Virgo Logbook

AdV-COM (AdV commissioning (1st part) )

casanueva, allocca, chiummo, trozzo, walet, bersanetti, masserot, carbognani... - 0:41 Friday 20 April 2018 (41158)

Afternoon shift - ITF recovery

This afternoon we worked on several topics.

Alignment: We explored different working points, both for the PR @ MICH offset 0.1 and BS @ DF. In the case of the PR we tweaked the offsets in order to reach the DF better aligned, so that the AA in DF needs to move less the mirror. For the BS we opened the loop and we tried to optimized the powers at all the ports. We found a particular working point that seemed to make the dark fringe darker and the sidebands recycling slightly higher at the same time (see Figure 1). We left the new offsets saved on the ini file for what concerns the BS. About this latter loop, there is still some improvement to do adjusting the gains of the TX loop.
OMC: we made a trial of locking the IMC without success, Michal took a look to it and adjusted one parameter, however we did not have time to re-try.
10 kHz:the SSFS signal was affected by a strong line at 10 kHz. Alain found and fixed the problem, related with the change of the frequency of the sidebands at the LNFS. More details will be posted by him.
We have added a line in Metatron which fixes the value of the crossing point between both loops of the SSFS. The parameter can be found on the CARM_DARM_LOCK.ini, and is called "carm_mc_cross_gain"

NOTA: After the work of Alain, the demodulation phases changed. We have adjusted only the ones allowing us to reach LOCKED_SSFS. Tomorrow, the rest have to be checked!

Images attached to this report

Comments to this report:

casanueva - 11:11 Friday 20 April 2018 (41163)

NOtice that by the end of the shift we disabled the FmodErr after every unlock, in case there was a problem on the logic. However, the scan of the RFC would bring the IMC very far from the good working point of the sidebands (~ 1mm). And also on the process the Thermal corrections of the laser would go to 1.3. I reseted them manually and that seemed to fix the problem for a while.

ALso while doing the FmodErr by hand I noticed that the IMC would unlock even for slow/small movements of the z, so maybe that can explain why while scanning the RFC it goes so far, if it unlocks often on the process. To be followed!

bersanetti - 21:16 Friday 20 April 2018 (41182)

About the IMC: the IMC is lock-cycled on purpose during FmodErr if the PZT correction is outside thresholds; if it does that very often, that could point to an issue between the PZT and the IMC length driving. Maybe it has a common cause with the fact that the IMC unlocks frequently while scanning for the RFC resonance, as "big" movements of the cavity length are done in the process.

About Lock Acquisition: all the phases should be restored, we can relock to LOW_NOISE_1 but the PR loop (in DF) should be re-checked, as it was not working properly; I removed the 150 Hz notch as it often killed the lock in DF; PRCL_GAIN for dark fringe is strangely lower than usual. To be checked.