Camilla, Robert, WP12232
While looking for coupling of CO2 chillers into DARM at Crab pulsar 59Hz 81246, and also CO2s effect on SQZ 72244, this morning we turned off the CO2s and stayed locked ~40 minutes which is longer than we expected. Unsure of the lock loss cause as maintenance activities had started.
We aimed to see if the 59Hz coupling to DARM peak changed (needs ~20 minutes+ of data), but the accelerators showed that by increasing the CO2 power dumped in the water cooled beam dump, the load on the chillers changed and the 59Hz peak moved ~0.1Hz which means that it would be very difficult to see in DARM.
- 15:41 Turned CO2X and CO2Y power output down to 0W.
- 15:51 closed iris at bottom of CO2Y periscope (there is no place in VP for guillotine)
- 16:01 onwards, Robert was doing backscatter tests on HAM3, making IFO glitches/noise
- 1624 Opened CO2Y irirs, IFO lost lost lock
In attached plot, can see that the SQZ (especially at high frequency) got worse without CO2s. The SQZ ASC also changed the alignment mainly in YAW, does that mean that the CO2s need some alignment improvements in YAW? Looking at HWS signals, the optics substrate absorption changes as expected and started to level out, although the simulation didn't expect them too level out yet.
In future, to repeat this test, we could dump to 1.7W going into DARM using a normal beam-dump to dump the 1.7W before the periscope so that the load on the chiller isn't changed but the CO2 is not on being injected and anything that could backscatter light after the periscope is blocked. Alternatively, we could shake the table. Still the VPs themselves could be a source of scatter as are only AR coated at 10.6um, meaning they reflect up to 15% of 1064nm per surface DCC D1100439.
