LTP The LISA Technology Package - Institut national de...
Transcript of LTP The LISA Technology Package - Institut national de...
XXXVIIIth RENCONTRES DE MORIOND
MORIOND WORKSHOP ON 22-29 marzo 2003 Gravitational Waves and Experimental Gravity
LTPThe LISA Technology Package:
goals and current baseline implementation
Rita DolesiDipartimento di Fisica, Università di Trento
INFN PD -Gruppo Collegato di Trento
XXXVIIIth RENCONTRES DE MORIOND
MORIOND WORKSHOP ON 22-29 marzo 2003 Gravitational Waves and Experimental Gravity
Contents
• LISA’s sensitivity goal and the test mass “free fall” requirement
• The “drag free” control loop strategy
• LISA Technology Package goal
• LTP architecture and the gravitational sensor current baseline
• Testing on ground with a torsion pendulum
XXXVIIIth RENCONTRES DE MORIOND
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Sensitivity GOAL
GW at 0.1 mHz – 0.1 Hz
Sensitivity
4 10-21 Hz-1/2 @ 1 mHz
5 106 km
Spacecrafts
Test Masses
Telescopes
LISA
Importance of free-fall TM
for LISA sensitivity ?
XXXVIIIth RENCONTRES DE MORIOND
MORIOND WORKSHOP ON 22-29 marzo 2003 Gravitational Waves and Experimental Gravity
separation between end-mirrors parasitic forces GW strain signal
2
2
2
2
F dd xdt
h Ldtm
+∆=δEquation of motion
“free fall” quality requirement LISA
LISA sensitivity at low freq
( )12
215
a 2
f m 1S f 3 10 13 mHz s Hz
− ≤ × +
0.1 mHz f 0.1 Hz≤ ≤
Level of parasitic forces acting on TM2 2
2
1 hL
x LFm
∆ω + ωω
=δ2 22
1 hL
x LFm
∆ω + ωω
=δ2 22
1 hL
x LFm
∆ω + ωω
=δ
XXXVIIIth RENCONTRES DE MORIOND
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Along the sensitive interferometer axis:
“drag free” control loop
The residual acceleration of the test mass will be
noisex
2parasiticmω
fb2Mω
mass S / CX −
extF
Requirements for max PSD of Fext, fparasitic/m, xnoise and for ωint and ωfb
parasiticf
mf
MFxa parasitic
fbCS
extnoiseparasiticresidual +
+≈ 2
/
2
ωω
S/C displacement wrt to test mass
XXXVIIIth RENCONTRES DE MORIOND
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10-15
10-14
10-13
10-12
FNSHz
Testing quality of free fall
LISA(ESA-NASA)
Torsion pendulumTrento
SMART-2
LTP (ESA) DRS (NASA)
XXXVIIIth RENCONTRES DE MORIOND
MORIOND WORKSHOP ON 22-29 marzo 2003 Gravitational Waves and Experimental Gravity
2-implement the drag free control loopalong the alignment direction
S/C is controlled on TM1TM2 follows the spacecraft
subject to low frequency suspension loop
3- diagnostic Interferometerreads TMs mutual distance
measure the residual differentialacceleration of the 2 test masses
5 106 km
LTP basic idea:1- squeezing 1 LISA’s arm to 35 cm
and place it in a S/C
Control logic is necessarily different than in LISA!xBxA
TM1A TM1B
xBxA
TM1A TM1B
•2 drag-free axes xa, xb
•S/C follows TM1a along xa and TM2b along xb
XXXVIIIth RENCONTRES DE MORIOND
MORIOND WORKSHOP ON 22-29 marzo 2003 Gravitational Waves and Experimental Gravity
DF LF
δxlaser interferometer readout
TM1 TM2
ares in LISA
Testing LISA Drag-Free with LTP
laser noise and baseline distortion<<
parasitic stiffnesses
low frequency suspension provides
sensitive to difference in stray forces BUT the lesser known (more dangerous!)
