Publications (42)62.03 Total impact
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Article: Interaction between stray electrostatic fields and a charged free-falling test mass.
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ABSTRACT: We present an experimental analysis of force noise caused by stray electrostatic fields acting on a charged test mass inside a conducting enclosure, a key problem for precise gravitational experiments. Measurement of the average field that couples to the test mass charge, and its fluctuations, is performed with two independent torsion pendulum techniques, including direct measurement of the forces caused by a change in electrostatic charge. We analyze the problem with an improved electrostatic model that, coupled with the experimental data, also indicates how to correctly measure and null the stray field that interacts with the test mass charge. Our measurements allow a conservative upper limit on acceleration noise, of 2 (fm/s2)/Hz(1/2) for frequencies above 0.1 mHz, for the interaction between stray fields and charge in the LISA gravitational wave mission.Physical Review Letters 05/2012; 108(18):181101. · 7.37 Impact Factor -
Article: Brownian force noise from molecular collisions and the sensitivity of advanced gravitational wave observatories
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ABSTRACT: We present an analysis of Brownian force noise from residual gas damping of reference test masses as a fundamental sensitivity limit in small force experiments. The resulting acceleration noise increases significantly when the distance of the test mass to the surrounding experimental apparatus is smaller than the dimension of the test mass itself. For the Advanced LIGO interferometric gravitational wave observatory, where the relevant test mass is a suspended 340 mm diameter cylindrical end mirror, the force noise power is increased by roughly a factor 40 by the presence of a similarly shaped reaction mass at a nominal separation of 5 mm. The force noise, of order 20 fN\rthz\ for $2 \times 10^{-6}$ Pa of residual H$_2$ gas, rivals quantum optical fluctuations as the dominant noise source between 10 and 30 Hz. We present here a numerical and analytical analysis for the gas damping force noise for Advanced LIGO, backed up by experimental evidence from several recent measurements. Finally, we discuss the impact of residual gas damping on the gravitational wave sensitivity and possible mitigation strategies.08/2011; -
Article: LISA Pathfinder: mission and status
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ABSTRACT: LISA Pathfinder, the second of the European Space Agency's Small Missions for Advanced Research in Technology (SMART), is a dedicated technology demonstrator for the joint ESA/NASA Laser Interferometer Space Antenna (LISA) mission. The technologies required for LISA are many and extremely challenging. This coupled with the fact that some flight hardware cannot be fully tested on ground due to Earth-induced noise led to the implementation of the LISA Pathfinder mission to test the critical LISA technologies in a flight environment. LISA Pathfinder essentially mimics one arm of the LISA constellation by shrinking the 5 million kilometre armlength down to a few tens of centimetres, giving up the sensitivity to gravitational waves, but keeping the measurement technology: the distance between the two test masses is measured using a laser interferometric technique similar to one aspect of the LISA interferometry system. The scientific objective of the LISA Pathfinder mission consists then of the first in-flight test of low frequency gravitational wave detection metrology. LISA Pathfinder is due to be launched in 2013 on-board a dedicated small launch vehicle (VEGA). After a series of apogee raising manoeuvres using an expendable propulsion module, LISA Pathfinder will enter a transfer orbit towards the first Sun–Earth Lagrange point (L1). After separation from the propulsion module, the LPF spacecraft will be stabilized using the micro-Newton thrusters, entering a 500 000 km by 800 000 km Lissajous orbit around L1. Science results will be available approximately 2 months after launch.Classical and Quantum Gravity 04/2011; 28(9):094001. · 3.32 Impact Factor -
Article: LISA Pathfinder data analysis
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ABSTRACT: As the launch of LISA Pathfinder (LPF) draws near, more and more effort is being put in to the preparation of the data analysis activities that will be carried out during the mission operations. The operations phase of the mission will be composed of a series of experiments that will be carried out on the satellite. These experiments will be directed and analysed by the data analysis team, which is part of the operations team. The operations phase will last about 90 days, during which time the data analysis team aims to fully characterize the LPF, and in particular, its core instrument the LISA Technology Package. By analysing the various couplings present in the system, the different noise sources that will disturb the system, and through the identification of the key physical parameters of the system, a detailed noise budget of the instrument will be constructed that will allow the performance of the different subsystems to be assessed and projected towards LISA. This paper describes the various aspects of the full data analysis chain that are needed to successfully characterize the LPF and build up the noise budget during mission operations.Classical and Quantum Gravity 04/2011; 28(9):094006. · 3.32 Impact Factor -
Article: The LISA Pathfinder interferometry—hardware and system testing
