past, present and future of gravitational wave detection science j. alberto lobo, bellaterra,...
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Past, present and future Past, present and future ofof Gravitational WaveGravitational Wavedetectiondetection Science Science
J. Alberto Lobo, Bellaterra, 13-October-2004
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Presentation summary
1. Current GW detection research status:
• Acoustic detectors
• Interferometers
• LISA
2. LPF and the LTP
3. The Diagnostics and DMU subsystems
4. Future prospects
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Earth based GW detectors
There are two detection concepts at present
Acoustic detection:
Interferometric detection:
Based on resonant amplification of GW induced tidal effects.
Based on GW induced phase shifts on e.m. waves.
VIRGO, LIGO, GEO-600, TAMA
EXPLORER, NAUTILUS, AURIGA, ALLEGRO, NIOBE
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Bar concept
Idea of an acoustic detector (bar) is to link masses with a spring:
so that
202 ( ) ( )
1( )( ) (
2)l t l t l ltl ht t
and GW signal gets selectively amplified around frequency .
202 ( ) ( )l t l t l
2co( , ) ( , )s sin n) i2 s( 2h t h t h t 0 0x x Strongdirectionality
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Real bar detectors
J. Weber
• Two well separated aluminum bars (~1000 km)• Resonance at ~1 kHz• Piezoelectric non-resonant transducers• Impulse sensitivity:
h~10-16
• Coincidence analysis• Tens of sightings claimed in one year
• Claims questioned and eventually disproved• Hawking and Gibbons: energy innovation theory• Giffard: bar quantum limit
New generation cryogenic and ultra-cryogenic bars
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EXPLORER detector at CERN (ROG)
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NAUTILUS, Frascati
Dilution refrigerator: 50 mK
Resonant transducer
h ~ 5x10-19
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Resonant motion sensor
Principle:
Resonant energy transfer to & fro
Mecahnical amplification
Beat spectrum:
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Bar detector sensitivity
Maximum bandwidth: 20Hzm
M
NAUTILUS, 1999
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IGEC(International Gravitational Event Collaboration)
Essential results:
• No impulse signals above 4x10-18
• Negligible false alarm when n>3 (<1/104 years)
Various controversial,single detector claimsavailable…
Remarkable… but insufficient
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MiniGrail, Leiden
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Interferometric detector working principle
1kHz 150km!!!f L
02 sin ,2
hL
c
interf
Resonance condition:2
LGW
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Interferometric detector design
Fabry-Pérot arms: GW 150km
Photodiode: dark fringe:
• Photon flux waste
• Shot noise important
Light recycling technique:
• Power recycling
• Signal recycling
Delay lines
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Details of VIRGO
Cascina site, near Pisa
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Details of VIRGO
Vacuum pipe
Highly reflecting mirror
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Summary status of LIGO
Nov. 1999: Official inauguration
Feb. 2002: Engineering run E7, 6 months
Sep. 2002: Science run S1, 17 days, + TAMA + GEO-600
Feb. 2003: Science run S2, 59 days,
Nov. 2003: Science run S3, 70 days, + TAMA + GEO-600
End of 2004: Science run S4: ~4 weeks
Spring 2005: Commissioning, ~6 months
Autumn 2005: Science run S5, ~6 months
After: Full observatory operation
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LIGO Science run S3, and GEO-600
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there are many GW sources at low frequencies
Earth-based detectors are seismic noise limited
If…
but…
then…
the solution is to go out to space
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LISALISA
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Brief chronology:
1993. Europe/US team submits LISA proposal as M3 project ofESA’s Horizon-2000 Science Programme.
1994. LISA is changed to cornerstone mission in ESA’sHorizon-2000 Plus, and approved as ESA alone.
1997. New studies to reduce cost: LISA is redefined as a three S/C Constellation, 1.4 ton payload.
NASA joins in (50% + 50%), launch advanced to ~2010.
