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Development of a new low-threshold Trigger

This study presents an analogue sum trigger concept utilizing a signal clipper for the MAGIC collaboration, aiming to improve signal-to-noise ratio and address the afterpulse issue. It includes discussions on photon summing, afterpulse problems, discriminator thresholds, signal clipping, and trigger optimization for gamma ray detection. The design offers advantages in cost-effectiveness, simplicity, low power consumption, and improved trigger efficiency.

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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

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