MPI Seminar, October 7, 2008Thomas Schweizer,

Development of a new Development of a new low-threshold Trigger low-threshold Trigger Development of a new Development of a new low-threshold Trigger low-threshold Trigger

•M. Shayduk,

•M. Rissi, T. Schweizer, N. Otte, M. Lopez

•for the MAGIC collaboration

Padova, October 8-10, 2008

MPI Seminar, October 7, 2008Thomas Schweizer,

Analogue sum trigger concept

o Summation of patch of 18 pixels in 24 patchesin a ring-shape

o Idea: a) Summing up all single photons increases signal to noise ratio b) Fluctuations of shower larger than Poissonian fluctuations of NSB background

o Afterpulse problem: high noise rate

o Solution: clipping of signal

Discriminator threshold in PhE

Single pixel spectrum

with afterpulses

NSB

Afterpulses

SignalClipper

Σ

Analog sum of 18 pixels

SignalClipper

...

Discriminator

...

Clipped at 6-8 PhE

Threshold at 24-27 PhE

Effect of clipping the signal/Comparison of prototype test and MC

NSB

Afterpulses

Showers

Sum of 18 pixels

Trigger rate distribution vs threshold

Analogue sum trigger concept

o Optimization of the trigger pattern

30 GeV gammalight pool

Maximal probabilityto trigger at ~100m

Trigger region should be a ring around 0.6deg

Average Phot.Angle vs Impact

MPI Seminar, October 7, 2008Thomas Schweizer,

Optimization of trigger for lowest threshold

- 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)

Effe

ctiv

e a

rea

[m2]

Effective area

Standard Trigger

10 100 GeV

Sum Trigger

At 20 GeV:Factor 6 improvement

Installation in La Palma (October 2007)

Thomas Schweizer

Nepomuk Otte &

Maxim shayduk

Michael Rissi

MPI Seminar, October 7, 2008Thomas Schweizer,

Performance: Comparison standard trigger and sum trigger

25 GeVthreshold

sum trigger

55 GeVthreshold

standard trigger

Event distribution

MPI Seminar, October 7, 2008

Sum Trigger: Advantages

1. Low cost + simplicity (20kEuro, 2/3 of price: SMA connectors and cables !)

conventional OpAmps: OPA699, OPA695 .

2. Lowest possible trigger threshold (prove of principle: Crab Pulsar

Detection, 16th October,

Science ) .

3. Handles PMTs with rather high afterpulse rate (choose cheaper

PMs) .

4. Very low power consumption (no fast ECL comparators).

200 channels ~100 Watt !!! (5Vx20A)