Details of vent of May 2016

Overview

Major objectives of this vent:

Clean ITMs and ETMs (both HR and AR faces) with FirstContact
Replace ETMX (south end) suspension with spare (re-suspend optic with new SOS suspension wire, replace Aluminum wire standoffs with Ruby standoffs)
Shorten Y-arm length by 2cm such that both arms have length 37.79m
Replace 40mm aperture baffles in ETM chambers with 50mm black glass baffles
Installation of new vacuum gauge

ITMX and ITMY did not have any magnets broken off during the vent - all five OSEM coils for both were removed and the optic EQ stopped for F.C. cleaning.
Both HR and AR faces were F.Ced, ~20mm dia area cleaned.
The coils were re-inserted in an orientation as close to the original (as judged from photos), and the shadow sensor outputs were made as close to half their open values as possible, although in the process of aligning the arms, this may have changed.
OSEM filter existence was checked (to be updated)
Shadow sensor open values were recorded (to be updated)
Checked that tables were level before closing up.
The UL OSEM on ITMY was swapped for a short OSEM while investigating glitchy shadow sensor outputs. This made no difference. However, the original OSEM wasn't replaced. Short OSEM was used as we only had spare short OSEMs. Serial number (S/N 228) and open voltage value have been recorded, wiki page will be updated.
ITMX seems to be prone to getting stuck recently, reason unknown. We have a somewhat cumbersome procedure to follow in the event c1susaux needs to be hard rebooted that minimises likelihood of ITMX getting stuck.
OL beam centering on in vacuum steering optics checked before closing up

UL, UR and LR magnets broke off at various points, and so have been re-glued.
No standoff replacement was done.
Re-suspension was done using newly arrived SOS wire.
Original OSEMs were inserted, orientations have changed somewhat from their previous configuration as we did considerable experimentation with the B-R peak minimization for this optic
OSEM filter status, shadow sensor open voltage values to be updated.
New wire suspension clamp made at machine shop is used, 5 in lb of torque used to tighten the clamp.
HR face cleaned with F.C.
Optic + suspension towers air baked (separately) at 34C for curing of EP30
Checked that tables were level before closing up
40mm O.D. black glass baffle replaced with 50mm O.D. baffle.
Suspension cage was moved towards ITMY by 19mm (measured using a metal spacer) by sliding along stop marking the position of the tower.

Al wire standoffs <--> Ruby wire standoffs (this has changed the pitch eigenmode frequency)
All magnets were knocked off at some point, but were successfully reglued
New SOS tower, new SOS wire, new wire clamp used
OSEM filter status, shadow sensor open voltage values to be updated.
OSEM orientation is close to horizontal (i.e. teflon spacers approximately parallel to tabletop) for all 5 OSEMs
Table leveling was checked before closing up.
40mm O.D. black glass baffle replaced with 50mm O.D. baffle.

Some issues with the OSEMs were noticed, and were traced down to the Al foil caps covering the back of the (short) OSEMs, which are there to minimize the scattererd 1064nm light interfering with the shadow sensor, shorting one of the OSEMs
To mitigate this, all Al foil caps now have a thin piece of Kapton between foil and electrical contacts on rear of OSEM
No OSEMs were removed from the suspension cage during this process, we tried to be as gentle as possible and don't believe the shadow sensor values changed during this work, suggesting we didn't disturb the coils (PRM wasn't EQ stopped either)
Subsequently, some work needed to be done to the LR signal chain in the PRM Satellite box. This was the channel that was shorted by the Al foil cap during the vent.

The optic itself wasn't directly touched during the vent - but was EQ stopped as work was being done on ITMY
It initially was NOT EQ stopped, and the shift in table level caused by moving ITMY cage to the edge of the table for F.C. cleaning caused the optic to naturally drift onto the EQ stops, leading to some confusion as to what happened to the shadow sensor outputs
The problem was diagnosed and restoring ITMY to its original position made the OSEM signals come back to normal.

OL beams were checked on in-vacuum input and output steering mirrors to make sure none were close to clipping
Insides of viewport windows were checked for general cleanliness, given that we have found the outside of some of these to be rather dirty. Insides of viewports checked were deemed clean enough.
Steve has installed a new vacuum gauge to provide a more reliable pressure readout.
We forgot to investigate the weird behaviour of the AS beam that Yutaro and Koji identified in November 2015.

This section is a work in progress...

Mode matching into the Y arm cavity given the arm length change
HOM content in transmitted IR light from Y arm given the arm length change (Finesse models suggest that the 2f second order HOM resonance may have moved closer to the 00 resonance)
Arm loss measurement
Suspension diagonalization
Check the Qs of the optics eigenmodes - should indicate if any of our magnets, re-glued or otherwise, are a little loose

To be updated...

Pictures from this vent have been uploaded to the 40m Google Photos page.