on last tuesday, I did a long-term measurement of the frequency drift when the heating cable is powered ON at 20V (2x 10V) @ t=0mn.
the freqeuncy drift (between the laser, locked in open loop on the FP-cavity, and the RF reference oscillator) acquisition was made by the National Instrument software.
the sampling rate of this acquisition is not set by the user but depends on several parameters of the acquisition... and then can be subject to change.
on can see on the data, in blue, a possible sampling rate change @ t~30mn.
@ t~100mn : the frequency sign changes but the measurement gives always the absolute value.
in orange, the fit is not very good... possibly due to the sampling rate change.
the conclusion we can have is only this frequency drift action has a very long time constant ~ 2h
and could be used to compensate, as soon as the power is in the FPcavity, the frequency drift coming from this power.
| Ronic Chiche wrote: |
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last friday, I locked the cavity and then, switched ON the heating cable after waiting the cavity reaches a steady state in frequency drift : see the figure.
blue : temperature of the probe on the heating cable
red : freqeuncy drift between FP-cavity (laser locked on it) and RF reference oscillator.
@ 10min : filling the FP-cavity with 50kW
@ 50min : "long" lock loss of about 1min => jumb in frequency => it is strange to see the cavity does not reach the same frequency steady state after the lock loss than before the lock loss.
(just before the small frequency jump, the frequency is increasing a bit because of the lock has been lost and the laser is drifting by itself in open loop. the jump, after that, corresponds to the moment where the laser is locked back to the FP-cavity)
@ 55min : switch ON the heating cable with 20V on the voltage supply => the probe stuck on the cable shows the temperature increases => and a bit later, one can see the frequency decreasing.
surprisingly, we don't reach a steady state ...
I suspect that filling the FP-cavity with power (without switching ON the heating cable) could first inscrease the frequency and later could decrease it if several parts of the mechanics are involved and if the thermal conduction is slow because of some isolation embbedded in the mechanics (for example ceramics balls).
it is possible to make the frequency drifting sensitivity test of the heating cable without locking the cavity at 50kW.
one can work in open loop, without power in the FP-cavity, and follow the frequency drift by keeping the main resonance at the same relative position to the laser PZT.
| Ronic Chiche wrote: |
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this afternoon, I started the heating cable after the warm-up of the FP-cavity :
14h20 : start to fill 50kW in the cavity
15h : start of the heating cable @10V (2x 5V) (iteration 2300)
15h16 : start of the heating cable @60V (2x 30V) (iteration 3400)
15h20 : start of the heating cable @20V (2x 10V) (iteration 3600)
the offset frequency, for 20V of voltage on the DC voltage supply, is 175Hz @500MHz (equivalent to 3.5µm)
| Ronic Chiche wrote: |
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today, I removed one of the DC voltage supply (as with 30V, we are already able to 30°C on the heating cable).
the remaining DC voltage supply is configured in series (2x30V = 60V max) and is at the IP address : 192.168.1.101
| Ronic Chiche wrote: |
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several days ago, we installed a heating cable around the output flange (close to the X-hutch) of the FP-cavity vessel.
we are able to heat this cable by applying a DC voltage coming from 2 DC voltage supplies in serie (2 devices with 2x 0-30V / 3A => 0-120V / 3A).
currently, we apply at maximum 7V DC on each channel => 28V DC on the cable. its temperature reach ~ 30°C after 1/2h or more.
this temperature increase on one vessel of the FP-cavity, changes very slowly the length of the FP-cavity.
see this post (red curve on fig. 2) for a typical temperature curve measured (exponential-like curve) on the heating cable itself : https://elog.lal.in2p3.fr/FPC/THOMX+commissioning/290
the length change rate of the FP-cavity, due to this heating, is difficult to estimate because it depends on the part of this exponential curve you make the measurement.
but globally the drift is about 50nm every 5 minutes, which is roughly equivalent to 10 steps of the FP-cavity motor every 5 minutes.
| Ronic Chiche wrote: |
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as the CFP motors displacements induce a cavity unlock, we try to change the cavity length by changing the temperature of elment of the cavity.
yesterday, we tried to put a "heating cable" borrowed to the vacuum group to change the temperature of one bellows between the FP-cavity and the electron ring.
we chose a below because it is flexible and should not apply a too strong force on the cavity vessels.
we heated the cable at ~30°C but we didn't see a clear effect on the FP-cavity frequency measurement.
then, we put a heating cable around the X-ray output flange of the FP-cavity vessel and we saw a clear effect : a relatively fast (at a "second" level) frequency change.
the problem is the heating system is not remotely driven.
the cable is R=55ohms impedance and can reach 450°C for 1kW dissipated.
so today, we will try to use 2 remotely controlled Siglent SPD3303X power supplies.
they can reach V=120V DC => P=V²/R=260W => we could reach more than 100°C
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