Microsoft PowerPoint - GG Bremen Sept2009.pptGG (Galileo Galilei) Test of the Equivalence Principle to 10-17
Results from industrial study and state of the art
Anna M Nobili, Dipartimento di Fisica “E. Fermi” Universita’ di Pisa & INFN, Pisa – Italia
Q2C4, Bremen 21-24 September 2009
Some newsSome news
• GG Phase A-2 Study led by TAS-I in Torino, ASI funded: Drag Free Control & GG space experiment simulator based on GOCE expertise of TAS-I Torino team (assume VEGA launcher)
• GGG lab & experiment basic funds from INFN-CSNII as a national experiment
• Additional ASI contribution to GGG: for new vacuum chamber and new instrument too improve GGG sensitivity +
• TAS-I (Torino) to contribute a “GGG Experiment Simulator” also based on heritage from GOCE, to be compared with GGG measurement data (“Remote Ground Test”)
TAS-I is prepared to complete GG in 4 yrs from start of Phase B for a total cost of: 70 M€ (everything included except the cost of launch with VEGA)
Expression of interest from JPL to particpate in GG by contributing to the payload
State of the art (I)State of the art (I)
E. Fischbach et al.: “Reanalysis of the Eötvös Experiment” PRL 1986
(-0.2 ± 2.8)x10-12Be − Al
Eöt-Wash, PRL 2008
Eöt-Wash, PRL 1999
(-1.9 ± 2.5)x10-12Be − Cu
Eöt-Wash, PRD 1994
(-0.3 ± 0.9)x10-12Al − PtSunTorsion balance. 8TMs. Not rotating. 24hr modulation by Earth rotation
Braginsky & Panov JETP 1972
Torsion balance. Not rotating. No signal modulation
Roll, Krotkov & Dicke Ann. Phys. 1964
Eötvös et al. ≈1900 collected in Ann. Phys. 1922
a a≡ η
EarthCold atoms droppingFray et al with T. Hänsch., PRL 2004
10-9g measurement with cold atoms (Cs) Peters, Chung & Chu, Nature 1999
a a≡ η
Target: 10-15
10-16 (10-17)
85Rb & 87Rb
State of the art (II)State of the art (II)
Ongoing
Differ by 2 neutrons only!!!
Satellite, orbit and the VEGA launcher Satellite, orbit and the VEGA launcher
To fly in near circular near equatorial orbit
GG satellite in the bay of VEGA (Kourou launch site)
2.2 m ~600 km altitude
Passive attitude stabilization by 1-axis rotation at 1 Hz
550 kg total mass (with 20% margin) of which ; 100kg launch adapter, 80 kg payload)
Drag Free Control around orbit frequency
To be operated from Italian station in Malindi (Kenya)
1 yr nominal mission duration (up to 3 yr)
1.6 m
GG differential accelerometer (I)GG differential accelerometer (I)
NOTE: We do not fly a vacuum chamber (use venting to space instead..)
GG differential accelerometer (II)GG differential accelerometer (II)
A second accelerometer has been designed could be accommodated:, same composition test cylinders (for zero check) CONCENTRIC with the EP violation one... There is only one center of mass of the spacecraft!! Only the EP accelerometer will fly: • Once you reach the target sensitivity (TMs relative displacements of 0.5 pm), the signature of an EP violation
signal in the field of the Earth is well known and so far we have found no perturbation with the same signature competing with it to the level of GG target
• TMs material choice to maximize physical chance of violation…
Test masses material choice in GG (I)Test masses material choice in GG (I)
Co-rotation makes many disturbing effects DC. Test masses do not need to be manufactured to very high precision => More freedom in the choice of materials to maximize chance of EP violation and significance of test
EP violation not expected to depend on macroscopic properties of matter (density, chemical, mechanical, electric or magnetic characteristics)
/ / /zB L Iµ µ µ
Barion number, Lepton number and z component of Isospin (normalized to mass in unit of the mass of H atom) have been identified (Fischbach & Talmadge, 1998)
=> choose test masses materials so as to maximize difference in all 3 these properties!
Test masses material choice in GG (II)Test masses material choice in GG (II)
Figure adapted (CH2 added) from : E. Fischbach, C. L. Talmadge: “The Search for Non- Newtonian Gravity; Springer- Verlag, New York, 1998.
Test masses material choice in GG (III)Test masses material choice in GG (III)
HDPE (High Density Polyethylene) identified – to be tested in GGG (has interesting side consequences.. Not conductive, capacitance read-out possible without capacitance plates in between test cylinders … differential by definition .. )
GG lock/unlock mechanismsGG lock/unlock mechanisms
Lock/unlock of inner test cylinder
1. Mechanical stops
3. Fine lock/unlock (inch-worm actuators)
“bunny ear” lock/unlock of coupling arm
Designed by DTM Technologies (Ferrari)
GG EP violation signal recoveryGG EP violation signal recovery
EP violation signal after demodulation (from 1Hz rotation)
Drivers and requirements: some numbers (I)Drivers and requirements: some numbers (I)
Drivers and requirements: some Drivers and requirements: some numbers (II)numbers (II)
Drivers and requirements: some numbers (III)Drivers and requirements: some numbers (III)
Drivers and requirements: some numbers (IV)Drivers and requirements: some numbers (IV)
Drivers and requirements: some numbers (V)Drivers and requirements: some numbers (V)
Drivers and requirements: some numbers (VI)Drivers and requirements: some numbers (VI)
…passive MLI sufficient
Electric charging & patch effects:
• passive electric grounding of the test masses • co-rotation of the test masses and the capacitance transdusers (make patch effects
DC or slowly varying if they do slowly vary.. .as they do…) • gold coating • direct measurement of the effects of any patches of charges on test masses, as we
have done in GGG (see later..)
