the RF frequency changed from 500.1003MHz to 500.0913MHz => it reduced by 9kHz @ 500MHz which is equivalent to 600Hz @ 33MHz (we measured 500Hz @ 33MHz). the electron orbit length increased, so we have to increase the cavities length => increase motor values by ~ 68µm.

for the laser cavity : 1.496 560 mm => 1.564 560 mm

the initial values for the motor of the FP cavity are : MOT.03=-130 000 steps and MOT.06=-900 000 steps.
68µm is roughly 11 000 steps (6nm/step) => MOT.03=-130 000 steps and MOT.06=-889 000 steps.

optimum CEP position : -210.8µm => -192µm

I got 80kW in the FP cavity after CEP and walking alignment
then, 82kW after waiting 3h.
then, 84kW after waiting 5h.

at the begining of the day, we started to get ~81kW in the FPC for 33% amplifier ratio and after ~1h, we got 84kW after CEP and alignment tuning.
at the end of the day, we got 89kW without walking alignment.

we tried to improve a bit the robustness of the FPC and RF locks:
see the capture for the new locking parameters.

today with Alice, we planned to do a long run with ~80kW in the FPC to check if the lock problems are coming from the interaction with the machine or not.
the goal is to check this assumption on a full day comparable with a day of X-ray production.

we started the amplifier at 10am.

during a move of MaY (injection mirrors of the FPC), we observed a sudden total loss of resonances...
the reason was an abnormal displacement of the motor despite the fact the measured position was reasonable.
we already observed an issue like that....
to fix the problem, one just had to move back MaY.

the cavity started to be locked at 11:15am

the RF frequency has been changed to 500.09595MHz equivalent to 33.33973MHz
but we don't have a beating signal @ 500MHz => one will ask to Vincent to fix the issue.

laser motor CH0 : 1.503453 mm
laser moror CH2 : - 50µm

~ 83kW at 12:30pm

we observed that :

- the MOT.03 motor always exhibits some perturbations on the transmitted, reflected and PZT signals (see "peaks" in the picture) in contrary to the MOT.06 motor.
does the differences come from the motor relative positions (-900 000 steps for MOT.06 and -100 000 steps for MOT.03) or from the controller configuration ?

- the stability limits (oscillations arise) of the PID for the RF/CFP locks are P = 1 / I = 0.0001 / D = 5
then we put the new PID parameters : P = 0.25 / I = 0.000025 / D = 1

- the 20Hz oscillations are stil arising from time to time

- the lock laser/CFP is pretty robust, one observes more RF/CFP lock losses.

- we removed the 250Hz filter on the RF/CFP error signal to increase the feedback BW but we didn't see a any improvement

- at 5pm, the laser/CFP lock seems as stable as in the morning, then we don't see any change in stability during time.

we loggued CFP power measurement and signals from the cavity (~ 1GB of data)

last thing we tried :

we removed the threshold on the FPC/RF error signal.
=> we cannot choose automatically the RF bucket anymore (we need to manually let the phase drift slowly and start the lock at the right moment).
=> but the FPC/RF lock seems more robust.

in that case, we have 2 different sources of lock losses:
- the ones dues to the laser or CFP motors move.
even at low speed or in "piezo scan" mode, one observes too fast mouvement that are not properly compensated and involving some phase shift.
- the ones not related to any action.
=> the 20Hz signal seems to increase until it makes the system losing the lock

This morning, I added an amplifier on the 33MHz beating signal in between the mixer+LPF and the scope/Laselock.

it seems to improve the robustness of the RF/FPC lock.

because of this gain, I increased the upper and lower thresholds on the search criterion of the RF/FPC lock from +/-50mV to +250mV/-200mV

=> see the picture of the Laselock parameters.

the optimum phase for X-ray production is roughly +3.6ns between C2 (machine trigger) and C4 (33MHz laser signal).

we have to use the machine at 70MeV with a new frequency at 500.0325MHz / 33.3355MHz.

=> we need to move the FPC tomorrow by roughly 60kHz @ 500MHz.

major result of the day: X-ray vertical scan by moving the hexapod

abscise : hexapod position
ordinate : xray flux in asynchronous condition

red curve : continuous injection at 10Hz (the scan lasts for ~5 minutes)
green curve : one single injection (the beam is not extracted).
blue curve : one single injection, ~ 10-15 minutes later

this morning, Kevin reduced the steering current in the IcePap controllers of the FP cavity motors.

the motor MOT.06 was producing a pattern in the Transmission signal when it was moved and doing a lock loss very often.
so, we changed its current from 0.8A to 0.4A and it fixes the problem => no more systematic lock loss.

so, we changed also the MOT.03 steering current from 0.8A to 0.7A.
on this motor, we have also a false warning about the Low limit switch which seems to be activated (strange because, we are always using it in the positive direction)
Kevin reverted the logic to remove the message.

we obtained 91kW in the FPC for 33% amplifier ratio after CEP and alignment tuning.

we did synchronized xray production with a relative delay between laser 33MHz and trigger (CH2-CH4) of +4 ns

this morning, I restarted the cavity after the Christmas shutdown.
everything went fine.

I got ~ 86kW for 33% laser amplifier ratio after optimization of the CEP and alignment with walking procedure.

IcePap controllers are OK and the displacements (MOT.03 and MOT.06) let the CFP locked.

