Operation with Exogam and with VAMOS

A dedicated data acquisition system is being assembled for EXOGAM, which will be based on the MIDAS system developed by the UK for the previous gamma-ray arrays Eurogam and Euroball. It will comprise a DT32 bus output from the VXI electronics (VME eXtension for Instrumentation), an event builder using VME processors, a VME tape server and several workstations for event monitoring and sorting. The multi-parameter event data are read out and transferred over the VXI back plane into a buffer in the crate readout controller. The readout of the data from the buffers takes place over a fast 32 bit data transfer bus known as the DT32 bus. The EXOGAM trigger system will use a simple ``common dead time" method of operation which means that once EXOGAM starts to process an event the system is dead and no further events will be accepted until the first event is either aborted or stored in the VXI readout buffers. The only effect that another event may have during the dead time is to cause pileup indicators to be set in the detector electronics cards. TIARA can trigger the readout using conventional NIM logic electronics to provide a single logic pulse to the system. The electronics for the VAMOS magnetic spectrometer is being designed to operate seamlessly in conjunction with Exogam. The buffering of the Exogam readout of events imposes complications on the operation of the system with other electronics for other detector arrays such as TIARA. The digitizing electronics must be similarly buffered and integrated into the system. The most effective solution is to take advantage of the complete Exogam infrastructure and to feed the amplified signals from the TIARA NIM electronics into VXI digitizing cards incorporated in Exogam. This is easily achieved by supplementing the Exogam standard system for so-called ancillary detectors with dedicated TIARA digitization electronics in the VXI crates. The necessary analogue-to-digital converters are a modification of the standard GANIL ADC's that are presently used by the Charissa collaboration with the type of electronics proposed here. The input circuits and performance are identical, and the modification is simply in the event-buffering of the output. These VXI ADC units are built by GANIL in 64-channel D-size VXI units. The UK has substantial development in the specification, implementation and maintenance of the Exogam data acquisition software, principally through the Daresbury laboratory.

 

Figure 10: Schematic layout of the Exogam data acquisition system, showing how the TIARA channels can be integrated with the events via the purchase of D-size VXI 64-channel ADC cards.

Thus, for TIARA operation with the Exogam array in its home location the best solution is to purchase 4 of the special buffered-output GANIL-style VXI ADC cards.