IEEE TRANSACTIONS ON NUCLEAR SCIENCE, VOL. 52, NO. 6, DECEMBER 2005 1 The Data Acquisition System of the Stockholm Educational Air Shower Array Petter Hofverberg, Henrik Johansson, Mark Pearce, Stefan Rydström, and Christian Wikström Abstract—The Stockholm Educational Air Shower Array (SEASA) project is deploying an array of plastic scintillator de- tector stations on school roofs in the Stockholm area. Signals from GPS satellites are used to time synchronise signals from the widely separated detector stations, allowing cosmic ray air showers to be identified and studied. A low-cost and highly scalable data acquisition system has been produced using embedded Linux processors which communicate station data to a central server running a MySQL database. Air shower data can be visualised in real-time using a Java-applet client. It is also possible to query the database and manage detector stations from the client. In this paper, the design and performance of the system are described. Index Terms—Aair showers, cosmic rays, high schools. I. INTRODUCTION T HERE are a growing number of cosmic ray air shower de- tector arrays operational around the world which use high schools sites as nodes for the detectors. Some examples are the ALTA [1], CHICOS [2], HiSParc [3], and WALTA [4] projects. A key aspect of these projects is that students and teachers are actively involved in the construction and operation of the de- tector systems. The Stockholm Educational Air Shower Array (SEASA) [5] project is establishing a network of cosmic ray air shower de- tector stations over the Stockholm region. Each station consists of three large plastic scintillator detectors arranged in a trian- gular formation (see Fig. 1 for an example of the detector setup). Cosmic ray activity at stations separated by arbitrary distances is correlated using timing signals from GPS navigation satellites. A primary aim of the project is to give high school students, aged between 16 and 18 years, the possibility to gain insight and work on a modern research project and so the detector sta- tions are located at the high schools (on roofs or in attics). The students themselves will participate in the construction, testing, installation, commissioning, and running of their detector sta- tion. As well as these “outreach” aims, scientific studies are also foreseen. A particularly interesting prospect is to study corre- lations between stations separated by large distances (e.g., be- tween towns) in order to identify cosmic rays sharing a common history. Such correlations could arise from the solar photo dis- integration of heavy nuclei [6] or transient cosmic gamma-ray activity [7]. During the first phase of the project in 2005, the net- work will consist of seven detector stations located at AlbaNova Manuscript received September 9, 2005;<AUTHOR: PLEASE PROVIDE REVISED DATE.> revised xxxx. This work was supported by the Göran Gustafsson Foundation. The authors are at the Royal Institute of Technology (KTH), Stockholm, Sweden (e-mail: petter@particle.kth.se). Digital Object Identifier 10.1109/TNS.2005.XXXXX Fig. 1. Top: One of the two detector stations on the roof of the main AlbaNova University Centre building. The scintillators are housed in car roof boxes for weather protection, and are separated by approximately 15 m. The GPS antenna can bee seen as a white triangle close to the leftmost car roof box. The white object in the centre of the image is a skylight. Bottom: One of the boxes opened showing the plastic scintillator, wrapped in reflective material, and the photomultiplier glued on top. University Centre and four high schools. Additional stations are expected to be installed at other high schools both within and outside of Stockholm in subsequent years. In the next section, an overview of the system design is given. This is followed in Section III by more details of the data ac- quisition system. Section IV describes the software design, and results are presented in Section V. Finally, conclusions and an outlook are given in Section VI. II. DETECTING AND VISUALISING AIR SHOWERS When a high energy cosmic ray interacts at the top of Earth’s atmosphere, a cascade of secondary particles is created and to a good approximation moves through the atmosphere as a thin disk. Depending on the energy of the primary particle, the radius of the disk at ground can range from tens of meters to kilome- ters for the highest energy particles. As the flux of the interesting highest energy cosmic rays is low, a large detecting area is de- sirable. 0018-9499/$20.00 © 2005 IEEE