I locked also on the RF frequency (I tuned the laser and CFP cavity length) => +4.1ns (C2-C4) between the 10Hz trig (C2) and the 33MHz laser signal (C4)
I observed that the search & relock range on the regulator B plays an important role on the RF locking stability.
so, I increased the previous range +/-0.25V to +/-0.5V.
we have always the 20Hz noise which can be increasing some time but the lock seems more robust.

today we did x-rays => we got 41 000 pA at maximum and 90kW in the FPC for 33% amplifier ratio.

finally, I changed the strategy for the feeback on RF.
i removed the integration and derivative parameters and reduced the gain parameter :

P=0.25 / I=D=0 => it seems to be more stable => less low frequency oscillations becoming larger and larger during a perturbation.

this morning, I restarted the lock of the CFP after almost 2 weeks without operation.
after quick alignment and CEP tuning, I got 88kW for 33% ratio for the laser amplifier.

the FPC seems pretty far from the RF frequency (2.8kHz @ 33MHz) but it's possible the present RF frequency has been tuned for 61.5 or 70MeV (the present FPC length is tuned for 50MeV).

Jean-Noel had to reinject some SF6 gas in the section pipe => it immediately produces some lock losses during the whole filling process and even several minutes after he finishes.
this is an interesting correlation with the vibrations from the beam pipe => one needs to install the accelerometer to check the behavior.
but the lock losses were not related to "high frequency" or "20Hz oscillations" noises which are the 2 main processes for lock losses, it was just like some "cuts" in the signals.

I finally got 90kW in the FPC for 33% ratio for the laser amplifier after walking alignment procedure.

this morning, the cavity was pretty misaligned => basic alignment in y direction helps a lot => 93kW for 33% amp ratio.

the Rigol 33MHz generator phase was adjusted : phase ch2 = phase ch1 (40 deg) + 36 deg = 76 deg.

today, the alignment of FP cavity was so bad that I tuned the 01 mode by error (CEP and alignment)...  insead of the 00 mode !!!
I was able to reach ~30kW and was limited at this value, so I used the camera to check what was happening and saw the 01 mode.

so, I moved the lock on a 00 mode and redid a full tuning (CEP and alignment).
I got ~93kW => ok

today, after 1 week of vacation, I was able to easily lock the cavity with 92kW with 33% amp ratio without too much optimizations (no walking alignment).

could it be related to the nice weather we got during this week ?
as in the past we observed more noise when the weather was changing and we had very difficult locking procedure after a simple weekend...

Today, I removed the NKT oscillator from the bunker to put it in the PLIC room.

I locked the FP cavity and obtained 97kW with 33% amplifier ratio, without any alignment, just by changing a little bit the CEP.

New locking parameters (I got 98kW for 33% amp ratio) :

Axis 18 position : +0009420
P = 0.05
I = 0.0005
D = 0.6

stability seems better than previous parameters.

We had a long run without any lock loss during ~1h with the 23kW recipie in the morning.
during the afternoon, we had some few lock losses but the FPC system was globally quiet and stable,
but at the end of the day, I observed more and more frequent high frequency noise which implies lock losses.

at the same time, Dalkia changed the temperature of the air flow in the bunker.
could it be the reason of the stability degradation or is it because the cavity is more unstable when hot ?

long run yesterday at relatively low power (~23kW) with double loop (FPC + RF) between 10am and 6pm

long run today at relatively nominal power (~90kW) with double loop (FPC + RF) between 13:30am and 6:30pm

list of possible causes of the high frequency noise which makes the system loosing the lock => to be checked.
(if you have some new idea, I will edit the post)

1- Laser
   1.1- vibrations on the laser box coming from the optical table / housing
   1.2- vibrations coming from the Smaract translation stages (Frep or CEP) inside the laser box
   1.3- pressure noise coming from the weather (the laser cavity is sealed) on the laser box

2- Amplifier
   2.1- vibrations coming from the fans in the controler crate
   2.2- vibrations coming from the chiller (water cooling cavitation)

3- Beam propagation
   3.1- vibration noise coming from the housing / the table
   3.2- vibration noise coming from the motors of the injection mirrors

4- Fabry-Perot cavity
   4.1- pressure noise on the cavity vessels coming from the weather/air cooling
   4.2- vibrations coming from the rust on the mechanics
   4.3- vibrations of the mirror mounts due to temperature related to cavity power
   4.4- vibrations coming from the electron ring mechanics
   4.5- "vacuum" index variation coming from local ionization due to the electron beam
   4.6- vibrations coming from the far position (related to the middle range) of some mounts and due to the spring of the translations stage.

5- Feedback system / Electronics / CEM
   5.1- CEM votage noise on the laser or FPC PZT's

4.3 - Vibrations of the mirror mounts due to temperature related to cavity power (the electrons machine is OFF)

1) to test this possible issue, we plan to make a run at low power in the FP-cavity, around 10kW, instead of ~90kW as usual.
for that, I will need to change the diffuser position on axis 18 to get the same error signal for the locking.
the initial axis 18 position is +11304

I used the Alphanov amplifier at its standard value : 33%

first, I did a step at 26kW in the FPC by tuning the CEP
at this power, I saw exactly the same kind of behavior with a sudden large high frequency noise which prevent the lock to run properly and which is impossible to compensate.
=> one just have to wait... until it becomes more stable.

then, I went to 13kW in the FPC by tuning the CEP.

• I did the same alignement optimisation than for high power to remove possible coupling to high order modes in the error signal
• I tuned the power in the FPC by changing the CEP => the equivalent LW of the cavity will be different => I got ~ 13kW
• I changed the diffuser position on axis 18 to -23079
• I tuned the PID parameters :

initial => final
P = 0.055 => 0.1
I = 0.0005 => 0.002
D = 0.6 => 1

I started to record a long trend of the FPC power => see attached picture

I still observed the ~20Hz noise and sometime some high frequency noise, but not at a level which prevents the locking system to work.
CONCLUSION :
at this power and with a larger LW (CEP is not optimized), the FPC seems much more stable without any lock loss during 1h !

2) then I will do a test by decreasing the Alphanov amplifier ratio to work at a lower input power but with an optimized CEP.
Now, I optimized the CEP and alignment and reduce the Alphanov amplifier ratio to 15% => 24kW power in the FPC.
on CH2, I got 60mV (when I got 250mV when I'm at 97kW in the FPC) => ratio ~ 4.2 => 97kW / 4,2 ~ 23 kW
I checked that the PID parameters are not over-valuated which can produce a power reduction and the CEP is optimum as well as the alignment.

