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.
| Ronic Chiche wrote: |
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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.
| Ronic Chiche wrote: |
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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.
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