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: |
|
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: |
|
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: |
|
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: |
|
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: |
|
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.
|
|
|
|
|
|