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JET Neutron Neutron cameras/ Gamma-ray detectors Data Acquisition System

Another important requirement to modern data acquisition systems for fusion experiments is the capacity for real-time pulse processing. Such demand is required to reduce the amount of raw data stored in the experimental databases and will become particularly necessary for steady-state experiments such as ITER.

An example of implementation of such system is the JET Neutron Cameras Data Acquisition system where intelligent modules, with FPGAs, are used for real-time data processing, e,g. Pulse height analyzer, Pile-up rejection and Pulse shape discriminator. The developed system is based on ATCA and contains a 6 GFLOPS ix86-based control unit and three transient recorders and processing (TRP) modules interconnected through PCI Express links (SR-TR-ATCA). TRP modules features timing synchronisms, auto-trigger functionality, analysis/data reduction based on real time algorithms and the possibility to choose from a set of settled sampling frequencies. The system is composed by 19 channels, featuring 13 bit resolution with accuracy equal or higher than 11 bit to cope with the expected signal-to-noise ratio of the input pulses and sampling rates up to 250MSamples/s with the possibility to achieve 400 MSamples/s. Each channel will has 500MByte of local memory. The core of each TRP module is two FPGAs able to perform real-time processing algorithms such as Pulse Height Analysis (PHA) and pile-up rejection of digitized pulses. These will allow data reduction by a factor of at least 8 and eventually spectra output in real-time.

The Spatial distribution of the gamma-ray emission sources in the energy range greater than 1MeV in JET plasmas is measured using a gamma-ray camera (GRC) consisting of two arrays of collimators, vertical and horizontal, with 9 and 10 lines of sight, respectively. Each line of sight uses a cesium iodide, CsI(Tl), detector coupled to photo-diode with integrated pre-amplifier. Experimental data obtained from the 19 lines of sight allows tomographic reconstruction of the local gamma-ray emissivity in a poloidal cross-section. This gamma-ray camera belongs to the fast-electron-bremsstrahlung diagnostic system incorporated into a neutron profile monitor.


Publications

R.C.Pereira et al, ”ATCA data acquisition system for gamma-ray spectrometry”, Fusion Engineering and Design, 83(2008) 341

A. Neto et al., “The control and data acquisition software for the gamma-ray spectroscopy ATCA sub-systems of the JET-EP2 enhancements”, Fusion Engineering and Design, Volume 83, Issues 2-3, April 2008, Pages 346-349


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