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Page 1LISA, Laser Interferometer Space Antenna
GP-B, Relativity Mission, Gravity Probe B
RADIATION HARD UV LED’S
Sasha BuchmanKe-Xun Sun
Stanford University
11th ICATPP ConferenceVilla Olmo, 5-9 October, 2009
LIGO Hanford
LIGO Livingston
Page 2
Outline
The UV LED
Charge managementThe Relativity Mission, Gravity Probe B GP-BThe Laser Interferometer Space Antenna LISALaser Interferometer Gravitational-Wave Observatory LIGO
UV LED Lifetime and Radiation TestingLifetime TestingRadiation TestingEnvironmental Testing
Page 3
UV LED Performance
UV LEDBased on gallium nitride (GaN)UV LED in TO39 packagingVarious other packaging~255 nm central frequency10 nm WHM
UV LED fiber coupled
UV LED with ball lens
Page 4
UV Charge Management
Use of UV SourcesPhotoelectrons for charge management of test bodies (TB)Photoemission from TB and its enclosureBipolar discharging using photoelectrons and bias
Test BodiesInsulators (LIGO, VIRGO, GEO600)Floating conductors (LISA, LPF, GP-B)
Charging SourcesHandling and installationPump-down or other gas flow Separation of dissimilar materialsCosmic radiationPatch effectsVacuum field emission (Field >107 V/m)
Charge MagnitudeTypically 1-100 pC/dayTypically <1nC/event
Page 5
Sources for Charge Management I
Ion Sprayers / Ion BarsFor use in airStandard for clean rooms and benches
UV photoelectronsFor use in vacuumGP-B, LISA, GEO 600
GP-B: Hg UV UV LED
SIMCO, Type P-Sh-NWorking distance10-600 mmVoltage7000 V - AC
STATIC CLEANDC Ionizer DC-ESR-CClean room use
Page 6
Sources for Charge Management II
Studies and ProposalsFor use in vacuumField emission cathodes 1
Ion & Electron guns 2
Thermal filamentsField emission cathodes
Electron GunELG-2/ EGPS-10225eV to 2000eV1nA to 10µASpot : 0.5 - 5mm
Ion GunIGL-2101 / IGPS-11015eV to 2000eV10eV to 1keVSpot : 1 - 20mm
Kimball Physics Inc.1 GP-B Gyroscope Charge Control Using Field Emission Cathodes, S Buchman T. Quinn, M. Keiser and D. Gill, J. Vac. Sci. Technol. B 11, (1993)
http://scitation.aip.org/getpdf/servlet/GetPDFServlet?filetype=pdf&id=JVTBD9000011000002000407000001&idtype=cvips&prog=normal2 Charge neutralization in vacuum for non-conducting and isolated objects using directed low-energy electron and ion beams S Buchman ,
R.L.Byer, D Gill, N A Robertson, and K-X Sun, Class. Quantum Grav. 25 (2008) 035004 http://stacks.iop.org/0264-9381/25/035004
Page 7
UV Lamps Lifetime
UV Lamp B Intensity vs Operating Hours
y = 957.68e-0.0043x
R2 = 0.9776
500
600
700
800
900
1000
1100
0 20 40 60 80 100 120 140
Operating Hours
Inte
nsity
Mon
itor
UV Lamp A Intensity vs Operating Hours
y = 1392.8e-0.0042x
R2 = 0.72
600
700
800
900
1000
1100
1200
1300
1400
1500
0 50 100 150 200 250
Operating Hours
Inte
nsity
Mon
itor
Normalized Discharge Rates vs Time - LAMP B, -3V Bias
-6.0E-03
-5.0E-03
-4.0E-03
-3.0E-03
-2.0E-03
-1.0E-03
0.0E+00
0 20 40 60 80 100 120 140
time (hours)R
ate
(DN
/min
/IM c
ount
)
G1G2G3G4