1998. ESA’s FPAG recommends industrial study phase.
1999. System & Technology Study begins. Prime isDornier Satellitensysteme, LIST strongly involved.
2000. Final Report delivered to ESA.
2003. TRIP Review panel considers LISA medium risk.
2003. ESA’s 4th Nov SPC approves LISA, and LPF.
2004. NASA’s new exploration programme defers LISA to 2013.
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LISA concept
Test masses
5 million km, 30 mHz
Transponder scheme
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LISA sensitivity
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Comparison with Earth detectors
2
1/ 2 21 -1/2( ) 4 10 1 Hz3 mHzh
fS f
4 110 Hz 10 Hzf
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LISA’s assured sources
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Cumulative Weekly S/N Ratios during Last Year Before MBH-MBH Coalescence
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LISA orbit
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Orbit dynamics
1o inclination0.01 eccentricity
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The three spacecraft
Thermal shieldDownlink antennas
FEEP
Baffle
Solar panels
Supportstructures
Science module
Star tracker
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The science module
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LISA mission summary
Detection of GWs, sensitivity: 4x10-21 at 1 mHz
Payload:
Objective:
Six capacitive inertial sensorsSix set of four FEEP per S/CTwo lasers per S/C: ND-YAG, 1064 nm, 1 W
Six test masses of Au-Pt alloy, 40 mm a side, in three S/C
Fabry-Perot cavities, stability 30 Hz/sqrt(Hz), transpondersQuadrant photodiode detectors, fringe resol: 54 10 / Hz30 cm Cassegrain telescopes
Orbit: 1 AU, 0.01 ecc, 1 deg ecliptic inclin, 20 deg behind Earth
Launcher: NASA’s Delta, launch date: 2013
Spacecraft: Total mass: 1380 kgTotal power: 940 W/compositePointing performance: few n-rad/sqrt(Hz) in bandScience data rate: 672 bps each S/C
Telemetry: 7 kps, 9 hour/2 days; Deep Space Network
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LISA PathFinder (formerly SMART-2)
LISA’s requirements are extremely demanding.
Drag free subsystem can not be fully tested on Earth.
A previous, smaller technology mission, will assess feasibility:
LPFLPF
It will carry on board the LTP.
However it will be in a smaller scale, both in size and sensitivity.
Essentially, LTP will check:
• drag free technology• picometre interferometry• other important subsystems and software
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LPFLPF
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LPF Funding Agencies and countries
Mission:
DLR
SSO
Payload:
Prime contractor:– Platform: Astrium UK– Payload: Astrium Friedrichshafen
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LTP concept
1. One LISA arm is squeezed to 30 centimetres:
2
1/ 2 14 -1/22
( ) 3 10 1 Hz ,3 mHza
f mS
s
1 mHz 30 mHzf
2. Relax sensitivity by one order of magnitude, also in band:
30 cm
LTP Objectives :
• Drag-free• Interferometry• Other…
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LTP functional architecture
Ground SupportEquipment
(GSE)
LTP flightdynamicssimulator
Integration GSE
IS GSE
Optical metrologyGSE
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LPF orbit
• Lagrange L1
• Launch: Sep-2008
• Travel time:
3 months
• Mission lifetime:
100 days LTP
100 days DRS
• Launch vehicle: Rockot
from Plesetsk
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LTP functional architecture
Inertial sensors(IS)
Chargemanagement
system
IS core
CagingMechanism
IS Front EndElectronics
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Drag-free subsystem
For LISA to work test masses must be (nominally) in free fall.
But there are perturbations which tend to spoil this:
External agents, e.g., solar pressure, magnetic fields…
Internal disturbances, caused by instrumentation itself
To compensate for these, a drag-free system is implemented.
It has two fundamental components:
A position sensor An actuation system
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Drag-free working concept
Courtesy of S. Vitale
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Drag-free working concept
Courtesy of S. Vitale
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Drag-free working concept
Courtesy of S. Vitale
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Drag-free working concept
Courtesy of S. Vitale
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Drag-free working concept
Courtesy of S. Vitale
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Drag-free working concept
Courtesy of S. Vitale
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Drag-free working concept
Courtesy of S. Vitale
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Drag-free working concept
Courtesy of S. Vitale
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Drag-free working concept
Courtesy of S. Vitale
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Capacitive position sensing principle
Bias: few volts at 100 kHz
Nanometre precision comfortably attained
outs
out 1 2 d dp
( ) ( ) ( ) sin (2 )N
V t C C V tV t f tN
x
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Rotational and translational control example
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Inertial sensor structure
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LTP functional architecture
Optical MetrologyUnit (OMU)
Optical MetrologyFront EndElectronics
Laser Unit
Optical Bench
Acousto-opticmodulator
Laser
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LTP optical metrology
To interferometer:Mach-Zenderheterodyne
Power = 1 mW = 1.064 m
hetcos c( )
( os 2)l
ft
t t
Signal:
1 2,f f few MHz
het 1 2f f f 1kHz
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LTP interferometer
Reference
x1-x2 x1
Frequency
Readout: quadrant InGaAs photodiodesA
C D
B
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The LTP EM optical bench
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The LTP EM OB: after-shake tests: phase
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LTP functional architecture
LTP structure(LTPS)
Structure
Gravitationalbalance system
Thermal Shield
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The LTP structure
ASD, courtesy of S. Vitale
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The LTP structure
ASD, courtesy of S. Vitale
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The LTP structure
ASD, courtesy of S. Vitale
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The LTP structure
ASD, courtesy of S. Vitale
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The LTP structure
ASD, courtesy of S. Vitale
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The LTP structure
ASD, courtesy of S. Vitale
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The science spacecraft
• The science spacecraft carries the the LTP and DRS, the micro-propulsion systems and the drag free control system. Total mass about 470kg
• Inertial sensor core assemblies mounted in a dedicated compartment within the central cylinder.
