Electronics for Large Arrays of Cherenkov Detectors Frank Krennrich, Iowa State University Actis et al. (CTA Consortium), arXiv:1108.3703v3 CPAD Electronics for large arrays of Cherenkov detectors Frank Krennrich Iowa State University
Cherenkov Telescope Array (CTA) • What is CTA? - ground-based successor to MAGIC , VERITAS, HESS & Fermi will revolutionize VHE ! -ray science - 10 GeV – 100 TeV with ten times better sensitivity - 1 km 2 array of Cherenkov telescopes - 3 different telescope sizes : Small Size Telescopes, Medium Size Telescopes , Large Size Telescopes • What will CTA do? Particle Physics Astrophysics & Cosmology - Dark Matter annihilation - Galactic/extragalactic particle acceleration - Lorentz invariance violation - Origin of intergalactic/cosmological B-fields - EBL; axion-like pseudoscalar bosons - Black holes & relativistic jets “ Discovery machine ” for particle astrophysics & astronomy at the TeV scale
Imaging Atmospheric Cherenkov Energy Range Major Step (flux sensitivity): advance the 100 GeV - 10 TeV regime: • 60 element array of 12m tels. • wide FOV • high resolution camera Major Step (expand E-range): • add 20-24 m tels. (LST) • add small size telescopes (SST) ( camera dominates cost ) Telescope design drawings from Actis et al. (CTA Consortium), arXiv:1108.3703v3 70 SST 4 LST 60 MST
The Road to better sensitivity # pixels ! # teles. + wide FoV + fine pixels # telescopes ! angular resolution collection area mid size telescopes small size telescopes 0.1-10 TeV 10 -100 TeV count rate limited background dominated
Air Cherenkov Technique: #$ / $ ~ 30-40% ! /hadron separation proton shower ! -ray shower ~ 10 km " C ~ 0.3 o – 1 o # t ~ 5 ns 5 o 300 m
Air Cherenkov Technique: #$ / $ < 15% Angular resolution shower height angular resolution ~ 0.1 o shower core location
Step 1: Large array concept Event containment: - angular resolution - background rejection - collection area x 10 100 m ! CPAD Electronics for large arrays of Cherenkov detectors Frank Krennrich Iowa State University
Step 2: wide field of view telescope Large Field of View: - increases # of telescopes in shower reconstruction - better angular resolution - improved background 100 m ! rejection Event containment only works for minimum size of array, so that combination of collection area and ang. Resolution are achieved! CPAD Electronics for large arrays of Cherenkov detectors Frank Krennrich Iowa State University
Optimum # of telescopes for 1 km 2 MST array? 1000 22 y, m 61 tels. (8° FoV) 1000 22 Cherenkov light images - Sky y, m 4 tels. (3.5° FoV) 20 800 20 800 18 18 600 600 16 16 400 400 14 14 200 200 12 12 0 0 10 10 -200 -200 8 8 -400 -400 6 6 -600 -600 4 4 -800 -800 2 2 -1000 -1000 -800 -600 -400 -200 0 200 400 600 800 1000 -1000 -1000 -800 -600 -400 -200 0 200 400 600 800 1000 x, m x, m 2 Detection Area, km ° 61 tel 8.0 ! ° 25 tel 8.0 ! ° 4 tel 3.5 ! array with 1 nearly optimum angular -1 10 Funk, S. & resolution Hinton, J. 2009 Bugaev, S. 2011 5 10 15 20 25 Minimal Number Of Triggered Telescopes
Step 3: Novel High resolution wide FoV telescope ~ 0.2° ~ 0.07° DC SC Focal plane – very compact 8° CPAD Electronics for large arrays of Cherenkov detectors Frank Krennrich Iowa State University
Step 3: Novel High resolution wide FoV compact camera Si-PMs ~ 0.2° ~ 0.07° DC SC Biland et al. 2011, Cherenkov light images Recorded under full moon MAPMTs CPAD Electronics for large arrays of Cherenkov detectors Frank Krennrich Iowa State University
Step 3: Novel High resolution wide FoV compact camera Si-PMs ~ 0.2° ~ 0.07° DC SC MAPMTs - reduced plate scale allows the use of Si-PMs & MAPMTs - significant potential cost savings through high QE, lower cost pixels & compact camera CPAD Electronics for large arrays of Cherenkov detectors Frank Krennrich Iowa State University
