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  • LIGO News: HEPI at LLO
    is a sensor actuator set mounted to the payload vertical and horizontal Each degree of freedom positions and angles is servo controlled with respect to HEPI displacement sensors and geophones This feedback reduces the vibration by a factor of a few in the 1 3 Hz band The displacement sensor signal is corrected for floor motion as measured by a low noise broadband seismometer the Streckeisen STS 2 in each direction Sensor correction further reduces the payload vibration at frequencies all the way down to 0 1 Hz Quiet Hydraulics As implied by its name HEPI uses forces generated by hydraulic pressure to partially cancel the forces from ground vibration The actuator is essentially a hydraulic Wheatstone bridge 2 viscous fluid is forced through it by a pump 1 Small deviations among the resistive elements of the bridge create a pressure difference between C1 and C2 which appears across an actuation plate 5 within a set of flexing bellows 4 Up to one mm of flex is available without any sliding friction or non laminar fluid flow Interferometric test of HEPI using LLO s 4 km X arm During the first two weeks of August 2004 we tested HEPI performance by using the single arm interferometer configuration of the LIGO detector The graph below shows a number of interesting outcomes The green solid trace is the velocity spectral density of the arm length changes due to vibration that are being corrected by feeding back directly to the test masses and so represents the effect of troublesome ground vibration with HEPI turned off The dashed green line is the accumulated root mean squared velocity in units of meter per second calculated right to left So nearly 4 µm s of disturbance is present and other statistics indicate that the day these

    Original URL path: http://www.ligo.caltech.edu/LIGO_web/0409news/0409liv.html (2015-06-02)
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  • LIGO Hanford Observatory News
    s set out to mark the paths and viewing areas provided local illumination while the distant lights of Hanford and Energy Northwest facilities glowed on the horizon The Perseids named for their apparent arrival from the constellation Perseus fall into our atmosphere as the earth annually intersects the debris trail left by comet Swift Tuttle on its 120 year journey around the Sun The night of 8 11 and morning of 8 12 represented the peak intensity of the shower predicted rates for the shower were 50 70 meteors per hour and this range compared reasonable well to counts taken by several viewers Particularly vivid episodes were marked by ooh s and aah s from the crowd of all ages mixed in with occasional notes of frustration from those who missed the big one because they were looking elsewhere in the sky The evening s program began at 10 00 PM with a talk on meteors by the TCAC s Dr Roy Gephart in the LIGO auditorium Roy a PNNL scientist by day and Tri City Herald astronomy columnist by night has observed showers for years His knowledge of shooting stars and his obvious enthusiasm for observing the sky primed

    Original URL path: http://www.ligo.caltech.edu/LIGO_web/0409news/0409han2.html (2015-06-02)
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  • LIGO Caltech News
    once again As it is said one has to move in order to stay After five years of many enjoyable challenges with LIGO my family and I will move to the East Coast I will pursue interesting physics problems as an Assistant Professor at Columbia University in the City of New York I intend to remain in close contact with LIGO through the LSC as my new research group has become a member of the collaboration as of this summer s LSC meeting My wife Zsuzsa will continue to tackle pressing problems in environmental atmospheric science It is both a very exciting and emotional time for us We have had a fabulous time in Pasadena and at Caltech I learned a great deal during these past years and am very grateful for all the support I received for the opportunities provided me and foremost for the help from everyone in assisting me to grow Now Columbia will be another exciting challenge and we expect that much adventure awaits us in the big City It will be quite a change though living in the heart of Manhattan instead of a quiet haven in the foothills of San Gabriel Many thanks to

    Original URL path: http://www.ligo.caltech.edu/LIGO_web/0409news/0409cit.html (2015-06-02)
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  • LIGO Hanford Observatory News
    wave research and the current Spokesperson for the LSC gave a one hour talk to an audience of local and regional residents in which he compared electromagnetic radiation to its gravitational counterpart Peter also discussed the scientific and engineering challenges of gravitational wave detection In attendance were several LSC scientists with significant histories in the field making the Chief Joseph Middle School auditorium the global center of gravitational wave expertise

