this morning, I did some walking procedure and CEP alignment to get ~80kW in the FPC with 33% amplifier ratio.

we have to check if this power drop comes from:

- a laser amplifier power drop
- or related to some cavity axis shift which could change the cavity gain due to L-shapes

the RF frequency is now 500.1003MHz which is equivalent (if divided by 15) to 33.34002MHz.

the frequency has to be changed by ~2kHz @33MHz <=> ~550µm /2 for one motor.

I changed the laser and the FP cavities frequency.

for the laser frequency, the smaract motor CH1 is at 1.500627m.

for the FPC frequency, the plane mirror motors are at MOT.03= - 123 130 steps and MOT.06

BE CARREFUL, when the offset frequency is large, as we measure it on a scope with a beat frequency, if the scope window is too large,
one gets some stromboscope effect and one measures a lower frequency depending on the number of points in the window.

we got ~81kW for 33% amplifier ratio

this morning, I shut off all the equipements (especially the computer) except the ones powered by the UPS : laser controller, laser peltier controller, laser motors controller.
and I disconnected the cables from the power plugs of the wall (to prevent any possible overvoltage).

Jean-Noël Cayla will need to shut off the electrical shelf (the one powering the UPS) during the afternoon, I will check at this moment if the laser controller is still properly powered thanks to the UPS.

this afternoon, I checked visually what happens when the AC power of the UPS is broken down => the laser controller has still its "emission" button ON... no AC interruption.
so, I guess the UPS switched properly the output AC line from the input AC line to the internal batteries.

this morning, I plugged back the 4 power cables which supply all the equipments.

all the equipments have restarted without problem, but the shutter of the laser amplifier needs a ThomX safety system grant to let the beam propagate to the cavity...
and then continue the commissioning of the restart after Christmas shutdown.

the laser coupled into the amplifier is still measured at ~3mW at the input, on the Alphanov software, once the Amp stage are started at 0% of power ratio.

this afternoon, Kevin restarted the 3rd safety system of ThomX to grant the opening of the beam shutter => now the shutter can be opened.

after adjusting the phase for the PDH system, I was able to find back the laser/CFP lock.

after some minimal alignement, one gets back 50kW for 30.5% of laser amplifier ratio, as before the Christmas shutdown.

I didn't try to lock the FP cavity on the 500MHz RF reference clock as I'm not sure if it has been set to 500.25MHz (as before shutdown) or at 500.1MHz (the future RF frequency) which is very far and will require to move the FP cavity on a long rage.
=> I will ask to Vincent Chaumat to confirm the present RF frequency.

this morning, I set the Ring frequency at 500.25MHz and after switching ON the power supply of the amplifiers for the RF signal coming from the laser,
I saw the beating frequency  (between ring RF and laser harmonic frerquencies at 500.25MHz) that I canceled, playing with the Smaract motor.

Now, I need to adjust the FP-cavity length to follow the laser cavity length but the IcePap DS (controlling the FP-cavity motor) freezes too often and it is almost impossible to make the adjustment.
Kevin sent a GLPI ticket to try to solve this problem.... waiting for IT answer...

on last friday (12/01/2024), the IcePap DS issue was solved and I was able to control the FP-cavity motors properly.
I was able to quickly lock either the laser on the FP-cavity and the FP-cavity on the RF reference as before.

then, we can close these posts on restarting the equipments after the Christmas shutdown

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.

this morning, with Vincent :

- we added the 10Hz trigger to the CH2 on the remote scope (192.168.229.21) to check the synchronization at the right timing.
CH1 : 33MHz RING
CH2 : LINAC/RING synchro signal
CH3 : 500MHz RING
CH4 : 33MHz FPC

we successfully lock both laser on FPC (87kW for 33% amp ratio) and FPC on 500MHz RF.
we saw the result on the scope.
suprisingly, the FPC/RF lock seems much robust than before.

the only problem is the MOT.06 which make the lock being lost at almost every move.
one reason could be the rust on the mechanics... we can try to change the position of both plan mirror motors to work in a proper region.
before, it was working well at -900 000 steps on MOT.06, now it is -780 00.
it's a quite long travel...

end of this posts thread

the 33MHz beating signal (phase) is used to start and stop automatically the lock on the 500MHz beating signal.

this 33MHz beating phase has a fixed range (typically +/-0.5V), so it is important to center this beating phase in the middle of its own range when the 500MHz signal is locked

=> tune the 33MHz phase in order to get ~ 0V on 33MHz beating signal when the 500MHz locking is ON.

this can be done by using the python script "Write_Phase_Rigol_33MHz located in the path /tmp_mnt/data/shared/commissioning_scripts/common