Reports 1-1 of 1 Clear search Modify search
AdV-COM (AdV commissioning (1st part) )
casanueva, masserot, gouaty, rolland, bersanetti, cohen, swinkels, genin, bertolini... - 22:54 Wednesday 18 April 2018 (41142) Print this report
Afternoon shift summary

The first part of today's shift was devoted to send the error signals from B2 to the SSFS DSP so that we can use both error signals for this loop. Unfortunately it turned out that the communication between the PD and the SSFS is not working.

After that we experienced a problem with the suspended injection bench, an oscillation around 1Hz appeared, that was causing the saturation of one of the actuators and would make the bench to oscillate. We opened and closed again the controls and the problem was solved. To do so Eric needed to unlock the PMC manually, from the laser lab. Later on we realized that the trigger possibly was due to the activity on SIB2 trying to investigate the lack of communication. We should remember that now that the EIB is suspended we can not walk next to it!!

Then the ITF relocked in Low Noise 1 kind of straightforward. We adjusted a bit the PR loop in order ot maxiize the sidebands recycling gain.

Then we faced another problem, DARM correction was saturating. In principle we thought that it was the fault of the 150 Hz, and we tried to make a deeper notch. However, we realzed that the frequency of this peak would change with time. The change in frequency changes from lock to lock, sometimes there is no saturation at all, sometimes the line would move very fast from 140-160 and we could also see appear a line at 174 Hz or even at 96 Hz. We do not understand its origin, but as it moves it is impossible to notch it and it causes the ITF to unlock. It would even seem that the line would move as I move the notch...

We have also tried to lock the OMC two times without success...

Comments to this report:
genin - 8:46 Thursday 19 April 2018 (41144) Print this report

I confirm the control of the EIB-SAS got crazy due to the access of people in the laser room as you can see on the attached plots (INF_LLAB_LUX senses the light in the room).

As you can see the bench got excited a bit before the light has been switched off.

Reminder: when the EIB is floating, it is recommended to avoid to pass close to it. In case of need we can block the bench or block the beam on the laser bench.

Images attached to this comment
mwas - 11:28 Thursday 19 April 2018 (41147) Print this report
I have looked at the two OMC lock attempts. For the second attempt the ITF unlocked before the OMC arrived to the carrier TEM00 peak.

Figure 1, for the first attempt the OMC correctly ignores the 56MHz TEM00, and then tries to lock on the carrier TEM00. There is clearly an oscillation in the control loop (that is using Peltier cells only at this stage), likely this is gain peaking around the loop UGF. The parameter controlling loop gain is SDB1_IMPINGING_POWER that should correspond to the amount of carrier TEM00 on the bench, there is 4mW on B1s2 PD1 when going through the OMC1 resonance, so the power is actually ~48mW instead of the used 96mW (which is the right value for a single bounce beam). I have lowered the parameter in the OMC_LOCK metatron file to 48 this morning which should prevent this oscillation.
Images attached to this comment
casanueva - 16:06 Thursday 19 April 2018 (41149) Print this report

I attach an FFTIME of one of the last locks that sees the movement of the "150 Hz line"

Images attached to this comment
Paoletti - 16:43 Thursday 19 April 2018 (41151) Print this report

it seems is not the third harmonic of the 50Hz mains.

swinkels - 19:12 Thursday 19 April 2018 (41154) Print this report
Note that during this period, the notch was moved to 'chase the line'. One possibility is that the notches themselves were the problem, by triggering an instability of the DARM loop. The frequency of the oscillation does not have to be exactly at the frequency of the notch itself, since it has an effect on the phase also further away.
Images attached to this comment
Search Help
×

Warning

×