Defense this Friday 2:15 (Phys./Astro. 102), Daniel Clark

All -

LIGO's a pretty demanding application of inertial sensing-based structural control.  If you're interested in learning more, Daniel Clark's defense would be a good place to start --

Roger

The Seismic Platform Interferometer – an auxiliary sensor enabling the control of differential motion between adjacent LIGO seismic isolation platforms

Daniel Clark

Dissertation Adviser: Prof. Daniel B. DeBra

Friday November 30, 2012

2:30 PM (Refreshments at 2:15 PM)

Physics and Astrophysics (04-470) Room 102

Abstract:
The Laser Interferometer Gravitational-wave Observatory (LIGO) is a large project designed to detect directly gravitational waves from astrophysical sources. LIGO utilizes three earth-based, long-baseline interferometers and is funded by the National Science Foundation (NSF).

Currently, LIGO is going through a sensitivity upgrade. As part of the upgrade, 30 six degrees-of-freedom Internal Seismic Isolation (ISI) platforms are being installed. The platforms are actively controlled relative to inertial space using seismometers and provide excellent performance at high frequencies. At low frequencies, however, the horizontal feedback seismometers have difficulty distinguishing horizontal accelerations from the component of gravity (g) due to tilt.

This talk addresses one method that could be used to overcome the difficulties caused by the tilt-horizontal coupling in the feedback inertial sensors. An auxiliary sensor, the Seismic Platform Interferometer (SPI), was developed and tested in the Stanford Engineering Test Facility (ETF). Using the information from the SPI, two adjacent platforms in the ETF were controlled in differential length, pitch, and yaw. Independent seismometers on the two platforms indicated an order of magnitude reduction in the differential length motion between the platforms from 50 mHz  to 5 Hz. Similar performance was also anticipated for differential pitch and yaw although the lack of independent sensors precludes direct measurement of performance improvement.

The SPI is a possible solution to unwanted motion at low frequency caused by the tilt-horizontal coupling in the feedback seismometers of the LIGO active ISI platforms.

Daniel Clark
Stanford University
6235 22nd St.
Rio Linda, CA 95673
916.769.2411 Mobile