Axis 18 position : -13188
PID parameters (P = 0.1 / I = 0.002 / D = 1.5)

I started to record a long trend of the FPC power => cf 2nd trend with gradually increasing of the power because of the drift of the CEP + feedback adjustments.

CONCLUSION :
at this power and with nominal LW (CEP is optimized), the FPC seems much more stable without any lock loss during 1h !

3) I found a stable position for FPC around 46kW

I used the recepie for 46kW => after some time, I observed a lot of high frequency noise which induces some lock loss.
 

today, we were able to store more than 93kW in the FP cavity, always with the same parameter : 33% laser amplifier ratio

today, we were able to store more than 94kW in the FP cavity, always with the same parameter : 33% laser amplifier ratio

today, we were able to store more than 95kW in the FP cavity, always with the same parameter : 33% laser amplifier ratio

today, we were able to store more than 97kW in the FP cavity, always with the same parameter : 33% laser amplifier ratio

yesterday, we were able to store more than 98kW in the FP cavity, always with the same parameter : 33% laser amplifier ratio

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
 

The temperature slitly increase in thomx Bunker from 23° to 24° during the last day.

The thermalisation of the CFP is very long...

In any case the operation of the CFP is so easy, it seems to be correlated to the weather... tody it's very nice as of hte rest of the week.

The stored power is easily 94 KW and there is not jump or delock problems.

The temperature of the bunker continiusly increase and now we observe some delocking du to high frq perturbations... may be the twe things are correlated.

after the new temperature setting for the bunker air cooling (winter to summer transition), the temperature drop from 24° to 20°C which induced a slight misalignment between the onefive oscillator and the fiber injection.
the amplifier photodiode PD_IN which checks the amplifier power injection drop also from 3mW to 2.885mW... hopefully, it is enough to start the amplifier without realignment.

but bad news, I don't see any transmission of the cavity... to be checked...

I finally got 93-94kW for 33% amp ratio.

I had to move the FP-cavity length to compensate the temperature change in the bunker.
doing that, I had the message "Low Limit SW pressed" when I tried to move P4z under -98 000 steps !!!
=> so, maybe this number is not the correct steps number and we are much closer to the end than we could expect.
=> could it be the reason for the 20Hz noise related to the too strong springs, as we already observed before ?

in the meantime, I changed the use of the P1z and P4z motors to not face the situation again.
so, P4z will be used to move to higher steps (even if its apparent position seems higher than P1z).
and P1z will be used to move to lower steps.

surprinsingly, the CEP position was almost already optimized...
 

we installed a measurement at the IP with the BPM for ion cleaning for electrons and we used a fast photodiode at the output of the FP-cavity and measured with a fast oscilloscope the phase jitter between the 2 signals.
in red, the BPM signal
in blue, the photodiode signal.

on the right of the picture, this is the trend of the phase difference measurement.
in yellow, this is the histogram of this phase difference.

one measured 35ps of FWHM which is equivalent to 15ps rms for a Gaussian distribution.

the phase between the 500Mhz ring RF oscillator and the electrons is measured on a BPM and is very stable after 2-3ms (<< 6ps, typically) !

in the same time, we can use the residual phase beating after our 500MHz mixer to estimate the phase noise coming from the laser part.
the rms noise of this signal is around 60mV for 1.25V peak (2.5 pk-pk) signal => ~ 50mrad rms

dt = dphi / 2pi * 2ns ~ 15 ps which is the noise measured between electrons and photons at the IP !!!

we clearly see that this rms noise level is correlated with the 20Hz oscillation observed on the FPC feedback signals.

BUT even when this rms phase noise varies, we DO NOT see any effect on the X-ray production at this time,
which means this is not yet a limiting factor.
this observation is confirmed by the X-ray production flux calculation for which the time jitter is "added" to the electron beam size parameter which seems to be dominant.

from now on, one reverts the FP cavity motors direction to compensate the long drift from the begining of the project.
the motor MOT.06 will be used for the upward direction (presently -1 082 650 steps)
and the motor MOT.03 will be used for the downward direction (presently +37 170 steps)

after CEP and walking alignment tuning, I got quickly 92kW.

the new MOT.06 and MOT.03 positions are : -1 071670 steps and +34 110 steps.
the CEP motor is at +345µm

this afternoon, we succeeded to get a quite long Xray production trend around 15-20 minutes with a flux above 25k on i1.

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.

I installed an accelerometer setup in the bunker.
presently, the accelerometer is placed on top of the housing and its signal is connected to the 2nd scope (33MHz and 500MHz RF beating) on channel 4.
the FPC is locked to ~90kW.

the accelerometer noise is filtered on the Labview Signal Express software in order to focus on the 20Hz noise.
one applied a RII elliptic 5th order low pass filter at 30Hz.

the 20Hz noise can be seen on the PZT which always compensate for CFP frequency drifts.

figure 1 : example of typical accelerometer filtered noise (yellow curve) when the PZT compensation (green curve) is quite (measurement on 4 seconds)

figure 2 : example of accelerometer filtered noise (yellow curve) when the PZT compensation (green curve) exhibits some 20Hz noise (measurement on 10 seconds)

conclusion : there is no clear evidence of a correlation between accoustic noise outside of the housing (measured by the accelerometer) and the 20Hz noise in the laser PZT compensation.
=> putting the 2 signals on 2 different scopes doesn't help because the slow acquisition done is not synchronous.

next try : use the same scope and put the accelerometer inside the housing, for example on top of one of the FPC vessel.

today I connected a copy of the laser PZT signal to the 2nd scope CH2 (with AC coupling to remove the DC offset) to be able to monitor synchronously the Accelerometer and laser PZT signals.
the accelerometer is still connected to the 2nd scope CH4 and placed on top of the housing.

