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Message ID: 2598     Entry time: Thu Nov 26 11:26:14 2020
Author: agupta 
Type: Summary 
Category: TempCtrl 
Subject: Cavity temperature estimate 

Measurement and estimation method:

  • 125N-1064 Thermal continuous tuning coefficient is 5 GHz/V
  • The south cavity is locked with nominal settings with slow PID switched on.
  • The cavity was first allowed to equilibrate at the nominal setpoint of cavity heater currents of 0.5 W common power and -0.09358 W Differential power.
  • After more than 9 hours, the cavity heaters are switched off and the cavities are allowed to reach equilibrium with the vacuum can.
  • The slow voltage control of the south cavity moves slowly in response to the temperature change of the cavity.
  • Cavity frequency change to length change factor is \frac{L_{cav} \lambda}{c} m/Hz.
  • Cavity spacer is made out of fused silica whose coefficient of expansion is 5.5\times 10^{-7}$ $\text{K}^{-1} [from Accuratus SiO2 datasheet]
  • Therefore, NPRO temperature tuning slow voltage to cavity temperature conversion factor is:

\frac{5 \times 10^{9}}{1} \frac{Hz}{V} \times \frac{L_{cav} \lambda}{c} \frac{m}{Hz} \times \frac{1 }{L_{cav} 5.5\times 10^{-7}} \frac{K}{m} = 32.265 \frac{K}{V}

  • After waiting for 60 hours, the cavity finally cooled down to equilibrium with the vacuum can. The out-of-loop temperature of the vacuum can at this point is used as the equilibrium temperature of the cold cavity.
  • The voltage change in slow voltage control of south laser from this point to setpoint is used to estimate the cavity temperature at beatnote measurement which came out to be around 37 degrees Celcius. I'm taking a generous uncertainty of \pm 1 ^\circ C during noise budget calculations to account for miscalibration of the vacuum can temperature sensor and other errors in this method.
  • The noise budget calculation was updated, Bayesian inference updated and the results in the paper draft have been updated.


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