The Hydraulic External Pre-Isolator (HEPI) is the first 6 degrees of freedom active seismic isolation system implemented at the Laser Interferometer Gravitational Wave Observatory (LIGO). Implementation was first completed at the LIGO Livingston Obse
rvatory (LLO) prior to LIGOs 5th science run, successfully cutting down the disturbance seen by LLOs suspended optics in the two most prominent seismic disturbance bands, the microseism (0.1-0.3Hz) and the anthropogenic (1-3Hz) bands, by a factor of a few to tens. The improvement in seismic isolation contributed directly to LLOs much improved duty cycle of 66.7% and LIGOs triple coincident duty cycle of 53%. We report the design, control scheme, and isolation performance of HEPI at LLO in this paper. Aided with this success, funding for incorporating HEPI into the LIGO Hanford Observatory was approved and installation is currently underway.
Effects of the growth velocity on the crystal growth behavior of Bi_2Sr_2Ca_1Cu_2O_x (Bi-2212) have been studied by floating zone technique. The results show that a necessary condition for obtaining large single crystals along the c-axis is that the
solid-liquid interface of a growing rod maintains a stable planar growth front. The planar liquid-solid growth interface tends to break down into a cellular interface, while the growth velocity is higher than 0.25 mm/h. Single crystals of up to 50x7.2x7 mm3 along the a-, b- and caxes have been cut in a 7.2 mm diameter rod with optimum growth conditions. Tconset is 91 K measured by magnetic properties measurement system (MPMS) for as-grown crystals. Optical polarization microscope and neutron diffraction show that the quality of the single crystals is good.
