Transcript Folie 1 - Astroteilchenschule

Prospects to Use Silicon Photomultipliers for
the Astroparticle Physics Experiments EUSO
and MAGIC
A. Nepomuk Otte
Max-Planck-Institut für Physik
München
Outline
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A. Nepomuk Otte
EUSO & MAGIC
Why new photon detectors?
Photon detector requirements
The SiPM principle
Development @ MEPhI and Pulsar
Development @ HLL in Munich
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Extreme Universe Space
Observatory
Atmospheric
Sounding
30°

400 km


EECR
Atmosphere
Fluorescence
Čerenkov
230 km
Earth
M .C .M .
‘0 2
http://www.euso-mission.org/
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Major Atmospheric Gamma
Imaging Cherenkov Telescope
Gamma
ray
Particle
shower
~ 10 km
~ 1o
~ 120 m
http://hegra1.mppmu.mpg.de/MAGICWeb/
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Motivation for new Photon Sensors
Photon detection efficiency (PDE) of state of the art photomultiplier tubes
≈20%
A higher PDE results in a better signal to noise ratio (SNR)
SNR 
PDE  signal
signal
 PDE 
PDE  ( signal  LONS )
signal  LONS
≈ 80% PDE improves SNR by a factor 2…3
Same effect as increasing the MAGIC mirror from 17m diameter to 70m
Both experiments can lower their energy threshold with more sensitive sensors
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What is gained by a lower Threshold?
MAGIC
EUSO
• access to lower γ-energies
→ deeper look into the universe
(higher redshifts)
→ new sources
→Egret 280 sources with 0.1m²
active detector area (<10GeV)
→ACT‘s 15 sources with 5•104m²
active detector area (>300GeV)
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• extend accessible energy
range
– overlap with existing
experiments AUGER,
AGASA, HIRES
• detailed study of GZK
cutoff
• improved energy resolution
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Photon Detector Requirements
sensitive
range
[nm]
sensor
size
[mm²]
single
photon
counting
dynamic
range
per sensor
[phe]
max. dark
noise
per pixel
[1/s]
rate
capability
per pixel
[1/s]
detection
efficiency
radiation
hardness
EUSO
330…400
4x4
yes
100
104
105
>50%
yes
MAGIC
300…600
30 x 30
yes
1000
107
108
>20%
no
most requirements are similar
large differences in sensitive range and pixel size
challenging: detection efficiency
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The Silicon Photomultiplier
An avalanche photodiode (APD) in Geiger mode is a high
efficient single photon counting device
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The Silicon Photomultiplier
An avalanche photodiode (APD) in Geiger mode is a high
efficient single photon counting device
BUT:
Output signal of a single Geiger APD is independent
of number of photoelectrons
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The Silicon Photomultiplier
An avalanche photodiode (APD) in Geiger mode is a high
efficient single photon counting device
…
BUT:
Output signal of a single Geiger APD is independent
of number of photoelectrons
Solution:
Combine an array of small Geiger APDs onto the
same substrate (less then 1 photon per cell)
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Development @ MEPhI and Pulsar
Enterprize
1 mm
P. Buzhan et al.
http://www.slac-stanford.edu/pubs/icfa/fall01.html
1 mm
about 20% active area limits photon detection efficiency
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Characteristics
characteristics of current prototypes:
geometry: 24 x 24 pixels = 576 pixels within 1mm2
available up to 1024 pixels / mm²
Operating voltage: 50 V to 58 V
Gain: 105 up to ~ 5•106
single pixel time resolution: 570 ps FWHM
single pixel recovery time: 1μs
dark count rate: 106 counts per second at room temperature
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R&D Goals to improve existing
MEPhI-Pulsar Prototypes
Luminescence of hot avalanche electrons gives rise to
crosstalk with neighboring APD cells (40% @ Gain 106)
Counter measures:
• grooves between pixels to absorb photons
• reduce gain (4% Crosstalk @ Gain 105)
Photon detection efficiency determined by:
• Intrinsic QE
• packing density of pixels
• Geiger breakdown probability
• transmittance of entrance window
work on:
• reduction of dead area
• improve blue sensitivity
• optimization of entrance window
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P. Buzhan et al. NIM A 504 (2003) 48-52
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Development @ MPI Semiconductor
Laboratory in Munich
Different approach to increase photon detection efficiency
use of back illumination principle
→ no dead area
photon
depleted bulk
path of the photo electron
avalanche regions
50µm … 450µm
Si
Blow up of one “micro pixel”
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Development @ MPI Semiconductor
Laboratory in Munich
shallow p+
drift path of a photo electron
photon
n bulk
drift rings p+
50µm...450µm
deep n
avalanche region
quench resistor
100µm
output line
Simulations are in final stage:
• Operating voltage of avalanche region 50V
• Geiger breakdown probability 60%...90%
• average drift time differences < 1ns
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Summary and Outlook
•We investigate the SiPM as photon detector in MAGIC and EUSO
•First SiPM prototypes are very promising
•SiPM prototypes already usable for some applications (e.g. PET, TileCal for Tesla)
•The development is pursued in two different ways
-front illumination @ MEPhI and Pulsar
-back illumination @ HLL in Munich
•A lot of R&D ahead:
increase effective QE up to 70%
increase UV sensitivity
reduce crosstalk
increase SiPM size
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