Development of a high-sensitivity differential accelerometer to be used in the experiment to test the Equivalence Principle in an Einstein elevator.

Transcription

1 Development of a high-sensitivity differential accelerometer to be used in the experiment to test the Equivalence Principle in an Einstein elevator. V. Iafolla, S. Nozzoli, E. Fiorenza iafolla@ifsi.rm.cnr.it Istituto difisica dello Spazio Interplanetario Rome, Italy E.C. Lorenzini, I.I. Shapiro, P.N. Cheimets, Harvard-Smithsonian Center for Astrophysics Cambridge, MA, USA S. Glashow Boston University, Boston, MA, USA Les Arcs France March 22-30, 2003

2 GReAT: General Relativity Accuracy Test estimated accuracy several parts in 10^15 Differential accelerometer with two proof masses of different materials Detector free falls (after release from top of capsule) for 30 s inside an evacuated capsule previously released from a balloon at altitude > 40 km Detector rotated during fall for signal modulation Experiment isolated from external noise sources acting on capsule

3 Ground-based vs. Free-falling Ground-based lab. tests limited by: Small signal strength 1/600 g or 1/1700 g Seismic noise g/hz 1/2 at low frequency Advantages of free-fall tests: Full Earth s gravity signal External acceleration noise can be < g Drag-free satellites Drag-shielded vertical free fall η = a a

4 Team Responsibility Free-fall system (SAO) Cryogenic/capsule system (with Janis Research) Release mechanism (key to cooling and clean release) Room temperature electronics and detector power source Detector (IFSI) Achieving the required values (e.g., Q-factor) Attenuating initial transients Achieving the desired common-mode rejection

5 Cryogenic Capsule Flight sequences Total length = 6.5 m External diameter = 1.2 m Total mass = 1300 kg

6 Facility Performances Spectral density of the Earth gravity gradient, Contribution due to the masses placed on the capsule, Inertial gradient due to the vibrations of the capsule walls, to the platform, via the residual gas in the capsule. Reference gravity gradient: 10 2 EU / Hz

7 Spinning mechanism and cryogenics Instrument package spun at 1 Hz before release into the vacuum capsule

8 EP experiment preliminary error budget Noise Source Max. differential x- acceleration Frequency content Amplifier noise 4x10-15 g/ Hz white Thermal noise 7x10-15 g/ Hz white Capsule's wall vibrations 5.6x10-17 g/ Hz white Residual gas in capsule 5x10-17 g 1/t fall Viscous drag 5x10-16 g f S Earth-magnetic-field ferromagnet. 4x10-20 g f S Capsule-equipment ferromagnetism 5x10-16 g f S Earth's gravity gradient (without balancing) < 3x10-13 g 2f S Capsule's gravity gradient (without balancing) < g 2f S f S = signal frequency Accuracy goal of EP test: 5x10-15 with 95% confidence level

9 ISA (Italian Spring Accelerometer) Space and Geophysical Applications BepiColombo Geostar

10 ISA (Italian Spring Accelerometer)

11 BepiColombo Three-axis accelerometer Mechanical part

12 f C Z T Q T m k a o n n r o b t + β ω ω ω 2 4 ) ( 2 f T Q T m k a p o n r o b t Ω + ω β ω ω 2 4 ) ( 2 no matching matching ISA electric scheme 2 2 o m r C ω α β = Ω = β ω tgδ Q p o e = Q m Q de Q / 4 = m Q T k a r o b bw ω

13 ISA Electrical and mechanical Parameters

14 ISA laboratory calibrations

15 Horizontal component of the seismic noise recorded at the MEDNET stations Line of minimum noise g / Hz Vertical component of the seismic noise recorded at the MEDNET stations Line of minimum noise 7*10 11 g / Hz

16 Geophysical Measurements x 10-3 Misure GEOSTAR Earthquakes 13 gen :33:29:22 Off Coast of Central America Registrazione Gravimetro Geostar Ustica Accelerazione [g] acceleration(g/sqrt(hz)) Tempo giorni dal freq(hz)

17 Preliminary design for laboratory tests Common-mode rejection equal to 10^4

18 Prototype of the differential accelerometer

19 Common-mode rejection 1 Rotating system around an axis not vertical

20 Common-mode rejection 2 Rotating system around an axis not vertical Correction performed adjusting only the amplitude Correction performed adjusting amplitude and phase Delta t = 4.4 e-3 sec Att>10^4

21 Common-mode rejection 3 Rotating system

22 Fast attenuation of the transient 1 Vacuum 1e-5 mbar Tauv 50s fo=18.125hz Qm=2900

23 Fast attenuation of the transient 2 1 Qt = Qm Qe 1 ωorc = β Qe 1 + ( ω RC) o 2 β C E = M ω Damping resistance R=50 M Voltage 1400V C=30pF Tauv=50 s Qt=2900 In this case β = Tauv=7,5 s Qt=441 Tauv=50 s

24 Release system

25 Conclusions Advantages Reusability and easy access to experiment Low cost Strong gravity signal (i.e., 1 g) Noise level comparable to drag-free satellites Disadvantages Short integration time In summary Estimated accuracy in testing the WEP several parts in with 95% confidence level Potential accuracy improvement of 2 orders of magnitude with respect to the state of the art

26 References V. Iafolla, S. Nozzoli, A. Mandiello High sensitive accelerometer for fundamental physics in space 2 nd Joint Meeting of the International Gravity Commission and the International Geoid Commission Trieste 7-12 settembre 1998 V. Iafolla, E.C. Lorenzini, V. Milyukov, and S. Nozzoli, "Gizero: New Facility for Gravitational Experiments in Free Fall." Gravitation & Cosmology, Vol. 3, No. 2(10), , V. Iafolla, S. Nozzoli, E.C. Lorenzini and V. Milyukov, Methodology and Instrumentation for Testing the Weak Equivalence Principle in Stratospheric Free fall. Review of Scientific Instruments, Vol. 69, No. 12, , V. Iafolla, S. Nozzoli, E.C. Lorenzini, I.I. Lorenzini and V. Milyukov, Development s of the general relativity accuracy test (GReAT): a ground-based experiment to test the weak equivalence Classical and Quantum Gravity F. Fuligni, V. Iafolla and S. Nozzoli, Experimental Gravitation and Geophysics. Il Nuovo Cimento, Vol. 20C, No. 5, F. Fuligni and V. Iafolla, Measurement of Small Forces in the Physics of Gravitation and Geophysics. Il Nuovo Cimento, Vol. 20C, No. 5, E.C. Lorenzini, F. Fuligni, J. Zielinski, M.L. Cosmo, M.D. Grossi, V. Iafolla and T. Rothman, "Balloon-Released Experiments in Gravitational Physics", Advances in Space Research, Vol. 14, No. 2, (2)113-(2)118, E.C. Lorenzini, I.I. Shapiro, F. Fuligni, V. Iafolla, M.L. Cosmo, M.D. Grossi, P.N. Cheimets and J.B. Zielinski, "Test of the Weak Equivalence Principle in an Einstein Elevator." Il Nuovo Cimento, Vol. 109B, No. 11, , F. Sanso, A. Albertella, G. Bianco, A. Della Torre, M. Fermi, V. Iafolla, S. Nozzoli, A. Lenti, F. Migliaccio, A. Milani, A. Rossi. Sage: An Italian Project of Satellite Accelerometry Towards an Integrated Global Geodetic Observing System (IGGOS) Munich, Germany 5-9- October 1998 S. Mazza, A. Morelli; ING, Roma Rumore Sismico a Larga Banda.