Error budget (I)Error budget (I)
How it is built
Run GG Simulator
Single out systematic effects and check their magnitude and signature
Error budget (II)Error budget (II)
A simulator in the lab: A simulator in the lab: ““GG on the Ground (GGG)GG on the Ground (GGG)””
GGG lab at INFN Pisa-San Piero a Grado
Same number of degrees of freedom; same dynamical properties; position of relative equilibrium of the test masses in the horizontal plane is NOT stabilized by local gravity (as it should be as a test of experiment in space…)
GGG sensitivity: major improvements (I)GGG sensitivity: major improvements (I)
FFT of relative displacements of GGG test cylinders in the horizontal, not rotating, plane of lab
GGG sensitivity: major improvements (II)GGG sensitivity: major improvements (II)
PSD of relative displacements of GGG test cylinders in the horizontal, not rotating, plane of lab
GGG current sensitivity to EP violation in the field of the SunGGG current sensitivity to EP violation in the field of the Sun
GGG has measured 6x10-9 m at diurnal frequency with coupling period of 13 s =>
ηsun~2.3x10-7
Limited by terrain tilts: apparatus not suspended, active tilt control only. Main issue: tilt sensors dependence on temperature
sGGGsGGG (suspended GGG) (suspended GGG) -- ASI funds (I)ASI funds (I)
New chamber has the right symmetry and has been designed to minimize disturbances on GGG
sGGG will be suspended inside chamber by cardanic joint (not rotating) to reduce low frequency terrain tilts passively, in addition to active tilt control now in use (Note: active tilt control is limited by thermal effects on tilt sensor and requires good thermal stabilization to be effective)
An Experiment Simulator will be built by Thales Alenia Space-Italy for the new GGG, similarly to the Simulator built for the space experiment, to be compared with experimental measurements …
New chamber + new rotor (under completion)
sGGGsGGG (suspended GGG) (suspended GGG) –– ASI funds (II)ASI funds (II)
• With the cardanic suspension already manufactured we expect a terrain tilt reduction at low frequencies by about 5000 (exploit lever effect…)
• With active terrain tilt control (+thermal stabilization) plus passive attenuation we expect to detect 1 pm displacements (GG target is 0.5 pm) i.e., with current natural test masses period of 13 s: => ηsun~4x10-11
Longer natural period possible (sensitivity would increasse quadratically..) but shall we encounter the motor ball bearings noise???
Thermal stability in new chamberThermal stability in new chamber
Thermal stability of tiltmeter inside chamber (multi stage thermal control): to a few tenths of mdeg down at diurnal frequency (requires 20 mW only)
A better A better tiltmetertiltmeter to improve active tilt control?to improve active tilt control?
Double pendulum (one simple + one inverted, aligned, coupled by tiny cantilever), based on knife edge suspensions.
Capacitance transducer with ad hoc electronic board developed in the lab based on the AD7745 24 bit capacitance to digital converter capable to measure up to 4 picoFarad to a few tenths of femtoFarad. No additional electronics is needed outside the vacuum chamber; data are transferred to the computer outside via USB port.
Designed to reach 100 s period (equivalent to a simple pendulum 2500 m long!!!) .. Extremely sensitive…
On first tests (only rough adjustment of period and alignment) we have measured 34.8 s period (equivalent to a 300 m simple pendulum..)
MeasurementMeasurement of of electricelectric patchpatch effectseffects (I)(I)
Apply a force to the external test cylinder with a capacitance plate (both grounded)
Since outer and inner test cylinders are coupled, they will move relative to each other
Their differential motion is measured by the capacitance bridges (main sensors) located in between the test cylinders
MeasurementMeasurement of of electricelectric patchpatch effectseffects (II)(II) 2
2 =V
Charge changes sign with applied potential, patch charge does not!
First, apply unipolar potential and measure effect on TMs; then switch to bipolar potential and measure effect on TMs (square wave with same period…)
0.75 0.18
2 ± ≡ =V patch
0.0275 0.006
q Vdisplacement displacement Q V
by measuring the displacements in the two cases we measure Vpatch …
From these measurements:
(Plate made of Al like test cylinders, no gold coating…. )
MeasurementMeasurement of of electricelectric patchpatch effectseffects (III)(III) • No modeling needed, very meat measurement
4 /applied patchV V
Note: the effect of the patch, in addition to being brought to the frequency of the applied potential is also amplified by the factor:
• You measure directly the effect of patch charges on the tests masses • We have done with GGG spinning for 10.6 d, to measure time variation of patch effect
amplitude….
Here it is about 500
⇒ the effect of patch charges (no coating at all) on GGG test masses, close to diurnal frequency is a few picometers
(GG target requires to measure 0.5 picometer)
““Galileo Galileo GalileiGalilei (GG)(GG)””
GG undergoing Phase A-2 Study by ASI (Agenzia Spaziale Italiana) Preliminary (April 2009) Report available on the Web:
http://eotvos.dm.unipi.it/PA2