Silica fibers for large mass upgrade on Advanced Virgo Plus

The observation of gravitational waves is highly influenced by the detectors sensitivity, that is limited at low frequencies (10 -100 Hz) by the thermal noise. For this reason, the monolithic suspensions are one of the most important upgrades of the interferometric detectors The Advanced Virgo Plus (AdV+) project, in order to get the target sensitivity, is planning to use larger reference masses, and this choice requires, among other things, a re-design of the silica fibers, and a new capability to produce and test them, in order to minimize the thermal noise in the band of interest and to fit the load constrains. This work will present the mechanical design of the silica fibers for large mass and the desired features. Moreover, some preliminary measures of the fibers profile and the breaking stress will be shown and compared with the design constrains. Finally, the impact of the new silica fibers on the thermal noise will be discuss with respect the AdV configuration.