UV lamp intensity decay time constant ~ 230 hours Large variability of discharge rates between gyroscopesThe GP-B Hg UV lamps met all requirements
Page 8
GP-B Charge ManagementCharging Sources Ground Test/Analysis SM Results
Levitation < 1V test 200 – 500 mVHe gas spin-up < 1V test Not observed: < 10 mVCosmic radiation ~ 0.1 -1 mV/day (GEANT) 0.1 – 1 mV/day
Variations in cosmic radiation chargingShielding: Decreasing from Gyro #1 to Gyro # 4 1 mV = 1 pCSolar flares
Rotor charge controlled with UV excited electrons2 UV Hg lamps (254 nm line)8 UV switches2 UV fibers per gyroscope
Continuous measurement at the 0.1 mV precisionControl to 5 mV (meets requirement of 15 mV)
UV switch #1AUV Lamp A
UV Lamp BUV switch #1B
Gyro #1
× 4 gyroscopes
Schematic of GP-B
UV architecture
Page 9
UV Electrode
GP-B Charge Control: Discharge of G#1G
yro1
Cha
rge
(mV
)
Day of year, 2004
450mV
100mV
0 mV
70mV/hourdischarge
Charge controlled to < 5 mV
UV Lamp Assembly
Lamp A Lamp B
UV Switches
Page 10
UV LED Lifetime Testing System(both vacuum & nitrogen tests)
FunctionGenerator
Nitrogen/Vacuum Chambers
ILX PrecisionCurrent Source
Computer
Modulation(1 kHz, 10% duty cycle)
UV Photodiode
GPIBAmp Oscilloscope
UV LED
Driving SignalDriving Signal
Signal from UV Photodiode
Signal from UV Photodiode
Signal to UV LEDSignal to UV LED
Fast LED Driver and Photodetection PCBFast LED Driver and Photodetection PCB
UV LED Lifetime and Radiation Testing
Page 11
UV LED Based AC Charge Managemente-
e-UVe-
e-UVOutputfast modulated to generateelectron packets
Modulationof electrodephase locked for steering electrons
Phaseadjusted for bipolar charge management
Page 12
Charging and Dischargingof a proof mass potential of +/- 20 mV
UV test facility
Results for AC charge transferstudies using a UV LED with observed power or ~11 µW at acenter wavelength of 257.2 nm
Page 13
UV LED Lifetime in Nitrogen, 1 atmSpectral Stability After 19,800 Hours
UV LED emission spectrumSpectral shift ≤ 2 nm shorter
UV LED power levelNo significant power variation
UV LED lifetime test in Nitrogen: > 28,000 hours (3.2 years)
Power Stability After 20,000 Hours
Page 14
UV LED Lifetime in Vacuum, 10-7 torr
UV LED lifetime test in vacuum: > 17,500 hours (2 years)
UV LED emission spectrum
Initial Spectrum
UV LED power levelNo significant power variation
Power Stability After 9,000 Hours
Page 15
Proton Irradiation63.8 MeV proton irradiation test
Test at UC Davis Total fluence 2x1012 proton/cm2
> 100 years of dose at LISA orbitUV LEDs maintained light output Spectral shape unchanged Power intensity unchanged
Page 17
Proton Irradiation Setup at UC Davis
Bread Board
Optics Table
Protons63.8 MeVProton
Accelerator
Ames Chamber(removed for
high flux proton irradiation) Stanford
PlatformAlignmentAperture
Lab Jack
Page 18
Radiation Qualification Test Setup
Flat Window UV LED
ElectronicsElectronics
SiC Photodiode
Si Photodiode
Ball Lens UV LED
Protons63.8 MeV
Beam current20-15,000 pA
Aluminum Shielding Block
Shielding Wall (>1 m Concrete)
Experimental setup (top view) for UV LED proton radiation tests.