are likely to be uncorrelated
XXXVIIIth RENCONTRES DE MORIOND
MORIOND WORKSHOP ON 22-29 marzo 2003 Gravitational Waves and Experimental Gravity
LTP goal
1 mHz f 30 mHz≤ ≤
In compliance with the following constraints:The sensor design to be tested has to be nominally identical to that to be used on
board LISA
Relaxation is allowed just with regard to stray effects due to the presence of the extra actuation and to the possibly more noise hostile environment
( )12
215
a 2
f m 1S f 3 10 13 mHz s Hz
− ≤ × +
0.1 mHz f 0.1 Hz≤ ≤
LISA goal
test of free-fall within 1 order of magnitude from LISA Goal
corresponds to LTP laser output measuring the residual differential acceleration
21 2 14n 2
f m 1S 4.5 10 13 mHz s Hz
− ≤ × +
Testing LISA Drag-Free with LTP
XXXVIIIth RENCONTRES DE MORIOND
MORIOND WORKSHOP ON 22-29 marzo 2003 Gravitational Waves and Experimental Gravity
From other signals !isolate different contributions
• TM1 position position sensor dominated by the residual jitter of S/C due to external forces
we exctract (thrusters!!)
• the interferomer measures also the position of TM1 wrt position sensor (along x)
we calibrate the position sensor noise xn!
• Measurement of the stray stiffness of coupling between the test mass and the spacecraft.
2S C fbF Mω
2pω
Alternative control scheme: TM2 servoed to null the interferometry signal (rather than its position sensor )
tune to zero isolate it is very sensitive probe!
XXXVIIIth RENCONTRES DE MORIOND
MORIOND WORKSHOP ON 22-29 marzo 2003 Gravitational Waves and Experimental Gravity
Test of the Charge Management proceduresTest of the Caging Mechanism: releasing and acquisition of the TMs on flight
Test of the low frequency suspension.......
Modulated electrostatic, magnetic and thermal disturbances can be purposely induced•measure of the charge onto the test masses (interaction with cosmic rays)
•characterization of force “feedtrough” of these disturbances
...diagnostic sensors•temperature transducer
•magnetometers
...moreover
Testing of other crucial aspects
XXXVIIIth RENCONTRES DE MORIOND
MORIOND WORKSHOP ON 22-29 marzo 2003 Gravitational Waves and Experimental Gravity
LTP +DRSLISA Test Packages on board SMART-2
Remarkable added value•Coordinated tests
•Mutual rescue against failure of one sensor or laser•……
XXXVIIIth RENCONTRES DE MORIOND
MORIOND WORKSHOP ON 22-29 marzo 2003 Gravitational Waves and Experimental Gravity
Noise budget for LISA and LTPwhich includes estimates of all known noise sources has been implemented with the aim of assessing the requirements on the performance and determining the feasibility of achieving
the noise specs for LTP and LISA
Main sources
work in progress
LISA
XXXVIIIth RENCONTRES DE MORIOND
MORIOND WORKSHOP ON 22-29 marzo 2003 Gravitational Waves and Experimental Gravity
Gravitational Balancing
DC differential force limit:
Force gradient limit:
2gravgrav nm/s .
mF
a 75<=∆
2gravgrav /s
xF
m82 101 −<
∂∂
≡ω
• Required meshing accuracy for 2 kg electronics box at ~70 cm of 3 cm, positioning accuracy at 2 mm, 1° level• Optical bench placement at 100 micron, 5mrad degree level
