Power shut down on September 23th, posted by Ronic Chiche at ThomX igloo about mechanics | lasers and optics | vacuum | detectors and electronics | cabling | software | utilities
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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. |
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Power shut down on September 23th, posted by Ronic Chiche at ThomX igloo about mechanics | lasers and optics | vacuum | detectors and electronics | cabling | software | utilities
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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... |
Power shut down on September 23th, posted by Ronic Chiche at ThomX igloo about mechanics | lasers and optics | vacuum | detectors and electronics | cabling | software | utilities 
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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 : |
High frequency noise, posted by Ronic Chiche at ThomX igloo about lasers and optics | detectors and electronics
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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. |
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High frequency noise, posted by Ronic Chiche at ThomX igloo about lasers and optics | detectors and electronics
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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. |
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High frequency noise, posted by Ronic Chiche at ThomX igloo about lasers and optics | detectors and electronics
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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. |
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High frequency noise, posted by Ronic Chiche at ThomX igloo about lasers and optics | detectors and electronics
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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. |
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Noise issue, posted by Ronic Chiche at ThomX igloo about lasers and optics | detectors and electronics
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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 |
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Noise issue, posted by Ronic Chiche at ThomX igloo about lasers and optics | detectors and electronics
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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. |
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High frequency noise, posted by Ronic Chiche at ThomX igloo about lasers and optics | detectors and electronics
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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" |
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Laser Amplifier used at 70%, posted by Ronic Chiche at ThomX igloo about lasers and optics
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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 |
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Increasing the FP-cavity power , posted by Ronic Chiche at ThomX igloo about lasers and optics 8x
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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. |
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Increasing the FP-cavity power , posted by Ronic Chiche at ThomX igloo about lasers and optics
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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) : |
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Increasing the FP-cavity power , posted by Ronic Chiche at ThomX igloo about lasers and optics
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new power increase after alignment of the waveplates and iris.
amplifier ratio (%) => FPC cavity power (kW) => FPC cavity coupling (%) => Vr unlock (mV)
33 => 98 => |
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Increasing the FP-cavity power , posted by Ronic Chiche at ThomX igloo about lasers and optics
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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) |
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Increasing the FP-cavity power , posted by Ronic Chiche at ThomX igloo about lasers and optics
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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 |
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Increasing the FP-cavity power , posted by Ronic Chiche at ThomX igloo about lasers and optics
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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 ! |
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removing of the M1 mirror, posted by Ronic Chiche at ThomX igloo about mechanics | lasers and optics | vacuum
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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. |
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removing of the M1 mirror, posted by Ronic Chiche at ThomX igloo about mechanics | lasers and optics | vacuum 6x
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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 |
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removing of the M1 mirror, posted by Ronic Chiche at ThomX igloo about mechanics | lasers and optics | vacuum
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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. |