Hang, Dan Brown
As there is no dedicated guardian for powering up from 20W to 35W we'll list what we do here:
- Get up to CHARD blend
- Manual to adjust power
- Monitoring these:
- For monitoring the drop in PRCL gain: ndscope H1:LSC-LOCKIN_1_DEMOD_1_I_OUTPUT
- PRCL gain drops from around 0.016 at 2W and keeps dropping. We'll lose all our optical gain as it reaches zero, as it drops lower and we go to higher power we increase PRCL digital gain in the LSC screen from ADJUST_POWER guardian.
- Monitor ASC: ndscope /ligo/home/hang.yu/Desktop/ASC/common/StripTools/ARM_ERR.yaml
- Monitor ASC: ndscope /ligo/home/hang.yu/Desktop/ASC/common/StripTools/CORNER_REFL_SEN_ERR.yaml
- Monitor CHARD-PRC2 coupling: diaggui /ligo/home/daniel.brown/templates/CHARD_PRC2_vs_TCS.xml
- When PRC2 gets too large in CHARD we started seeing a 0.5Hz oscillation so that may start increasing
- Monitor TCS signals: ndscope /ligo/home/daniel.brown/templates/TCS_REFL_AS_POP_MON.yaml
- This display a bunch of signals I have been using to tune TCS
- For monitoring the drop in PRCL gain: ndscope H1:LSC-LOCKIN_1_DEMOD_1_I_OUTPUT
- Wait until RF18 has leveled off
- Increase to 25W
- Wait for RF18 to level off, 5 mins
- Increase to 30W
- Wait for RF18 to level off, 10 mins
- Increase to 35W
- Lose lock for some reason and repeat
The reason you need to wait between each step is that the adjust power guardian state adjusts the PRCL gain as we thermalise. If you go too fast then it increases the gain too much and you'll see some peaks appearing in the lengths around ~110Hz. This could be done in a more neat way but we ran out of time.
Once we reached 35W the PRG became noisy. This coincided with the length loops becoming noisier between 10-100 Hz, from the low PRCL gain perhaps. This was happening at 28W before too but some TCS tuning managed to fix it. Here, you can see 45 refl becomes very noisy once powered up. This seems to coincide with a noisy PRG and bad PRC2/CHARD coupling. I tried the CO2's and they didn't help, then I tried increasing the common ring heater powers in steps. I didn't have Danny's new RH filters on at this stage. I remembered to switch them on when I got to the ETM. To switch these on you need to set the RH guardians to the filtered state, not nominal.
For TCS tuning I have been aiming to keep the REFL9Q and REFL45 signals near zero and quiet, increase the PRG, RF18, and AS45. Also keep an eye on PRCL gain as this can drop quickly with some differential TCS changes. Each time I try the CO2s first to see how they improve these metrics (right now we've only got 0.6W on CO2X left to reduce). As we're trying to go for more power I then gradually increased the ITM/ETM RH in steps observing how things change.
Some more notes from trying high power tonight:
Was probably too early to declare 35W stable it looked better yesterday, we've had a few fast locklosses between 32-35W and two slow 0.1Hz ring up. The slow ring ups show up in the INP/PRC1/CHARD control signals. 30W seems fine though. I was starting to have a look at the PRC1 sensing matrix and CHARD couples strongly and gets worse with increased power.
DRMI has felt a bit slower to acquire today at times. Today I've been dropping back to PRMI and MICH fringes a few times to double check the alignment was ok as the flashes were bad. BS/PRM has needed tweaking up a bit each time. I haven't had to wait ages for DRMI though, the worst was 5 minutes, the last 3 I had were 1-2 minutes. The new TCS settings have more CO2 power at 2W than before to compensate the increased ring heater power for 35W. PRMI looks messier than before. Perhaps that's why it's more sensitive to DRMI alignment now.
I get the feeling that the time it takes to get from lockloss to acquiring DRMI plays a part to. The self heating decays much faster than the CO2 heats back up again, which means we can end up dipping below an acceptable thermal state making DRMI harder to acquire as the flashes aren't as good. I feel the fastest acquisitions happen when ALS wasn't dropping all the time and FIND_IR was fast.
The unoptimised 2W TCS state is apparent in the RF18 buildup which doesn't get much better than ~68 now (was 80 prior to these changes). It's probably worth spending some time tuning TCS and CO2 alignments for 2W and find out what it likes given some ring heater setting.
I had reduced CO2X at 30W input from 0.6W to 0W, it didn't seem to like being reduced. I tried 0.3W and given I have had more lock losses than yesterday I have just set it back to 0.6W. As ITMY absorbs more it might be that it prefers having additional CO2X to compensate for the differential self heating. You could also differentially tune ITM RH more, increase RHY and decrease RHX, but I didn't have time to try it.
I missed the 7,2 quake from Palau warning which put an end to my tests, the interferometer held on for about 10 minutes before it gave up. I pushed the big red button when we lost lock, not sure if it was too late to push it by this point?
Note that wind and microseism have been exceptionally quiet the last few days which has helped getting to high power no doubt.