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.
| Ronic Chiche wrote: |
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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...
| Ronic Chiche wrote: |
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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
| Ronic Chiche wrote: |
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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.
| Ronic Chiche wrote: |
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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.
| Ronic Chiche wrote: |
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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.
| Ronic Chiche wrote: |
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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.
| Ronic Chiche wrote: |
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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
| Ronic Chiche wrote: |
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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
| Ronic Chiche wrote: |
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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.
| Ronic Chiche wrote: |
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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
| Ronic Chiche wrote: |
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we observed that :
- the MOT.03 motor always exhibits some perturbations on the transmitted, reflected and PZT signals (see 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)
| Ronic Chiche wrote: |
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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
| Ronic Chiche wrote: |
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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.
| Ronic Chiche wrote: |
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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.
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