1. Active Seismic Isolation Systems for Enhanced and Advanced LIGO Jeffrey S. Kissel 1 for the LSC 1 Louisiana State University The mechanical system for the single-stage in-vacuum seismic isolation platform was designed to LSC specifications by High Precision Devices, Inc. (HPD) in Boulder, CO. Optical Table Circumscribed around a 193 cm circle, the 6 sided optical is where the payload will rest. The surface is flat to within 0.25 mm, and has a matrix of over 1000 tapped holes for optics. Suspended Stage, “Stage 1” This stage contains all stiffener plates and seismometers. The stage 1500 kg stage is only attached to the support stage at the three flexure points. Support Stage, “Stage 0” 190 x 150 x 10 cm solid aluminum plate which is the base of the platform. Shown in orange on the SolidWorks drawing are the support posts that pass through the suspended stage and hold the blade springs. Top-down view of suspended stage The platform’s triangular symmetry aids in sensing and control of all horizontal degrees of freedom and easy projections into a Cartesian coordinate system. Cantilever blade spring The 1500 kg Stage 1 is suspended via three 51cm long by 1 cm thick Maraging 300 Steel triangular springs of (vertical) stiffness 8.34 x 10 4 N/m. The spring’s profile is slightly curled when unloaded, as seen on the right. Once loaded, the springs lie flat between the optical table and the suspended stage. Wire Flexure These three 4 mm thick maraging steel rods are the only mechanical point by which the suspended stage connects to the support stage. Horizontal and Vertical Seismometers Horizontal Capacitive Position Sensor Inertial and Displacement Sensor Drive to Response Transfer Functions Taken in early March (while the platform was still on its testing stand, not yet installed) these transfer functions confirm the plant conforms to designed specifications. In particular, there are no bending mode resonances at low frequencies. Simulated Isolation Performance Using both active and passive isolation, ground motion is predicted to be reduced by a factor of 50 at 10 Hz. Horizontal Translation and Tilt Transfer Functions Shows tilt radius to be over 300 m. Fully installed single-stage in-vacuum seismic isolation (HAM ISI) platform at LIGO Livingston Observatory! Identical assembly and installation now in progress at LIGO Hanford Observatory! Two-stage in-vacuum seismic isolation platform prototype is currently being commissioned at MIT! Installing the HAM ISI fully assembled into vacuum chamber The internal isolation system was assembled outside of the vacuum system. The 3000 kg assembly was rolled into the HAM vacuum chamber on two aluminum rails. LIGO DCC #G080192-00-D In order to mitigate the dominant low-frequency noise source for the next generation of interferometric gravitational wave detectors, several new systems are in development that will actively isolate optics and readout sensors from ground motion. - Single-stage In-vacuum Seismic Isolation (HAM ISI) platform - Two-stage In-vacuum Seismic Isolation (BSC ISI) platform Here we present details of the design, construction and first results of the single-stage seismic isolation platform for Enhanced LIGO, the baseline for Advanced LIGO. Vertical Electromagnetic Actuator The HAM ISI sensor and actuator array actively controls all six degrees of freedom of the suspended stage. In order to mitigate horizontal-tilt coupling, actuators are placed within 1 mm of the lower zero moment plane of the spring-flexure system. In addition, sensors are placed right next to the actuators and are spaced out as far as possible from the center of the table. SolidWorks rendering of HAM ISI Horizontal Access Module (HAM) vacuum chamber with HAM ISI The LIGO Vacuum Chamber System Basic Symmetric Chamber (BSC) vacuum chamber with BSC ISI