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ABSTRACT: Preparations for the LISA Pathfinder mission have reached an exciting stage. Tests of the engineering model (EM) of the optical metrology system have recently been completed at the Albert Einstein Institute, Hannover, and flight model tests are now underway. Significantly, they represent the first complete integration and testing of the space-qualified hardware and are the first tests on an optical system level. The results and test procedures of these campaigns will be utilized directly in the ground-based flight hardware tests, and subsequently during in-flight operations. In addition, they allow valuable testing of the data analysis methods using the MATLAB-based LTP data analysis toolbox. This paper presents an overview of the results from the EM test campaign that was successfully completed in December 2009.Classical and Quantum Gravity 04/2011; 28(9):094003. · 3.32 Impact Factor -
Article: From laboratory experiments to LISA Pathfinder: achieving LISA geodesic motion
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ABSTRACT: This paper presents a quantitative assessment of the performance of the upcoming LISA Pathfinder geodesic explorer mission. The findings are based on the results of extensive ground testing and simulation campaigns using flight hardware and flight control and operations algorithms. The results show that, for the central experiment of measuring the stray differential acceleration between the LISA test masses, LISA Pathfinder will be able to verify the overall acceleration noise to within a factor two of the LISA requirement at 1 mHz and within a factor 6 at 0.1 mHz. We also discuss the key elements of the physical model of disturbances, coming from LISA Pathfinder and ground measurement, that will guarantee the LISA performance.12/2010; -
Article: Increased Brownian force noise from molecular impacts in a constrained volume.
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ABSTRACT: We report on residual-gas damping of the motion of a macroscopic test mass enclosed in a nearby housing in the molecular flow regime. The damping coefficient, and thus the associated thermal force noise, is found to increase significantly when the distance between the test mass and surrounding walls is smaller than the test mass itself. The effect has been investigated with two torsion pendulums of different geometry and has been modeled in a numerical simulation whose predictions are in good agreement with the measurements. Relevant to a wide variety of small-force experiments, the residual-gas force noise power for the test masses in the LISA gravitational wave observatory is roughly a factor 15 larger than in an infinite gas volume, though still compatible with the target acceleration noise of 3 fm s(-2) Hz(-1/2) at the foreseen pressure below 10(-6) Pa.Physical Review Letters 10/2009; 103(14):140601. · 7.37 Impact Factor -
Article: Gas damping force noise on a macroscopic test body in an infinite gas reservoir
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ABSTRACT: We present a simple analysis of the force noise associated with the mechanical damping of the motion of a test body surrounded by a large volume of rarefied gas. The calculation is performed considering the momentum imparted by inelastic collisions against the sides of a cubic test mass, and for other geometries for which the force noise could be an experimental limitation. In addition to arriving at an accurated estimate, by two alternative methods, we discuss the limits of the applicability of this analysis to realistic experimental configurations in which a test body is surrounded by residual gas inside an enclosure that is only slightly larger than the test body itself.07/2009; -
Article: Direct force measurements for testing the LISA Pathfinder gravitational reference sensor
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ABSTRACT: We present results of testing of the LISA Pathfinder gravitational reference sensor (GRS) using a 4-test-mass torsion pendulum facility aimed at measuring low-frequency force-noise sources in the LISA and LISA Pathfinder frequency band. This pendulum, for the first time, allows us to make measurements which are sensitive to all forces acting along the sensitive axis of the test mass, not only those that create a torque. We will report on a campaign of testing using the LISA Pathfinder 'engineering model' prototype GRS which has set upper limits on the overall force noise acting on the test mass contributed by surface effects within the sensor at a level of 100 fN Hz−1/2 at 2 mHz and measured specific sources of unwanted disturbances. These sources include forces arising from the electrostatic coupling between the sensor and test-mass motion, electrostatic fields due to surface-potential variations and thermal-gradient effects within the sensor. Finally, we describe the extension of this campaign to the LISA Pathfinder flight-model replica GRS which will be crucial in verifying the design and performance of the flight instrument.Classical and Quantum Gravity 04/2009; 26(9):094012. · 3.32 Impact Factor -
Article: Ground testing, with a four mass torsion pendulum facility, of an optical-read-out for the LISA gravitational reference sensor
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ABSTRACT: In the last few years the Lisa group in Napoli has developed an Optical Read-Out (ORO) system based on optical levers as an auxiliary and backup readout for the Gravitational Reference Sensor (GRS) of LISA. Bench-top measurements, with a rigid set-up have successfully proven that the ORO fits the requirements for sensitivity both in translational and rotational DOFs, exceeding the capacitive sensor performance in a wide range of frequencies. Last year an ORO system designed in Napoli in collaboration with the Trento LISA group, has been installed, as an auxiliary readout system, on the four mass torsion pendulum developed in Trento. In this paper we report on the testing of this ORO device and its performances in comparison with the capacitive one; we also outline further improvements and their advantages for the torsion pendulum facility performances.Journal of Physics Conference Series 04/2009; 154(1):012012. -
