DARM Coupled Cavity Pole -- No Clear Correlation with IFO Parameters

J. Kissel

I've compared many different IFO parameters which we suspected might contribute to the change in DARM Coupled Cavity Pole (DCCP) Frequency against the most recent 11 measurements,
Meas Num    Date                          DCCP Freq
    [ 2]    'Apr 02 2015 08:34:20 UTC'    [320]
    [ 3]    'Apr 06 2015 23:45:13 UTC'    [320]
    [ 4]    'Apr 13 2015 04:15:43 UTC'    [290]
    [ 5]    'Apr 13 2015 06:49:40 UTC'    [290]
    [ 6]    'Apr 15 2015 07:53:56 UTC'    [290]
    [ 7]    'May 01 2015 18:52:59 UTC'    [355]
    [ 8]    'May 02 2015 20:35:54 UTC'    [355]
    [ 9]    'May 06 2015 11:37:31 UTC'    [270]
    [10]    'May 07 2015 07:08:12 UTC'    [260]
    [11]    'May 11 2015 15:50:43 UTC'    [303]
    [12]    'May 14 2015 09:21:34 UTC'    [355] << -- This one is new, it was put under my pillow by the DCCP fairies last night
And they're summarized in the following attached plots. 

The message -- still no clear correlation between any of these parameters and the DCCP frequency.

Details:
For each measurement data, I gather the following collections of EPICS channels for the duration of the measurement, and take the mean to represent the value of the parameter during the measurement:
_RCGs.pdf : 
Transmitted ARM Power (for carrier recycling gain), POPAIR 18 I (for 9[MHz] power recycling gain), POPAIR 90 I (for 45 [MHz] sideband SRC "reflectivity"), ASAIR 90 I (for 45 [MHz] sideband "DRMI" recycling gain)
_ITMCTRL.pdf  : 
ITM Alignment control (Using the DSOFT and CSOFT filter banks) and ITM optical levers
_Oplev(Pit/Yaw).pdf  : 
Pitch and Yaw of all other core opic optical levers
_IFOPWR.pdf  : 
Pre-PSL-periscope IOO BBPD (for power into the IMC), MC2TRANS (for MC1 to MC2 intracavity power), IM4TRANS (for power into PRM)
_FF.pdf  : 
MICH and SRCL FF subtraction gains and output (to indicate whether they were in use)
_TCS.pdf  : 
ETMX Ring Heater Power, ITMX CO2 Laser POWER
Virtually all of these parameters were stable over the course of them measurement, so I'm comfortable with using the mean as representative. The only which were not are the optical levers (no surprise), so I show them with an error bar that is the std deviation over the duration. For all of these, the error bar is much smaller than the variation between measurements, so I still think they're a good representation of the alignment. Not great, thought -- this drift could still be a result of the optical lever drifting and not the actual optic alignment change, so take it with a grain of salt.

The remaining attachments are the time series of data during each measurement, so you can just for yourself if you believe that taking the mean is representative.

Specific parameters that *don't* apparently have a correlation that we expected to reveal something:
POP90 -- (look at _RCGs.pdf, bottom left panel) 
Remember, our intuition says this is a proxy for the effective "reflectivity" of the SRC, and because the SRC is a signal extraction cavity (i.e. over coupled), the lest reflection the better. The three measurements where we had a highest cavity pole frequency at 355 [Hz] (two during the minirun, and one last night) had a POP90 value of 16.02, 16, and 12.28 [uw/W], which is inconsistent, BUT, one could argue that the other measurements where the cavity pole was lower, POP90 was higher -- except for measurement 11 which is slightly lower than 16, and has a DCCP frequency of 303. Further, when the DCCP frequency stays the same, the POP90 value is varying -- take the first three measurements -- DCCP frequency of 320, 320, and 290 [Hz] against POP90 value of 16.64, 18.26, and 21.11 [uw/W]. Not a consistent story here.

Carrier Power Recycling Gain -- (look at _RCGs.pdf, middle left panel) 
This one's a little confusing because Elli/Sheila has renormalized the end-station QPDs to the red single arm power at measurement 9, and the power recycling gain improved two measurements before they did so (see measurements 7 and 8). However, it's still clear where the consistent improvement in recycling gain happened -- between measurement 6 and 7 (the renormalization only results in an ~5% change in reported value for those two measurements, as opposed to the 25% increase in gain). All this taken into account, the "high" recycling gain period sees the entire range of DCCP frequencies from 355 to as low as 260 [Hz].

ITM pitch and Yaw -- (look at _ITMCTRL.pdf) 
No clear correlation between DCCP frequency and the state of ITM alignment. In fact -- as I mentioned the other day, this gift from the DCCP fairies (measurement 12) is the only measurement in which the ITMs were under control, and the alignment to which the DSOFT and CSOFT loops steered the optic which acheieved a high recycling gain seems no more remarkable than when it was high during the mini-run.

PR3/SR3 alignment -- (look at _Oplev(Pit/Yaw).pdf) 
I know the scale is a little rough here (the optical levers were probably centered between measurement 2 and 3), but I've zoomed in the .png, and I still don;'t see a correlation.

Input power -- (look at _IFOPWR.pdf)
no correlation here: consistent power for the past 4 measurements, in consistent DCCP frequency.

MICH/SRCL -- (look at _FF.pdf)
there is a distinct similarity here -- whenever the SRCL FF is OFF, the DCCP is high. I'm not sure what drives the commissioning vanguard to have this on or off, but maybe there's a clue there, given that we're having so much trouble with the stationarity of the SRCL to DARM coupling as well.

TCS -- (look at _TCS.pdf)
no correlation here, but last night's measurement did have a significant change in ITMX CO2 laser power... I'll have to have a conversation with the team about this, 'cause I don't see anything in the log about it

So ... yeah ... no strong conclusions in any direction ... yet. Maybe folks can make better sense of the data than I can...