• DRS Colloid thrusters mounted on opposing outer panels.
• Payload electronics and spacecraft units accommodated as far away as possible from the sensors to minimise gravitational, thermal and magnetic disturbances.
• FEEP and cold-gas micro-propulsion assemblies arranged to provide full control in all axes.
Courtesy of G. Racca
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LTP functional architecture
Diagnostics andData
Management Unit(DMU)
Diagnostics enditems
DMU anddiagnostics box
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DDS: Data Management & Diagnostics Subsystem
Diagnostics items:
• Purpose:– Noise split up
• Sensors for:– Temperature– Magnetic fields– Charged particles
• Calibration:– Heaters– Induction coils
DMU:
• Purpose:– LTP computer
• Hardware:
– Data Processing Unit (DPU)– Power Distribution Unit (PDU)– Data Acquisition Unit (DAU)
• Software:
– Process phase-meter readout– Charge management control– UV light control– Caging mechanism drive (TBC)– DFACS split (?)
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Noise analysis concept
2 2
2 2
d x d ha L
dt dt
F
m
2 2a x Lm
hF
1/ 21/ 2
2
( )( ) ,F
h
SS
mL
equivalent signal
2
1/ 2 22
1 -4 1/( ) 1 Hz ,3 mH
3 10za
f mS
s
1 mHz 30 mHzf
Test mass equation of motion (1 dimension):
In frequency domain:
Thus spurious forces fake GW signals, with spectral density:
LTP top level science requirement rephrased:
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S / C
S C2intnoise p n 2
fb
x S/ C TMrelative displacement
Ffa x
m M
Noise apportioning
Direct forces on test mass:
Thermal gradients Magnetic forces Fake interferometer noise
Coupling to S/C:
Test mass position fluctuations Drag free response delay Charged particle showers
Diagnostics items
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Noise reduction philosophy
Problem: to assess the contribution of a given perturbation to the noise force fint.
Approach: 1) Apply controlled perturbation to the system
2) Measure “feed-through” coefficient between force and perturbation:
int( )f
F
3) Measure actual with suitable sensors
4) Estimate contribution of by linear interpolation:
int ( ) ( )f F
5) Substract out from total detected noise:
red int int ( )f f f
6) Iterate process for all identified perturbations
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Example
Courtesy of S. Vitale
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Various diagnostics items
Temperature and temperature gradients:– Sensors: thermometers at suitable locations– Control: heaters at suitable locations
Magnetic fields and magnetic field gradients:– Sensors: magnetometers at suitable locations– Control: induction coils at suitable locations
Charged particle showers (protons):– Sensors: radiation monitor (Mona Lisa)– Control: non-existent
Direct forces
Coupled to S/C
Specifications follow from mission top level requirements
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Diagnostics science requirements
Ref. num
LISA LTP
Req. 107 Temperature PSD (optical bench) 10-4 K/Hz 10-4 K/Hz
Req. 108 Temperature difference PSD (IS) 10-5 K/Hz 10-4 K/Hz
Value
Magnetic Field T
T/m
Magnetic Field Fluctuation PSD 650 nT/Hz
25 (nT/m)/HzMagnetic Field Gradient PSD
Magnetic Field Gradient
Magnitude
Overflow for 108 p/cm2 Solar Energetic Proton (SEP, >100 MeV) at peak flux
BB
RMRM
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DDS current development status
Thermal:
• NTC and RTD devices identified and procured (EM)• FEE designed and built (EM)• First round of tests and data analysis complete• New tests underway
Magnetic:
• Some preliminary studies and surveys• New team has recently assumed responsibility
Radiation monitor:
• Full conceptual design ready• Front-end Electronics Designed• Rest of components selected from ESA/NASA qualified parts• Some other parts to be defined
DMU:
• In situ design and manufacture (price)• Advanced state of development, redundancy requested• Software writing in progress
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Long term:
– LISA is fully endorsed by FPAG and SSAC
– Full, first class participation in LISA:
Technology developments Science yield
– LISA PathFinder:
Fulfill accepted LTP/DDS commitments• MEC funds until 2007, 3.9 MEU• New projects needed until LPF launch in 2008
Create qualified Science and Technology teams Can Science already be done with LPF?
