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Prospects to Use Silicon Photomultipliers for the Astroparticle Physics Experiments EUSO and MAGIC A. Nepomuk Otte Max-Planck-Institut für Physik München Outline • • • • • • A. Nepomuk Otte EUSO & MAGIC Why new photon detectors? Photon detector requirements The SiPM principle Development @ MEPhI and Pulsar Development @ HLL in Munich MPI für Physik 2 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/ A. Nepomuk Otte MPI für Physik 3 Major Atmospheric Gamma Imaging Cherenkov Telescope Gamma ray Particle shower ~ 10 km ~ 1o ~ 120 m http://hegra1.mppmu.mpg.de/MAGICWeb/ A. Nepomuk Otte MPI für Physik 4 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 A. Nepomuk Otte MPI für Physik 5 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) A. Nepomuk Otte • extend accessible energy range – overlap with existing experiments AUGER, AGASA, HIRES • detailed study of GZK cutoff • improved energy resolution MPI für Physik 6 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 A. Nepomuk Otte MPI für Physik 7 The Silicon Photomultiplier An avalanche photodiode (APD) in Geiger mode is a high efficient single photon counting device A. Nepomuk Otte MPI für Physik 8 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 A. Nepomuk Otte MPI für Physik 9 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) A. Nepomuk Otte MPI für Physik 10 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 A. Nepomuk Otte MPI für Physik 11 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 A. Nepomuk Otte MPI für Physik 12 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 A. Nepomuk Otte MPI für Physik P. Buzhan et al. NIM A 504 (2003) 48-52 13 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” A. Nepomuk Otte MPI für Physik output 14 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 A. Nepomuk Otte MPI für Physik 15 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 A. Nepomuk Otte MPI für Physik 16