Article: LISA Pathfinder test mass injection in geodesic motion: status of the on-ground testing
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ABSTRACT: The LISA Technology Package (LTP) onboard the LISA Pathfinder mission aims to demonstrate, in orbit, several critical technology milestones for LISA, including the purest geodesic motion ever achieved for a macroscopic body. The gravitational reference sensor in the LTP hosts a heavy test mass (TM) surrounded by electrodes, at a relatively large 'gap' distance of several mm, which are used to measure and control the TM position and attitude. The large gaps-–necessary to minimize the force noise acting on the TM-–limit the available level of electrostatic actuation force that can be applied to the TM and thus the authority to control its position and velocity. Due to the large mass and gaps, a caging mechanism is required to securely hold the TM during the launch phase, when the whole payload endures large accelerations. Later in orbit, the TM must be injected into its geodesic trajectory, through the release from the caging mechanism and subsequent capture by the electrostatic actuation. During the release phase, the constraining device must limit adhesion forces that exert a net impulse upon rupture, such that the required forces needed to control the TM do not exceed the actuation authority. The TM injection into geodesic motion, and most critically the release phase, constitutes a potential point of failure for the mission. The on-ground verification of this phase is performed by measuring the momentum transferred between TM-representative surfaces and the release device, reproducing the dynamics that will take place in flight. This paper reports on the testing activities performed at the Department of Mechanical and Structural Engineering of the University of Trento.Classical and Quantum Gravity 04/2009; 26(9):094011. · 3.32 Impact Factor -
Article: LISA Pathfinder: the experiment and the route to LISA
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ABSTRACT: LISA Pathfinder (LPF) is a science and technology demonstrator planned by the European Space Agency in view of the LISA mission. As a scientific payload, the LISA Technology Package on board LPF will be the most precise geodesics explorer flown as of today, both in terms of displacement and acceleration sensitivity. The challenges embodied by LPF make it a unique mission, paving the way towards the space-borne detection of gravitational waves with LISA. This paper summarizes the basics of LPF, and the progress made in preparing its effective implementation in flight. We hereby give an overview of the experiment philosophy and assumptions to carry on the measurement. We report on the mission plan and hardware design advances and on the progress on detailing measurements and operations. Some light will be shed on the related data processing algorithms. In particular, we show how to single out the acceleration noise from the spacecraft motion perturbations, how to account for dynamical deformation parameters distorting the measurement reference and how to decouple the actuation noise via parabolic free flight.Classical and Quantum Gravity 04/2009; · 3.32 Impact Factor -
Article: Thermal gradient-induced forces on geodetic reference masses for LISA
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ABSTRACT: The low frequency sensitivity of space-borne gravitational wave observatories will depend critically on the geodetic purity of the trajectories of orbiting test masses. Fluctuations in the temperature difference across the enclosure surrounding the free-falling test mass can produce noisy forces through several processes, including the radiometric effect, radiation pressure, and outgassing. We present here a detailed experimental investigation of thermal gradient-induced forces for the LISA gravitational wave mission and the LISA Pathfinder, employing high resolution torsion pendulum measurements of the torque on a LISA-like test mass suspended inside a prototype of the LISA gravitational reference sensor that will surround the test mass in orbit. The measurement campaign, accompanied by numerical simulations of the radiometric and radiation pressure effects, allows a more accurate and representative characterization of thermal-gradient forces in the specific geometry and environment relevant to LISA free-fall. The pressure dependence of the measured torques allows clear identification of the radiometric effect, in quantitative agreement with the model developed. In the limit of zero gas pressure, the measurements are most likely dominated by outgassing, but at a low level that does not threaten the LISA sensitivity goals.07/2007; -
Article: Testing of the UV discharge system for LISA Pathfinder
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ABSTRACT: We present the results of tests that demonstrate the functionality and performance of the test‐mass discharge system for LISA and LISA Pathfinder. In space, the LISA and LISA Pathfinder test‐masses will accumulate charge from energetic charged particles. Using the photoelectric effect, a system of ultra‐violet (UV) illumination will discharge the test masses. Testing of this UV discharge system, integrated with the LISA Pathfinder engineering model sensor in the torsion pendulum facility at the University of Trento has shown that: isolated test‐masses can be charged positively or negatively using UV light; the rate of charging can be measured and is proportional to the UV power; the test‐mass charge can be continuously held near zero with a combination of light illuminating the test mass and the surrounding sensor housing, without introducing excess force noise above the pendulum detection limit. © 2006 American Institute of PhysicsAIP Conference Proceedings. 11/2006; 873(1):220-224. -