Short-medium term:
Conclusion and future prospects
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End of presentationEnd of presentation
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IGEC
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Garching delay line prototype
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Delta launcher
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LPF operation orbit and injection
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LPF operation orbit and injection
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FEEP (Field Emission Electric Propulsion)
Cs or In ions
Range: 0.1 N < F < 100 N
Resolution: 0.1 N
Power: 50 mW/N
Negligible sloshing
Long life: 9 gr/thruster.2 yr
Low noise, no mechanical parts
LISA needs six sets of four thrusters per S/C for full drag free control
3 1/ 21.66 10 Newtone fF I U
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The entire payload
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Various launcher alternatives
Rockot Dnepr Ariane 5
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The LTP optical bench
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Thermal diagnostics: current status
Sensor choice: NTC & RTD to be tested
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PIC C
HP34402A
IEEE-488
USB
RS232
USB
FE
E
Al blockFOAM
CH0
CH1
CH2
CH3
CH4
CH5
CH6
CH7
MUX, GAIN control
16 bit data
NTC type sensor
RTD type sensor
Reference resistor.Vishay S102J 10k
Test setup only. Not part of DMU-LTP
LabVIEW
NTC2
NTC1
NTC1
NTC2
NTC2
NTC3
NTC3
NTC2
NTC2
RTD1
RTD1
RTD2
RTD2
NTC3
NTC2
RTD2
Test Philosophy
Thermal diagnostics: current status
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Thermal diagnostics: clean room at NTE
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Thermal diagnostics: foaming process
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Thermal diagnostics: sensor inserts
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Thermal diagnostics: first NTC results
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• Magnetometer top level requirements from LTP magnetic requirements (TBC).
Magnetic Field 10 μT
Magnetic Field Gradient
5 μT
Magnetic Field PSD 650 nT
Magnetic Field Gradient PSD
25 nT
Sample rate: 0.33 sample/second (x 3 components)
Bits/sample: 16
Range: variable (± 10 μT, ± 30 μT ± 100 μT)
Resolution (FS/216) variable (0.305 nT, 0.91 nT, 3.05 nT)
Noise (for SNR=10 dB in ± 10 μT range) 40 pt / sqrt Hz @ 0.15Hz
Mass, power, drift.
• Survey of suitable magnetometer technologies. Candidate: Fluxgate Magnetometer.
Technology FGM AMRM GMRM HEM
Measurement Vectorial Vectorial Vectorial Vectorial
Range 1 pT – 1 T 100 pT- 1 T 100 pT- 1 T 1uT- 100 T
Precision(noise) 5-10 pT/√Hz @ 1 Hz 3-10 nT/√Hz @ 1 Hz 20 pT/√Hz @ 100 Hz 10 nT/√Hz @ 1Hz
Drift0.2 nT/yr
30-50 ppm/ºC
(temp)
600 ppm/ºC
(temp)
600 ppm/ºC
(temp)
600 ppm/ºC
Power Consumption <0.5W <0.5W <0.5W <0.5W
Magnetic diagnostics
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Magnetic diagnostics
Helmholtz coil configurations analysed:
Preliminary magnetometer survey: flux-gate, Hall effect,…
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Radiation monitor
18 x 18 mm2
10 x 10 mm2
10 mm
Telescopic Configuration reduces the Angular acceptance on particles and gives a better spectral resolution.
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ChargeAmplifier
Pulse Shaper
DiscriminatorPeak
Holder ADC
Control Logic
ChargeAmplifier
Pulse Shaper
Discriminator
Rear Detector
B1
B2
B3
B4
B5
B6
B7 B8
B9
HV
Counter
Front Detector
Counter
INTERFACE
LOGIC
HV
DMU
Test PulseGenerator
VoltageReference
B10
B11
B12
HV Conv.
+12V
-5V Reg.
-12V +5V GND
DMU
Analog Front End DMUInterface
PowerControl
B13
B14 B15
B16
D1
D2
Radiation Monitor
Data Control & Analysis
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Analoge Block
Power Block
IS FEE PCUIsolated DC/DC
Auxiliary PowerSupply
Isolated DC/DC
EMIFilter
EMIFilter
+28V-1
+28V-2
+5V +/-12V +/-48V
Processor Block
Shieldedamplifiers
Hardwire commands
RS-422 to S/C
4xRS-422 to PhasemeterD
AT
A B
US
PO
WE
R B
US
Drivers
Temp. sensors
Heaters & Coils
Magnetometer
DMU Block Diagram
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DMU mechanical design
Box Cover
Analog Box
Procesor BoxPower Box
CoverBlackplane
220290
95
162.5
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DMU mechanical design
Structural Ears
PCB
Frontal Connectors
Rear Connectors
Frame
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