A novel FRS Data Acquisition

In the experiments involving the use of in-flight radioactive beams the selectivity and the detection of the rare products are very demanding. Using faster processing and data acquisition (DAQ) is also important and can be crucial for the realization of those experiments that otherwise may require a non realistic beam time. In particular, here we concern with experiments which can be performed at the GSI Fragment Separator (FRS) [1], where the count rate is limited to 10 6 pps due to an event-by-event basis detection. Depending on the reaction channel the number of parameters involved can change up to a factor 100. This is strictly connected to the used detectors and their electronics. Until now the FRS standard DAQ was working under the GSI Multi-Branch-System (MBS) [2] in the so called single event mode. The data sender is a RIO-3 CES (800MHz) processor which is located in the FRS VME crate. In this case, each event (i.e. VME ADC, TDC, QDC signals) is read out at each accepted trigger as 34 words. During this period, typically 120 μs, the DAQ is busy and any other trigger is rejected. This fixes the dead time. Recently we have considered the use of a more efficient read out in BLock Transfer mode (BLT), which is supported by the VME Caen modules. A BLT read out of 32x34 words takes place and allows to read all events stored in the buffer (multi event mode). Whenever the buffer is empty a Bus error is generated.