the RF frequency is now 500.1003MHz which is equivalent (if divided by 15) to 33.34002MHz.
the frequency has to be changed by ~2kHz @33MHz <=> ~550µm /2 for one motor.
I changed the laser and the FP cavities frequency.
for the laser frequency, the smaract motor CH1 is at 1.500627m.
for the FPC frequency, the plane mirror motors are at MOT.03= - 123 130 steps and MOT.06
BE CARREFUL, when the offset frequency is large, as we measure it on a scope with a beat frequency, if the scope window is too large,
one gets some stromboscope effect and one measures a lower frequency depending on the number of points in the window.
we got ~81kW for 33% amplifier ratio
| Ronic Chiche wrote: |
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this morning, I did some walking procedure and CEP alignment to get ~80kW in the FPC with 33% amplifier ratio.
we have to check if this power drop comes from:
- a laser amplifier power drop
- or related to some cavity axis shift which could change the cavity gain due to L-shapes
| Ronic Chiche wrote: |
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this morning, I did some walking procedure and I got 82kW in the FPC with 33% amplifier ratio (after CEP optimization too).
but when I move the FP cavity motors to adjust the frequency, I cannot keep this power and it is reduced.
could it be we get a stronger correlation between axis than before in the mechanics has more rust than before ?
I'm able to keep the power quite easily with a stable phase related to the 33MHz RF generator,
so, we are ready to produce X-rays again.
we could do also a measurement of the amplifier power vs ratio, as maybe it reduced a bit which could explain why we have this small power drop compare to before.
| Ronic Chiche wrote: |
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Today, after setting the locking parameters, I got 80kW in the FPC for 33% amplifier ratio after CEP tuning (Smaract CH2 ~ -423.5µm) and alignment.
maybe the alignment has to be improved by some walking procedure.
| Ronic Chiche wrote: |
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This afternoon, we scanned the optical table vertically with the hexapod in asynchronous mode to find its optimum position, looking at the X-ray production.
then, we searched for the correct bucket and phase in the bucket thanks to the Kevin script on the 500MHz and the 33MHz phases.
we got relatively easily some stable X-rays.
on the gain "0" on the current amplifier of the X-rays photodiode, we got 15 000 pA (380k Xrays / pA => 5.7.10^9 Xrays).
but we saw, when the cathode charge was fluctuating, that we could be saturated above 20 000 pA !
the power in the cavity was ~84kW after CEP and alignment tuning.
the command to launch the X-rays measurement window is:
taurustrend -r 100 /XLI/OP/TMD.01/I1
| Ronic Chiche wrote: |
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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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