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The dependence of the CsI(Tl) scintillation time constants and intensities on the particle ionization profile is at the basis of the Charge and Mass identification technique for Light Charged Products in Intermediate Energy Nuclear Physics multi-detector arrays. The possibility of storing the digitized waveforms in true beam experiments allows performing further offline analyses and makes available a data set related to the interaction of different particle types in a wide energy range.

A 100 Msamples/s 14-bit sampling analog-to-digital converter has been used to perform digital pulse-shape acquisition of signals collected from CHIMERA telescopes. Two different kinds of tests have been carried out to check the performances. The signals from a typical CHIMERA detection cell have been collected using both a standard CHIMERA electronic chain up to the amplifier, and a very simple analog front end, basically reduced to the preamplifier. The obtained on-beam and on-line results are presented.

The CHIMERA 4/spl pi/ detector trigger system is described. The trigger decisions are based on a combination of geometrical multiplicity of detected particles and other logic signals. The trigger can manage the buffer memory of the used analog to digital converters. This allows performance of parallel data conversion and readout and substantial improvement of the acquisition system dead-time performances. The trigger module generates all the necessary gate signals for the converters and the control signals necessary to synchronize the readout. It also allows the remote control of the whole system.

We have built and tested a computational unit for on-line processing of special algorithms to be embedded in the central processing unit VERSAmodule Eurocard (CPU VME)-crate of the CHIMERA data acquisition system. The computational unit consists of a number of VME digital signal processor (DSP)-based commercial boards delivering 720 MFlops/board.

In nuclear physics at intermediate energies, the use of multidetector arrays consisting of thousands of detectors is customary. This paper presents a novel approach to the automatic classification of data collected by the 4/spl pi/ detector CHIMERA, constituted by 1192 telescopes of a thin silicon transparent detector coupled to a thick CsI(Tl) scintillator. The method is based on spatial density data processing and produces frequency distributions of the most significant physical parameters. These one-dimensional spectra can be more easily analyzed than the standard two-dimensional scatter plots. With respect to manual or semiautomatic procedures, presently used for data analysis, our method offers the advantages of drastic time reduction and unbiased criteria for cluster identification. The proposed method can be successfully used in both off-line data analysis and multidetector stability control.

CHIMERA is a second generation 4/spl pi/ detector for high resolution light particle and fragment measurements in the field of intermediate energy nuclear reactions. An enhanced data acquisition, control and trigger system has been developed to manage the almost 5000 electronic channels of the detector. The data acquisition system is based on a Fast Data Link (FDL) connection between 9U VME crates. The FDL is a highly programmable VME device. It performs data readout and transfer to a destination VME CPU, the FIC8243, running the real time OS9 operating system. Data read and transfer is performed by a fast protocol (Sparse Data Scan) whose performances have been improved introducing the Chained Block Transfer mode (CBLT) technique. Data collected by the CPU are broadcast to analysis work-stations for on-line data analysis and storage. All commands from and to the VME CPU are sent by socket-based network protocols. Complete remote control of the electronic front-end is obtained by a system of client-server applications. A first level event selection and control during readout is made by a trigger system based on a new VME 9U board (MUSE), fully integrated with the FDL readout system.

A commercial two-DSP-based board is the basic unit of the on-line computational and control system under development for the multidetector array CHIMERA. The system design includes a small scale parallel and distributed architecture of PCs and DSP boards. The PCs are used both as host computer and interface between user and network. Each PC can host up to three DSP boards. The system is able to accomplish the on-beam control of CHIMERA, by means of the on-line computation of special algorithms, instead of using the usual techniques of special pulses to be sent off-beam. The physical data, collected and organized in UDP packets by the data acquisition system, are read through a 10 Mbit/s Ethernet network. The PC software, running under Windows NT 4.0, is based on threads and assures the communication and program managing as well as the result presentation. The DSP-software is written in C++ and takes care of the communication with the PC and of the computation of algorithms. The preliminary on beam results for the first three wheels (about 100 telescopes), obtained by employing two biprocessor boards located in the PCI bus of a Pentium MMX PC, are also presented.

CHIMERA (Charged Heavy Ions Mass and Energy Resolving Array), a new 4/spl pi/ detector for charged particles is under development at various sites of the Istituto Nazionale di Fisica Nucleare. This paper describes the new data acquisition system built to handle the signals coming out from the detector with a rate up to 1 kHz on almost 5000 electronic channels. The required average throughput for the system is in the order of the 1 MB/s. The used converters allow double-range conversion on 15 bits, in less than 50 /spl mu/s for all the 64 channels. The FDL link connects the different VME 9U crates performing a programmable hardware readout with a rate up to 100 MB/s. It uses a fast hardware protocol (Sparse Data Scan) to read the data buffers and send them to a FIC 8243 CPU board. A FIC 8243 dual-processor board forwards data (through Ethernet) to the analysis station (266 MHz Digital AlphaStation or Sun Sparcstation). A DLT (Digital Linear Tape) unit connected to analysis station is used to store data. The new data acquisition system has been tested under beam conditions at the Laboratorio Nazionale del Sud (Catania, Italy) and at GANIL (Caen, France).