I filtered both signals in the Labview Signal Express software with a low-pass filter at 30Hz to focus on low frequencies noise (~20Hz).

now, I need to wait to work with the bunker closed to compare with normal operation (if some people work in the same time in the bunker, obviously, we will get some correlation between the accelerometer and laser PZT signals.....)

this morning, I did some measurement with nobody interfering with the tests.

- the "no noise" image shows a standard situation during 10s when there is no noise either on PZT or Accelerometer.
most of the time, we are in this situation.

- the "slaping door" image shows the case where the large igloo door is opened and slaping when it closes.
the accelerometer and the PZT exhibit correlated noise when the door is slaping.
we can see a PZT "recovery" time longer than the perturbation.
but these events are rare and are not the source of the problematic perturbations.

- "noise 1,2,3" images show the typical situation when the PZT start to compensate large noise without any correlation with accelerometer placed on top of the housing.

=> conclusion, some external noise (to the housing) should not be the source of the perturbations on the PZT.

then, I moved the accelerometer on top of the "X-hutch side" vessel, placed directly on the metal top case, inside the housing.

- the "no noise same range" image shows a standard situation during 10s when there no noise either on PZT or Accelerometer.
on can compare the noise level on the accelerometer with the previous post when it was outside on top of the housing.
its noise is much much lower... which means the housing is properly dumping the acoustic noise at this frequency around 20-30Hz.

so, we increase the accelerometer measurement sensitivity to better measure its noise.
- the "no noise new range" image shows a standard situation during 10s when there no noise either on PZT or Accelerometer but with a smaller range.

- the "noise 1,2,3" images show the situation when the PZT start to compensate large noise with good correlation with accelerometer placed on top of the optical vessel.

- the "noise 1,2,3 not clear" images show the situation when the PZT start to compensate large noise with correlation with accelerometer but the signal level is not the same as before.
this make me think the origin of the noise is maybe not coming from the inside of the optical vessel.

=> conclusion : we see for the first time a correlation between the PZT noise and some vibration/acoustic noise.
now, we have to investigate the precise origin of this noise (or the different sources).

at the end of the day, I moved the accelerometer from the top of the cavity vessel to the top case of the Onefive laser.

I quickly saw again quite strong correlations between the vibrations compensated by the PZT and the accelerometer signal.
when one does a laser motor step which makes a systematic lock loss, one doesn't see any signal on the accelerometer.
=> more measurements have to be done.

I would like also to put also the accelerometer on the mechanics attached to the pipe at the IP.
=> to be discussed to find the best place as a lot of cables, the 2 dipoles and the aluminium sheets around the vacuum stufs don't let a lot of place to put the accelerometer....

this morning, I did some new plots with the accelerometer placed on the top of the case of the OneFive laser.
I previously observed with the accelerometer placed on the top of one cavity vessel, the correlation between the accelerometer signal and the PZT noise is pretty good but not 100%.

I will move the accelerometer on the optical cavity table.

new plots, with the accelerometer placed directly on the optical cavity table (on the marble part), close to the oscillator.
the correlation seems a bit better....

we would need to put the accelerometer on one foot of the table to check if the table has not some micro-movement or at the IP to check if the water in the dipole are doing some vibrations.

one possible source for this acoustic noise was the vibrations coming from the water cooling of the dipoles which is normally never turned off even when the machine is off.

this afternoon, Kevin turned off the main valve of the water cooling of half of the dipoles (the half on the FPC side), and we recorded the peak-peak value of accelerometer signal on a long trend (~20mn) but we didn't see a clear difference before and after.

I keep recording the accelerometer pk-pk signal during the night in case of one could see something different...

here is the pk-pk measurement of the accelerometer during the whole night.
the recording started at 5pm yesterday and has been stopped this morning at 10am.

one got 28k points in 17 hours => 1.65k points / h

the "last" peak in the evening at 8.5k points is equivalent to 10pm.
the "fisrt" peaks in the morning at 23k points is equivalent to 7am.

I discussed with Jean-Noël but we don't any clear correlation of this schedule with some equipment schedule in ThomX....

I restarted a new acquisition at 10.30am.

here is the acquisition from 10:30am to 5:30pm

11k point in 7h => 1.57k points / h

the noise is almost the same during the daylight, a little bit increasing from 1:30pm.

I restarted an acquisition at 5:30pm to check if the noise reduction during the night is repeatable or not....

here is the same kind of measurement (pk-pk of 1 sec of acquisition) done on the laser PZT when the FP is at 90kW.
it's from 6:20pm to 7:10pm => ~2.4s by point

the minimum values are for the PZT being off.
the maximum values are for PZT scanning or lock loss.

in between, we get the measurements of the perturbations.

at 6:30pm (~250 points), Jean-Noel stopped all the water cooling circuit of ThomX.
at 6:46pm (~650 points), Jean-Noel restarted the main water cooling circuit.
at 7pm (~1000 points), Jean-Noel restarted all the water cooling circuit.
at 7:10pm (~1250 points) => we stopped the acquisition.

conclusion : no clear effect of the water cooling circuit on the locking stability.

long term pk-pk measurement of the accelerometer (placed on the optical cavity table, on the marble part close to the laser oscillator) from 5:30pm to 9am => ~ 2.255s / pt

start of the quiet period : ~ 5k pts <=> 8:45pm
3 peaks at ~ 7.5k, 8.5k, 9.5k pts <=> 10:10pm, 10:50pm, 11:30pm
begining of the noise : big peak at ~20.5k pts <=> 6:20am

conclusion : relatively same behavior than the previous measurement made in the same condition except the "quiet" and "wake up" schedule of the noise is not strictly the same.

I installed the accelerometer on the ground close to one feet of the FP cavity hexapod (see picture) and restarted the acquisition at 6:40pm on 20th of february.

the acquisition corresponds to the night between the 20th and the 21th of february.

