Power Recycled Interferometer

Abstract

In the previous chapter we have introduced the problematic that faces the commissioning of the Advanced Virgo arm cavities. The next step in the commissioning process concerns the Power Recycling configuration of the interferometer (PRITF) and it will be presented here. Notice that this is the target configuration for the first Scientific Run of Advanced Virgo. The aim is the same as for the cavities, that is, to control the interferometer both longitudinally and angularly. However the full configuration involves several optical cavities bringing new problems of coupling between error signals and thermal transients, increasing the difficulty of finding a lock acquisition scheme, even if at this early stage the thermal transients are not yet relevant. In this chapter we will define the working point of the PRITF, both for the carrier and for the sidebands. The lock acquisition procedure used in the past to reach the working point will be presented, as well as a detailed study of each of its steps and its validity for the Advanced Virgo optical design. This study will be done using different simulations, in order to find the most convenient set of error signals both during the lock acquisition and in the target configuration, adapting the old sensing when necessary. Also the optical configuration of the Power Recycling Cavity (PRC) requires a special consideration for being marginally stable. The implications of this fact will be explained as well as the strategies proposed to deal with it.