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AdV-COM (AdV commissioning (1st part) )
ruggi, swinkels, carbognani - 21:10 Friday 26 May 2017 (37751) Print this report
MICH noise versus FmodERR

We found a method to perform by hand a fine tuning of IMC length which minimize  Fmod ERR. In figure we see MICH noise when IMC length is good, compared to the case of 80 um and 260 um of mistuning. The experiment confirms that the high level of MICH noise depend on the mistuning of modulation frequency with respect to IMC length.

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swinkels, ruggi, carbognani - 23:27 Friday 26 May 2017 (37759) Print this report
The manual procedure was roughly: unlock the RFC, increase the line amplitude, and move the MC top stage to zero FMOD_ERR. After that, unlock the IMC, set the master laser thermal correction to the value when it was last locked to the RFC, and relock everything. Any residual mistuning could in future be nulled by tuning the modulation frequency once locked, but for now this causes an unlock in the SSFS. Something similar should be implemented in Metatron.

The mistuning of 80 and 260 um of the IMC length should correspond to a mistuning of the 56 MHz of respectively 30 and 100 Hz.
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