presently, the voltage on the laser PZT is 0-10V, but during the several runs we did, this voltage is too low to compensate low frequency fluctuations:
we need to change often the motors position implying a cavity lock loss.

we have to check if running the laser PZT with the HV output of the Laselock is possible without too much additionnal noise.
=> it can be done simultaneously with the fast feedback loop implementation, which has to be done.

Yesterday, I checked the 2 output HV channels of the LaseLock : they work properly but the noise is bigger than the low voltage outputs
~ 1mV rms on 0-10V outputs
~ 8 mv rms on 0-100V output

This afternoon, I connected the HV output of the Laselock (instead of the standard 0-10V output) to the FP-cavity PZT to increase the locking range.
I didn't see any degradation of the FP-cavity/synthesizer lock.

Après avoir utilisé la chaine : driver ISP - cable ISP DB9 - Feedthrough enceinte DB9-DB9 - cable perlé DB9-SUB-C - Capsule SUB-C,

l'ensemble de tous les vérins 6mm et 20mm ont été testés => ils fonctionnent TOUS.

Les vérins 6mm ont TOUS subis un HOME. cette commande cherche une fin de course du vérin et le place ensuite en position médianne.

Au niveau soft, la course d'un vérin 6mm va de -22 000 à +22 000. Après un HOME, chaque vérin est postionné à la valeur 0.

Précision : le HOME sur les vérins de 6mm place AUTOMATIQUEMENT le vérin en position médianne après avoir atteint une fin de course (FDC)

Pour les vérins de 20mm, la commande HOME place le vérin sur sa FDC positive : +1 650 000 mais NE DEPLACE PAS ensuite automatiquement le vérin en position médiane.

Il faut le faire de façon manuelle.

Tous les vérins 20mm vont subir un HOME et être placés manuellement en position 0.

Il faut ensuite leurs envoyer un offset +825 000 ou -825 000 selon les vérins pour que la cavité ait une conformation rectangulaire.

(actuellement elle ne l'est pas à cause de cales de longueurs différentes selon les axes pour anticiper les effets thermiques à compenser ultérieurement).

* les vérins de 20mm (axe Z) ont été testés sur table grace à une rallonge SUB-C - DB9, au chassis ISP et au soft SUPERVISEUR écrit en labwindows CVI par Didier.

pour rappel, la course soft va de  -1 650 000 à +1 650 000 pour 20mm de course, soit 0.6mm pour 100 000 de course soft.

ils ont été réglés en positions minimale (-1 650 000) pour que Yann puisse les intégrer facilement dans le chassis mécanique.

* une fois installés dans la capsule, les signaux passent par le feedthrough de la capsule.

MAIS cette capsule a vocation a être intégrée au chassis mécanique, intégré lui-même dans une enceinte et les signaux passent alors par un autre feedthrough, celui de l'enceinte.

Il faut donc IMPERATIVEMENT ce feedthrough (ou l'effet miroir qu'il produit) pour tester correctement les vérins dans leur capsule !

telescope of Koheras is removed, information record here:

- distance between collimator edge and -50 lens mount edge is 14.7cm,

- distance between another edge of -50 lens mount and +250 lens mount edge is 14.3cm,

- distance between another edge of +250 lens mount and edge of bread board is 25cm.

today, we had a strange effect :
both the laser and the FP cavity were locked on the RF frequency (500.10045 MHz), and we were producing X-rays but with a slowing (several seconds) fluctuation exactly as the electrons-photons phase was drifting and the fluctuation can goes to 0 Xrays produced even at the "right" phase.
but the ring people says there is no phase fluctuation in their measurements.
and I looked the baseline of the 500MHz beating (which is the synchronisation signal with electrons) and I didn't see any fluctuation either.

we tried 2 other ring frequencies : 500.10030 MHz and 500.1 MHz.
there were still X-rays production fluctuations but with a faster rate.
when we went back to 500.10045 MHz, we found back the same X-rays production fluctions at a slow rate.

to remove this effect, I had to add an integrator gain (I = 1e-6) in the Laselock in the FPC/RF loop.
this integrator was not used (I = 0) in the previous stable X-rays productions....

it means that we have now a slow phase fluctuation.
we have to check if we see these fluctuations in the 500MHz beating signal.
loosing the Xrays means we moved by the packet length dt ~ 50ps which is equivalent to 9° @ 500MHz of fluctuation.
with A= +/-1V signal, it would be equivalent to a drift of ~ A*(2pi*dt/T) ~ 157mV !!!
it is strange we didn't see it => to be checked !!!

conclusion : now, we have to put this I=1e-6 in the FPC/RF loop to get a stable Xray production.
but the locking acquisition works better with I=0.
so we need to remove it before starting to lock and then, when the lock is stable (but the X rays are poor), we need to put I=1e-6 => the Xray flux inscreases dramatically.

from several weeks, the maximum power stored in the FP-cavity was ~ 5kW.

today with Daniele, we finished to investigate the problem, and now the power inside the FP-cavity is back to ~50kW for 30% of laser amplifier ratio (~16W).

we optimized the signal received by the PDH photodiode by installing a large DET100 to collect more light.