23.3k points from 6:40pm to 9am => 2.215s / point

the large peaks in between 2k and 3.5k points correspond to 7:55pm to 8:50pm => some working operation in the bunker (maybe finish the work of the kicker).

one does not observe a clear decrease of the vibrations during the night.
I added a vertical zoom of the acquisition => it seems there is a small decrease during the night but nothing clear.

the last plot shows exactly the same data but with a strong filtering (raw data in blue, filtered data in red).
we see a little bit better the reduction of the vibration during the night.

for this 20Hz oscillation, could it be a natural resonance of the optical table placed on its feet ?

typical mass of the table m ~ 8T

feets :
young modulus of steel E ~ 210 G N/m²
length L ~ 1m
diameter d ~ 10cm
rigidity for 6 feets => k ~ 6. pi.d²/4L E ~ 9.9 G N/m

rough estimation of the oscillation frequency : f = sqrt(k / m) / 2pi ~ 177 Hz

if the rigidity of the real moving feets is lower (~ by a factor 80) than if they were made of plain steel, we are not so far.
to be continued...

 

the machine people saw a correlation between BPM jumps and vacuum gauges peaks related to breakdowns in the beam pipe.

these breakdowns could produce some accoustic noise which could be related to our lock losses.

=> we tried to do a corrrelation between our lock losses and the vacuum gauge peaks => WE DON'T SEE any correlation !!!

The goal of these measurements is to check if one can find some correlation between the CFP lock losses observed during a run and some CEM noise in the bunker.
the main issue is coming from a 20Hz noise apearing/disapearing in the laser cavity PZT signal.
is it a real cavity length noise that must be compensated or is it a pickup noise in the error signal which produce some unwanted compensation ?
the second issue (apearing much less often) is a higher frequency noise visible mainly in the transmission signal of the CFP which becomes wider and noisy during 1-2 seconds.

This morning, I installed a simple wire loop all around the table (the machine is OFF).
this wire is connected to the wire of a BNC connector at one end and to the ground of the same BNC connector at the other end to form a loop.
this BNC connector is connected to a 1kHz low pass filter to remove high frequency CEM noises and connected to a 10-1000 variable gain amplifier, plugged to the CH3 of the CFP scope (instead of the PDH/PZT-CAV signal).

I locked the CFP above 80kW after tuning the CEP.

I took several pictures to illustrate what I observed :
- on the right, the scope signal in time domain (blue = TRANS / green = PZT laser / cyan = REFLECT / pink = LOOP noise)
- on the left, the spectral analysis in frequency domain (red = PZT laser / white = LOOP noise)

in these 3 measurements, I don't do anything to the CFP, I just wait for the signals.

1) normal condition : see picture "Without Noise @ 20Hz"
the PZT signal in time domain is relatively flat and the 20Hz noise is barely visible in frequency domain.
we don't see any correlation with the LOOP noise for which one can see clear 50Hz and 100Hz peaks.

2) 20Hz noise condition : see picture "With Noise @ 20Hz"
the PZT signal in time and frequency domain exhibit a clear 20Hz oscillation.
the REFLECT and TRANS signals are also correlated to this 20Hz oscillation.
but still no correlation with the LOOP noise in time or frequency domain.

3) 20Hz noise lock loss condition : see picture "Delock @ 20Hz"
because of the lock loss the spectral analysis of the PZT signal is meaningless,
but in time domain, one can clearly see the growth of the 20Hz signal, inducing large noise on TRANS and REFLECT signal but still no correlation with the LOOP noise.

Conclusion : the 20Hz noise seems not related to any CEM noisy signal but more probably to a real mechanical noise in the CFP (not in the laser cavity because it would be seen in the phase noise measurements).

in this measurement, I tried to produce a tone around 400Hz with my voice, close to the FP cavity.
it is difficult to right volume as the cavity can easily lose the lock.

4) Voice noise condition : see picture "Voice noise @ 400Hz"
here, I changed the spectral span to 500Hz.
one can see a small bump in frequency domain around 400Hz due to the accoustic noise in the PZT signal.
the general shape of the PZT spectral signal is maybe related to the PID parameters : one can see more signal at lower frequencies.
in time domain, one can see TRANS and REFLECT signals are more noisy than before and these signals shapes seems identical to what has been observed when one has lock loss due to high frequency noise.
maybe we could put a mic in the bunker, connected to one scope to check if sometime one doesn't have much more accoustic noise...
 

This afternoon, we started almost all the parts of the machine with Vincent and Nicolas, and we didn't see any change in the Loop noise signal.
we saw only a peak comb at 10Hz on the Loop noise signal when the septum is ON. the amplitude of the peaks is then related to the voltage on the septum.
but we still don't see any noise correlation on the PZT signal.

the global conclusion about CEM noise is it is not related to laser PZT noise.

if the 20Hz oscillation is coming from a mechanical unstability in the CFP, we should be able to trigger it by moving the longitudinal motors of the CFP.
we tried also to move the MOT.03 and MOT.06 motors and we didn't see any clear correlation with the 20Hz oscillation.

the 20Hz oscillation could come from the CTA pressure variations on the housing => we can try to trigger the oscillation on the housing.

this morning, with Daniele, we checked the amplifier power, right after the CVBG (the power meter has to be placed on a metal plate above the large table hole), and just at the input of the FP cavity, after the 1/4 and 1/2 waveplates (the power meter has to be placed on flat beam dump+ Thorlabs beam dump + V metallic mount to be at the right height).

