Following the discussion done in the previous commissioning meeting about the 56MHz DPHI trend, see presentationVIR-0390A-18, I have analyzed the decay time of that signal in few locks comparing to the decay time of the thermal transient in the ITF (B8 DC and B4 DC as example).
The data sets have been chosen having the ITF in dark fringe (ITF status > 120) with locks longer than 700 sec. An example of the data set is visible in Figure 1 where the locks period are the one with a treshold of 200.
The B4 56MHz DPHI, B8 DC and B4 DC have been fitted as y = a*exp(-t/T) + c, an example of B8 and 56MHz DPHI fitting is shown in figure 2 and 3.
The B8 DC and B4 DC decay time measured are more or less the same between each others while the time constant for B4 56MHz DPHI is much larger, see figure 4. This could imply that the drift is not related with the main thermal constant which dominates the powers.
this work will be continued