LIGO Document T1800077-v4

Optimal control of the ARM alignment with digital compensation of the Sidles-Sigg radiation torque

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T - Technical notes
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We apply the optimal control techniques (H-infinity and mu-syntheses) to align the aLIGO arm cavity. For the soft mode, it can be further combined with the digital subtraction of the Sidles-Sigg torque so only one set of filters is needed for different input power levels.

We show that our scheme can simultaneously improve the low-frequency rms motion and the high-frequency sensing noise. Moreover, the controller is robust under typical fluctuations in the arm power and/or sensing gain.

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GWADW 2018 held from 12 May 2018 to 17 May 2018

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