we compared with the power measured the 9th of september : https://elog.lal.in2p3.fr/FPC/THOMX+commissioning/356

the 3 collumns are the measurement close to the CVBG on 9th of september / same position today / just befor the FPC today

amplifier ratio (%)                 power after compressor (W)                 (new) power @ CVBG   (new) power @ FPC      ratio FPC/CVBG power (%)
10                                               0.91                                                  0.93                                    0.83                                       89.2
20                                               8.6                                                    8.6                                      8.0                                         93.0
30                                              16.7                                                  16.9                                    15.8                                        93.5
40                                              25.5                                                  25.6                                    24.0                                        93.7
50                                              34.5                                                  34.6                                    32.5                                        93.9
60                                              42.5                                                  42.5                                    39.5                                        92.9
70                                              50.0                                                  50.0                                    45.0                                        90.0

we observed with the viewer the beam on the powermeter.
at 70% of amplifier ratio, the beam size is as big as the powermeter detector.
then, the 93% to 90% transport efficiency drop could come from this "too small" powermeter detector.

we observed also at this power ratio (70%) that the 1/4 and 1/2 waveplates were not perfectly centered and we burn a part of the platic mount at this power.

we did a long term run (25 mn) with the powermeter located at the FPC position at 33% amplifier ratio.

the initial power was 18W .
then, it goes to 18.5W in 10 minutes, then 5 minutes later, it goes to 18.3W and stay stable until  the end the run.

I put back and aligned the 1/2 waveplate only and I get 71kW max after its optimization and optimizing the CEP and alignment (without walking procedure).
this waveplate change a lot the reflected power seen on the CH2 of the scope.

to be continued this afternoon...

this afternoon, we put back the 1/4 and 1/2 waveplates and after a long alignment/angle tuning/CEP optimization process, we hardly got 80-81kW in the cavity for 33% amplifier ratio. the transmission photodiode is then ~ 7.5 divisions (500mV/division) on the scope.

BUT during the 1/2 and 1/4 waveplate angle tuning process, we clearly saw:
- a reflection signal level which is very sensitive to the input polarization
- a coupling which can be almost zero with ~70kW inside the cavity
- the more important: ~9.5 divisions (500mV/division) on the scope with only 70-75kW in the powermeter
        => which device should we believe ?

the problem is all these photodiodes (reflection, error signal, transmission) and powermeter are aligned with mirrors which seem to be sensitive to the polarization state of the beam... and for the "output" beam side of the cavity, we cannot remove the mirrors because of the mechanics of the cavity which prevent a direct view of the ports. for the "input" beam side of the cavity, the output port is used for the cavity beam size measurement with a Basler camera.

we have to think to how to solve this issue !

here are the (good) lock parameters used this morning.

for the RF/FPC lock, the 33MHz beating signal used to select the right bucket is 1Vpp
=> beating signal : V0 . sin(phi) with V0=0.5V.

to discrimate a 500MHz bucket, we need to get dV < V0 dphi.

dphi = 2pi / 15 = 420 mrad => dV < 0.2 V => dV < +/- 0.1V

we used dV = +/- 0.02V but perharps we can relax the constraint.

we also reduced the RF scanning speed at 0.1V/s to let the system find the right phase when the system is slowly drifting.

Today with Daniele and Alice, we operated to cavity.
we obtained 84kW for 33% of amplifier ratio.
we had to tune the CEP @ -565µm and the FP-cavity alignment.

then we locked properly the FP-cavity on the ring RF frequency.
we quite easily relock with the correct phase when we are loosing the lock.

the ThomX machine was running during these 2 locks, so we are ready for doing X-rays again.

This morning, I wanted to test quickly if the Smaract motors can be used in open loop instead of closed loop or in piezo scan.

the goal is to do very fine steps without to much vibrations (like with piezo scan mode) but with the full motor range (the piezo scan mode has a very limited range).

I can check what happens to the 33MHz beating frequency between the laser and the RF frequency without the laser amplifier or the lock of the FP-cavity.
1Hz of beating freqency variation is equivalent to 270nm of round-trip length, which is 135nm of motor displacement !

=> the full range of the piezo scan mode is difficult to estimate because the measurement sensitivity is not good enough but around 5Hz.

=> 1350nm in closed loop is equivalent to ~ 10Hz => 135nm is equivalent to 1Hz => ok

=> 1 step in open loop is equivalent to ~ 10Hz !!! => this is a way too coarse tuning !!!! => cannot be used unless one finds a way to set the motion differently in the settings parameters.
but usually, the settings parameters are used only to tune the speed, not the step size.

This afternoon, we scanned the optical table vertically with the hexapod in asynchronous mode to find its optimum position, looking at the X-ray production.
then, we searched for the correct bucket and phase in the bucket thanks to the Kevin script on the 500MHz and the 33MHz phases.

we got relatively easily some stable X-rays.
on the gain "0" on the current amplifier of the X-rays photodiode, we got 15 000 pA (380k Xrays / pA => 5.7.10^9 Xrays).
but we saw, when the cathode charge was fluctuating, that we could be saturated above 20 000 pA !

the power in the cavity was ~84kW after CEP and alignment tuning.

the command to launch the X-rays measurement window is:
taurustrend -r 100 /XLI/OP/TMD.01/I1

Today, after setting the locking parameters, I got 80kW in the FPC for 33% amplifier ratio after CEP tuning (Smaract CH2 ~ -423.5µm) and alignment.

maybe the alignment has to be improved by some walking procedure.

this morning, I did some walking procedure and I got 82kW in the FPC with 33% amplifier ratio (after CEP optimization too).
but when I move the FP cavity motors to adjust the frequency, I cannot keep this power and it is reduced.
could it be we get a stronger correlation between axis than before in the mechanics has more rust than before ?

I'm able to keep the power quite easily with a stable phase related to the 33MHz RF generator,
so, we are ready to produce X-rays again.

we could do also a measurement of the amplifier power vs ratio, as maybe it reduced a bit which could explain why we have this small power drop compare to before.