if one installs a small photodiode (DET10) in the middle of the beam, the carrier signal when a FP-cavity crosses a resonance is larger because the photodiode "sees" only the part of the beam which is geometrically coupled to the cavity in its small active area, but :
1- once we will improve the geometrical coupling, the part of the incoming beam coupled to the FP-cavity will increase.
2- one need to work with a diffuser in front of this photodiode to precisely adapt the feedback loops gain : in that case the photodiode is sensitive to the whole input beam, whatever his active area size.
so, we decide to put a DET100 (which is given for 35ns rise time / 10MHz BW when connected on 50ohms).

see the scheme in attached file.
and a picture of the desktop with all the lock parameters :

the quality of the lock, seen on the reflected power signal is very good !
and the stability is only limited by the necessity to act on the laser Smaract motors to let the PZT in its working range.
dark blue : transmitted signal
green : PZT
pink : error signal
light blue : reflected signal

conclusion : it is not clear that the cavity Finesse have significantly increased during the last weeks, as we are roughly at the same level than before (47kW).
but as we precisely adapted the signal levels in the feedback scheme (PDH S/N ratio and Laselock parameters), the result is a more stable lock.
 

temperature in the casemate ~ 19.5°C stable

this morning, I measured the power directly at the output of the fiber coupler (through the output fiber), after the strecher : ~5mW
then, I connected the EOM used for the PDH technic : ~2.5mW
then, I connected the fiber of the EOM to the Alphanov amplifier input fiber.

LAL Alphnov software :
PD_IN           = 3.289mW
PD_PULSE   = 33.372MHz

=> nothing to do ! :-)))

I switched ON the preamplifier (3rd stage @ 0%) => PD_Preamp2 = 152.44mW

I refilled the chiller and the stabilized temperature is @ 25°C

we started the 3rd stage of the Alphanov amplifier at 30% => PD_OUT is fluctuating around 1-1.4W => it's not related to the real output power !

the photodiode connected to the scope CH2 is around 210mV @ 50ohms

we clearly see some small peak on the transmission signal (scope CH1) => we need to optimize the laser cavity length and the CEP

we had to move the laser cavity motor to find the resonances and change a lot the CEP.

the CEP motor is at -524.1µm

we got ~75kW in the FP cavity without alignment but with CEP optimization.

the coupling (the cyan color) is ~ 62% !

=> we need to do some alignment

after doing some alignment (walking procedure on the Y axis), and CEP optimization, I got 83kW for 33% on the laser amplifier with a coupling of ~60%

=> we have to check the input power after the amplifier.

I adjusted the FP and laser cavity motors to have a small 33MHz detuning with the RF reference (~10 Hz of beating @ 33MHz)

pb : I don't see the 500MHz beating signal => to be checked

during the motion of the FP-cavity motors, I observed a systematic delock when moving MOT.06 on P1z and no delock with MOT.03 on P4z when I move by 10 steps.
Kevin checked that both IcePap controller have the same configuration and then, the problem is maybe coming from the rust observed on the mechanic.
 

this morning with Daniele, we are measuring the amplifier power just before the FP-cavity.
Casemate temperature @19.5°C

@0% : 205mW
@10%: 755mW
@20%: 7.44W
@30%: 14.3W
@33%:16.3W
@40% : 20.3W
@50% : 24W
@60% : 26W

=> there is a power issue !!!

the normal casemate temperature should be in between 21 and 22°C.
cf this post (https://elog.lal.in2p3.fr/FPC/THOMX+commissioning/133) to get previous amplifier power.

=> it seems we need to redo the compressor CVBG alignment !
first, we will check the amplifier power before the compressor.

After the summer power shutdown, I restarted all the equipements and got quickly ~80kW for 33% amplifier ratio with CEP optimization and without Alignment optimization.

CEP motor position : -506µm

amplifier power measurement before the compressor CVBG.
we used a mirror in between the amplifier output and the compressor + a 2-mirror periscope to match the powermeter height.

amp ratio (%)          power (W)

0                               0.7
10                             1.65
20                             13
30                             25
40                             37.7
50                             50.5
60                             62
70                             74
80                             86
90                             99
100                          110

we had an alarm @100% of amplifier ratio => the reason is not clear... maybe it's coming from a discrepency between some internal measurement and the expected value.
we checked the power after the alarm => still OK

conclusion, the amplifier seems to be OK... we need to redo the alignment of the compressor CVBG.
 

after redoing the alignment of the CVBG, we got back the initial power in the FPC (87kW)

now, I checked the RF locking signals on the 2nd oscilloscope.
I get a strange ratio between the 33MHz beating and the 500MHz beating signals.
beat @ 33MHz ~ 40kHz !
beat @ 500MHz ~ 700Hz !

maybe the 33MHz generator frequency is not matching the 500MHz RF frequency ?
 

now, the Ring RF frequency is set to 500.067MHz.

so the CFP/laser frequency should be 500.067MHz/15 = 33.3378MHz.

the frequency was set to 33.378MHz !!! => it explains the frequency shift only on the 33MHz beating => I corrected the frequency on the generator and informed Nicolas Delerue.

=> now, I can try to lock the CFP to the RF frequency.

I changed a little bit the locking parameters (see picture) for the RF/FPC loop and it locked rapidely.

I asked Vincent to connect on the same scope the synchro signals to check if the FPC lock was OK => he connected 33MHz signals coming from the laser and from the 33MHz RF generator.
=> the signals are not locked even when the FPC seems to be locked to the RF.

=> it can be normal because he forgot to connect also the synchro trigger signal which gives the moment of synchronization of the machine... to be finished on Monday.