Array data handler

The Array Data Handler (ADH) is the ACADA subsystem responsible for handling the event triggers and the raw data from the data producers on-site . The main source of raw data are the Cherenkov cameras of telescopes, with a total throughput of 200 and 300 Gbps for the Northern and Southern sites, respectively. Such a volume would be difficult to transfer off-site and very costly to store and process. ADH thus implements the Software Array Trigger component and Data Volume Reduction step to only record events detected simultaneously by several telescopes and reduce the amount of data by a factor of 50, while retaining most of the information relevant to Science. Another factor of 2 or more will be achieved via formatting and lossless compression. The remaining data produced on-site can be categorised into three types: monitoring, engineering and auxiliary. The former two will be acquired from the monitoring subsystem once per day. Auxiliary data will be directly written to the on-site repository by the relevant subsystems. ADH is a cornerstone real-time subsystem of ACADA, featuring many interfaces and a distributed architecture. The coordination of this work is done at the Department of Astronomy / UniGe with Dr Eng. Etienne Lyard in first line and involves also ETHZ and partners in Germany and Poland. The interfaces to the Cherenkov cameras are designed and implemented with contributions from camera teams throughout Europe, Japan and the USA.