aLIGO LHO Logbook

H1 AOS (INS, SEI, SUS)

jason.oberling@LIGO.ORG - posted 14:13, Wednesday 30 July 2014 - last comment - 15:24, Friday 01 August 2014(13080)

ITMy Final Alignment Numbers

Here are the final alignment numbers for the ITMy, CPy, and the WBSC1 ACB:

ITMy

X axis position: -200.8 mm*
- Target: -200.0 mm
- Error: -0.8 mm
- Tolerance: ±1.0 mm
Y axis position: 4982.7 mm
- Target: 4983.1 mm
- Error: -0.4 mm
- Tolerance: ±3.0 mm
Z axis position: -79.2 mm
- Target: -79.8 mm
- Error: +0.6 mm
- Tolerance: ±1.0 mm
Pitch: 366 µrad down**
- Target: 340 µrad down (352 µrad down FC correction - 13 µrad up target pitch)
- Error: 26 µrad down
- Tolerance: ±50 µrad
Yaw: 17 µrad CW
- Target: 0 µrad
- Error: 17 µrad CW
- Tolerance: ±50 µrad

* The X axis position is currently being held in place with a +300000 nm HEPI bias offset (see alog 12922). Hugh plans to offload this bias onto the HEPI springs at a later date.

** We are assuming that when the FC is pulled the ITMy will move up in pitch by 352 µrad per E1200791. This will put the final pitch of the ITMy at 14 µrad down. IAS equipment has been pulled from the spool for CPB install so we will be unable to verify this move. To get some idea of the pitch change we can weigh the FC after it has been removed and use the pitch compliance number in E1200791 to calculate the pitch change.

CPy

Pitch: 833 µrad down***
- Target: 1.296 mrad down (to match the ITMy AR surface assuming zero ITMy pitch error; the ITMy has a vertical wedge of 0.075°, or 1.309 mrad down)
- Error: 463 µrad up
- Tolerance: ±1.4 mrad
Yaw: 31 µrad CCW
- Target: 0 µrad (to also match the ITMy AR surface)
- Error: 31 µrad CCW
- Tolerance: ±1.4 mrad

*** This is the actual pitch of the CPy. The listed error is relative to where the CPy needs to be to be parallel with the ITMy AR surface, assuming the ITMy has zero pitch error; this does not include any FC correction done on the ITMy. Since we cannot verify the ITMy pitch after FC removal, we also cannot verify the CPy pitch relative to the ITMy AR surface after FC removal. We have to assume that E1200791 is correct (we have only been able to test this one time at the ETMy, which moved upward by 442 µrad, but one data point does not a trend make) and that the ITMy will pitch up by ~352 µrad upon FC removal. Therefore our expected relative pitch between ITMy and CPy upon FC removal is 490 µrad up (14 µrad down ITMy HR pitch + 1309 µrad down wedge - 833 µrad CPy pitch = 490 µrad up relative pitch). As stated above we can weigh the FC to get some idea of the pitch change.

ACB (relative to the ITMy)

Lateral position error: -0.3 mm
- Tolerance: ±2.0 mm
Vertical position error: +1.2 mm
- Tolerance: ±2.0 mm

This completes IAS alignment of ITMy; our equipment has been removed from the Y manifold spool area to allow for the Cryopump Baffle installation. This also ends the IAS alignment of the aLIGO H1 interferometer.

Comments related to this report

jason.oberling@LIGO.ORG - 15:24, Friday 01 August 2014 (13158)

Link

First off, small correction to the ITMy target pitch: it should be 339 µrad, not the 340 µrad as listed. This puts the ITMy pitch error at the time of IAS equipment teardown at 27 µrad down.

Measured the mass of the First Contact removed from ITMy today.

Mass = 2.8 g (Expected Mass = 3.114 g)

Pitch compliance = 0.113 µrad/mg (from E1200791, page 4)

ITMy pitch change = 316 µrad up (mass * pitch compliance)

Assuming the pitch compliance number is correct, this puts the ITMy pitch at 50 µrad down, which is a pitch error of 63 µrad down. This is outside of our ±50 µrad tolerance.

Unfortunately the mass of the FC came in under the expected mass and below the allowed variation; if you look at E1200791 the allowed variation of the FC mass is 0.159 g, which results in a low end mass expectation of 2.955 g, not the 2.8 g I measured.

This also puts the CPy pitch with respect to the ITMy AR surface at 526 µrad up. Not the 490 µrad we expected, but still well within our ±1.4 mrad tolerance.