Jenne earlier in the week (referenced in LHO aLOG 36276). In support of this, I attach similar 25 day trends of all PRMI optic's lowest stage OSEMs in (5) Pitch (in [urad]) (6) Yaw (in [urad]) so we're not that close with any optic according to *those* references. Also another bit of evidence is that we cannot find a return beam from the Hartman Table (LHO aLOG 36332). I've discussed with Betsy whether it's possible that the balance of the suspension has changed throwing off all the OSEMs, but she says essentially "no way." All that was done to the SUS was to slide in teflon rails between the test mass's lower barrel EQ stops and the optic, and then the optic was gently raised into its upper EQ stops. The process was reverse when finished. No OSEMs were touched, no balance of any mass was adjusted. Since there is still suspicion that the IMC is in the wrong place (LHO aLOG 36329) people are reluctant to launch on a big "restoration of the alignment based on short lever arm local things" adventure before we get the arms and global alignment control back. To clear up potential memory failure leading to confusion, it was ITMY's optical lever that was swapped a few days before the vent (see LHO aLOG 36029), not this one.