Article: Torsion pendulum facility for direct force measurements of LISA GRS related disturbances
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ABSTRACT: A four mass torsion pendulum facility for testing of the LISA GRS is under development in Trento. With a LISA-like test mass suspended off-axis with respect to the pendulum fiber, the facility allows for a direct measurement of surface force disturbances arising in the GRS. We present here results with a prototype pendulum integrated with very large-gap sensors, which allows an estimate of the intrinsic pendulum noise floor in the absence of sensor related force noise. The apparatus has shown a torque noise near to its mechanical thermal noise limit, and would allow to place upper limits on GRS related disturbances with a best sensitivity of 300 fN/Hz^(1/2) at 1mHz, a factor 50 from the LISA goal. Also, we discuss the characterization of the gravity gradient noise, one environmental noise source that could limit the apparatus performances, and report on the status of development of the facility. Comment: Submitted to Proceedings of the 6th International LISA Symposium, AIP Conference Proceedings 200611/2006; -
Article: Ground Based 2 DoF Test For LISA And LISA Pathfinder: A Status Report
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ABSTRACT: On-ground tests are required to study the couplings between LISA test masses and the spacecraft that host them. In order to study couplings that might act between two ore more degrees of freedom in measuring the position and acting on the position of each test mass, a many degrees of freedom facility is needed. Here we present the status of our new 2 DoF double torsion pendulum, that will be used to test LISA Gravitational Reference Sensor (GRS) on the ground.10/2006; 873:210-214. -
Article: Ground based 2DoF test for LISA and LISA PF
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ABSTRACT: On-ground tests are required to study the couplings between LISA test masses and the spacecraft that host them. Very interesting and useful results have already been obtained with a 1 DoF torsion pendulum. In order to study couplings that might act between two or more degrees of freedom in measuring the position and acting on the position of each test mass, a many degrees of freedom facility is needed. Here we present a new 2 DoF double torsion pendulum that will be used to test LISA Gravitational Reference Sensor (GRS) on the ground. The facility will be located at INFN Laboratory at Gran Sasso (LNGS), in order to reduce the local ambient noise that limits the sensitivity of the system.Journal of Physics Conference Series 03/2006; 32(1):180. -
Article: Characterization of disturbance sources for LISA: torsion pendulum results
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ABSTRACT: A torsion pendulum allows ground-based investigation of the purity of free-fall for the LISA test masses inside their capacitive position sensor. This paper presents recent improvements in our torsion pendulum facility that have both increased the pendulum sensitivity and allowed detailed characterization of several important sources of acceleration noise for the LISA test masses. We discuss here an improved upper limit on random force noise originating in the sensor. Additionally, we present new measurement techniques and preliminary results for characterizing the forces caused by the sensor's residual electrostatic fields, dielectric losses, residual spring-like coupling, and temperature gradients. Comment: 11 pages, 8 figures, accepted for publication Classical and Quantum Gravity12/2004; -
Article: Measuring the LISA test mass magnetic proprieties with a torsion pendulum
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ABSTRACT: Achieving the low frequency LISA sensitivity requires that the test masses acting as the interferometer end mirrors are free-falling with an unprecedented small degree of deviation. Magnetic disturbances, originating in the interaction of the test mass with the environmental magnetic field, can significantly deteriorate the LISA performance and can be parameterized through the test mass remnant dipole moment $\vec{m}_r$ and the magnetic susceptibility $\chi$. While the LISA test flight precursor LTP will investigate these effects during the preliminary phases of the mission, the very stringent requirements on the test mass magnetic cleanliness make ground-based characterization of its magnetic proprieties paramount. We propose a torsion pendulum technique to accurately measure on ground the magnetic proprieties of the LISA/LTP test masses. Comment: 6 pages, 3 figures12/2004; -
Article: Improved Torsion Pendulum for Ground Testing of LISA Displacement Sensors
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ABSTRACT: We discuss a new torsion pendulum design for ground testing of prototype LISA (Laser Interferometer Space Antenna) displacement sensors. This new design is directly sensitive to net forces and therefore provides a more representative test of the noisy forces and parasitic stiffnesses acting on the test mass as compared to previous ground-based experiments. We also discuss a specific application to the measurement of thermal gradient effects.12/2004;
Top co-authors
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Institutions
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2003–2012
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Università degli Studi di Trento
- Department of Physics
Trento, Trentino-Alto Adige, Italy
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2011
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Fondazione Bruno Kessler
Trento, Trentino-Alto Adige, Italy
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