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Transcript of SAO 1 of 17 A New Laboratory Test of the Equivalence Principle R.D. Reasenberg and J.D. Phillips...
![Page 1: SAO 1 of 17 A New Laboratory Test of the Equivalence Principle R.D. Reasenberg and J.D. Phillips Smithsonian Astrophysical Observatory Harvard-Smithsonian.](https://reader035.fdocuments.us/reader035/viewer/2022081520/56649ee75503460f94bf879e/html5/thumbnails/1.jpg)
SAO 1 of 17
A New Laboratory Test of the Equivalence Principle
R.D. Reasenberg and J.D. Phillips
Smithsonian Astrophysical Observatory
Harvard-Smithsonian Center for Astrophysics
APS Meeting, Jacksonville Florida, 14 April 2007
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SAO 2 of 17
Roland Eötvös
1922, 5 10-9
Robert Dicke
1964, 1 10-11
Vladimere Braginsky
1972, 1 10-12
Eric Adelberger
today
Torsion balances are exquisitely sensitive force detectors.
Solar and horizontal gravity down by 10-3.
Depends on mechanical behavior of stressed fiber.
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SAO 3 of 17
Alternative: Galilean test.• Faller and Niebauer at JILA: σ (Δg) / g = 5 × 10-10
• Limited by systematic error associated with lateral separation of falling masses in separate chambers.
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SAO 4 of 17
POEM Chamber Optics, Gen-I
Key Technologies:
Laser gauge;
Capacitance gauge;
Motion system.
POEM long-term goal:
σ(η) = 5 10-14
requires second pair of TMA
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SAO 5 of 17
Gen-I TMA
Φ = 44.5 mm
h = 36.5 mm
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SAO 6 of 17
TFG, Classic Realization
Stabilized Laser
Frequency Shifter (ADM)
Phase Modulator
L
VFS
Int
(Hopping) Controller
VCO
Frequency Counter
Analog Output
~fm
Tracking Frequency laser Gauge: loop closed by Pound-Drever-Hall locking.
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SAO 7 of 17
Measurement Precision
TFG early results: Nov 1991
σ(length) < 2 pm, 1 min < τ < 400 min0 0 0
2
( )( )acc T K
Q T
12 5 27K
( ) /( 2)acc R g
For 1 pm @ 1 s, Q = 0.8 s, R = 0.3,
σ(η) = 1.1 10-11, single toss.
σ(Δg)/g = 5 10-14 => 5.1 104 tosses
(22 hours ) 1 s 10,000 s
1 pm
10 pm
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SAO 8 of 17
New TFG
Tunable Laser
Phase Modulator LVFS
Int
Hopping Controller
~
Frequency Counter
Analog Output
Reference Laser
fm
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SAO 9 of 17
POEM Capacitance Gauges
TMA ADC24 bit
100 kHz
Cal.
Correlators/w in PCf1, f2, …, f5
+-
+-
~ f1
Vacuum
Moving Static
Estimates of 5 positions (x, y: top and bottom & z) per TMA, at 1 kHz
Collaboration with Winfield Hill, Rowland Institute at Harvard
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SAO 10 of 17
TMA, exclusive of feet.
Drive plates, 3 of 5 sets.
Pick-up ring.
Drive: 0.1 V rms, 10 – 20 kHz
Sensitivity: < 8 nm @ 1 s.
Electrode gaps: 1 mm (nominal)
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SAO 11 of 17
Motion System Requirements
• Follow free-falling TMA.• Rapid reversal of motion at bottom.
– Minimize shock, vibration & energy loss.
• Lateral velocity deviation < 10 μm/s.– Simplify Coriolis correction.
• Smooth transition through zero-g to launch TMA.• Structural resonances high.
– Avoid interaction with motion servo.
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SAO 12 of 17
Present Motion System• Slide (commercial).
– Follow nominal trajectory.
• Torsion bar bouncer.– Store and return energy.– Do no harm. (Cause no
shock.)
• Horizontal cable hit by moving system.– Soft onset of force on moving
system, from geometry.– Effective mass of cable, 0.05
kg (chamber, 40 kg).
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SAO 13 of 17
New Motion System
• Granite beam as way for air bearings. [ordered]• Porous graphite air bearings. [stock items]• Aluminum box to hold bearings. [parts ordered]• HEIDENHAIN linear position encoder.*• Aerotech motor controller.*• Massive steel base. [designed]• Mechanical modes > 40 Hz.
* Corporate donation.
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SAO 14 of 17
Systematic Error, I
• Earth’s gravity gradient.– Δg / g = 1.6 10-7 (for Δh = 0.5 m)
• Goal (TMA): σ (Δg) / g = 1.5 × 10-14
• => require σ(Δh) < 0.05 μm.
– Second pair of TMA. – Absolute distance measurement.– Top-bottom interchange.
• Requires breaking vacuum =>
separate runs 1 or 2 days apart.
A
B
B
A
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SAO 15 of 17
Systematic Error, II
• Gravity gradient due to local mass (parked cars).– SUV assumed 2000 kg, on street, 9 m from TMA.
• On street closest to TMA => 9 10-12 g (top-bottom).
– Second pair of TMA.• SUV, worst location (26 deg) => 6.2 10-14 g (double diff.)
– Inventory of cars during night.• Model using estimated masses.
– Frequent left-right interchanges of TMA, if needed.TMA separation (70 mm) → seating error (<< 0.1 mm).
Would address all variabilities in local gravity.
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SAO 16 of 17
Systematic Error, III
• Coriolis force and transverse velocity.– Capacitance gauge measures velocity.
• Require ve-w be measured to 33 nm/s [bias < 0.25 nm/s].
• Air slide reduces vibration => reduced transverse velocity, and thus dynamic range requirement.
• Rotation of TMA around horizontal axis.– Vertical offset, optical reference point from CM,
εz=2 μm; 1 mrad/s rotation: δa=2×10-13 g
– Measure rotation with capacitance gauge and calibrate εz by inducing fast rotation via high voltage on capacitance gauge electrodes.
– Correction to 0.5×10-14 g.
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SAO 17 of 17
More Information
• www.cfa.harvard.edu/poem
• 617-495-7108
• 617-495-7360