This afternoon, we installed a new M1 mirror, the only one for which the box was not already opened.

as the mirror should be "brand new", as the LMA has packaged it, we decided not to clean it with ultra-pure water and to install it out of the box.

we realigned it with the iris previously installed for that purpose.

primary and turbo pumping are in process. one has to wait until the vacuum level is low enough to start the ionic pumping and to reopen the isolating valve.

let's cross our fingers...

this morning, with Daniele, we took some images of the M1 mirror HR surface :

1- large image span of the mirror surface (~center) before being cleaned :
one can see a lot of spots

2- zoom in on some spots in the middle of the mirror.
Daniele saw 2 suspicious spots among many.
difficult to be sure if it's only some dust or if it's some damage

3- large image span of the mirror surface after being cleaned with the spin coater machine
only the 2 suspicious spots remain, all others have been washed.

4- zoom in on the 2 suspicious spots
if one compares with the image before cleaning, one can see the spots are much larger

5&6- zoom in on the 2 suspicious spots separately after a 2nd cleaning process with the spin coater,
it seems the spots are even a bit larger than before

conclusion : it seems that these spots are presently showing some damage on the mirror surface.
it is strange that there are 2 in the same time.
one possible explanation is that, as we had to move the z-axis motor before, and we know that the mechanics are rusty, it's possible that it released some metallic particles on the mirror surface.
and 2 were in the beam area.... 

after trying to increase the power and after moving S3 to try to change the size of the beam on the mirrors, the FPC power suddenly droped.

so, we need to remove M1 to check if it has been damaged.

we placed an iris in reflection of the FPC to keep the alignment for the new mirror M1.
the alignment has been done with an iris and the amplifier at 10% (to get a quite round beam) and the beam profiler.
once the iris is almost closed, the alignment is good, using the diffractions rings.

Last friday, with Daniele, we did some realignement on the 2nd CVBG of the compressor : the beam shape seems better, now.

this morning, we checked that the injection path (periscope and injecton mirrors) is not sensitive to the polarization state of the beam.

we checked also the power at the input of the FPC for 70% amplifier ratio : 40W !

so, with 100% coupling, we can only expect 400kW in the FPC !

this morning with Daniele, we set the amplifier ratio to 33% => 97kW

then, we set the amplifier ratio to 50% => 124 kW (position of the diffuser on Axis 18 : +11775)

we changed the waveplates axis => no effect

we changed the position of the L-shape :
- lower button / clockwise / 1/20 of a turn (one has to decrease the laser motor position to compensate) => no effect but the misalignement is very sensitive for this axis

- upper button / anti-clockwise (the Lshape position is getting down) / we went to the limit (not very sensitive in alignment) => no effect ! (no beam cut nor HOM apparition)

=> conclusion : now, the L-shape is badly positionned (it's off the beam) but it cannot be the reason for a lake of power in the cavity.

PS : the lock seems very stable for long term (~ 130kW)

I installed a stronger optical filter on the reflection photodiode and loaded it on 1kOhms.

70% amplifier ratio => 575 mV => 575 µA => no more photodiode linearity issue

amplifier ratio (%) => Vr unlocked (mV)
10 => 14
20 => 156
30 => 295
40 => 412
50 => 491
60 => 545
70 => 575

to be compared to : https://elog.lal.in2p3.fr/FPC/THOMX+commissioning/378

=> still a big discrepency => could we have some clipping in the reflective wedge ?
=> I tried in realigning the wedge but got roughly the same result.
=> could it be the size of the PhD (DET36 presently) ?

