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Entry  Wed May 9 04:47:20 2012, Jenne, Update, Locking, PRM is really moving when PRMI locked PRM_louder_when_aligned.pdf
    Reply  Wed May 9 09:19:22 2012, Koji, Update, Locking, PRM is really moving when PRMI locked 
Message ID: 6629     Entry time: Wed May 9 04:47:20 2012     Reply to this: 6631
Author: Jenne 
Type: Update 
Category: Locking 
Subject: PRM is really moving when PRMI locked 

A few things tonight.  Locked both arms simultaneously (IR only).  Locked MICH, Locked PRMI, although it doesn't like staying locked for more than a minute or so, and not always that long.

Locking PRCL was possible by getting rid of the power normalization.  We need to get some triggering going on for the power norm.  I think it's a good idea for after the cavity is locked, but when PRCL is not locked, POP22 is ~0, so Refl33/Pop22 is ~inf.  The PRCL loop kept railing at the Limit that was set.  Getting rid of the power normalization fixed this railing. 

I took some spectra of PRM's oplev, while PRMI was locked, and unlocked.  The PRM is definitely moving more when the cavity is locked.  I'm not sure yet what to do about this, but the result was repeatable many times (~6 or 7 over an hour or so).  The OpLev spectra when PRMI was locked didn't depend too strongly on the PRM's alignment, although I think that's partly because I wasn't able to really get the PRM to optimal alignment.  I think POP22I is supposed to get to 7 or so...last week with Koji it was at least flashing that high.  But tonight I couldn't get POP22I above 4, and most of the time it wouldn't go above 3.  As I was aligning PRM and the circulating SB power increased, POP22I fluctuations increased significantly, then the cavity unlocked.  So maybe this is because as I get closer, PRM gets more wiggly.  I tried playing 'chicken' with it, and took spectra as I was aligning PRM (align, get some improvement, stop to take spectra, then align more, stop to take spectra....) but usually it would fall out of lock after 1-2 iterations of this incremental alignment and I'd have to start over.  When it relocked, it usually wouldn't come back to the same level of POP22I, which was kind of disappointing. 

In the PDF attached, pink and light blue are when the PRMI is locked, and red and dark blue are no PRCL feedback.  The effect is more pronounced with Pitch, but it's there for both Pitch and Yaw.

Also, I need to relook at my new restore/misalign scripts.  They were acting funny tonight, so I'm taking back my "they're awesome, use them without thinking about it" certification.

Attachment 1: PRM_louder_when_aligned.pdf  57 kB  | Hide | Hide all
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