    Original URL path: http://www.ligo.caltech.edu/LIGO_web/0409news/0409han3.html (2015-06-02)
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  • LIGO MIT News
    and payload then sends a signal to each of the actuators The actuators offset the ground motion and hold the optics table motionless At left an Hydraulic External Pre isolator Right a Magnetic External Pre Isolator The HEPI system differs from the previously installed Magnetic External Pre Isolator MEPI system only by the actuator being used to push on the stacks Where the MEPI system used an electromagnetic actuator the HEPI system uses hydraulics All other components at the chambers offload springs housing sensors controller remain the same allowing a comparison of the results The photo at left above shows an HEPI pre isolator mounted to the Beam Splitter Chamber pier at the LASTI facilities the photo at right shows a MEPI pre isolator mounted on one of the Horizontal Access Module piers The power to move the six ton stack is supplied by a pump station which was designed and built at Caltech Running through the pump is a clear food grade and water soluble hydraulic fluid Tubing and manifolding deliver the fluid to eight actuators where a control valve on each actuator creates the pressure differential required to move the payload in six degrees of freedom The hydraulic

    Original URL path: http://www.ligo.caltech.edu/LIGO_web/0302news/0302mit.html (2015-06-02)
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  • Quiet, Please! Second Science Run Now Underway!
    between 150 300kpc for H2 This monitor is a key indicator of interferometer performance and we are quite pleased by the numbers Opening run calibrations and in run astrophysical injections were performed impacting the duty cycle slightly Still lock duration records were broken in the first week on both interferometers 35 hours for H1 and 30 hours for H2 with 21 hours of continuous overlap Most recently H1 achieved an

    Original URL path: http://www.ligo.caltech.edu/LIGO_web/0302news/0302s2r.html (2015-06-02)
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  • VIRGO Sees First Light!
    the power recycling and input optics bench towers through the 3 km long tube up to the northeast transmission window The laser light spot was visible on a screen placed behind the tower This is the first light transmitted over three kilometers First light along the full length of VIRGO s 3 km North Arm is a major milestone achievement This along with another recent milestone of having reached high

    Original URL path: http://www.ligo.caltech.edu/LIGO_web/0302news/0302vir.html (2015-06-02)
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  • LIGO Livingston Observatory News
    Ranger spacecraft Gerry remained in this section for the next 20 years being steadily promoted until he became Group Supervisor of the Nuclear Power Sources Group In 1983 he transferred to Project SP 100 which centered on the research and development of nuclear space reactor power His decade long tenure on this project ended when Gerry came over to Caltech in 1993 to join the LIGO Project as Deputy Chief Engineer During the past ten years Gerry has been a key contributor to the LIGO Project as Deputy Group Leader in the Facilities Group during the sites planning and construction phases as Facilities Manager at the LIGO Livingston Observatory and most recently as a contributor to the development of the prototype active seismic isolation systems planned for future implementation in LIGO On January 8th LIGO officially celebrated Gerry s retirement An afternoon social break followed by a technical conference was held to celebrate Gerry s many and varied accomplishments There were several talks on space based nuclear power systems with which Gerry had long been associated during his days at JPL Other presentations highlighted his more recent involvement in LIGO Colleagues from his past as well as many from the LIGO community attended and wished him well Festivities continued at the Athenaeum where about 20 joined Gerry and his wife for dinner Above Left Gerry and his wife Gloria enjoy cake at the afternoon celebration held in Gerry s honor Right At the Athenaeum dinner LIGO Deputy Director Gary Sanders presents Gerry with a plaque of appreciation Without LIGO what will Gerry do Move After living in Louisiana Gerry has chosen to live in Gold Beach Oregon Though he s never lived there he s heard it s a nice place to set up house And in his words most

    Original URL path: http://www.ligo.caltech.edu/LIGO_web/0302news/0302liv.html (2015-06-02)
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