M.Sc. degree thesis
accepted by Max-Planck-Institute for Physics, Munich, Germany

Dennis Haefner

Supervisor: Thomas Schweizer

Development of a new analog Sum-trigger for the MAGIC experiment with a continuously adjustable analog delay line and automatic calibration

 Keywords:

• Gamma telescopes
• Analogue electronic circuits
• Digital electronic circuits
• Trigger concepts and systems (hardware and software)

 Abstract:
The thesis presented here deals with a development in the field of high energy gamma-ray astronomy. In particular, I have improved and refined a novel trigger concept for the MAGIC telescope. MAGIC is currently the world's largest atmospheric Cherenkov telescope with the lowest energy threshold among ground-based systems dedicated to the detection of cosmic gamma radiation. With these telescopes one observes the Cherenkov light of so-called extended air showers induced by high energy cosmic rays impinging on the atmosphere. Due to their extremely faint intensity, these Cherenkov light flashes can only be observed in clear, dark nights. With a fraction of less than 0.01 percent of all air showers, gamma-ray induced showers are rather rare and strongly masked by the night sky background light of more than 10 to the 12 photons per square metre, second, and steradian. These dominating background processes require special trigger techniques and limit the lowering of the energy thresholds. The aim of my thesis is the development and fabrication of a completely revised and enhanced version of a new trigger concept - the so-called Sum-trigger - to further lower the energy threshold. The reduction of the trigger threshold opens up new prospects in the observation of pulsars, active galactic nuclei of high redshift and the so far not understood gamma-ray bursts in the energy range of 20 to 100 GeV. In addition, the trigger can contribute to the wider study of many other cosmic gamma-ray sources and to a deeper understanding of the formation processes of this radiation. The new Sum-trigger developed in this thesis is based on a first prototype made by the MAGIC collaboration in 2007. On three different printed circuit boards I built up and successfully tested the new trigger electronics. The extensive circuits combine analog and digital electronics, as well as programmable logic devices. To eliminate the need for costly manual tuning and maintenance demanded by the first prototype, a fully software-controlled, automatic calibration method was developed. The key element of the circuit is a novel, electronically controlled continuously variable analog delay line. It enables the temporal equalization of the signals from the camera photo sensors, whose timing differences are in the order of nanoseconds. This adjustment significantly reduces false triggers from background signals. The new trigger setup was successfully tested on the MAGIC telescope and a final version will soon be applied in the experiment, mainly intended for pulsar studies.