JILA Meeting on seismic isolation, test mass suspension, and thermal noise issues for GW detectors

Joe Giaime, JILA, University of Colorado

On August 11 - 12, 1998, about 35 people came to Boulder, Colorado to attend the JILA Meeting on seismic isolation, test mass suspension, and thermal noise issues for GW detectors.

The first session included talks on the measurements of ground noise (Gabriela Gonzalez), seismic low-frequency ``pre-isolation" systems (Ken Strain, David Shoemaker, Francesco Fidecaro), gravity noise (Kip Thorne), and an interferometric GW detector experiment from 1970 (Judah Levine). Next, there was a session on test mass suspension systems (Mike Plissy, Norna Robertson), a novel method of thermal noise monitoring and reduction (Yuri Levin), a proposal for cryogenic thermal noise reduction (Warren Johnson), as well as a talk on the use of a metal-insulator-metal diode as sensitive element for an accelerometer (Alessandro Bertolini). The topics for the third session included passive and active seismic isolation in the GW band for LIGO-I (Mark Barton), GEO 600 (Ken Strain), VIRGO (Giancarlo Cella), and for the future (Joe Giaime, Dan Debra).

Immediately afterwards, on August 13 - 15, the third meeting of the LIGO Science Collaboration was held. About 80 collaborators were in attendance.

Barry Barish gave an update on the state of the LIGO construction. LIGO is 85% complete as of August '98. 1999 will see the interferometric detectors installed in the vacuum systems. The system will be commissioned in 2000, engineering tests will be conducted in 2001, and the initial coincidence data runs will begin in 2002. He also gave brief updates on the construction and system test progress at the sites, and summarized the financial and staffing issues within the LIGO Laboratory, and enumerated the membership of the LSC. Raffaele Flaminio, Norna Robertson, and David McClelland presented progress reports on VIRGO, GEO 600, and ACIGA. VIRGO and GEO 600 have start dates in the same approximate time frame as LIGO.

The three leaders of the experimental development groups presented their reports. These groups have been studying the technical issues of future LIGO detector enhancements. The focus was on preparing a white paper for the PAC recommending a coherent research plan for LIGO-related research that will lead to detector upgrades in 2004 and 2008 (or so.) This goal has forced the three groups to consider straw-man designs for the first upgrade and a fairly wide range of possibilities for the second. The first upgrade may include an all fused silica double or triple pendulum similar to the one designed for GEO600, a more powerful laser, some kind of low-frequency active pre-isolation, and higher-quality optics. More massive mirrors and signal recycling are also being considered. The second upgrade will likely need even more challenging technology. This may include cryogenic suspensions and/or monitoring-balancing schemes to suppress thermal noise, lower-frequency isolation, alternative test mass materials with lower optical losses in order to tolerate still more powerful lasers, and signal-tuned or adaptive interferometric length detection schemes to maximize SNR for particular sources. The three presenters were David Shoemaker, Stochastic forces, Isolation Systems, and Suspensions; Eric Gustafson, Sensing Noise - Lasers and Optics; and Ken Strain, Interferometer Configurations. Work is now underway to produce an LSC-wide white paper.

The scientific goals driving the detector upgrade path were discussed during two talks given by Peter Saulson and Kip Thorne. It was pointed out that for NS-NS binary coalescences, most of the contribution to signal-to-noise ratio comes from the trough in the noise curve between the falling pendulum thermal and radiation pressure noise at low frequencies and the rising shot noise at high frequencies, so a detector is optimized for this source by lowering noise in the trough. This is quantified in the form of a detection range for a reasonable source SNR; the initial LIGO's NS-NS range should be approximately to the VIRGO cluster, while the first upgrade ought to improve that by a factor of 5 - 10. Other sources can involve different weighting, and various examples were discussed.

When Rainer Weiss introduced the content of the meeting, he highlighted the need for the LSC experimenters to get more involved with the three data- and astrophysics-oriented analysis groups, especially the Detector Characterization group. Reports from these groups reflected quite a bit of progress over the last six months. The Detector Characterization Group report, given by Daniel Sigg, described the task's organization into data reduction, transient analysis, performance characterization, and the production of simulated data sets. Bruce Allen gave the Astrophysical Signatures group's talk, describing the tasks of using current astrophysical knowledge to determine expected source characteristics, developing algorithms, and developing the software implementation. The Validation and Detection Confidence group report, by Sam Finn, explained this group's role as using the knowledge collected by the previous two groups to determine answers to detection confidence questions by statistical means.

Kathleen Johnson and Zeno Greenwood of the Center for Applied Physics Studies at Louisiana Tech University and Alexander Sergeev of the Institute of Applied Physics in Nizhny Novgorod, Russia, made presentations to the LSC describing their institutions and proposing to join the collaboration. Later in the meeting, during the business meeting of the LSC Council both groups were approved for membership. In addition, the Council appointed a nominating committee, which will begin the process of replacing the current appointed leaders with elected ones.

The conference viewgraphs are available in Acrobat form on the LIGO web site,

Jorge Pullin
Mon Sep 7 17:37:02 EDT 1998