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

On Friday 11th of October, due to the Yvette flooding, all the AC power of ThomX have been shut down.
After the shutdown, I had to restart the Onefive oscillator but the laser modelock was lost.
I had to do a step of 1mm at 10mm/s with the Smaract motor on the rep rate channel (CH1)

After the step, the laser was mode-locking again, and I put it back in the original position at a much lower speed, ~10µm/s, to prevent a new modelock loss.
the power detected by the laser amplifier software is still above 3mW! => OK

Surprisingly, the laser amplifier software is not able to detect the oscillator frequency.
hopefully, the internal photodiode of the oscillator is sent to the CH4 of the R&S scope (192.168.229.21)
and we measured a correct 30ns of period, corresponding to 33MHz.

Because all the safety procedures are not fulfilled, the laser amplifier is not granted to start.
Maybe it is the Reason for the lack of measurement => to be verified later
 

This morning, I verified the reason why the seeder frequency was not displayed on the amplifier software screen:

one needs to start the amplifier (even at 0%) to see the seeder frequency !!!
now, we have 33.371MHz as expected ! => OK

the last thing to do is to tune again the PDH demodulation frequency, as the generator has been shut off during the AC shut down.
 

After the new Yvette flooding of the last week and the consecutive AC-shut down, I restarted this morning the laser with the same procedure (step of 1mm at 10mm/s with the Smaract motor on the rep rate channel (CH1)).

now, we have again 33.371MHz and 3.1mW input power as expected ! => OK

the last thing to do is to tune again the PDH demodulation frequency, as the generator has been shut off during the AC shut down.

For the modulation/demodulation generator for the PDH signal,
after a power shutdown, on can :
1) restart the generator to get the correct parameters:
CH1:3Vrms on 50 ohms @ 8.4MHz (demod)
CH2: 100mVrms on 50 ohms @ 8.4MHz (modulation on EOM)

2) do an "Align phase" on the generator

3) put 270° on CH2 (0° on CH1) to get the max Error signal
and use a "positive" sign on the Laselock : cf https://elog.lal.in2p3.fr/FPC/THOMX+commissioning/365

Yesterday Ronic and I worked on the high laser power measurements with the Vertical set-up of the Focus Tunable Lens. We went upto 38W@4 dpt at the begining and then also changed the focal power at 38W.

Observation:

1. We observed nice rings @38W 4dpt, maybe it hits some optics we have to check.

2. We also observed flactuations of power for two adjacent index of the beam profiler when we increase the laser power, which we need to understand.

3. We could see that the vertical deformation is not present for this set-up, we could remove the effect of gravity by this set-up.

this morning, I try to find a new region for MOT.03 and MOT.06 where we can move them without unlocking the cavity.

I started from the position:
MOT06 : ~ -785 000
MOT03 : ~ -200 000

and I do -10 000 steps (dz = 10k x 6nm = 60µm) at a time on both motors.
previously a good region for MOT.06 was -900 000 !

I moved also the laser cavity by 40µm to cancel the beating with the RF frequency.

MOT06 : ~ -795 000
MOT03 : ~ -191 000

Max power after optimazing the CEP ~ 65kW => I need to realign => 78kW
I need to increase the D parameter on the PID to compensate the (85kW / 78kW ratio).

I changed the MOT.03 and MOT.06 speed to 30steps/s => it seems a bit better.
but I still see some lock losses during a move.

.... to be continued...

this morning with Daniele, we did a quite long run with this motor position and it seems we don't lose the lock too much.

the motor positions are:

MOT.03 (M4): -186 500 steps

MOT.06 (M1): -797 500 steps

we got 85kW after CEP optimization and rough alignment optimization.

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

this morning, we tried to find the origin of the 20Hz oscillation.

- we switched OFF the laser Smaract motors controller => no change

- then, we addionally disconnected the FP-cavity PZT cable from the Laselock (we put a charge of 1kohm) => no change

- then, we switched ON the laser Smaract motors controller and switched OFF the FP-cavity motors controllers => no change

in conclusion, we don't really know where this instabillity comes from.
the amplitude is roughly 1Vpp (when the oscillation is at its maximum) on the laser PZT <=> length oscillation of ~20nm pp

could it come :
- from the air cooling regulation with pressure variation ?
- from vibrations of the hexapod below the table ?
or is it from inside of the laser or FP cavities ?

see these posts for the first measurements on this issue: https://elog.lal.in2p3.fr/FPC/THOMX+commissioning/257

this afternoon, we did 2 tests to better understand this 20Hz oscillation:

- we locked the amplified laser directly to the 500MHz ring reference oscillator, without any intermediate locking to the FP-cavity => no change
the 20Hz oscillation is still present in the correction signal of the laser PZT.

- we switched OFF the controller of the hexapod => no change.

conclusion:
the 20Hz oscillation is coming from the laser cavity
or is coming from "outside" and could be measured, maybe at a higher level, with an external "noises & vibrations measurement system".

yesterday I did 2 tests to try to understand the origin of the 20Hz oscillation which is dominant in the remaining 10-20ps rms jitter between the transmitted pulses and the RF reference generator.

10ps rms jitter is equivalent to phase jitter dphi = 2*pi*f0*dt = 2mrad rms @ 33MHz or 30mrad rms @ 500MHz.

with V0 = 1Vpeak of beating signal amplitude, the equivalent rms beating voltage is dV = V0 * sin(dphi) ~ V0 * dphi = 2mV rms @ 33MHz or 30mV rms @ 500MHz

1) I did a beating between the internal photodiode of the laser with an external 33MHz oscillator (the photodiode is too slow to use higher harmonic).
the difficult part is to see the 2mV rms noise on a 2Vpp oscillating signal, so I locked the external 33MHz reference oscillator with the beating signal => see first plot.
there is no trace of 20Hz oscillation in the beating signal => the lock is too good and removed the oscillation ?

