OBSERVATORY

Future application of SiPMs for the fluorescence detectionof extensive air showers

Lukas Middendorf

Physics Institute IIIA

Digital Counting Photosensors for Extreme Low Light LevelsLisbon, 20.4.2012

Lukas Middendorf SiPMs for fluorescence detection of EAS 1

Outline

1 Extensive Air Showers

2 The Pierre Auger Observatory

3 FAMOUS – SiPM based fluorescence telescopeDesignExpected Performance

4 Summary & Outlook

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Lukas Middendorf SiPMs for fluorescence detection of EAS 2

Cosmic ray induced extensive air showers (EAS)

Earth atmosphere is constantly hit by cosmic ray particles with energiesup to several 1020 eVvery low flux⇒ no direct detection possible⇒ use earth atmosphere as calorimeter with large ground based detectorinteraction of particles with air produces multiple secondary particles⇒ extensive air showers down to the ground level

Lukas Middendorf SiPMs for fluorescence detection of EAS 3

Fluorescence detection of extensive air showers

edge of atmosphere

ground

X1

number of p

articles,

N

Xm

axslant

depth

θ

path of shower

fluorescence light

Xtelescope

FOVfluorescence lig

ht

air emits fluorescence light isotropicallywhen excited by shower particles (UV)light ∝ number of particles ∝ energymeasure longitudinal air showerdevelopmentdetermine energy and Xmax

[nm]λfluorescence photon wavelength250 300 350 400

Inte

nsity

Lukas Middendorf SiPMs for fluorescence detection of EAS 4

The Pierre Auger Observatory

hybrid cosmic ray detector for energies above 1018 eVin Argentine Pampameasures properties of extensive air showers

Surface Detector1600 water-Cherenkovdetector stations1.5 km tank spacingmeasures lateral distribution

Fluorescence Detector4 fluorescence telescope sites24 telescopesat array bordersfield of view (FOV) per site:6 · 30 × 30

Lukas Middendorf SiPMs for fluorescence detection of EAS 5

A Fluorescence Telescope

Schmidt cameraaperture diameter 2.2 m3.8× 3.8m2 mirror30 × 30 field of view (FOV)UV-pass filter

440 hexagonally arranged PMTs1.5 FOV per pixelPMT quantum efficiency ≈ 30%

Lukas Middendorf SiPMs for fluorescence detection of EAS 6

A Fluorescence Telescope

Schmidt cameraaperture diameter 2.2 m3.8× 3.8m2 mirror30 × 30 field of view (FOV)UV-pass filter

440 hexagonally arranged PMTs1.5 FOV per pixelPMT quantum efficiency ≈ 30%

Lukas Middendorf SiPMs for fluorescence detection of EAS 6

FAMOUS

First Auger Multi-pixel-photon-counter camera for the Observation ofUltra-high-energy air Showers

Small prototypefluorescence telescope for the measurement of extensive air showers

with silicon photomultipliers

Developed in Aachen, Granada and LisbonPedro Assis, Pedro Brogueira, Antonio Bueno, Miguel Ferreira, Josef Grooten, Thomas Hebbeker, Markus Lauscher,

Luís Mendes, Lukas Middendorf, Sergio Navas, Tim Niggemann, Barthel Philipps, Mário Pimenta, Angel Ruiz,Maurice Stephan, Franz-Peter Zantis

Lukas Middendorf SiPMs for fluorescence detection of EAS 7

SiPMs for

much higher possible photon detection efficiency (∼ 70%) compared tocurrently used PMTs (∼ 30%)demonstrated in prototypes (not currently available for purchase)better angular resolution possible

Build now to learn by manufacturing and demonstrate feasibility

Use Hamamatsu S10985-100C 2× 2 array with 100µm pitch (6× 6mm2

total size), ≈ 30% PDE in UV range

3.0 3.0

ch1 ch4

ch2 ch3

0.4

3.0

3.0

9.0±0.15

8.2 ± 0.15

Lukas Middendorf SiPMs for fluorescence detection of EAS 8

Basic telescope design

Fresnel lens Tube Camera pixels

510 m

m

107 m

m

OA

Focal plane

510 mm

simple refractive design

Lukas Middendorf SiPMs for fluorescence detection of EAS 9

1.5 field of view per pixel

Fresnel lens

remove thick “dead material” of lens⇒ concentric annular sections (“grooves”)approximate curved surface with linearslopeskeeps refraction power of original lens

reduced weightreduced absorptioncheap

compromise in image quality(bigger spot size)

small f /D possible⇒ much light per solid angle⇒ big field of view

Cut thick parts

groove

groove depth

Lukas Middendorf SiPMs for fluorescence detection of EAS 10

Fresnel lens

D = 510mmf = 510mmUV-transparentplastic (PMMA)

Lukas Middendorf SiPMs for fluorescence detection of EAS 11

Point spread function

Distribution of photons in focal plane

x / mm

­6 ­4 ­2 0 2 4 6

y /

mm

­6

­4

­2

0

2

4

6

rela

tiv

e i

nte

ns

ity

0

5

10

15

20

25

­310×

= 1.6 mm90

R

° = 0 in

θ

Optical System

Object Plane Focal Plane

LightLightSpotSpot

90% of light included inred circle R90: 1.6mm≈ 100% included in pixel(green)

simulation with Geant4

point size sufficient for 1.5 field of view per pixel

Lukas Middendorf SiPMs for fluorescence detection of EAS 12

Focal planemodular designhexagonal arrangement of pixelsone pixel: Winston cone (light concentrator) and 6× 6mm2 SiPM arrayUG-11 UV-pass filter64 pixels plannedmanufacturing test with 7 pixels

