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Development of a new low-threshold Trigger
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  1. Development of a new low-threshold Trigger • M. Shayduk, • M. Rissi, T. Schweizer, N. Otte, M. Lopez • for the MAGIC collaboration Padova, October 8-10, 2008

  2. Analogue sum trigger concept Signal Clipper Signal Clipper • Summation of patch of 18 pixels in 24 patchesin a ring-shape • Idea: a) Summing up all single photons increases signal to noise ratio b) Fluctuations of shower larger than Poissonian fluctuations of NSB background • Afterpulse problem: high noise rate • Solution: clipping of signal Single pixel spectrum with afterpulses Analog sum of 18 pixels NSB Σ ... ... Afterpulses Discriminator Threshold at 24-27 PhE Discriminator threshold in PhE Thomas Schweizer, MPI Seminar, October 7, 2008 Clipped at 6-8 PhE

  3. Effect of clipping the signal/Comparison of prototype test and MC Trigger rate distribution vs threshold Sum of 18 pixels NSB Afterpulses Showers

  4. Analogue sum trigger concept • Optimization of the trigger pattern 30 GeV gamma light pool Maximal probability to trigger at ~100m Average Phot.Angle vs Impact Trigger region should be a ring around 0.6deg

  5. Optimization of trigger for lowest threshold Effective area Sum Trigger Effective area [m2] Standard Trigger At 20 GeV: Factor 6 improvement 10 100 GeV - Pulse width of sum signal: 2.5-3.0 ns (Signal/NSB ratio) - Number of pixels in analogue sum: 12-18 pixels - Clipping level (6-8 PhE) - Shape of patches (oriented toward center) - Topology of trigger region (optimal for 10-20 GeV showers) Thomas Schweizer, MPI Seminar, October 7, 2008

  6. Installation in La Palma (October 2007) Nepomuk Otte & Maxim shayduk Thomas Schweizer Michael Rissi

  7. Performance: Comparison standard trigger and sum trigger Event distribution 25 GeV threshold sum trigger 55 GeV threshold standard trigger Thomas Schweizer, MPI Seminar, October 7, 2008

  8. Sum Trigger: Advantages • Low cost + simplicity (20kEuro, 2/3 of price: SMA connectors and cables !) conventional OpAmps: OPA699, OPA695 . • Lowest possible trigger threshold (prove of principle: Crab Pulsar Detection, 16th October, Science ) . • Handles PMTs with rather high afterpulse rate (choose cheaper PMs) . • Very low power consumption (no fast ECL comparators). 200 channels ~100 Watt !!! (5Vx20A) MPI Seminar, October 7, 2008