Environmental Requirementsthat impact onto S/C and LTP design
• Magnetic
• Thermal
BBM ∇⋅
µχ+
00
Radiation pressure radiometric effects
1/2/B nT/m/Hz S 7021 <∇
T/m B µ<∇ 5
T B µ<10
1/2/T /HzS 421 10−<
1/2/T /HzS 521 10−
∆ <
XXXVIIIth RENCONTRES DE MORIOND
MORIOND WORKSHOP ON 22-29 marzo 2003 Gravitational Waves and Experimental Gravity
Noisy Charging
Thermal stability related effects
Radiometer
Radiation Pressure
Outgassing
Sources inside the readout circuits
Noise sources in the gravitational sensor coreInteraction of the TM with the electrode housing
radS P Tam 4 T
∆=
3pr
Sa 10 T Tm c
σ≈ ∆
( )( )( )
hole channel holeoutoutgas sin g
channel hole channel hole
C 4C CP PAa TM T T 2C C 6C C
+−Θ= ∆+ +
L
L
n2L
Cp
Cp
VAC
100 kHzCfb
VACT2
VM
Csens1
Csens2
+ δVAC
+ δVACT
+ δVACT
+ δL
− δL
+ δCfb
vthL
L
n2L
Cp
Cp
Cp
Cp
VAC
100 kHzCfb
VACT2
VM
Csens1
Csens2
VMVM
Csens1
Csens2
+ δVAC
+ δVACT
+ δVACT
+ δL
− δL
+ δCfb
vthvth
( ) 1 21 216 V
12o eff
S m 15 mm 0.1mHz3.7 10m 5 mV 16 s fs Hz
−−
ω σ λ = × l
Stray forces and accelerations produced by position noise coupling
through the parasitic stiffness
XXXVIIIth RENCONTRES DE MORIOND
MORIOND WORKSHOP ON 22-29 marzo 2003 Gravitational Waves and Experimental Gravity
• Cross talking, optical alignment, demand high sensitivity and relatively low stiffness also on the non-measurement axes
• yn kept low (1.8 nm/Hz1/2) to be used as second drag-free axis if one sensor is lost on LISA
• φn, θn, ψn all kept to 200 nrad/Hz1/2 (~ few nm/ Hz1/2 translational noise for ~4 cm mass)
• “off-axis” stiffnesses ω2z, ω2
φ, … held to ~ 10-6 /s2 on LISA, 4 10-6 /s2 on LTP
For the remaining degrees of freedomnot along the interferometer axis
XXXVIIIth RENCONTRES DE MORIOND
MORIOND WORKSHOP ON 22-29 marzo 2003 Gravitational Waves and Experimental Gravity
Test-masses(gravitational sensor)
Interferometer
The LTP architecture and main subsystem
XXXVIIIth RENCONTRES DE MORIOND
MORIOND WORKSHOP ON 22-29 marzo 2003 Gravitational Waves and Experimental Gravity
XXXVIIIth RENCONTRES DE MORIOND
MORIOND WORKSHOP ON 22-29 marzo 2003 Gravitational Waves and Experimental Gravity
LTP Interferometer layout.
The laser metrology channels:Position of TM1 relative to TM2 along xPosition along x of TM1 relative to the OBPosition along x of TM2 relative to the OB Attitude of TM1and TM2 along φ and ηby means of quadrant photodiode
(Max Planck Inst.,Hannover, K.Danzmann, G. Heinzel)Heterodyne Mach-Zehnder interferometry
XXXVIIIth RENCONTRES DE MORIOND
MORIOND WORKSHOP ON 22-29 marzo 2003 Gravitational Waves and Experimental Gravity
Carlo Gavazzi Space Ref. S1-038 ITT AO/1-3898/01/NL/PB
Inertial Sensor Definition for LISA
A proposal in response to ITT AO/1-3898/01/NL/PB
Vol. 1 Technical Proposal
August 2001
Carlo Gavazzi Space
ONERA
The University of Birmingham
The University of Trento
Gravitational sensordefinition for LISA
Carlo Gavazzi Space (prime)
Uni of Birmingham (control algorithm)
ONERA (FEE)
RAL (Caging Mechanism and supportfor gravitational sesnor definition)
Imperial College (Charge Manag.Syst.)
