S. Dwyer, J. Kissel
While inspecting HAM6 regarding the broken OMC REFL Beam Diverter Dump, we took the opportunity to check out the fast shutter.
We saw several things of concern:
(1) The cabling that emanates from the shutter itself looks (and has been previously confirmed to be) very close to the main IFO beam path. Koji indicated in his LHO aLOG 28969 that "the clearance does not look great in the [above linked] photo but in reality the beam is clearly away from the wire."
(2) One of these wires (the wire closer to the IFO beam) has a kink in it, but no visible burn marks, so we suspect this is from mechanical manipulation during install.
(3) OM3's readout cables are kinked in a stressed position to make room for the fast shutter, which is a little forward (-Y, away from the beam splitter) of the position indicated in the drawing likely because of this interference.
(4) Some small fleck of particulate on the inside of the "toaster" face, on the HR (back towards OM1) side of the shutter.
I attach picture collections of these things (admittedly the particulate pictures are not great -- we tried lots of times to get a good picture but failed).
Hopes:
Re (1): Can we find a way to route these cables below the beam line, instead of surrounding it?
Re (2): Same as (1)
Re (3): Can we replace OM3's OSEM cables with a 90 deg backshell, so as to clear room for the fast shutter and relieve stress on the cable?
Re (4): hopefully this is not from the HR surface of the fast shutter optic
We were motivated to look at the fast shutter wires by the incident on July 17th where the wire from the fast shutter must have been clipping the to OM1 from HAM5. My original alog about this might not have spelled things out well enough, so here are some plots.
The first plot is from July 17 2017 5:51:00 UTC, this was after Jim, Cheryl and I figured out that the fast shutter was malfunctioning. We locked DRMI, and opened and closed the fast shutter several times. The top panel shows the state of the shutter, 0 is open 1 is closed. The second panel shows AS_A_SUM, which is downstream of the shutter, and goes to zero when the shutter is blocking the beam as it should. The third panel shows AS_C, which is upstream of the shutter but downstream of the place where the wire is close to the beam (check Jeff's annotated photo). You can see that moving the shutter causes dips in the amount of light on AS_C, and that the wire must land in a slightly different place in the HAM5 to OM1 beam causing a different level of light to be seen on AS_C
The second attachment shows that the shutter did seem to block the beam going to the AS WFS in the July 16th lockloss before we had this malfunction. Chandra also checked vacuum pressures for a spike in HAM6 pressures similar to what happened when we burned the OMC in August 2016, and saw nothing. I had been wondering if the fast shutter might have failed to durring a lockloss where the OMC was unlocked, which could result in a lot of power being on the beam dump. It seems like this didn't happen on July 16th.
Note, we played with this shutter cable last in Aug 2016. We struggled with getting this wire away from the beam at that time. The pictures in the log from Aug 2016 28969 show that we left the wire in a larger arc than the pictures show now. I suppose it's not so surprising that the wire has maybe migrated into the beam path over the numerous cycles over the last year.