Reports until 17:57, Thursday 08 September 2016
H1 ISC (ISC)
jenne.driggers@LIGO.ORG - posted 17:57, Thursday 08 September 2016 - last comment - 10:28, Friday 09 September 2016(29553)
Frequency noise coupling to DARM as a function of TCS

[Sheila, Kiwamu, Matt, Jenne, etc]

We changed the TCS CO2 settings after we had thermalized at 20 W for a while, and were watching several metrics.  Here I'll talk about the frequency line at 900 Hz, and Sheila will append her OSA plots as a function of time.

I injected a line at 900 Hz into H1:LSC-EXTRA_AO_2_EXC, which goes to H1:LSC-REFL_SERVO_COMEXC.  I demodulated Refl 9 and Refl 45 like Stefan did last night (alog 29509), and also added another demodulator of OMC DCPDs.  For each of these, I ran a zservo to adjust the demod phase to keep the Q signal at zero. 

In the attached plot, bright red is the PSL power, and yellow and taupe are the X and Y TCS CO2 powers.  Purple, cyan and brick red are Q-phase signals, so can be ignored.  Green is REFL 9, blue is REFL 45. Orange is OMC DCPDs, indicating the coupling of frequency noise to DARM.  Note that the range for blue, green and orange are all symmetric about zero, so while it looks like the frequency coupling is decreasing, in fact it is increasing.  Sorry for a poor choice of demod phase.

After about 40 min at 20 W, the CO2 powers were stepped differentially.  X went from 0.2 W to 0 W, while Y went from 0 W to 0.2 W.  When this happens, you can see that the frequency coupling to DARM gets worse even faster than it had been while thermalizing with the usual TCS settings at 20W.  The REFL 45 and REFL 9 traces don't change in character when we alter the TCS settings.  Clearly this is the wrong direction for freq noise coupling, but it's nice to see that we can definitely affect it.  Sheila will post her results when her plots are ready, but it looks like the sideband imbalance gets worse when we made this TCS step, so it's good that everything hangs together.

Next lock, we'll try increasing the ITMX CO2, and leave the ITMY CO2 at 0 W.  This is a combination of common and differential, but it's all we can do before stepping the ring heaters later tonight.

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sheila.dwyer@LIGO.ORG - 10:28, Friday 09 September 2016 (29560)

Here is a plot of sideband imabalce for the 45 MHz dirring this test. 

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