# of Pixels Current CTA southern site Beyond CTA generation: 2016 - … 2020 - … MAGIC, HESS, VERITAS # telescopes 2 - 4 ~ 140 ? # pixels/camera 500 – 1,000 1,300 – 12,000 ? pixel size [°] 0.15 – 0.2 0.07 – 0.25 0.02 – 0.1 field of view [°] 3.5 – 5 5 – 10 ? total # pixels 1,500 – 4,000 ~ 600,000 ~ 10 7 – 10 8 ? photo detectors PMTs ($300) MAPMTs/SiPMs/ PMTs SiPMs, …? cost per pixel [$] $1,000 – 2,000 $ 100 - $400 < $10 CPAD Electronics for large arrays of Cherenkov detectors Frank Krennrich Iowa State University
Signal Recording Cherenkov light flashes from air showers are short: ~ 2-10 ns CPAD Electronics for large arrays of Cherenkov detectors Frank Krennrich Iowa State University
Signal Recording Sampling with ~ 1 GHz adequate … recording pulse shapes with sufficient resolution important : - muon/cosmic-ray rejection - noise rejection from NSB (night sky background) - account for time gradients across C-light images - jitter detection and correction (systematics) CPAD Electronics for large arrays of Cherenkov detectors Frank Krennrich Iowa State University
Signal Recording Sampling with ~ 1 GHz adequate … recording pulse shapes with sufficient resolution important : - muon/cosmic-ray rejection - noise rejection from NSB (night sky background) - account for time gradients across C-light images - jitter detection and correction (systematics) CPAD Electronics for large arrays of Cherenkov detectors Frank Krennrich Iowa State University
Analogue sampling memories Actis et al. (CTA Consortium), arXiv:1108.3703v3 recording pulse shapes with analog sampling memories : - highly integrated into a single multi-channel ASIC (16 TARGET, 8 DRS4) - low cost per channel of a few $10 - TARGET for high pixelation cameras - separate circuitry for trigger (buffer 16 µ s) - low power 10 – 50 mW/channel CPAD Electronics for large arrays of Cherenkov detectors Frank Krennrich Iowa State University
Alternative Signal Recording Sampling with ~ 200 MHz marginal … CPAD Electronics for large arrays of Cherenkov detectors Frank Krennrich Iowa State University
Flash ADCs ~ 1 GHz Actis et al. (CTA Consortium), arXiv:1108.3703v3 recording pulse shapes with FADCs : - continuously digitizes photo-sensor signals - no separate camera trigger circuitry needed ( fully digital trigger ) - high power usage & cost " not suitable for compact/high res. cameras - available inexpensive FADCs limited to ~ 200 MSamples/s CPAD Electronics for large arrays of Cherenkov detectors Frank Krennrich Iowa State University
Triggering & clock distribution *single telescope: 10 kHz, 10 3 – 10 4 pixels, 2 bytes/pixel caveat : bursts/ rate fluctuations up to 1 MHz possible due to NSB CPAD Electronics for large arrays of Cherenkov detectors Frank Krennrich Iowa State University
Array Trigger Scenarios - exchange of time stamps " n-tel time coincidences (reduce rates from NSB, reduces CR background by factor of 2) - exchange of imaging info " basic stereoscopic analysis (reduces background from CRs by factor of 10) 3 different approaches : a) no real-time array trigger: perform event building in off-line analysis (rate spikes ! paralyze DACQ!) b) write data into camera buffer (FPGA) continuously, distrib. time stamps (coincidences), determine if data be kept (1 ms) c) distribute image & timing info from FPGA-based camera trigger to neighbor telescopes, form array coincidences based on time stamps & simple stereo analysis (<10 µ s) CPAD Electronics for large arrays of Cherenkov detectors Frank Krennrich Iowa State University
Array Trigger ! FPGAs Timing + Stereo Imaging in real-time ( < 3 µ s) Fast FPGA, ATCA CPAD Electronics for large arrays of Cherenkov detectors Frank Krennrich Iowa State University
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