Jeff K, Kiwamu, Jim W,

As a prep for the mini run, we aimed to confirm that we can run in the low noise state. Most of the attemps were successful today and the interferometer stayed at a recycling gain of more than 35 most of the time and 39 at one point.

Here are items that we could not get done today:

• MICH and SRCL feedforwarding
• DHARD and CHARD roll off filters
• High PSL power (we stayed at 2.7 W)
• Closing ITM alignment loops using the transmon QPDs
• Decent DARM open loop measurement

Also, an earth quake hit us at around 8:20 UTC which we think is from Papua New Guinea at around 8:06 UTC with 7.1 M. This is a good execuse to go home for the night.

(ITM camera position updated)

As planned yesterday (alog 18125), we did initial alignment from scrach. We started from the classic dither-based TMS alignment which gave us well-centered beam on ITMs. Then ITMs and ETMs were manually aligned to obtain high build up in the arm cavities for the green light. After this arm alignment, we updated the ITM camera positions. Moreover, we did the Y arm red/green co-alignment again. We started from BS alignment using the ETMY baffle (see for example alog 18035) and optimized ITMY and ETMY to get high build up in red. Then steered TMSY and green QPD pointing to maximize the green transmitted light. I introduced offsets of -0.2 and 0.2 counts in QPD_A_YAW and QPD_B_YAW respectively. Note that these QPD offsets were confirmed to be good afterwords with the interferometer fully locked and optimized for high recycling gain.

The full-scratch alignment seemed to have helped increasing the recycling gain and therefore we did not have an issue in reducing the CARM offset which was very problematic yesterday seemingly due to a poor recycling gain (alog 18125). Once we fully locked the interferometer, we maximized the recycling gain by manually steering both ITMs in pitch and yaw as usual. This resulted in a recycling gain of 39 acrroding to TRX and TRY. The camera positions were then updated again for the high recycling gain condition. Also, I updated the ITMY aperture which I disabled two days ago (alog 18108) because the aperture was basically not doing a good job at all. I attach a picture of the ITMY camera with the new aperture masking. This seems to be working fine so far.

(Some udpates on ISC_LOCK guardian)

Since we have been focusing on the recycling gain issue in the past days, many commands (e.g. ASC roll offs (alog 17966) and etc.) had been commented out in ISC_LOCK which had helped the interferometer staying robust. However for the automation purpose for mini run, I uncommented all the commented lines in ENGAGE ASC so that now it engages all the loops. So far we did not see an issue with these ASC loops except for the DHARD/CHARD roll offs which apparently make the loops unstable for some reason. They remain uncommented. Also, I kept the roll mode damping commands commented out because I am worried about a situation where the modes rang up so high that the damping signals saturate the DACs. We increased the DARM offset from 2x10^-5 to 3x10^-5 counts in order to obtain more light on the OMC DCPDs. This gave us a total current of 10 mA when PSL was at 2.7 W.

After we edited the guardian, we confirmed that the ISC_LOCK could take us up to the low noise ETMY ESD state. This is a step far from the final state, the LSC feedforward. We did not get a chance to check out the LSC feed forward tonight.