Commissioning Team

For the meeting tomorrow, here is a list with the things that we changed this week, and they are now part of the baseline locking sequence:


1) more aggressive cut-off in MICH, to reduce coherence with DARM above 50 Hz (log 20020 );

2) more aggressive cut-offs in the  ASC_AS_A / AS_AS_B --> OM1 / OM2 centering loops (from 100 Hz to 20 Hz) to remove some coherence with those signals reported by Bruco;

3) more aggressive cut-offs in the OMC SUS alignment loops ( log 20087 ) to remove unwanted OMC length motion which was observed to cause fringe wrapping by Josh et al (log 20079 );

4) heroic modification of the DHARD loops (both PITCH and YAW) during the locking sequence, aimed to make the transition to REFL/TR and carm offset reduction more stable by increasing the phase margin of this loop, which was kind of poor and was seen to cause several lock losses in the past (log 20084 ); these loops have now high ugfs (~ 5 Hz) and >30 degrees phase margin.  Note that the ASC work is not done yet: tomorrow we will add cut off filters, and attack CHARD. Also, we haven't yet succeeded in turning off the ITMs optical levers, which are still on;

5) modification of the ISS loop to improve phase/gain margin (log 20088  and log 20088 );

6) IMC WFS --> PSL PZT loop to reduce ~300 Hz peaks in DARM ( log 20051 );

7) found and fixed a sneaky ramp time problem which was causing the switch from ESD ETMX --> ETMY to fail repeatedly (log 20076 ), Jenne got a BIG PLUS for this one;

8) added an offset to PR3 during the CARM offset reduction to counteract the wire heating ( log 20055 )

9) the Guardian usercode has been modified to speed up the locking sequence ( log 20055 ), and improve IMC_LOCK;

The interferometer has been happily locked in low noise at ~ 65 Mpc for nearly 2 hours with all the above changes implemented, and the Guardian has been updated. 

10) (Later edit) Evan just optimized the MICH feed forward, and he reduced the MICH coupling between 30 and 50 Hz; the sensitivity is now better in that region. 

Other things in our to-do-list for tomorrow:

1) More alignment work (cut-offs and CHARD)

2) Test the whole sequence again to check robustness

3) Track down the TMSX weirdness (log 20078)

4) Noise investigations and injections for noise budget