=> we should also check the amplifier power at FPC input before increasing power

new power increase after alignment of the waveplates and iris.

amplifier ratio (%) => FPC cavity power (kW) => FPC cavity coupling (%) => Vr unlock (mV)
33               => 98                      => 57              => 260
35               => 101                     => 56             => 280
40               => 107                    => 53             => 320
45               => 109                    => 49             => 354
50               => 114                    => 48             => 381
55               => 114                    => 44             => 403
60               => 110                    => 40             => 420
70               => 100                    => 31             => 453

We still observe a discrepancy between the measured and estimated input power (using the unlocked reflection photodiode) as the amplifier ratio increases.
But this time, the estimated FPC power is also badly estimated.
So, it is possible that the reflection photodiode is operating in a nonlinear regime, as 300 mV across 50 Ohms is equivalent to 6 mA, which may be too much to remain in the linear regime.
It could be interesting to reduce the photodiode's power (add an optical filter) and use a 1k-Ohm load impedance.

today with Alice and Daniele,

we checked the distance of the optical setup :

from the amplifier output (the fiber output) to the 2nd lens (+200 mm) :
131.5+41+17+28 cm = 217.5 cm

from the 2nd lens (+200 mm) to the FP cavity window :
133+97+70+14+22 cm = 336 cm

1st lens : -100 mm
2nd lens : +200 mm
distance between them : 11 cm

we checked also the alignment of the different iris and waveplates of the optical setup :
we had to realign a little bit the 2 waveplates.
after the realignment, we obtain the 96-97kW in the FPC for 33% of amplifier ratio !

Last Friday, we tried to increase the FP-cavity power by just increasing the amplifier ratio from 35% to 70%.

It took a bit longer than expected because it started with the surprise of finding our entire setup powered off…
The power had tripped, and the switch that allowed us to remotely reset the power supplies had been damaged.
The switch was bypassed, and the instruments restarted → OK.

As usual, the locks were pretty unstable (as has been the case for several weeks), and we couldn’t hold them for more than 10–20 seconds…
So I removed the HV amplifier between the LaseLock and the laser PZT.
Since the Smaract MCS2 controller is much less noisy than the MCS1, we can use it directly without unlocking the cavity or going through "piezo-scan" mode.
So basically, having a larger range on the laser PZT is less useful.
Result: perfectly stable locks in the short term (as before installing the amplifier) AND in the long term as well… no more random unlocks!!!
So the amplifier must have been picking up parasitic noise that was being reinjected into the loop and causing regular unlocks… it works much better now! :-)

Actual power ramp-up was done entirely from the control room:

Previously measured relation between amplifier ratio and input power to the cavity:

Amplifier ratio =    10     20     30      40      50      60     70 %
Amplifier Pin =     0.8     8     15.8     24    32.5    39.5  45 W

We performed 7 measurement points:

1. Amplifier ratio = 35%
   Vr unlocked = 248 mV
   Vr locked = 103 mV
   Coupling = 58.5%
   Stored power = 90 kW
   Vpdh = 50 mV rms
    
2. Amplifier ratio = 40%
   Vr unlocked = 282 mV
   Vr locked = 130 mV
   Coupling = 54%
   Stored power = 97 kW
   Vpdh = 52 mV rms
    
3. Amplifier ratio = 45%
   Vr unlocked = 311 mV
   Vr locked = 152 mV
   Coupling = 51%
   Stored power = 103 kW
   Vpdh = 55 mV rms
    
4. Amplifier ratio = 50%
   Vr unlocked = 328 mV
   Vr locked = 171.5 mV
   Coupling = 47.7%
   Stored power = 103 kW
   Vpdh = 51 mV rms
    
5. Amplifier ratio = 55%
   Vr unlocked = 353 mV
   Vr locked = 204 mV
   Coupling = 42%
   Stored power = 96 kW
   Vpdh = 51 mV rms
    
6. Amplifier ratio = 60%
   Vr unlocked = 375 mV
   Vr locked = 227 mV
   Coupling = 39.5%
   Stored power = 95 kW
   Vpdh = 53 mV rms
    
7. Amplifier ratio = 70%
   Vr unlocked = 396 mV
   Vr locked = 272 mV
   Coupling = 31.3%
   Stored power = 82 kW
   Vpdh = 53 mV rms

Normally, the unlocked Vr voltage should be proportional to the incident power on the cavity.
But it clearly isn’t at all!

We need to verify that this photodiode remains well aligned as power increases.
Or whether we might be clipping on a lens edge as the power increases.
Or whether the power still follows the amplifier ratio/power relation measured several months ago.
To be checked during the power ramp-up from the bunker.
We didn’t go above 103 kW!!! :-(((

I think the main reason is that we are probably hitting a mount edge, and the coupling drops so quickly that it dominates
→ so we absolutely need to redesign a proper telescope.

