As part of the today's commissioning work on the MIR/MAR reallocation between IMs and EMs, the logic of the two LowNoise configurations has been changed: a new parameter, bypass_ln1, is defined as boolean in the [ITF_LOCK] section of the ITF_LOCK.ini file.

When this parameter is set to True, during the LOW_NOISE_1 transition we will keep using the Input Mirrors to actuate. And obviously nothing will be done on the relays. Also, we will prepare the End Mirrors to use directly their LowNoise configuration, i.e. LowNoise2.

During the LOW_NOISE_2 transition, we will jump directly from HighPower to LowNoise2. The only caveat here is whether we can survive acting on the IM relays when already in LOW_NOISE_2 (we usually do that in LOW_NOISE_1). The other caveat is that with the very high useism we have now, the standard lock acquisition would probably not work anyway given our current problems.

More information on the changes at the level of the actuators are reported in the aforementioned entry.

After the (unfortunately temporary) fix of DC Readout we managed to test the new logic described here; unfortunately, as feared, acting on the IM relays while already in LowNoise2 made the ITF to unlock, at least in the single test that we could make (unlock at 23:19:51 UTC); this is apparently strange, as this kind of action was done in the past for the charge measurements, but it could be that the full switch on both IMs at the same time is too much. We could think of acting on them in series on one IM at a time, to be studied.

After this test, and seeing that the useism is going down (still far from being low, though), we reverted to the standard strategy, which needs a check anyway since it is embedded in the same new logic. Unfortunately we started to have issues again in the OMC/DC Readout phase, so this is still ongoing at the time of writing.