2) I did a beating between the photodiode in reflection of the FP-cavity (so the signal is not coming only from the oscillator but is going also through the Alphanov amplifier) with the 500MHz RF Ring generator.
I cannot the lock the generator anymore, so the measurement is done in open loop. I adjust the laser Frep with the motor to try to cancel the beating frequency => see 2nd plot
there is no trace of 20Hz oscillation in the beating signal => it is in contradiction with the previous post : "conclusion: the 20Hz oscillation is coming from the laser cavity" ?!?

maybe we need a more complex measurement scheme with the possibility to measure in the same time the 10-20ps rms jitter coming from the locked FP-cavity transmitted signal/500MHz Ring generator
AND the beating signal between the laser or amplifier with 500MHz local reference generator... to be done...

what does this 10ps phase jitter mean in term of cavity length variations ?

L = L0 + dL sin(2pi fm t) = L0 (1 + dL/L0 sin(2pi fm t))

F = c / L ~ F0 - F0² dL / c sin(2pi fm t) with F0 = c / L0

d/dt(phi) = 2pi F => phi = 2pi F0 t + F0² dL / (c fm) cos(2pi fm t) => dphi = F0² dL / (c fm)

dphi = 2pi F0 dt => dL = L0 * 2pi fm dt

dt rms = 10ps @ fm = 20Hz of modulation frequency <=> dL rms = 10 nm (L0 = 9m)

measure to be done next week to check the 20Hz noise on the laser amplifier signal:

- install a DET10 in reflection of the FP-cavity to get a high BW and measure the 500MHz harmonic.
- do the beating with the 500MHz Ring RF generator
- with the laser motor try to be close to the 500MHz Ring RF frequency => beating frequency below 1kHz
- send the beating signal to some RF spectrum analyzer to use its large dynamic range.

for example, with the Siglent RF spectrum analyzer, it is possible to detect easily a peak @ -96dBm <=> 3.5µV rms
so, one should be able to make the measurement @ 500MHz or even @ 33MHz even if the phase sensitivity is lower :

for example V0=100mV peak beating signal @ f0=33MHz should produce a 20Hz noise signal of:
dV ~ V0 * dphi = V0 * 2*pi*f0*dt = 200µV rms with jitter dt=10ps rms

could it be possible this 20Hz oscillations comes from anouncements in the bunker, puting the housing+table in vibration ?
(there are such anouncements during restricted access) => to be asked to Harold

the CVBG of the compressor module seems to have an issue.

here is the plan of the work :

1) faire des résonances avec la CFP
2) ajuster les iris d'alignement du faisceau de l'ampli pour être sur de ne pas perdre la référence de l'axe de la CFP

3) installer des wedges haute puissance à proximité du compresseur + beam profiler
4) verifier la forme du faisceau au beam profiler en fonction de la puissance de l'ampli

5) ouvrir le boîtier du compresseur
6) prendre des images du boîtier à la caméra thermique en fonction de la puissance

7) éventuellement shunter le 2e CVBG avec un D shape et regarder le mode et caractéristique en sortie d'ampli.
8) ajuster l'injection dans le premier CVBG ou le second ou les deux en fonctions des résultats précédent

here are some useful logbook posts:

D-shape + images thermiques du compresseur qui peuvent servir de référence :

https://elog.lal.in2p3.fr/FPC/THOMX+commissioning/147

https://elog.lal.in2p3.fr/FPC/THOMX+commissioning/150

post des images du faisceau en fonction de la puissance de l'ampli :

https://elog.lal.in2p3.fr/FPC/THOMX+commissioning/135 (et autres posts du fil)

https://elog.lal.in2p3.fr/FPC/THOMX+commissioning/195 (et autres posts du fil)

1) this morning, I aligned to CFP to get back 82kW in the cavity for 33% of amplifier ratio.
thus, we can ajust the iris positions on the optical table to fix the CFP optical path before touching the CVBG.

2) we aligned the 5 iris. all of them were misaligned by 1-2mm, principaly vertically (maybe because we had to change the CFP frequency some time ago to match the new RF frequency?).

3) we opened the compressor box and found out the beam on the last mirror was really on the border => we have to move it.

=> we recorded several beam profiles at 20-70% of amplifier ratio (see images before realignement)
above 50% of amplifier ratio, the beam is deformed.

=> we realigned the 2 last mirrors of the compressor and compensate the axis displacement with the 2 inches injection mirrors at the output of the compressor to get back the telescope axis.
amplifier ratio (%)                 power after compressor (W)
0                                                 0.286
10                                               0.91
20                                               8.6
30                                              16.7
40                                              25.5
50                                              34.5
60                                              42.5
70                                              50.0
80                                              57.0
90                                              64.0
100                                            70.0

small power drop for ratio < 40% compared to previous measurements : https://elog.lal.in2p3.fr/FPC/THOMX+commissioning/133

the power is back => OK ! :-)))

we took some images with the beam profiler at high power after the realignement (see images after realignement)

tomorrow, we have to realign the amplifier beam axis to the CFP axis.

this morning with Daniele, we realigned the amplifier beam axis on the iris position.
it was pretty fast an easy => we got rapidely some resonance and we locked back to 87kW @33% amp ratio after tuning CEP and alignment.

we tried to play on the L-shape but we didn't a clear effect.

we also played on the 1/2 and 1/4 waveplates to tune the polarization.
we see very clearly the locked reflected signal changing without almost changing the transmission !

Aurélien suggested to slightly focusing the beam in the DET36 photodiode to have a better estimation of the coupling.
presently, the beam is clearly larger than the DET36 photodiode area which artificially increases the measured coupling.
(I cannot use a DET100 because I need 500MHz BW to get some RF signal for beating with the 500MHz reference signal).

I added a +75mm lens in front of the DET36 reflection signal photodiode => now, the beam is rougly 1-2mm diameter, centered on the DET36.
when I optimize the alignment and the CEP, I get 86-87kW in the CFP and 45% coupling => cf plot

end of the CVBG issue posts.