We also took beam images for different Pin values, but since the power in the cavity barely changes, it’s not very informative.

The last plot shows that the signal from the reflection photodiode indeed corresponds to the incident power in the cavity.
There is a strong chance we are hitting something when changing the power… to be checked in the bunker!!!

Have a nice weekend

Daniele & ronic

today, I installed a laser dump just before the telescope to avoid any high power (50W instead of 17W usually) issue in the injection line.
last time, we saw some plastic mounts of the polarizers slightly burnt because of some small misalignment.
I used a thorlabs LB2 (see picture) which is able to manage 80W CW or 25J/cm2 pulses => this is OK in both cases : 50W CW / 1.5µJ/pulse for ThomX.

I started the laser amplifier at 70% which produces 50W at the amplifier output and 45W at the input of the FPC.

start : 15h10
immediately, the Temp Amp1 increases from 26°C to 30°C
the Temp Amp2 stays around 26°C
PD_OUT = 79,2W

start + 5-10 min
Temp Amp1 : 31°C
Temp Amp2 : 27°C
PD_OUT = 79,2W

start + 30 min
Temp Amp1 : 31,6°C
Temp Amp2 : 27,5°C
PD_OUT = 79,2W

start + 1h00
Temp Amp1 : 31,6°C
Temp Amp2 : 27,6°C
PD_OUT = 79,2W

start + 1h30
Temp Amp1 : 31,7°C
Temp Amp2 : 27,7°C
PD_OUT = 79,2W

start + 2h00
Temp Amp1 : 31,7°C
Temp Amp2 : 27,7°C
PD_OUT = 79,2W

start + 2h30
Temp Amp1 : 31,7°C
Temp Amp2 : 27,7°C
PD_OUT = 79,2W

This morning, I installed a high-voltage probe (1:1000) on the AC-line to see if one could detect a correlation between lock losses and AC-line voltage variations.

I observed many lock losses but without any variation or correlation of the AC-line signal (scope set in "peak detect" with "envelope" arithmetics).

see attached figure.

yesterday, in the same conditions, we had so many locking issues... exactly in the same way than before. :-(
so we still have "locking issues" depending on something we didn't find...

today, we removed the "1/2 voltage divider" before the PZT amplifier to get back the full dynamic.
we have a little bit more noise and we lose some power on transmission (85kW instead of 90kW) but it worked pretty well.
we had quite long X-rays runs ~ 20 minutes without any lock losses => see the picture.

but we have to keep in mind that maybe it was just a "good" day and an another day can be "bad".
we still have to understand where do these perturbations come from.

the good news is we brought back the previous setting of the FPC.

since several days, we see that the locking is more and more unstable and the lock duration was sometime less than 20-30 seconds !

1) I tried to optimize the feedback loops

I discovered that the gain on the fast loop on the laser EOM was very low and was almost uneffective for the global stability of the lock (I can remove the cable of the HV to EOM and it does not change the stability of the signals).
when I tried to increase this loop gain in open loop for the PZT loop, I clearly saw an improvement of the transmission signal stored in the cavity.
but when I close the PZT loop, it does not help to get a better locking.
so, at the end, I cancel this loop gain (HV amplifier for the EOM is OFF !) and only the slow feedback loop on the PZT is working.

I reduced the by a factor 2 the range on the PZT loop side to reduce the noise due to the amplified Laselock (voltage divider 1/2 before the HV amp for the PZT).
and I switched off the laser motor controller (Smaract MCS).
after optmization of the PID parameters, I was able to get back the 90kW we had in the past for 33% laser amp ratio and with a very good stability :
the transmission signal is a line and the reflection signal is almost a line too.
in this condition, I seems that I can lock the laser and the FPC indefinitely.

