The TPC Trigger for the Delphi Experiment

A hardware trigger has been designed for the Time Projection Chamber of the DELPHI Experiment. It will have two different levels, a fast and simple one, and a second one, which is more precise. On the first level, a system of shift registers is used to search for track pieces in less than 1 μs. The second level uses a specialized track finding device (the "Contiguity Processor") with a highly parallel structure. It follows tracks through the TPC in about 8 its after the drift time. The use of specially designed gate arrays permits to build a system with high granularity at reasonable complexity and cost, which also will provide a good background rejection. In this report, we describe briefly the general trigger situation in the experiment and then the principle ideas of the two TPC trigger systems. In addition, we describe the technical implementation of both systems.