Advanced LIGO subsystems
are the organizational units of the overall project. Follow the links below to view the mission and progress of each subsystem.

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Advanced LIGO News

LIGO O1 Progress Report

LIGO's O1 observing run, the first data run of the advanced gravitational wave detector era, began in September 2015. An array of always-on software monitors continues to provide detector diagnostics as the run proceeds. These tools indicate a solid level of performance in most aspects of instrument operations, and their measurements continue to inform LIGO's plans for continued commissioning on the path to design sensitivity.

Sensing range   Through early November 2015, LIGO's astrophysical sensing range has been encouraging. For gravitational waves from the inspiral of a pair of 1.4 solar mass neutron stars (the "standard candle" for gravitational wave interferometry), H1 and L1 typically range to an all-sky average of about 250 million light years, roughly a factor of four above LIGO's 2010 sensitivity. A significant portion of the range improvement comes from the gain that LIGO has realized at low frequencies. The Initial LIGO interferometers were insensitive to astrophysical signals at 40Hz. Currently, both L1 and H1 operate with a displacement sensitivity of better than 10-19 meter per root Hertz at 40Hz. When a post-O1 round of commissioning begins in January 2016, LIGO will continue to push the 10-19 m design sensitivity benchmark closer to 10Hz.

Double-coincidence up time   Currently LIGO has spent 47% of time in O1 with L1 and H1 running together, just below the O1 target of 50%. The improved stability of the interferometers has led to some very long lock stretches, including a 60(+) hour lock stretch on L1 that began on November 4. The photo shows 12 hours of H1 (red) and L1 (green) "double coincidence" operation with an average neutron star inspiral range of about 75 MPc (244 million light years).[range] Once a lock loss occurs, the path to re-locking sometimes is lengthy. Roughly 15% of available time has been used attempting to lock, a figure that LIGO aims to reduce. LIGO's new technique for locking the long arms independently, named arm length stabilization, has proven to be rapid and robust. Locking the optical cavities near the beam splitter (a set of cavities named the dual recyled Michelson interferometer, or DRMI) and bringing the DRMI and the long arms under unified control requires more time and oversight.

We should add that the GEO600 detector in Germany continues to score high marks in duty factor as it runs alongside LIGO in O1. GEO600 often operates for 90% of available time over long time spans.

Environmental influences   When locked, H1 and L1 demonstrate significantly better immunity to environmental effects than did Initial LIGO. The combination of out-of-vacuum hydraulic pre-isolators, in-chamber active isolation systems and multi-stage optic suspensions are delivering as expected. The sensing range of the detectors has become much more insensitive to local fluctuations in natural and anthropogenic seismicity. Unsurprisingly, large earthquakes and other disturbances that elevate ground velocities to levels above a few microns per second usually cause lock losses.

A locked detector provides a full set of control signals that enable a vigorous seismic defense. When an environmental disturbance pushes the detector from its operating point, a number of these signals disappear, and their absence creates challenges for detector operators on the path back to lock acquisition. A LIGO-authored software system known as Guardian regulates the digital controls that stabilize non-resonant cavities; both Guardian and the lower level controls continue to evolve with the help of the operations specialists who 'drive' the interferometers. The photo below shows a LIGO Livingston operator (right-side work station) attending to a fully-locked L1.


Online data monitoring   LIGO continues to deepen and broaden its ability to scrutinize incoming data and rapidly generate triggers for potentially interesting events. Dozens of observatories around the globe are collaborating with LIGO to develop the capability of using gravitational wave triggers to look for companion signals that could be electromagnetic and/or neutrinos. In O1, various LIGO Scientific Collaboration (LSC) working groups are implementing and strengthening programs of hardware and software injections (artificial signals) designed to sharpen data analysts' abilties to quickly and accurately characterize triggers.

Of course glitches in the interferometers can masquerade as signals of interest. Detector commissioning and engineering teams, working closely with the Detector Characterization group of the LSC, continue to identify glitch sources, other noise sources, and instabilities in the detectors. Some sources receive mitigation from the control room. Others will require configuraton changes that will occur during the next commissioning break. LIGO plans to continue O1 through mid-January 2016.

LIGO Livingston control room photo courtesy of Amber Stuver, Living LIGO.


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