In preparation for the input mode-matching measurement, Michal asked us to switch on the PR ring heater at the end of the DAS tuning activity.
To do this, Fabio, Maria, and Aaron went onto the platform in the CB to switch on the PR-NI ring heater power supply.
After completing the DAS outer rings power tuning, with the ITF in LN2, the PR ring heater was switched on at 1 W (V = 6.1 V) at 16:56 UTC.
Following Michal’s indication, at 19:18 UTC, in order to make the effect induced by the ring heater more evident, we increased the power to 3 W (V = 10.6 V).
The PRM ring heater was then switched off at 21:14 UTC.
Figure 1. The effect of the ring heater was clearly visible in the arm power, with a decrease in arm power. There was no associated peak in the B1p power. However, superposed to it there is a trend of increase in the B1p power that started before the PR RH was turned on, and continued afterwards. Also the difference in power has not returned to its starting state.
Figure 2. A likely explanation is that the etalon loop has been changed yesterday, which resulted in a transient during the night spanning 0.07 degrees (1/3 of an etalon fringe?). We have seen the etalon loop affect the arm cavity power, especially increase the difference between B7 and B8. So the steady state difference in arm powers after the PR RH transient is likely due the etalon, although there is also the tail of the PR RH cooling, this will complicate a quantitative analysis of this data.
Figure 3 The B1p and B1s power also increased during the night, on a slow time scale, likely due to the etalon. The order 3 mode has increased by a factor 4, and we have seen last week that the etalon can do that for a half a fringe variation.
This morning I have reenabled the EDB B1t photodiode by hand, it must have turned off during the unlock around 6:00 UTC.