SiPMs

Light

Lukas Middendorf SiPMs for fluorescence detection of EAS 13

Winston cones

light concentrator

x [mm]-8 -6 -4 -2 0 2 4 6 8

z[m

m]

0

5

10

15

20 optical axis1r

2rcone

maxθ

light up to θmax is collected

tilted paraboloid surfacelight concentrated by factor 5maximum transmitted incidentangle θmax = arcsin(r2/r1) = 26.6

high exit angles up to 90

Lukas Middendorf SiPMs for fluorescence detection of EAS 14

Emergent angle of light from Winston cone

/ degout

θemergent angle 0 10 20 30 40 50 60 70 80 90

fracti

on

en

trie

s / t

ota

l co

un

t

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

0.2

0.22 ° = 0 in

θincident angle

° = 26 in

θincident angle

= 6.7 mm1r

= 3.0 mm2r

Lukas Middendorf SiPMs for fluorescence detection of EAS 15

Angle dependence of PDE

measured in AachenUse LED to illuminateSiPMnormalize signal to 0

correct for projection ofactive area

measurements can bedescribed by Fresnel equation(transmission and reflectionon surface of SiPM)

90% relative PDE up to incident angles of 60

Lukas Middendorf SiPMs for fluorescence detection of EAS 16

Readout electronics

based on MAROC3 chip64 channels (threshold)8 analogue sums (of 8channels)internal ADCs

individual control of bias voltagefor each pixelFPGA handles all digital functionsincluding trigger

design and production:Lisbon

SiPM signals

trigger &digitalization

digitalizedsignals

first prototype currently in productionLukas Middendorf SiPMs for fluorescence detection of EAS 17

Simulation of

Conex ShowerSimulation

Conex ShowerSimulation

EminEmax

ϕ ,θ

particle

interaction model

Auger OfflineSoftware

Auger OfflineSoftware Geant4Geant4

Fluorescence LightSimulation

Root Export

Modules

Atmosphere

Photon Propagation

telescope geometrynight-sky measurementsSiPM characterization

ComponentsComponents

Winston ConesWinston Cones

Fresnel LensFresnel Lens

SiPMsSiPMs

shower profile photons

shower distance

Lukas Middendorf SiPMs for fluorescence detection of EAS 18

event display

simulated vertical 1018.25 eV proton shower in 2 km distance

Lukas Middendorf SiPMs for fluorescence detection of EAS 19

Simulation of SiPM voltage traces

t / ns

18000 20000 22000 24000 26000 28000 30000

V /

mV

­6000

­5000

­4000

­3000

­2000

­1000

0

night­sky brightness

air shower

Aachen

baseline

phenomenological simulation of SiPM in progressLukas Middendorf SiPMs for fluorescence detection of EAS 20

1018 eV proton shower2 km shower distance

simulation

Expected performance

Expected event rates of air showers in Aachen for different energies E andshower distances Rp

(E/eV)10

log14 15 16 17 18 19

/ k

mp

R

2

4

6

8

10

12 ­1even

ts d

ay

­710

­610

­510

­410

­310

­210

­110

1­1Integral = 16 events day

S/N > 3

= 12 degfov

α

= 3.14 sr0Ω

= 10 %∈duty cycle Noise in Aachendominated by skybackground (90%):≈ 10 photonsper 33 ns - time binper pixel

Multiple events per night possible, even in AachenLukas Middendorf SiPMs for fluorescence detection of EAS 21

au Integral = 16 events per dayaaa

Summary & Outlook

Summaryextensive SiPM characterization studies doneoptical design for the new SiPM prototype fluorescence telescope

chosenDAQ and trigger electronics currently under developmentmechanical production partly donesimulations of make great progress

Outlookfinalize and build electronicsbuildfirst light this year

Lukas Middendorf SiPMs for fluorescence detection of EAS 22

Backup

Backup

Lukas Middendorf SiPMs for fluorescence detection of EAS 23

Absorption of Fresnel lens

[nm]λwavelength

200 300 400 500 600 700 800 900 1000

tra

ns

mis

sio

n T

[%

]

0

20

40

60

80

100

fluorescence light

Transmission of PMMA 8N (Reflexite, October 2004, d=3mm thickness)

]­1

[m

mα

ab

so

rpti

on

co

eff

icie

nt

0

0.1

0.2

0.3

0.4

0.5

0.6

dln T = ­ α

Transmission is > 90% for λ > 350 nm

Lukas Middendorf SiPMs for fluorescence detection of EAS 24

SiPM characterization studies in Aachen

temperature dependent breakdown-Voltagephoton detection efficiency

wavelength dependentovervoltage dependentangle dependent

crosstalk probabilityafterpulse probabilitytemperature dependent thermal noise rate

Lukas Middendorf SiPMs for fluorescence detection of EAS 25