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The electronics of the INDRA 4Pi detection array

J. Pouthas et al

Nuclear Instruments and Methods in Physics Research A 369 (1996) 222-247

INDRA is a 4Pi detection array designed for the studies of "hot nuclei" at the heavy ion accelerator GANIL. The INDRA
multidetector is composed of 96 ionization chambers, 196 silicon detectors, 324 CsI(T1) scintillators and 12 NE102/NE115
phoswich detectors. This article describes the associated electronics. The signal treatment is performed through specifically
designed modules, most of which are in the new VXIbus standard. This standard allows us to considerably reduce the
number of modules by regrouping many functions in the same module. For example, all the functions related to 24 CsI(T1)
scintillators are stacked in one D-size module. VXIbus also provides the opportunity to locate all the electronics close to the
detector, in the beam cave, with full remote control (VXI-VME buses) including visualization of analogic and logic signals
on oscilloscopes. The large dynamic range (4000 to l) required for the silicon detectors is reached by means of a new
method : a low noise amplifier providing a unipolar signal which is charge integrated and converted on two dynamic ranges.
The trigger system relies on a new working mode called "asynchronous mode" and performs event selections based on
multiplicity functions which are built up from subgroups of detectors. The performances of the data acquisition and the
graphical software packages which were developed to set up and control the electronic parameters are also presented.