External seismic pre-isolation retrofit design

This technical note outlines the design of an external seismic pre-isolation system proposed for use in LIGO Livingston. The goal is to reduce the effects of the site’s excess ground noise in the 1 3 Hz frequency band, allowing detector noise performance equivalent to that of the 4 km LIGO Hanford detector. The center histogram in Figure 8 shows the most troubling aspect of the excess noise quite clearly. The typical 1 3 Hz RMS velocity at LHO is about 2× 10−8 m/s, but at LLO it is typically 10 20 times that during the day. This both makes length control servo lock difficult, and requires greater test mass actuation that adds noise in the gravitational-wave band. In addition, Figure 9 shows that peak velocities in at LLO in the 1 3 Hz band are often as large as 2 5 μm/s. In order to achieve the promised detector performance at LLO, we are considering proceeding with the rapid development, testing, and installation of an additional stage of seismic isolation, shown in Figure 1. This stage would physically support