Jennie W, Jenne D, Keita K, Elenna C, Rahul K, Fil C, Jim W,
Summary: Today we started the replacement of the ISS array with its spare. JAC REFL PD was aligned and JAC locked but some problems encountered with MC2 which we need to fix so we can check the current ISS array alignment before removing it.
First part of day - JAC locking
- We had a bit of trouble locking the JAC till Keita reminded me to check the error signals. The beam needed aligned on the IOT1 table. Jenne and I did this with the two mirrors before REFL PD that are not common to the WFS path.
- After this we could lock JAC.
Checking beam in HAM2.
Checking the beam coming towards MC3 with the flashes transmitted back through the IMC, Keita and co realised that the IMC and input beam from the JAC were not well aligned.
Jenne and I consulted with Jim and isolated the HAM1 chamber, plus reset the set points for the HAM2 CPS. This means that the residuals for HAM1 were low but both HAM2 and 3 which have their ISIs locked, are out of nominal alignment, ie. higher in pitch and lower in yaw than their nominal.
The positions we want for MC2 to put compensate for the ISI relative alignment change are M1-OPTICALIGN_OFFSEt_P = 864/858
M1-OPTICALIGN_OFFSET_Y = -451.5/-354.5
The positions we want for MC3 are M1-OPTICALIGN_OFFSEt_P = 417
M1-OPTICALIGN_OFFSET_Y = -185.4/-190.6
The positions we want for MC1 are M1-OPTICALIGN_OFFSEt_P = -686
M1-OPTICALIGN_OFFSET_Y = 1352/1358
Unfonrtunately while trying to align MC2 we encountered some problems with the suspension so that is in the process of being debugged. Possible culprit is the D6 feedthrough swap last Thursday on HAM3 as MC2 top mass osems changed a lot that day. Left record of values we need to align osems to above so we can come back to this when we have fixed MC2 problems.
ISS Array
In the meantime Keita, Rahul and Elenna opened the box with the new ISS unit in the clean room and prepared to swap out the base with the one in chamber (our new unit is set for L1 beam height). To do this thye had to removed the blue glass beam dumps to reach the 1/4-20 screws at the four corners of the middle ISS mounting plate.
About the installed unit.
New ISS unit is SN1202965 with a base D1101073 (ALIGO IO PSL ISS PD L1 BASE).
Our plan was/is to reuse the base that is already in chamber, D1101074 (ALIGO IO PSL ISS PD H1 BASE), together with the strain relief assemby. (FYI, there's also supposed to be an obsolete base D1101075, ALIGO IO PSL ISS PD H2 BASE.) In other words, in the first attachment, the parts outlined in red will stay in chamber, only the blue part will be replaced.
One complication is to make sure that the SMP cables are connected to the PDs in correct polarity, otherwise the PDs will be forward-biased and damaged. However, it turns out that array PDs in the new one we're installing and the old one in chamber are all angled in a consistent manner that, seen from the back of the PDs, cathode is to the left and anode is to the right. See the 2nd (new unit) and the 3rd/4th picture (old one). This means that we don't have to use tags or anything to ID SMP cables, all we need to do is to make sure that the cables won't fall out of the strain relief. Once the main body of the array (PD array and QPD) is swapped, we can just connect cables based on the position of the strain relief holes they're in.
A note about misalignment of the IMC seen from inside HAM2.
We did not see "flashes" because it didn't flash at all. We were able to see the MC1 transmission and the return beam after one round trip inside the IMC, and the latter was more than 1" higher than the former. There was also YAW difference. All in all two beams were about 1.5" apart. MC1 transmission beam position looked OK.
This was eventually traced back to the problem of MC2 top OSEMs, which will be alog-ed by somebody else.
tagging for photos