Reports until 23:42, Tuesday 10 February 2015
H1 ISC
daniel.hoak@LIGO.ORG - posted 23:42, Tuesday 10 February 2015 - last comment - 07:49, Wednesday 11 February 2015(16620)
IFO locked on DC readout

Alexa Daniel Dan Evan Jeff Lisa Sheila (+ many others)

Like a coffee hipster who won't touch beans that haven't passed through a civet, the IFO now measures DARM_ERR with the light transmitted through the OMC.

 

After the BS WFS were commissioned earlier today, we had several steady locks with 2.8W input power in which we attempted the handoff to DC.  We measured the DARM loop gain and set the UGF to be at the maximum of the phase bubble to make the transition as stable as possible (30Hz, ~30deg margin).  We experimented with different DARM offsets and settled on 5e-5 counts; with a preliminary calibration of 3x10^-7 m/ct this corresponds to an offset of 15pm.  The carrier TEM00 mode was somewhat larger than expected (see the attached pdf, peak at ~43 volts), about 15mA in DCPD sum, almost as much as the 45MHz sidebands.  We used this DARM offset for the rest of the evening.

We measured the OMC-DCPD_SUM --> DARM_IN1 transfer function and adjusted the OMC-READOUT_SCALE factor and LSC-OMC_DC_OFFSET to enable the handoff from AS45_Q.  The values we used are an offset of -2.33e-05 counts and a gain of -2e-6, these values were tuned at the few percent level in subsequent locking attempts to match gains as well as possible.  (Note that the gain comes before the offset, which makes trimming a little more straightforward.)  After these were applied the OMC-to-DARM noise TF looked like Fig. 1.  At this point we attempted the handoff to DC.

This blew the lock.  We realized the OMC input to DARM was subject to the normalization factor of sqrt(NPTRX).  We implemented an awkward fix by holding the output of the TR_X and correcting for the power normalization in the OMC-->DARM input matrix element.  The correction factor is 6.25, this changed by ~1% from lock to lock.

After that, the handoff to low noise worked.  The OMC DCPDs currently have no whitening enabled because the ETMY violin modes (at 508.1 and 508.2 Hz) are rung up and even a single stage of whitening will saturate the ADC.  So, we are ADC noise limited above ~400Hz.  One of our next steps will have to be the commissioning of the violin mode damping.  The ETMY bounce mode is also rung up; so far this isn't a problem, and we are nervous about turning on the damping before we're ready to end the lock.  A spectrum of the DCPD noise is in Fig. 2.

Images attached to this report
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Comments related to this report
alexan.staley@LIGO.ORG - 23:56, Tuesday 10 February 2015 (16621)

We locked on DC readout at 22:45:00 PT on Feb 10, 2015. We unlocked after an hour due to the bounce mode ringing up in ETMY.

lisa.barsotti@LIGO.ORG - 00:39, Wednesday 11 February 2015 (16622)ISC
This is a trend of 9 Mhz sideband power and arm carrier over 10 hours. After the first few failed locking attempts earlier today, we went through the locking sequence step by step to isolate the offending transition (engaging a boost in the DARM loop). After modifying the boost, we had several consecutive successful locking sequences. The last lock in this plot is on DC readout (with growing bounce mode). Overall, the interferometer has been locked for about 6 hours today. Engaging the  BS angular loops  greatly improved power stability, and they have been working robustly for the last 3 locks.

We made an attempt to close CHARD as well, but we need to work on that more.

For the records, no wind at all today.
Images attached to this comment
koji.arai@LIGO.ORG - 00:30, Wednesday 11 February 2015 (16623)

Wow!

alexan.staley@LIGO.ORG - 00:57, Wednesday 11 February 2015 (16624)

Here is an OLTF of DARM on DC.

The template can be found here: /ligo/home/alexan.staley/Public/DARM/OMCDC_DARM_OLTF_20150211.xml

Images attached to this comment
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alexan.staley@LIGO.ORG - 01:03, Wednesday 11 February 2015 (16625)

And just because ...

 

Some people were not that excited.

Images attached to this comment
daniel.hoak@LIGO.ORG - 01:44, Wednesday 11 February 2015 (16627)

A few notes about the noise:

 - The ISS first loop is off, has been since Tuesday maintenance.  The input intensity noise is about as bad as it could be.

 - The DCPD NULL channel is only a factor of ten below DCPD SUM, implying that our DCPD balance is not so good at the 10% level. (?)

 - As mentioned before, the switchable DCPD whitening is all off thanks to the violin mode.  We suspect this might be impressing noise onto the OMC length servo - we had to increase the amplitude of the length dither @ 3300Hz by a factor of ten.  There is a prominent comb of ~8Hz harmonics at high frequencies.

Images attached to this comment
david.shoemaker@LIGO.ORG - 03:59, Wednesday 11 February 2015 (16630)
Excellent! Yet again, Congratulations!
gabriela.gonzalez@LIGO.ORG - 04:32, Wednesday 11 February 2015 (16631)
Congratulations!!! 
stefan.ballmer@LIGO.ORG - 05:31, Wednesday 11 February 2015 (16633)
You guys are on a role! Fantastic!
fred.raab@LIGO.ORG - 07:45, Wednesday 11 February 2015 (16637)
Great news to wake up to after return from India. Congratulations!
joe.giaime@LIGO.ORG - 07:48, Wednesday 11 February 2015 (16638)
Congratulations from your LLO colleagues!
david.reitze@LIGO.ORG - 07:49, Wednesday 11 February 2015 (16639)
Fantastic! Amazing progress in the past few weeks!  The picture is great -- Daniel and Evan look positively thrilled.