Page 19
UV LED Spectral Shift Measurements Before and After Proton Irradiation
UV LED 63.8 MeV proton irradiation test Central wavelength 255 nm for both, no shift observed
Page 20
Proton Irradiation ResultsUV LED + SiC Detector
Reference for proton test of other LED and laser diodes:A. H. Johnston and T. F. Miyahira, “Characterization of Proton Damage in Light-Emitting Diodes”, IEEE Trans. Nuclear Science, 47 (6), 1999
Proton energy: 59.0 MeV for 80 pA59.0 MeV for 500 pA63.8 MeV for 15,000 pA
Space proton energy:2~5 MeV
Total fluence: > 100 year Proton fluence in LISA orbit
80 pA Run 500 pA Run 15,000 pA RunProton Fluence Proton Fluence Proton Fluence1x1010 p/cm2 6.3x1010 p/cm2 2x1012 p/cm2
Page 21
Environmental Testing
UV LED in TO39 packaging tested at Ames Center Shake: 3g + 7g random vibration in all three axes Bake: thermal vac chamber -30°C~+ 60°C, including soakBeam profile, spectra, V-I-P curves staged measurementsPreliminary conclusion: PASS
Fiber coupled UV LED UV LED mounted for testing
Page 22
The Shake & Bake Setup at NASA AmesBake Chamber
UV LEDSMA
Packaging
Grating &Mount
UV LEDTOS39
Packaging
Z-direction shake test platform
x, y - direction shake test platform
Page 23
Shake & Bake Results
Before test After shake After shake & bake
BeamProfile
V-I-PCurves
Spectrum
Page 24
UV LED’s for LISA & LIGO Charge ControlLong lifetime >28,000 hours to dateRadiation hardLower power consumptionLower massAC modulation up to 1 GHz
UV LED
UV LED Performance
Page 25
NASA- StanfordGravity Reference NanoSatellites
NASA-Ames provides nanosatellitePlatform, payload integration, and mission operations
Stanford provides gravitational reference technologies
About one mission per year beginning in 2011
Estimated total cost per mission is $3-5M
RoadmapRoadmap2007 2008 2009 2010 2011
Technologies
Platforms
Launch Opportunities
Atlas VFalcon 1 Minotaur IVMinotaur I
3U Cubesat
Microsatellite Sorties
6U Cubesat
UV Diode Grating & Laser
Grating Displacement
Grating Interferometer
Caging Mechanism
Micro/Nanothrusters
Drag Free Flight
Formation Flying
Microsatellite Constellation
Tech. Integration
2Q 08 1Q 09 3Q 09 1Q 10 4Q 10 2Q 11 4Q 11
GeneBox ; Flown 16 July 2006GeneSat-1; Flown 16 Dec 2006Pharmasat-1; Launch 10 Dec 2007
Other Instruments
Other Capabilities
Overarching Goal: Provide Rewarding, Focused Objectives for the Next Generation of Space Scientists and Technologists
Towards ultra high precision gravitation referencesensors and multi vehicle space interferometry
1 pm/Hz1/2 Grating CavityDisplacement Sensor
256 nm Deep UV LED Roundest sphere and dragfree sensor
1 nrad/Hz1/2 gratingangular sensor
The ProgramFrequent launches on ride-along platformsStandard low cost bus configurations12 - 24 month project duration
The BenefitsNew science: Physical, Life, EngineeringCritical technology demonstrationsFast advance of NASA mission objectives Train engineers & scientists for the future
AMESGENESAT
STANFORD NANOSAT
Page 26
The First Planned ProjectUV LED Space Demonstration 2009-2011
Charge management for high precision GRSCalibration source for UV and X-ray telescope Telescope surface and window de-chargingLife maintaining system for space flight
Payload Functional Components
UV LEDUV LED PerformanceGENESAT
Nick Leindecker
Page 27
UV LED Testing to Date
63.8 MeV proton irradiation test
Output power maintained for total fluence 2x1012
proton/cm2 (>100 yr LISA )
Spectral shape and power intensity unchanged after proton irradiation
Lifetime test in N2> 28,000 hours
Llifetime test in vacuum: >17,500 hours
The spectra in N2 shifted to shorter wavelength ~2 nm
Lifetime TestLifetime Test Radiation TestRadiation Test
1) LED deep UV source for charge management of gravitational reference sensors, Ke-Xun Sun, B. Allard, S. Buchman, S. Williams, and R. L. Byer Class. Quantum Grav. 23 (2006) S141–S150 http://stacks.iop.org/0264-9381/23/S141
2) UV LED Space Qualification, Ke-Xun Sun, N. Leindecker, S. Higuchi, S. Buchman, R. L. Byer, J. Goebel, M. McKelvey, R. McMurray, Draft in refereeing
Shake test 3g + 7g random vibration in all three axes
Bake: thermal vacchamber -30°C~+ 60°C, +soak
Spectral shape and power unchanged
Shake& BakeShake& Bake