An upgraded data-acquisition system for the balloon-borne liquid xenon γ-ray imaging telescope LXeGRIT

LXeGRIT is a balloon-borne Compton telescope for MeV gamma -ray astrophysics, based on a liquid xenon time projection chamber (LXeTPC) with charge and light readout. The first balloon flights in 1997 revealed limitations of the trigger electronics and the data-acquisition (DAQ) system, leading to their upgrade. New electronics was developed to handle the xenon scintillation light trigger. The original processor module was replaced by a commercial VME processor. The telemetry rate was doubled to 2 x 500 kbps and onboard data storage on hard disks was implemented. Relying on a robust real-time operating system, the new DAQ software adopts an object-oriented design to implement the diverse tasks of trigger handling, data selection, transmission, and storage, as well as DAQ control and monitor functions. The new systems performed well during two flights in spring 1999 and fall 2000. In the 2000 flight, the DAQ system was able to handle 300-350 triggers/s out of a total of about 650 Hz, including charged particles.