Progress toward Commissioning the LIGO detectors

Stan Whitcomb, LIGO Laboratory
This past year has seen great progress in two distinct detector activities: installation-defined as getting working subsystems into position-and commissioning-making the subsystems work together to operate as a complete detector with full sensitivity. Our installation and commissioning plan has evolved into one where each of the three interferometers has a well-defined role, and the scheduling of the work on each one has been tailored to its role. The Hanford 2 km interferometer is the first in line and serves as a "pathfinder" to identify problems early. The Livingston 4 km interferometer follows about 6 months behind, and is used for problem resolution and detailed characterization. We will initiate coincidence testing as soon as the first two interferometers are operational, but we will deliberately delay installation of some elements of the Hanford 4km interferometer (primarily control electronics) to enable lessons learned from the first two interferometers to be realized in redesign before installation. The LIGO I science run will begin when reliable and calibrated coincidence data on three interferometers can be taken while keeping the configuration stable for substantial periods of time. The improvements to reach final design goals in sensitivity and reliability will be alternated with data running in a way that optimizes both the early running and obtains integrated high sensitivity data taking before the completion of the initial LIGO science run. On the installation front, the fabrication of the detectors was completed (with the exception of some electronics components), and most detector components have been delivered to the Observatories for installation. Installation of the Hanford 2 km interferometer was completed in May 2000. Installation of the Livingston 4 km interferometer is being completed as this Newsletter goes to press (September 2000). As mentioned above the Hanford 4 km interferometer installation has been intentionally delayed, but substantial progress has been made: the seismic isolation has been installed and the infrastructure (networking, data acquisition, monitoring equipment) has been installed and tested. Commissioning the LIGO detectors began even before the installation was complete. On both the Hanford 2 km interferometer and the Livingston 4 km interferometer, the pre-stabilized laser has been integrated with the mode cleaner (a suspended cavity to stabilize the laser beam before it enters the interferometer). Initial characterization of the laser/mode cleaner system has been completed and show that the combination is already very close to meeting their performance requirements. In December 1999, we began a four month test of the 2 km interferometer in which each arm of the interferometer was separately locked to the laser. This test was performed to measure optical properties of the arms, to test the interferometer sensing and control electronics, to gain information about the environmental noise sources and to exercise the data acquisition and control networks. Lock sections up to 10 hours were obtained and all planned investigations were successfully concluded. At the end of the testing, a 24-hour stretch of data was taken and archived for use by groups developing software and techniques for data analysis and detector characterization. During the past summer, we have gradually begun to bring the entire 2 km interferometer on-line. We began by operating it in the recycled Michelson configuration, (without the long arm cavities). This simple configuration allowed us to test the control systems: verifying the myriad connections, measuring transfer functions, setting modulation/demodulation phases, all of the nuts and bolts of precision interferometry that must be in place before everything will work. Most recently, we have locked the power-recycled Michelson with one Fabry-Perot arm also locked on resonance. This initiated another set of control system measurements which should lead to locking the full interferometer early this fall. Of course, a number of problems have been encountered along the way, but many have been solved, solutions to others are in the works, and none will jeopardize the performance or schedule significantly. We are on track to initiate the first triple coincidence science runs by early 2002.