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Title: Tomographic analysis of neutron and gamma pulse shape distributions from liquid scintillation detectors at Joint European Torus

Abstract

The Joint European Torus (JET, Culham, UK) is the largest tokamak in the world devoted to nuclear fusion experiments of magnetic confined Deuterium (D)/Deuterium-Tritium (DT) plasmas. Neutrons produced in these plasmas are measured using various types of neutron detectors and spectrometers. Two of these instruments on JET make use of organic liquid scintillator detectors. The neutron emission profile monitor implements 19 liquid scintillation counters to detect the 2.45 MeV neutron emission from D plasmas. A new compact neutron spectrometer is operational at JET since 2010 to measure the neutron energy spectra from both D and DT plasmas. Liquid scintillation detectors are sensitive to both neutron and gamma radiation but give light responses of different decay time such that pulse shape discrimination techniques can be applied to identify the neutron contribution of interest from the data. The most common technique consists of integrating the radiation pulse shapes within different ranges of their rising and/or trailing edges. In this article, a step forward in this type of analysis is presented. The method applies a tomographic analysis of the 3-dimensional neutron and gamma pulse shape and pulse height distribution data obtained from liquid scintillation detectors such that n/γ discrimination can be improved tomore » lower energies and additional information can be gained on neutron contributions to the gamma events and vice versa.« less

Authors:
 [1];  [2];  [1];  [3];  [4]; ; ; ;  [1]
  1. JET-EFDA, Culham Science Centre, Abingdon, OX14 3DB (United Kingdom)
  2. (Italy)
  3. (Sweden)
  4. Department of Physics, Università degli Studi di Milano-Bicocca, Milano (Italy)
Publication Date:
OSTI Identifier:
22253529
Resource Type:
Journal Article
Resource Relation:
Journal Name: Review of Scientific Instruments; Journal Volume: 85; Journal Issue: 2; Other Information: (c) 2014 Euratom; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; DEUTERIUM; ENERGY SPECTRA; GAMMA RADIATION; JET TOKAMAK; LIQUID SCINTILLATION DETECTORS; NEUTRON DETECTORS; NEUTRON EMISSION; NEUTRON SPECTROMETERS; NEUTRONS; PLASMA; PULSE SHAPERS; TRITIUM

Citation Formats

Giacomelli, L., Department of Physics, Università degli Studi di Milano-Bicocca, Milano, Conroy, S., Department of Physics and Astronomy, Uppsala University, Uppsala, Gorini, G., Horton, L., Murari, A., Popovichev, S., and Syme, D. B. Tomographic analysis of neutron and gamma pulse shape distributions from liquid scintillation detectors at Joint European Torus. United States: N. p., 2014. Web. doi:10.1063/1.4864122.
Giacomelli, L., Department of Physics, Università degli Studi di Milano-Bicocca, Milano, Conroy, S., Department of Physics and Astronomy, Uppsala University, Uppsala, Gorini, G., Horton, L., Murari, A., Popovichev, S., & Syme, D. B. Tomographic analysis of neutron and gamma pulse shape distributions from liquid scintillation detectors at Joint European Torus. United States. doi:10.1063/1.4864122.
Giacomelli, L., Department of Physics, Università degli Studi di Milano-Bicocca, Milano, Conroy, S., Department of Physics and Astronomy, Uppsala University, Uppsala, Gorini, G., Horton, L., Murari, A., Popovichev, S., and Syme, D. B. Sat . "Tomographic analysis of neutron and gamma pulse shape distributions from liquid scintillation detectors at Joint European Torus". United States. doi:10.1063/1.4864122.
@article{osti_22253529,
title = {Tomographic analysis of neutron and gamma pulse shape distributions from liquid scintillation detectors at Joint European Torus},
author = {Giacomelli, L. and Department of Physics, Università degli Studi di Milano-Bicocca, Milano and Conroy, S. and Department of Physics and Astronomy, Uppsala University, Uppsala and Gorini, G. and Horton, L. and Murari, A. and Popovichev, S. and Syme, D. B.},
abstractNote = {The Joint European Torus (JET, Culham, UK) is the largest tokamak in the world devoted to nuclear fusion experiments of magnetic confined Deuterium (D)/Deuterium-Tritium (DT) plasmas. Neutrons produced in these plasmas are measured using various types of neutron detectors and spectrometers. Two of these instruments on JET make use of organic liquid scintillator detectors. The neutron emission profile monitor implements 19 liquid scintillation counters to detect the 2.45 MeV neutron emission from D plasmas. A new compact neutron spectrometer is operational at JET since 2010 to measure the neutron energy spectra from both D and DT plasmas. Liquid scintillation detectors are sensitive to both neutron and gamma radiation but give light responses of different decay time such that pulse shape discrimination techniques can be applied to identify the neutron contribution of interest from the data. The most common technique consists of integrating the radiation pulse shapes within different ranges of their rising and/or trailing edges. In this article, a step forward in this type of analysis is presented. The method applies a tomographic analysis of the 3-dimensional neutron and gamma pulse shape and pulse height distribution data obtained from liquid scintillation detectors such that n/γ discrimination can be improved to lower energies and additional information can be gained on neutron contributions to the gamma events and vice versa.},
doi = {10.1063/1.4864122},
journal = {Review of Scientific Instruments},
number = 2,
volume = 85,
place = {United States},
year = {Sat Feb 15 00:00:00 EST 2014},
month = {Sat Feb 15 00:00:00 EST 2014}
}
  • A digital pulse shape discrimination system (DPSD) has been used in conjunction with collimated NE213 scintillators for neutron spectroscopic measurements at high count rates (MHz range) in Joint European Torus discharges (DD and DT fueled, neutral beam injection and rf heated). The system, developed at ENEA-Frascati, is based on a commercial 200 MHz 12-bit analog to digital transient recorder card, which digitizes the direct output signal from the anode of a photomultiplier. Among the unique features of this DPSD system are the possibility of postexperiment data reprocessing, high count rate operation, and simultaneous neutron and gamma ({gamma}) spectroscopy. Separation betweenmore » {gamma} and neutron (n) events is performed by means of dedicated software exploiting the charge comparison method; separate n and {gamma} pulse height distributions are obtained and an example of neutron spectrum unfolding is shown. Implications of the DPSD in future neutron diagnostic systems on large and next step tokamaks are discussed.« less
  • A method of tomographic reconstruction of the neutron emissivity in the poloidal cross section of the Joint European Torus (JET, Culham, UK) tokamak was developed. Due to very limited data set (two projection angles, 19 lines of sight only) provided by the neutron emission profile monitor (KN3 neutron camera), the reconstruction is an ill-posed inverse problem. The aim of this work consists in making a contribution to the development of reliable plasma tomography reconstruction methods that could be routinely used at JET tokamak. The proposed method is based on Phillips-Tikhonov regularization and incorporates a priori knowledge of the shape ofmore » normalized neutron emissivity profile. For the purpose of the optimal selection of the regularization parameters, the shape of normalized neutron emissivity profile is approximated by the shape of normalized electron density profile measured by LIDAR or high resolution Thomson scattering JET diagnostics. In contrast with some previously developed methods of ill-posed plasma tomography reconstruction problem, the developed algorithms do not include any post-processing of the obtained solution and the physical constrains on the solution are imposed during the regularization process. The accuracy of the method is at first evaluated by several tests with synthetic data based on various plasma neutron emissivity models (phantoms). Then, the method is applied to the neutron emissivity reconstruction for JET D plasma discharge #85100. It is demonstrated that this method shows good performance and reliability and it can be routinely used for plasma neutron emissivity reconstruction on JET.« less