Uni of TRENTOtechnical coordination activities
responsibility for the gravitational sensor definition
will perform on ground GS testingby means of a torsion pendulum
based facility
XXXVIIIth RENCONTRES DE MORIOND
MORIOND WORKSHOP ON 22-29 marzo 2003 Gravitational Waves and Experimental Gravity
The gravitational sensor
• GRAVITATIONAL SENSOR CORE – A free floating cubic, 27% Pt-73% Gold TM,2 kg– 6-DOF capacitive motion sensor– An electric field based TM actuation system
• CHARGE MANAGEMENT SYSTEM (ICL):– TM charge management control– UV light, photo electron extraction based,
• CAGING MECHANISM (RAL)– cages the mass via the action of a plunger that
pushes it against end-stops – prevents both translation and rotation– allows multiple operation including re-caging– releases the TM form the centre of the housing
• VACUUM ENCLOSURE
XXXVIIIth RENCONTRES DE MORIOND
MORIOND WORKSHOP ON 22-29 marzo 2003 Gravitational Waves and Experimental Gravity
XXXVIIIth RENCONTRES DE MORIOND
MORIOND WORKSHOP ON 22-29 marzo 2003 Gravitational Waves and Experimental Gravity
Capacitive position sensor electrodes configuration
• symmetric all gap-sensing• 6 sensing /actuation electrode pairs
• combinations of 6 2-channel pairs give 3 translational and 3 rotational TMdisplacement measurements
•large sensing gaps, 4 mm along x (to reduce unmodelled surface forces...)• 46 mm test mass (~2 kg)
Gap dx
x
y
φ
s
1
2
Gap dy
din = 4 mmΣCin = 4.40 pF
y
z
x
dy = 2.9 mmCy = .83 pF
dx = 4 mmCx = 1.15 pF
dz = 3.5 mmCz = .61 pF
Ctot = 25.6 pFVM0 ~ .6 VVINJ ~ 3.5 V
XXXVIIIth RENCONTRES DE MORIOND
MORIOND WORKSHOP ON 22-29 marzo 2003 Gravitational Waves and Experimental Gravity
VACT2
Csens1
Csens2
+ δVACT
+ δVACT
vth
PSD
L
L
x
FEEE
VAC
100 kHz+ δVAC
z
ToComputer
VACT1
VACT2
Csens1
Csens2
+ δVACT
+ δVACT
vth
PSD
L
L
x
FEEE
VAC
100 kHz+ δVAC
z
ToComputer
VACT1
Position sensor with one channel connected to its readout circuit
XXXVIIIth RENCONTRES DE MORIOND
MORIOND WORKSHOP ON 22-29 marzo 2003 Gravitational Waves and Experimental Gravity
Baseline for the implementation of the electrode housingMolybdenum –SHAPAL (sapphire)
high thermal conductance composite structure
•margin against thermal gradients •flexibility supporting the caging loads more securely and simply
geometrical tolerances of the order of 10 micron
XXXVIIIth RENCONTRES DE MORIOND
MORIOND WORKSHOP ON 22-29 marzo 2003 Gravitational Waves and Experimental Gravity
10-4
10-3
10-2
10-1
100
101
10-8
10-7
10-6
10-5
10-4
10-3
SV1/
2 (V/H
z1/2 )
Frequency (Hz)
30000 s econd run230000 s econd runThermal Limit
10-1
100
101
102
103
Sx1/
2 (nm
/Hz1/
2 )
Top and Bottom
Lids
Central frame
Test Mass
position sensor noise measurements
Compliant with the LTP requirement!!!
Prototype already existing in Trento
XXXVIIIth RENCONTRES DE MORIOND
MORIOND WORKSHOP ON 22-29 marzo 2003 Gravitational Waves and Experimental Gravity
Torsion Pendulum Ground Testing of Inertial Sensor• Test mass suspended as inertial member of a low frequency
torsion pendulum, surrounded by sensor housing
mHz 221
0 ≈Γ=I
fπ
• 25 µm W fiber, Q~1000• ~1 m long
• 100 gm test mass • 2 cm electrode separation
(“arm length”)
Twist angle
10-13 m/s2/sqrt(Hz) @ 1mHz
•Measure stray forces
thermal noise limit
•Measure coupling to sensor as deflections of pendulum rotation, with optical angular
readout
at level relevant for LISA
•Measure TM charge,electrode DC voltage imbalance,spurious TM magnetic moment...
XXXVIIIth RENCONTRES DE MORIOND
MORIOND WORKSHOP ON 22-29 marzo 2003 Gravitational Waves and Experimental Gravity
3x10-13 m/s2/sqrt(Hz) @ 1mHz
Stray Force Upper Limit: Pendulum Angular Noise
XXXVIIIth RENCONTRES DE MORIOND
MORIOND WORKSHOP ON 22-29 marzo 2003 Gravitational Waves and Experimental Gravity
XXXVIIIth RENCONTRES DE MORIOND
MORIOND WORKSHOP ON 22-29 marzo 2003 Gravitational Waves and Experimental Gravity
XXXVIIIth RENCONTRES DE MORIOND
MORIOND WORKSHOP ON 22-29 marzo 2003 Gravitational Waves and Experimental Gravity
Daniele BortoluzziPaolo Bosetti
Ludovico CarboneAntonella Cavalleri
Ilaria CristofoliniMauro Da Lio
Rita Dolesi
GiorgioFontanaVigilioFontanari
C.D. HoyleMauro HuellerStefano Vitale
J.W. Weber
Trento Team