LIGO Document E1900220-v1
- The SR3 ROC Actuator, Ceramic Heater sub-assemly was tested while at elevated (operating) temperature. The intent was to use the measured rate of increase in optical absorption and optical scatter loss (both at the 2 sigma level) over time in order to set the maximum allowed operating temperature of the SR3 ROC actuator. This test was limited to the ceramic heater sub-assembly; It did not include the mounting hardware which includes some polymers. The elevated temperature of the heater sub-assembly will raise the temperature of the mount assembly as well (via conduction and radiative exchange)
The optical absorption loss increased (2.3 ppm/yr ± 0.23 sigma) over the 7 month test period (albeit with a fair amount of scatter in the measurements). When scaled to LIGO vacuum pumping conditions this corresponds to 0.010 ppm/yr (@ 2 sigma) in the corner station for a single SR3 ROC actuator operating at 87C (and at 120C for 5 weeks).
The optical scatter loss experienced a significant reduction during a limited period of time during the course of the testing at elevated temperature. This transient, or unstable, period may have been due to a slow shift in the alignment so that a different spot on the cavity mirrors was being sampled. Alternatively perhaps a contaminant on a cavity mirror was evaporated off. As a conservative estimate of the monotonic increase in scatter loss over time, the fit to the data after the transient period is used: 9.7 ppm/yr ± 4.3 sigma over a 10 week period. When scaled to LIGO vacuum pumping conditions this corresponds to 0.066 ppm/yr (@ 2 sigma) in the corner station for a single SR3 ROC actuator operating at 87C.
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