2) issue with Smaract controller

I put back the Smaract controller only for the CEP channel => one can clearly see a bit more noise on the PDH signal but the transmssion and the reflection signal stay almost the same with a very good stability.

then, I put back the Smaract controller for both channels (CEP and laser cavity length) => the lock was very bad, even after a PID optimization despite the fact it was a "Low Vibration" (LV) Smaract MCS controller.

we tried to change the 3-channels LV controller by a standard 3-channels (not LV) spare controller => it was OK for the CEP channel but not good at all the laser cavity length channel => very noisy.
so, we kept this standard controller for the CEP channel and we took 1-channel LV spare controller for the laser cavity length channel => it was ok. no more additionnal noise and we can work without delock in piezo-scan mode.

important parameters :
I used 1ms for hold time in the Smaract controller configuration.
I used 1V/s in piezo scan mode for the speed => it does affect the noise level when the piezo is moved !

3) IP Smaract controller parameters :

I used the MCSNetworkInterfaceConfig.exe software to configure both IP addresses of the 2 controllers.
it's easy, one just has to choose the options.

the IP address for controller ruling the laser cavity length is : 192.168.1.200:5000
the IP address for controller ruling the CEP is : 192.168.1.201:5000

4) final long run test

We did a 1/2h run test to check how many lock loss one gets... see the picture.
we had some few lock losses (with the RF feedback lock ON too) but most of the time, the RF phase was not lost and the X-rays should be continued to be produced.
a test should be done tomorrow.

we did some tests with Marie to make some vibrations on the door.
below, I exhibit some pictures of the scope with the accelerometer plugged on it without or with noise...
this level of noise is not able to make the FPC loosing the lock.
even when saturating the noise signal on the accelerometer, the FPC is not loosing the lock all the time.

then, when a day is very windy, it's possible it could have some effect, but for a normal day, it's seems very doubtful that is the reason...

After this observation, we did a test with Daniele to try to correlate the road traffic in front of the Igloo with the lock losses observed on the FPC.
We didn't see any clear correlation. Cars or buses are not the direct origin of the FPC lock losses... only when some heavy load is hitting the building, we observed a clear correlation.

So, we still observed a lot of FPC lock losses when the day is windy... 
One possible cause could be the large door of the igloo (~20 m²) hitting the Igloo when the day is windy.
I installed the accelerometer on the rail on the bottom of the large door to see if there is any correlation.

At the end of the day, we found out what was the origin of this noise : some road renovation work with jackhammer and road roller just at the entrance of the "Igloo".

this origin was 100% correlated with a large increase of the accelerometer signal.
but we clearly saw that the FPC is much more sensitive than the accelerometer... the signal can have a small increase or just one peak and the cavity lock is lost.

then, we can make the assumption that all the "high frequency noise" which produces some lock losses could come from acoustic noise due to the road traffic or from the equipments in the bunker itself.

Today, the lock of the FPC was particularly bad (maybe the worst ever seen), with a lot of high frequency noise.
the lock was impossible during several minutes !

we tried to switch off all the equipments of the machine, one by one without any effect on the lock.

at the end, we looked at the accelerometer installed inside the housing to check if there was some correlation.
and for the 1st time we clearly saw a 100% correlation beween the accelerometer signal with a noise oscillating above +/-300mV
but we didn't find the origin of this noise.

This morning I did a phase alignment on the PDH signal generator (Rigol DG4102)
this procedure ensure that both phases of the sine wave signals are aligned before finding the correct phase for maximizing the error signal.

so, from now on, in case of power shut down, one just need to :

1) do a phase alignment

2) put the correct phase number on the 2 channels according to the picture (if not automatically done by the generator itself).

340° on channel 1
270° on channel 2

1) and 2) can be done in any order.

the 33MHz/500MHz RF frequencies from the Ring seems different from the previous state (maybe working at an energy of 50MeV instead of 70MeV which was the previous energy ?).

so, I let the FPC at the present position and wait to discuss if it is necessary or not to move the FPC motors for the correct energy...

this morning, I restarted all the equipments of the FPC.

everything was fine after being able to get back the correct PDH phase between modulation and demodulation...I got 88kW with 33% amplifier ratio after basic alignment and CEP tuning.

the Pico1 server used for the X-ray photodiode TMD.01 doesn't want to start...
I tried with Astor. the server start to run (red => blue => green colors)
but when I start the Jive panel, it gets down again (red color)... to be solved