LIGO-G W Commissioning Data on Vibration Isolation & Suspensions Fred Raab 24 October 02

LIGO-G W LIGO Laboratory2 Vibration Isolation Systems »Reduce in-band seismic motion by 4.5 – 6.0 orders of magnitude »Little or no attenuation below 20Hz »Large range actuation for initial alignment and drift compensation »Quiet actuation to correct for Earth tides, microseism at 0.15 Hz, and active stack damping during observation HAM Chamber BSC Chamber

LIGO-G W LIGO Laboratory3 Seismic Isolation – Springs and Masses damped spring cross section

LIGO-G W LIGO Laboratory4 Seismic System Performance Horizontal Vertical HAM stack in air BSC stack in vacuum HAM chamber view

LIGO-G W LIGO Laboratory5 Earth-Tide Compensation Using Fine Actuation Feedforward Calibration Feedback Earth tide magnitude is hundreds of fringes

LIGO-G W LIGO Laboratory6 Tidal Compensation Data Tidal evaluation on 21-hour locked section of S1 data Residual signal on voice coils Predicted tides Residual signal on laser Feedforward Feedback

LIGO-G W LIGO Laboratory7 Microseism Trended data (courtesy of Gladstone High School) shows large variability of microseism, on several-day- and annual- cycles Reduction by feed-forward derived from seismometers Microseism at 0.12 Hz dominates ground velocity

LIGO-G W LIGO Laboratory8 Core Optics Suspension and Control Local sensors/actuators provide damping and control forces Mirror is balanced on 1/100 th inch diameter wire to 1/100 th degree of arc Optics suspended as simple pendulums

LIGO-G W LIGO Laboratory9 Background Forces in GW Band = Thermal Noise ~ k B T/mode Strategy: Compress energy into narrow resonance outside band of interest  require high mechanical Q, low friction x rms  m f < 1 Hz x rms  2  m f ~ 350 Hz x rms  5  m f  10 kHz

LIGO-G W LIGO Laboratory10 Actuation/Isolation Transfer Function Should Be 1/f 2

LIGO-G W LIGO Laboratory11 Thermal Noise Observed in 1 st Violins on H2, L1 During S1 Almost good enough for tracking calibration.