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LISA, 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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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.

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

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

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

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

Shake & Bake Results

Before test After shake After shake & bake

BeamProfile

V-I-PCurves

Spectrum

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

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

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

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

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