Search

A new high efficiency, high resolution, fast γ-ray spectrometer was recently installed at the JET tokamak. The spectrometer is based on a LaBr3(Ce) scintillator coupled to a photomultiplier tube. A digital data acquisition system is used to allow spectrometry with event rates in excess of 1 MHz expected in future JET DT plasmas. However, at the lower rates typical of present day experiments, digitization can degrade the energy resolution of the system, depending on the algorithms used for extracting pulse height information from the digitized pulses. In this paper, the digital and analog spectrometry methods were compared for different experimental conditions. An algorithm based on pulse shape fitting was developed, providing energy resolution equivalent to the traditional analog spectrometry method. [ABSTRACT FROM AUTHOR]

In fusion plasmas gamma ray emission is caused by reactions of fast particles, such as fusion alpha particles, with impurities. Gamma ray spectroscopy at JET has provided valuable diagnostic information on fast fuel as well as fusion product ions. Improvements of these measurements are needed to fully exploit the flux increase provided by future high power experiments at JET and ITER. Limiting aspects are, for instance, the count rate capability due to a high neutron/gamma background combined with slow detector response and a modest energy resolution due to the low light yield of the scintillators. This paper describes the solutions developed for achieving higher energy resolution, signal to background, and time resolution. The detector design is described based on the new BrLa3 scintillator crystal. The paper will focus on hardware development, including a photomultiplier tube capable of stable operation at counting rate as high as 1 MHz, the magnetic shielding, and the fast digital data acquisition system. [ABSTRACT FROM AUTHOR]

The magnetic proton recoil neutron spectrometer has been upgraded (MPRu) with a new focal plane hodoscope detector as a major part to improve the immunity to background and to extend the measuring range from 18 down to 1.5 MeV. The MPRu detector project has entailed the development of the phoswich technique for this application. This was done through tests of prototype scintillators to reach the final design. The article reports on the tests conducted, the projected specification, and demonstrated performance through the first MPRu results obtained at JET. [ABSTRACT FROM AUTHOR]

The MPRu is an upgrade of the magnetic proton recoil (MPR) neutron spectrometer that has been used for 14 MeV DT neutron measurements at JET during the DTE1 (1997) and TTE (2003) campaigns. In this contribution the principles of the MPR and its upgrade will be presented. The MPRu allows measurements of the full range of fusion relevant neutron energies, 1.5–18 MeV, including the 14 MeV DT neutrons, now with significantly reduced background, and also new high-quality measurements of the 2.5 MeV DD neutron component. This improvement is made possible by the use of a new proton recoil detector in combination with custom-built transient recorder cards. The importance of these instrumental improvements for extending the use of the MPRu in diagnosis of D and DT plasmas will be discussed. Results from the first 2.5 MeV measurements performed with the MPRu during JET high level commissioning in April 2006 are presented. [ABSTRACT FROM AUTHOR]

A new, real-time, distributed, control and data acquisition system architecture for long duration fusion experiments was developed based on the new optical communications technologies and the "System on a Chip" methodology. The architecture integrates data routing, data storage, real-time data processing and control and data acquisition nodes, interconnected by a switched-packed, gigabit, point-to-point, communications network. The routing nodes provide connections to the autonomous storage and processing nodes through standard network links. The control and data acquisition nodes are connected to the routing nodes by specifically designed optical links which provide both data transport and timing/synchronism support. The acquired data are time stamped and can be dynamically processed for local control or sent to the external storage, the real-time processing or the control nodes. The standard processor and the reconfigurable field programmable gate array included in each node allow the programming of the data reduction, adaptive signal processing, and control algorithms from a high level system description language. All nodes will be controlled through an instrumentation-specific implementation of the Extensible Markup Language. A control and data acquisition node with 32 independent and galvanically isolated analog channels of 16 bits resolution is under development. All input signals are continuously and simultaneously sampled at a rate of 2 MSPS, time stamped, optionally digitally filtered, and stored in a large circular memory buffer. Three other node configuration sets will also be implemented: 16 channels, 20 MSPS, 16 bit; 8 channels, 100 MSPS, 12 bit; 2 channels, 1 GSPS, 8 bit. [ABSTRACT FROM AUTHOR]

This article presents a new event-driven processing platform which uses a mixture of digital signal processors and field programmable gate arrays to provide data reduction and real-time processing and control capabilities for long discharge fusion experiments. The architecture and physical implementation aims to provide more processing power, a mathematical algorithm description interface, and an easy integration with existing acquisition systems as well as the seamless integration with an event-driven data acquisition and control system for current and upcoming fusion experiments. A complete framework from the algorithm description to the physical implementation of the new platform in a heterogeneous processing system will be described. [ABSTRACT FROM AUTHOR]

A time-of-flight neutron spectrometer (TOFOR) has been developed to measure the 2.45 MeV d+d→3He+n neutron emission from D plasmas. The TOFOR design features the capability to operate at high rates in the 100 kHz range, data collection with fast time digitizing and storing, and monitoring of the signals from the scintillation detectors used. This article describes the principles of the instrument and its installation at JET and presents preliminary data to illustrate the TOFOR performance as a neutron emission spectroscopy diagnostic. [ABSTRACT FROM AUTHOR]

A set of PCI instrumentation modules was developed at the EURATOM/IST Association. The modules were engineered around a reconfigurable hardware core which permits one to reduce the development time of instrument for new applications, provide support for long time or even continuous operation, and is able to perform real-time digital signal processing. The core was engineered at low cost and the modules incorporate a high number of channels, which contribute to reduce the total cost per channel. Field results are as expected in terms of performance both in data throughput and input characteristics. Currently, a 2 MSPS, 14-bit, eight channel galvanic isolated transient recorder; a 200 MSPS, 8-bit, four channel pulse digitizer; an eight channel time-to-digital-converter with a resolution of 0.4 ns, and a reconfigurable hardware expandable board, are implemented. [ABSTRACT FROM AUTHOR]

A diagnostic for the magnetohydrodynamic (MHD) mode identification is being implemented on the Tokamak ISTTOK using the signals from the set of 12 equally spaced Mirnov coils. These poloidal magnetic field sensors have been recently installed inside the vessel and were designed for plasma shape and position equilibrium determination. The data acquisition and processing system is based on a locally developed galvanic isolated, eight channel fast PCI transient recorder module with a 2 Msamples/s sampling rate, 14 bit resolution, and a total memory of 256 Mwords. This module includes a digital signal processor and field programmable gate array allowing real-time determination of MHD modes using advanced identification algorithms, in a submillisecond cycle time. Poloidal m number and amplitude measurements are available in real time to feed event-driven active control systems. This solution enables high performance distributed computing, effective data reduction, and event detection at a relatively low cost. [ABSTRACT FROM AUTHOR]