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Message ID: 11187     Entry time: Wed Apr 1 03:54:15 2015
Author: Jenne 
Type: Update 
Category: LSC 
Subject: PRMI to 1f twice 

I got the PRMI transitioned from REFL165 over to REFL55 two times tonight.  Also, I had 2 long-ish locks, one 9 minutes, and one 6 minutes.  All the other locks were short - less than a minute or two.

I've done some shuffling around of the point in the CARM transition when the anti-boosts (1:20 filters) come on in the CARM A filter bank.  I've moved the turn-on of these filters a several gain steps earlier, but I'm not sure that they're in the best place yet.  Fiddling with the turn-on of the anti-boosts makes the big CARM oscillations last for longer or shorter - if they last too long, they blow the lock, so we don't want them to get too big.

The PRMI angular feedforward has helped a lot tonight, I think.  I've added a line to the up script to enable the output of the OAF after the PRMI is locked, and the down script turns it off again.  It's not so great when the PRM isn't aligned, since it's designed to work when the oplev is on, so it should be off unless the PRM is aligned.  I tried to get a comparison of off vs. on PRC powers with the arms resonating, but I can't hold the lock for long enough when the OAF is not on to get even one average on my 0.01Hz bandwidth spectrum. 

I've turned the arm ASC on a few times, but not every lock.  Around 12:34am, I set the offsets when CARM and DARM were on RF signals, and I had hand-aligned the ETMs to minimize the power at the AS port.  But, this wasn't a good spot for the next lock - the AS port was much darker with the ASC off for that lock.  It would be nice to think about trying some dither alignment, and then maybe resetting the setpoints every lock.  I'm using Q's original loop shapes, but as he left them yesterday, only actuating on the ETMs (with Yarm Yaw gain 0.7 rather than 0.9).

The CARM crossover might need more tuning.  There's some gain peaking around 400 Hz that goes mostly away if I turn the digital CARM gain down by 2dB.  (I'm not using any filters in the CM_SLOW filter bank).

I think that the CARM/DARM transition is more likely to be successful if the FSS slow DC is greater than 0.55ish.  So far this is pretty anecdotal, but I think I have more success when it's higher.  We should pay attention, and see if our trouble locking later in the nights correlates with smaller FSS slow DC values. 

I got the PRMI over to 1f two times, at 1:54am and at 2:25am.  I did not re-phase "POP"55 (which is the REFL55 signal), but I did check the values for the input matrix.  I needed MICH = 0.01*POP55Q and PRCL = 0.008*POP55I.  The first time I lost lock because I turned down the CARM digital gain too much.  The second time I forgot to turn down the PRCL gain (I was *actually* using 0.01*POP55I for the PRCL input matrix, but needed to lower the gain from -0.08 to -0.07, which is about the same as just using 0.008 in the input matrix).  Anyhow, I think PRCL loop oscillations were the cause of the second lockloss.


Here's a strip chart of my first lock of the night, which was the 9 minute lock.  Up until about -6 minutes, I was hand-aligning (including the dip around -7.5 minutes, where I was figuring out which direction to move the ETMs).  Around -3.5 minutes there is a significant dip down, that corrected itself.  By the time I realized that the power had gone down, and was trying to figure out why, it came back.  Maybe the same thing happened at the end of the lock, but it kept getting worse?  Self, re-look at this time (around 11:50pm) to find out why the power dips. 

My tummy feelings (without any data) make me think that this could be something with ITMX, like Q saw earlier today.  Or, maybe ETMX, like we've seen for ages.  Anyhow, my tummy feeling says this is an optic pointing problem.  I certainly think this might be the same thing we see at the end of many locks, the power going low suddenly.  So, it might give a big clue to our locklosses.  Maybe.

RXA: I've changed the above text into pink Comic Sans to lend it the appropriate level of gravitas, given its scientific justification.

Attachment 1: FirstLock_9min_arms150_1154pm.png  50 kB  | Show | Show all
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