J. Oberling, R. Savage, P. Thomas
Today we tuned up the FSS path (due to a slow drop in the TPD) and restarted h1pslctrl0 (WP 8544).
FSS Tune Up
The RefCav TPD had been trending down over the last week or so, and today was at 2.5 V, so Rick and I went into the enclosure to tune the FSS. All work was done with the ISS OFF.
We began by measuring the power at a few points:
- AOM in: 144 mW
- AOM out: 88 mW
- EOM in: 66 mW
Looking at where we left things after our last tune up in December 2019, the power into the AOM is unchanged but the power out is a decent bit lower; this indicates the alignment through the AOM had slightly shifted. With the RefCav locked, the alignment of the AOM was tweaked; the tweaks were primarily in the vertical direction, with some pitch adjustment as well. When done, the TPD read ~5.2 V, an over 100% improvement from where we started. We then measured the power in the same places as above and found the following:
- AOM in: 143 mW
- AOM out: 110 mW
- EOM in: 81 mW
This matches better with where we left things in December. We then fine tuned the RefCav alignment using the picomotor-equipped mirror mounts and ended with a final TPD of ~5.54 V. To end, we measured the TF of the FSS loop. We started with a common gain of 20 and a fast gain of 16, and measured a UGF of 536 kHz. The common gain was dropped by 2 dB to 18 to give a little more gain margin, with the fast gain unchanged at 16; with these settings the UGF is ~406 kHz, with 52° of phase margin (see attachment). The change in common gain was accepted in SDF.
h1pslctrl0 Restart (WP 8544)
With the FSS tuning complete, we then grabbed Patrick (our resident Beckhoff expert) and proceeded to restart h1pslctrl0. The PSL stabilization loops were disabled, then the PSL was turned off and the chillers shut down. This complete, we restarted the computer; it came back without issue. The chillers were restarted and the PSL was turned back on; all this occurred without a single problem. We confirmed the OPC-IOC shell was functioning correctly by looking at the Laser MEDM screen (this screen is populated primarily by channels forwarded to EPICS by the OPC-IOC shell) and confirming the values were displaying correctly; they were. As a further test, and so we could open the external shutter to provide light to the PMC, the EPICS Alarm interlock was reset from the Laser MEDM screen (the only place this interlock can be reset without forcing the variable in Beckhoff); this worked without issue and I was able to open the external shutter. As a further further test, I enabled both power watchdogs from MEDM (at 19:14 UTC, 11:14 PST, completing FAMIS 10751 in the process); this also functioned correctly. Therefore we conclude that the restart of h1pslctrl0 was a success and all PSL Beckhoff channels are once again available within EPICS. This completes LHO WP 8544.
With the above complete and with the laser having warmed up for ~30 minutes, I enabled the PMC and FSS. The PMC reflected power was reading 11.9 W, which is a little high, so I quickly tweaked the beam alignment into the PMC using the picomotor-equipped mounts. The best I could get quickly was a reflected power of 11.7 W, which gave a transmitted power of 51.8 W. I then turned the ISS ON, and found the diffracted power at ~1.6%; a little low, but not enough to worry about at this point (I'll give this and the PMC reflected power a little more attention during a future maintenance window). This completes all PSL work for this maintenance window. The PSL is currently, with the 1st loop ISS ON but the 2nd loop ISS OFF, outputting ~52.5 W; the FSS TPD is currently reading ~5.6 V.
