Reports until 04:30, Wednesday 13 May 2015
H1 ISC
stefan.ballmer@LIGO.ORG - posted 04:30, Wednesday 13 May 2015 - last comment - 09:17, Wednesday 13 May 2015(18402)
Fine-tuned MICH FF
Evan, Stefan

We fine-tuned the MICH correction todonight.
- Added the SB300vio BS violin stop band filter to MICH_FF to cancel their effect.
- Measured MICHFF_OUT to DARM_IN twice:
    1) drive disconnected at the ITMY. This measures the MICH_OUT to DARM_IN path.
    2) MICH_FF input off, driving MICH_FF. This measures the MICHFF_OUT to DARM_IN path. 
  This data is in plot 1.

- 1)/2) is the desired filter, shown in  plot 2.

- Finally, we used a p:60:z:80 filter to fine-tune the phase a bit. (Plot 3) This significantly improved the achievable subtraction.

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Comments related to this report
evan.hall@LIGO.ORG - 04:34, Wednesday 13 May 2015 (18403)TCS

Attached is a comparison of the three different FF states (no FF, FI FF, and FD FF).  DTT file is in my folder under Public/2015/05/Feedforward/MichFf.xml.

Attempting to print these plots as a pdf caused DTT to crash. :(

On a different note, we also tried briefly punching the ITM ring heaters (upper and lower) to 0.5 W each to see if we could do anything about the drift in POP90. I turned them on at 2015-05-13 10:56:20 Z, and then off again at 11:03:15 Z. The interferometer unlocked about 20 minutes later, we don't have enough data to say whether this helps or hurts.

 

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aidan.brooks@LIGO.ORG - 09:17, Wednesday 13 May 2015 (18408)

I calculated the thermal lens response of the ITM to this 7-minute ring heater pulse (see attached image). After 7-minutes of heating and a further 20 minutes of waiting the total thermal lens in the ITM is around -5E-7 diopters, or an additional 0.2m added to the radius of curvature. It's unlikely this had any noticable effect.

Note: the glass elements of the RH have a time constant, tau, of around 7 minutes. That is, the power radiated to the test mass from the RH is roughly P_elec*(1-exp(-t/tau)) and P_elec is the electrical power requested.

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