Keita, Sheila, Kiwamu

 We installed a high power beam dump in HAM1 this afternoon.
Then we attempted to align the interferometer REFL beam path in HAM1 to let it go through a viewport, but we gave up doing it this time.
We will try to align the REFL beam next time in near future when the IMC flashes.


Installation of high power beam dump:
 Since Cheryl recovered the alignment of the IMC this afternoon and made it flashing, we were able to see the interferometer REFL beam which is downstream of the IMC. The first thing we did was re-positioning of the first steering mirror such that the REFL beam lands on the center of the mirror. The second thing was the installation of the high power beam dump in the REFL path. By design most of the REFL beam is supposed to be dumped at this high power beam dump using a high-reflective BS. After the dump was placed and dog-clamped the beam splitter was aligned such that the reflected beam hits the center of the beam dump.

Alignment of the REFL path to viewport:
 We attempted to align the REFL path. The beam after the high-reflective BS is the one which is supposed to get out of HAM1 through a viewport to ISCT1. As the beam goes through the high-reflective BS the beam became weak and basically the beam power was too low to work with. First of all the sensor card wasn't useful any more due to the too low power. Alternatively we tried to see the beam from the outside using an IR viewer but it was quite hard to tell if we were really seeing the beam because the beam spot was a bit too far away (~ 2 m) to look from the outside and also simply too weak. So we gave up this time. If we can bring an IR viewer in the chamber, this might help us to see the spot. In any case we will come up with some alternative strategies for this issue. Another thing which prevented us from a smooth work was the PRM watchdog as described below.

PRM watchdog kept tripping :
 PRM wasn't in a great condition in the sense that it kept tripping every 2 minutes or so. Because the interferometer REFL beam relies on the alignment of PRM, we had to stop working and wait for it many times. After we carefully kept watching the MEDM screens, eventually we got a hypothesis --- due to a big bias applied on the top mass in pitch, enabling the control slowly brings the PRM alignment to a point where the OSEM readout hits the ADC watchdog threshold of 10,000 counts. Actually the pitch bias had been increased this evening by Cheryl and Sheila to get the beam retro-reflected and it is at the edge of the MEDM slider range.
 Another thing I would have to mention here is that I accidentally leaned on the HAM2 ISI when I was checking the beam around. This tripped the watchdogs of all the suspended optics on the HAM1 table at once. After we recovered all of them we found PRM behaving in that way.

RFEL beam seems clipped :
 Keita claimed that the beam looked clipped at its bottom and slightly its side. This was found after the PRM watchdog mambo jumbo. It is unclear what happened.