The CIP2k first-level trigger system at the H1 experiment at HERA

The ep-collider HERA at DESY, Hamburg/Germany has been upgraded in the years 2000-2002 to deliver a five-fold increased specific luminosity to the collider experiments H1 and ZEUS. In order to cope with the increased event rate, modifications have been made to the experiments. One of the upgrade projects for the H1 experiment was a new set of multiwire proportional chambers (CIP2k) providing information to distinguish between events induced by beam background, and ep-interactions at an early stage of the trigger. This new first-level trigger system provides a trigger decision using a total of about 10 000 channels of the chamber digitized at a speed of 10.4 MHz. The trigger decision is delivered within 1.5 μs. Since all stages of the trigger are based on an event pipelining technique the trigger system is running dead-time free. The trigger logic is realized in large field programmable gate arrays (FPGAs) using the hardware description language Verilog. The CIP2k trigger system was installed in 2001 in parallel to the HERA startup and is now being commissioned in order to optimize its performance. The flexible programmable hardware clearly is a big advantage here.