Heidelberg 2015 – scientific programme

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HK: Fachverband Physik der Hadronen und Kerne

HK 41: Instrumentation 13

HK 41.2: Talk

Wednesday, March 25, 2015, 15:00–15:15, M/HS1

A new FPGA-based Time-over-Threshold System for the Time of Flight Detectors at the BGO-OD Experiment — •Oliver Freyermuth for the BGO-OD collaboration — Physikalisches Institut, Nussallee 12, D-53115 Bonn

The BGO-OD experiment at the ELSA accelerator facility at Bonn is built for the systematic investigation of meson photoproduction in the GeV region. It features the unique combination of a central, highly segmented BGO crystal calorimeter covering almost 4π in acceptance and a forward magnetic spectrometer complemented by time of flight walls.

The readout of the ToF scintillator bars was upgraded to an FPGA-based VME-board equipped with discriminator mezzanines including per-channel remotely adjustable thresholds. A firmware was developed combining a time-over-threshold (ToT) measurement by implementing a dual-edge TDC, a configurable meantimer trigger logic including a special cosmics trigger, adjustable input delays and gateable scalers, all inside a single electronics module.

An experimentally obtained relation between ToT and slope of a PMT signal can be used for a time walk correction to achieve time resolutions comparable to a classical chain of CFD and standard TDC. Additionally, the time-over-threshold information can be exploited for gain matching and allows to monitor online the gain-stability and check for electronics problems such as pulse reflections or baseline jitter.

The system is well-suited for a wide range of PMT-based fast detectors with many channels and further applications foreseen.

This work is supported by the DFG (SFB/TR-16).